Jump to content

Search the Community

Showing results for tags 'timing'.

  • Search By Tags

    Type tags separated by commas.
  • Search By Author

Content Type


Forums

  • Dirt Bikes
    • General Dirt Bike Forums
    • Make / Model Specific
    • Dirt Bike Technical Forums
    • Special Interest Forums
    • Dirt Bike Regional Discussion
  • General
    • General Forums
  • ATV / UTV
    • General ATV / UTV Forums
    • Make/Model Specific
    • ATV / UTV Regional Discussion
  • Inside TT
    • Community Sponsors
    • Advertise on ThumperTalk
    • Site Usage, Bug Reports & Suggestions
  • ThumperTalk Clubs FAQ & Help's FAQ/Help & Discussion
  • Chadwick, Missouri: Information & Riding's Topics
  • So Cal Flattrack's Club Forum
  • Thumperjunkies - Ottawa & Eastern Ontario Riders's Discussion
  • Jersey MX and offroad's Places you ride
  • Jersey MX and offroad's Discussion
  • SE Ohio Riders's Club Discussion
  • NorCal Trail Riders's Topics
  • Northern Nevada Roaming Bastards's Discussion
  • North Texas Enduro Riders's Topics
  • Twistin it in PHX's Introduce yourself!
  • Twistin it in PHX's Discussion
  • So-Cal Track and Trail's 1st club ride coming soon...
  • Moto TnT Track & Trail's Moto Tnt Racing Questions
  • Moto TnT Track & Trail's Rider's Forum
  • Dualspot Riders Orange County So~CaL's Club Discussion
  • Chester County PA DS/Adventure's Im here
  • Chester County PA DS/Adventure's Ride Dates & Times
  • Niagara region's Club Discussion
  • Walker Valley Single Track Riders's Unanounced ride(s) recap(s)
  • Walker Valley Single Track Riders's Supplements & recovery aids
  • Walker Valley Single Track Riders's Bikes maintenance & restoration
  • Walker Valley Single Track Riders's Safety gear & apparel
  • Walker Valley Single Track Riders's General
  • Walker Valley Single Track Riders's Riding technique
  • Sacramento Area Trail Riders's Club Discussion
  • Sacramento Area Trail Riders's Info from another club
  • NC woods riders.'s Club Discussion
  • Colorado US Route 50 Rides's Club Discussion
  • Middle GA Off-Road & Trails's Club Discussion
  • WNY Dual Sport Trail Riders's General Discussion's
  • SoCal JUST RIGHT riding club's SUNDAY 10.13
  • OREGON Riders Club's Club Discussion
  • Glamis bike crew's Topics
  • Glamis bike crew's One last trip
  • Glamis bike crew's Let’s hit the dunes!
  • South Texas Dirt riders's Topics
  • PNW Trail Maintenance Club's Trail equipment and how to carry it
  • PNW Trail Maintenance Club's General Discussion
  • PNW Trail Maintenance Club's Introduce Yourself
  • New England riders's Events
  • SC Dirt Riders's Topics
  • Club RMX's Photos and videos
  • Club RMX's Engine & Engine tuning
  • Club RMX's Chassis, Suspension, & tuning
  • Club RMX's Electrical and electronics
  • Club RMX's Body, fender, & Graphics
  • Club RMX's Build projects
  • Club RMX's Everything else
  • Club RMX's Classifieds
  • North GA Trail Riders's Topics
  • NorOnt Trail Riders's Topics
  • Virginia Supermoto's Club Discussion
  • Kentucky Trail Riders Club's Topics
  • ADK ADV's Notes
  • Pennsylvania Dirtbike Riders's introductions
  • Missouri Dual Sport Riders's General discussion
  • Missouri Dual Sport Riders's General discussion
  • Missouri Dual Sport Riders's Adventurepalooza 2021
  • Missouri Dual Sport Riders's Organized ride section
  • Missouri Dual Sport Riders's Gpx files
  • Missouri Dual Sport Riders's For sale items
  • WISCONSIN TRACK RIDERS's Racing
  • Yamaha WRz's Topics

Categories

  • Powersports Gear & Apparel
  • Universal Parts & Accessories
  • Parts & Acc. - Japanese Bikes
    • Honda Parts & Accessories
    • Kawasaki Parts & Accessories
    • Suzuki Parts & Accessories
    • Yamaha Parts & Accessories
  • Parts & Acc. - Euro Bikes
    • Beta Parts & Accessories
    • Husqvarna Parts & Accessories
    • KTM Parts & Accessories
    • Other Euro Parts & Accessories
  • Motorcycles
    • Off-Road Motorcycles
    • Dual Sport Motorcycles
    • Street Motorcycles

Products Categories

Vehicles Categories

Garages

Blogs

  • Speed Through Fitness
  • Moto Mind
  • Test Blog
  • Trail Tales of Enduro in South America
  • Michael File
  • Greg 198
  • Jason Bohl
  • Cole B
  • Loves dirt
  • RodneyBell
  • Johnnyship
  • michael
  • chunky bits of metal in oil

Calendars

  • ThumperTalk Clubs FAQ & Help's Club Calendar
  • Chadwick, Missouri: Information & Riding's Events
  • So Cal Flattrack's Club Calendar
  • So Cal Flattrack's Events
  • Thumperjunkies - Ottawa & Eastern Ontario Riders's Club Calendar
  • Thumperjunkies - Ottawa & Eastern Ontario Riders's Events
  • SE Ohio Riders's Events Calendar
  • NorCal Trail Riders's Ride & Event calendar
  • Northern Nevada Roaming Bastards's Stuff that happens on a particular date
  • Central Washington riders's Events
  • Central Washington riders's Group ride?
  • Central Washington riders's Events
  • Dualspot Riders Orange County So~CaL's Events Calendar
  • Niagara region's Club Events Calendar
  • Walker Valley Single Track Riders's I love Mondays trail ride
  • Sacramento Area Trail Riders's Events Calendar
  • Sacramento Area Trail Riders's First round of Hollister 2020
  • NC woods riders.'s Club Calendar
  • Colorado US Route 50 Rides's Club Calendar
  • Middle GA Off-Road & Trails's Club Calendar
  • OREGON Riders Club's Club Calendar
  • PNW Trail Maintenance Club's Calendar
  • North County San Diego - DirtbikesWithDad.com's 2020 Calendar
  • Club RMX's Calendar
  • North GA Trail Riders's Ride Calendar
  • Virginia Supermoto's Club Calendar
  • Kentucky Trail Riders Club's Events

Find results in...

Find results that contain...


Date Created

  • Start

    End


Last Updated

  • Start

    End


Filter by number of...

Joined

  • Start

    End


Group


Facebook


Instagram


Twitter


TikTok


YouTube


TeleGram


LinkedIn


Website


Interests

  1. Just finished adjusting the valves on my 2008 crf250r, I kicked once and the motor turned over maybe one rotation and then it locked up. I thought the cam was set correctly but it' possible its off. I also forgot to use the engine locking bolt on the bottom side that locks it at tdc while working on it but I wasn' concerned because I didn' feel like I was turning the engine the chain while working on it. Before the valve adjustment it kicked over fine. What could the issue be?
  2. If I'm adjusting the timing on my rmz 250 and the timing is slightly or barely off, will it start? If it will would it get damaged over time or something? I just wanted to know just in case I timed it slightly wrong on accident.
  3. 1981 Honda XR200R Starts fine, idles fine, runs fine on 1st 2/3 of throttle. When hitting higher RPM it starts to sputter and looses power. It has a new carb and premium pump gas. I bought it as a basket case so I don't know if it has ever been right. I think the timing is off but have no idea how to check it or test it.
  4. Recently did a top end rebuild on my 2008 WR450, took her for a short test ride no problem, sounds good felt great, took her for a longer rider and about 10mins in suddenly souldnt rev past approx. 4000 (red light coming up on dash). Babied her home but I am stumped. Timing is good, TPS is within spec. The only thing I can think of is the flywheel/magneto rotor was stuck on tight and to get it off to replace the timing chain required some heat, yes used the correct tool. What im currently thinking is that the heat caused the flywheel/magneto rotor to lose magnetism preventing the CDI from seeing where the crank is located. She starts and runs fine at idle/low rpm. Has anyone had a similar issue or can provide a solution?
  5. Hello, hope i'm posting this properly! So my first 4 stroke rebuild was going well, so i thought! I'm trying (hard) to put my sons bike (2013 rmz 250) back together after a top end and valve service. I am having a difficult time placing the timing chain over the camshafts. Sounds silly, I know! The tensioner is removed, the engine is at top dead center on compression stroke. The chain guide appears to be installed correct and the chain goes over the exhaust cam fairly easy while pulling the chain taut with no slack down to the crank or under the crank sprocket (the video appears as if i'm allowing slack to drop to the left below the sprocket but i'm not, the guide is pressing with tension against the chain & the bottom teeth of that sprocket & holding the tension from dropping there). The marks are at 12 o'clock and 9 for the left cam and 12 & 3 for the right. None of that should really matter for slack though, the book calls for 13 pins between the top marks which i can count but I just can't loop it over the intake cam. Now maybe it's a simple mistake, and hopefully i'm missing something simple. Again my first 4T rebuild but I have tried to pay attention to detail and do things proper. I do have a manual & have followed it to a tee! For $100 its pretty vague on the subject, it just says follow the reverse order to assemble. Someone recommended I start the chain on the exhaust cam and then turn the crank to ride it up over the teeth like we all did to our bicycles as kids! The manual does not say this and it seems I would lose TDC if I did that. Is that a proper procedure? I would appreciate any tips on what I'm missing. Here are some pics at tear down and my video plea for help! Thanks in advance!
  6. Hi, i am completely new to posting on this site so i am sorry in advance if i do something incorrect. I have a Honda crf 250r 2007 that i cannot get the timing marks to line up properly. When i line either the crank timing mark correctly or stater mark correctly the opposite sides marks will not line up at all. I am going to attach photos of when the stater marks are lined up and show where the crank mark sits. I am trying to figure out what my problem is so i know what to buy or break a part first. The bike ran previously but it ran like crap so i re-shimmed the bike back into spec and now the bike will not run and the timing marks look like this. I am uncertain if the marks had been off this whole time or not. I am not sure if the crank side gears had been put on a tooth off from correct spot ( i don't believe this to be the issue) or if the stater has just moved over a bit somehow. I do not have enough knowledge about the internals to really know from a guess. On the crank side i have all the marks lining up properly that i can see, the water pump gear is lined up to the inner gear and outer gear from the crank. (unsure of the right terms for them but all 3 dots are in line. I would have torn off the side covers and looked deeper into this but i do not have a proper torque wrench to place everything back together and i do not have a flywheel puller/strap wrench. I am just looking for some possible ideas to my problem before i buy the tools and try to fix it myself or give it to a shop and be out quite a bit of money.
  7. I've been doing research over week now. Bought a 04 crf250r for $900 on terms it needed a cam chain. Come to find out the cam chain tension failed and the chain was shot. However there was a surprise. the left cam lobe closes to the cam wheel (in the head) destroyed the heads housing around the valve. Yes destroyed. Chucks of metal were found and the cap above the valve (under the cam lobe) was also destroyed and chewed up. The bike did run before i opened it decently well but did make noise (2nd 3rd kick). I didn't want to blow it up so i torn it apart. Now i have a new cam chain and tension valve cover gasket and flywheel stator (left side engine gasket) also new head is on its way. PROBLEM- Guys at the motorsports store said valves looked good and jug looked fine along with the piston (valves were still in head and he just glanced at them). QUESTION-Do i reuse the old valves in my new head (probably not) so if i order new valves can i use the old springs with the new valves? Last question, since ill have a new head and (if need be valves,springs,locks,seals) what size shim (referring to the small metal circles under the lifters) do i use since it'll be OEM. Please get back with me asap. Thank you!!
  8. How do I fix this mess I've gotten myself into? I was adjusting valves and turned the engine over without the cam chain tensioner in place and ended up with the arrows at 11:30 and not 12:00. The bike is at TDC compression stroke. I am in the 15th pin though.
  9. I have recently done a lot of maintenance to my WR 450f and there are still some issues which concern me with it, when I took out the clutch basket there was a gear with a bent piece on it (picture attached) This was probably done by the previous owner but I think it should probably be replaced? - When I checked the valves they were only opened for measuring when the knob things were pointed down instead of up, (picture attached) I dont know if the timing is messed up or if it has been retarded to the yz specs. ( the picture of the cam chain was when the valves were open, at the same time as the knob things were downwards in the other picture). -There is also a clattering noise from the engine but it seems to run fine? I will try to make a video for mine soon but it sounds pretty much like this persons - sorry about the bad pictures.
  10. I recently purchased a 2010 KX250F from a friend of mine that had been sitting in his garage for about 5 years. The bike seemed to be in decent shape and the price was right so i picked it up. I went through most of the bike before riding it (air filter, oil, greased all the bearings, adjusted suspension, changed all the fluids, etc) The valves sounded a bit loose so i decided to have a "Buddy of mine" adjust the valves. I get the bike back, go for a ride and the cam chain tensioner falls out while i was riding, luckily i caught it very soon after it happened and it never jumped timing. I put the tensioner back in and continue to ride the rest of the day. as the day goes on the valves sound much looser than they were originally before the adjustment was done, I decided to call it a day and tear the bike down myself. I shim the loose valves and button the bike back up, but now the thing sounds god awful. Straight up clacking coming from the right side of the top end. Since then ive probably had the bike apart and back together 4 or 5 times trying to figure out the problem. Its not the auto decompression valve, every valve is in spec, timing is solid, and the cam chain tensioner is working fine. I'm stumped. anyone have any thoughts?
  11. I bought a drz400 in pieces but the motor was assembled just put the wiring harness and all those goodies back on. Timed it to Front exhaust cam to 2 and the rear intake to 3. 15 pins in between and to TDC. I went to fire the bike its got a new jug, new rings, new piston. It will pop and shoot flames when it has compression but sometimes it’ll just spin freely with no compression sounds. if i keep winding on the starter it gains and looses compression over a certain amount of time. For 10 seconds winding the starter it’ll have compression, the next 10 seconds it wont have compression while winding the starter. Its very weird ive never seen anything like it. I hate to take it to a shop, i do everything myself. Thanks.
  12. Hi everyone, I have a new-to-me 2005 CRF230F. This forum has helped me several times in the last couple months, but I created an account this time as I was unable to find an answer to this question: I removed the timing hole cap and crankshaft hole cap. The problem I'm having is as I approach the T timing mark by rotating the crankshaft counterclockwise, it spins right past it. I go by the F mark and then about 1/2 or 3/4 of a inch before the line to the left of the T would be lined up, it spins right past. I tried using a screw driver with the socket on the end instead of a ratchet so that I could try to hold it on the T. I am able to do that, but as soon as I release pressure, it spins past. Any help would be appreciated.
  13. I am putting an 02 cylinder on a 99 kx 250 i bought. Ignition time for 99 is 11° BTDC @ 7000 rpm and timing for the 02 is 13° BTDC @ 7000 rpm. Is that a big enough difference where the stator should be adjusted or should it run fine?
  14. Hi guys I took of my stator cover and starter. i Put everything back together in correct order but no spark dont know if there are any wires that could have pulled out or disconected Please if any body has an idea or know of anything i can look at it would be much appreciated.. Kind Regards. Clueless
  15. I just finished rebuilding the top end on my 2001 wr250f. The bike has an Athena 290 big bore cylinder and piston. I never checked the valve clearance before the rebuild. After rebuilding, I checked the valve clearances. All three intake valves have zero clearance. I cannot get my .03mm gauge to slide in. The exhaust valves are only slightly on the tight side with .015mm each. I double checked and made sure I wasn't on the exhaust stroke. I have zero clearance on all valves on the exhaust stroke. I even tried turned the flywheel back and forth from TDC and measuring to see if my timing was off, causing the zero clearance. These test also had zero clearance on the intake valves. Have all three of my intake valves worn down to the point where there is no clearance? When I had the head off, the bottom of the valves looked decent. Slightly blackened, with a small amount of carbon, but I didnt notice any major wear, chips or cracks. Anyone got any idea what's going on here? Thanks in advance for your guys' wisdom.
  16. HI guys, last post recieved great help so hoping the same here, basically I think I’m experiencing some timing issues on my 02 rm125. The timing marks on the magneto were slightly out by like a degree or less, in favour of an earlier spark, worried that I was gunna fry the piston, I moved the timing marks by a degree in favour of a later spark just for piece of mind that I wasn’t harming my freshly rebuilt engine, since doing this o think I can hear the bike ‘pinging’ when riding at a steady speed, and has developed a ticking noise from the top end, it runs okay maybe a little splutter before the valve opens and possibly down on power a little but I ride a sports bike so maybe it’s just not that fast compared, but once it’s cleared out it sings through the gears as it should, can anyone help? Will post a picture of current position on magneto, also I haven’t proper tool for measuring tdc but by feel on the fly wheel this is pretty much where it’s at, that can’t be right considering the crank turns anti clockwise?
  17. Timing, they say, is everything, and that’s particularly true with engines. Understanding how and when the individual events happen, and why they happen when they do will help you understand why they have to be set up as they are, and that always makes it easier to figure out what’s going on when problems arise. Let’s start by going over the basic way the engine works, and what events need to occur and when. First, we’ll look at the simple basics, then at the reason things happen exactly when they do. To simplify the discussion, and to make it more closely relevant to dirt bikes, we are only going to discuss single cylinder engines during this explanation. The term, “four-stroke cycle” means that the engine needs to move the piston up or down the bore 4 times to complete all the functions that go into producing power from gasoline. Because the piston is connected to the crank via the connecting rod, each “stroke” takes a half revolution of the crank, or two full revolutions for the four necessary strokes. The Four-Stroke Cycle A lot of folks have seen this simplified version, but let's review. The cycle starts with the Intake Stroke, near top dead center (TDC), where the piston is at its highest possible position, with the intake valve opening and the piston moving down the bore toward bottom dead center (BDC). This creates a void above the piston that is filled by air from outside rushing in through the intake port to fill it, and that air carries with it the fuel added by either the carburetor or a fuel injection system. The rotating crank then begins to move the piston up the bore and the intake valve closes, trapping the fuel and air in the cylinder. As the piston continues upward, the air/fuel mix is compressed, which heats it and increases the amount of force with which it will expand when ignited. This is the compression stroke. The power stroke begins near the top of that second stroke, when ignition takes place, starting the fire. The crank rotates past TDC as the burning fuel begins to expand, and the combustion force pushes the piston down the bore, creating the rotating force on the crank that drives the whole works. As the piston nears BDC again, the exhaust valve opens, and the piston is run up the bore to pump the spent gasses out through the exhaust port to complete the cycle with the exhaust stroke. Half Speed Notice something here: The engine’s crankshaft rotated twice to produce four trips up and down the cylinder for the piston, but each valve only opened and closed once during that time. To make this work, the camshafts have to turn at one half the engine speed, so the chain and sprockets, or gears, or toothed belt and sprockets used to drive them are set up at a 2:1 ratio. Ignition also has to happen right on time, so each ignition system, whether simple ‘50’s style points, or the most sophisticated electronic, has to have something to signal when that is. Traditionally, this signaling trigger has been attached to the camshaft so that the spark occurred only once every other revolution, but engineers seeking to simplify the design of single cylinder dirt bikes found no reason that there could not be a spark on every revolution, so the trigger sensor was mounted at the crankshaft instead. That means there is a spark on every revolution, instead of only once per each two-revolution cycle of the engine. The second spark happens at the end of the exhaust stroke, so there’s nothing present in the cylinder that would burn. It also makes setting up the timing during assembly somewhat simpler by eliminating what used to be a common mechanic’s mistake of picking the wrong top dead center position. Getting Ahead of Things (The Engine is Dynamic) Simplified explanations of the cycle like the one we started with here always show the valves opening and closing right at TDC and BDC, but if you watch the piston position as you turn an engine over by hand to watch the valve gear operate, you will notice that the valves don’t open and close at the exact top and bottom of their respective strokes. That’s because the engine is a dynamic system, which means it’s something that moves, and it does so at a pretty high speed. Most MX 450’s make peak power at around 9000 RPM, which means they make two full revolutions and complete an operating cycle in about 13 milliseconds at that speed. The crank spins continuously, but the intake, exhaust, and combustion all stop and start again while that’s going on. That means that all of these events actually have only a certain amount of time in which to occur, so they have to be started in advance so that they happen on time. Again, we’ll look at the intake stroke first. With the crankshaft spinning along at a few thousand revolutions per minute, if we were to wait until top dead center to open the intake valve, the piston will travel well down in the bore by the time the valve is open wide enough to let much air into the cylinder, so the intake valve begins to open around 20 degrees or more before top dead center (BTDC). This does a couple of things. For one, the exhaust stroke is just ending, and the inertia of the spent gasses leaving the cylinder creates a bit of a vacuum that helps get the intake air moving in. There’s a little bit of built up pressure right behind the intake valve as a result of the intake valve having been slammed shut on a moving column of air at the end of the previous intake stroke, and that helps, too. But mainly, we want the intake valve to have time to be open nice and wide as the piston moves through the fastest part of its down stroke so we can get the cylinder as full as possible. On top of that, we’re going to keep the intake valve open until well after bottom dead center (ABDC) to take advantage of the inertia of the incoming air. Which brings us to the compression stroke. The piston is now rising and pushing against the load of incoming air, stalling the flow into the cylinder, so the intake valve closes as this balance is struck, about 130 degrees BTDC. With both valves now closed, the piston compresses the air and fuel mix to less than 1/10th its original volume to heat it up and to increase the force with which it expands as it burns. This compression will continue until TDC, but the ignition has to happen well before that in order to extract the maximum power from the burning of fuel. The Power stroke, then, is initiated before the piston actually starts down. This “spark advance” allows the burning gasoline time to start at one small point near the spark plug and spread across the combustion chamber to the point where it becomes confined by the piston and must push it down out of the way. That’s where the power comes from. If the spark occurs too late (is “retarded”), the piston will outrun the fuel burn and not much pressure will be applied. On the other hand, if it happens too early (“advanced”) then too much pressure will be created while the piston can’t get out of the way fast enough, which leads to damage from detonation and the like. The faster the engine turns, the more advance the ignition needs to keep up, so modern systems advance the timing as the RPM increases. At about 120-130 degrees ATDC, the energy from the fuel burn is so low that it really isn’t putting a lot of force on the piston any more, and the leverage that the piston has on the crank is getting pretty low, so the exhaust valve starts open before reaching BDC. The pressure that remains from the burn starts the gasses flowing outward, boosted by the piston as it rises and pumps the bore clear. The exhaust valve remains open past TDC to utilize gas inertia and help restart the intake airflow for the next cycle. Am I 180 Out? People ask this a lot when they have trouble getting an engine running after they’ve set the cam timing up, or when they bring the piston up to Top Dead Center and find both valves open. This is the common mistake we mentioned earlier, and it's one of the things that's more easily understood when you have a good grasp of the complete cycle. It’s more of a car thing, but if you have an old classic four-stroke from the ‘70’s or before that uses cam driven breaker points, it’s sometimes possible. These days, the answer is usually, “no.” The old way of connecting the ignition to the engine mechanically, that of using a distributor or some other device driven at half speed by the cam, allows a mistake in assembly to be made. A mechanic could position the engine at TDC, and if not careful to check, he could position the ignition trigger to fire during the exhaust stroke instead of the compression stroke. This was referred to as being “180 degrees out” because the distributor or point plate was 180 degrees away from the correct position on the camshaft because of this. Actually, going by the crank, the ignition timing was 360 degrees out. But with the ignition trigger located on the crankshaft instead, as is the case with virtually all modern single cylinder dirt bike 4 strokes, that’s not possible. Without the cams connected to the crank, one TDC is exactly like another; the rod’s at the top, and the spark signal is given as the crank gets there, every time. So, the only thing that determines which stroke is which is the camshaft(s), and how they are positioned by the assembler. That’s why the service manuals for such engines make no mention of checking for which of the two different TDC’s is used. In operation, there is a second, "wasted" spark that happens near the end of the exhaust stroke. What About Automatic Decompression? This is another area where really understanding the four-stroke cycle helps clear things up. It's extremely common to hear people tell someone with a modern four-stroke single to "find TDC" before starting, but that's wrong. When you turn the engine over slowly, you find it rotates fairly easily until you come to a "hard spot". Without auto decompression, the hard spot is the point at which the intake valve closes to begin the compression stroke. That looks like the picture below, "Non AD". From this point, you would need to force the engine to compress about 80% of it's full stroke length worth of air, and that can be nearly impossible with the high compression ratios used these days. What automatic decompression does is use a speed sensitive mechanical system to lift the exhaust valve off its seat at very low speeds (slower than the engine will idle at) until the engine gets a lot closer to TDC, but not past it, so that when kicked over from this position (or spun through it by a starter motor) there will still be enough compression to start, and both valves will be closed as the spark happens and the end passes top dead center. That looks like the "Auto Decomp" picture above. You can see that there will be a lot less effort needed to compress the air/fuel charge from here than from the normal, non auto decompression setup. This, by the way, is where you want to be if you have an older manual decompression engine. If you go past TDC instead of stopping just prior to it, you would have to kick the engine through nearly two full revolutions to get back to the compression stroke again, and it would still be at full strength. Once you have the whole picture set in your mind, you'll make fewer assembly mistakes, and you'll be able to catch on to problems more quickly. A crusty old mechanic told me a long time ago, "The best way to figure out why something works wrong is to know how it's works when it works right".
  18. 2008 yz450f backfiring issue. Minnesota, 0-1,000', 70°-90°. Bought my friends '08 YZ450F w/ 167hrs, ran fine last time he rode it and the entire 3 years of ownership. He's never done any internal engine work or even messed with the carburetor other than cleaning it. Last time he rode it the rear wheel hub broke on the sprocket side and the chain jammed the front sprocket and stopped the engine. It hasn't been ridden or even started since-about 3 months ago. I bought it for a grand and threw my yz250 wheel on and thought it'd be ready to go... nope! 😩 starts right up, idles good, revs good, rides good until the exhaust is hot then it backfires like a mf (any throttle pos. but way worse wide open) and eventually dies until its cold again. New Air filter w/ fresh oil. Fresh 91 gas. Oils good, coolants good. Cleaned the carb, couldn't get to the a-pump or needle clip bc the screws were too tight. 75 PSI of compression. New spark plug, gap was good, insulator was mostly visible with a light grayish layer, electrode and outer ring had a light black layer, center electrode had the slightest bit of white residue. New plugs insulator was completely clean and the electrode and ring was black after 10 mins idling, 10 mins riding and messing with the fuel screw and idle. There was an air leak at the exhaust clamp, sealed that. There were cracks in the carburetor-engine intake boot, replaced that. The main jet was a JD170, replaced that with the standard 160 jet even though according to my friend the jets haven't been changed in 3+ yrs. The pilot jet is a JD48, standard is 45. Idles best 1/2 a turn out on the fuel screw with either jet, runs the same with both. Put the JD170 back in since that's what he always had in it. There was slack in the timing chain, tightened the tensioner. Timing is good I think? Cams lined up properly but the crank is just the tiniest bit past the timing mark. If I jump a tooth on the cams then the crank is further past in the other direction. Is this what the issue is?? How can I adjust the timing at the crank? Is that even a thing? Idk what else I can try at this point other than forcing my way into the accelerator pump to clean it Plz send help
  19. Maybe someone can help me out. My 19’ KX250 is bogging real bad to the point it will cut off when I’m riding anywhere from 1/2 throttle to wide open. Starts up fine and idles no problem. I just had the valves adjusted and are within spec, I checked the stator with a multimeter and checks out good, tps is good, ignition coil is good, new spark plug with proper gap, did the 9V battery trick to clean the injectors and just put a new fuel pump and filter in the tank. Also fresh clean gas from when I did the pump, plus a fresh clean air filter. Can’t figure out why it keeps dying out. It’s gotta be fuel/air related because when I pulled the plug out it’s extremely lean... any ideas guys?? Thanks.
  20. Might be a long shot but i just rebuilt my motor, never did the crank only top end. When i go to put my camshaft in and the chain is on, the rear bearing is raised up about a 1/4 inch or so. The only way to get it to go down is to tighten the holder down and then the chain is bar tight without the tensioner on. It was the same timing chain as before and same camshaft help. Only thing that was changed was piston and the valves. Tried taking the shims out to see if it would help but never. I dont know what i could have did wrong.
  21. Just rebuilt bottom end, top end, and all case bearings on a 2017 KTM 65 at 158 hrs. Engine would not start after rebuild. Good spark, compression, fuel... pulled hair out. Used a PRox crank, Vertex top end, Hot Rod bearings. Finally I have determined that the woodruff key slot on the rotor side of the crank is machined in the wrong position, making it impossible to properly time the engine. The only way I can align the timing marks on the stator and rotor using the nihilo deck height/timing tool is after TDC. Has anyone ever had this issue??? Plan to remove woodruff key and align rotor so I can properly time engine to verify. Any thoughts?
  22. I have this spark plug o ring left to install, and I cannot for the life of me figure out where to put it and I don't want to chance it and install it the wrong way. will someone please tell me where this thing goes.
  23. Alright, so I just got done rebuilding the top end on my 07 KX 450F and as I am getting ready to install the top of the cylinder head I notice I have one last piece remaining that I can't account for. I mark everything and take several pictures so I can make sure everything is put back together perfectly, but somehow this piece evaded me. I showed where I think it goes in one of the pictures I provided. Can someone tell me if I am right or if this piece goes somewhere completely different?
  24. I've tried adjusting my accelerator pump so the squirt just barely hits the slide. The best I've been able to accomplish is the squirt starting as the slide is half way up, this is with the adjustment screw back out all the way. The original setting was 4.25 turn out and at that setting the squirt started once the slide was almost all the way up. I recorded the different setting with my phone and went frame by frame to check. I can't seem to figure out how to post a video with slow-mo to show what I am seeing. From what I've read I should be able to back the adjustment screw out until the squirt actually hits the slide but I can't do that with my bike. I do get a fairly bad lean bog, although I haven't tested it since getting the squirt to be somewhat faster. My question is what would cause the squirt to be so delayed compared to what I've read in other bikes? Anywhere I can start trouble shooting? Thanks! (I have the stock 55 leak jet)
  25. Hey guys Scott here, sorry to post this as the first post, but i have spent quite a while searching various threads with no luck. So here goes, got a 2017 140L for my son for Christmas. Very clean, seemingly good running bike. While riding today, he choked it down while on start off on a slight incline, then when tried to re-start, it sounded like the starter was free spinning. So we loaded it up and got it back to the house. After looking at the starter gear and limiter gear, it appeared fine. I pulled the side cover (magneto/generator/rotor cover maybe?) and noticed the rotor/magneto bolt was very loose. I tightened it, but not knowing spec, I tightened with a ratchet until I couldn't hold the magneto/rotor and it would spin over. Buttoned it all back up and it fired up and ran. It being cold out, it cut off even with the choke on, I tried to start it again and the magneto seemed to slip again, so i used a dewalt 1/4" impact driver to tighten the bolt, thinking it maxed out at about 100lbs of torque and should be ok, if I didn't stay on the bolt, just snug it up decently. After tightening the bolt, I put the covers back on and tried to start it. It now acts as if the timing is out, but the engine turns over easily and I am getting a spark at the plug. I would think that if timing was out it would be difficult to turn over. I pulled the cam chain cover and lined the cam gear up with TDC, but the magneto/rotor isn't lined up with "T" being in the 12:00 position. Could this be an issue? My question is, could the magneto slip in position, while the flex plate/flywheel stays in place without shearing the key? and does the magneto need to be lined up and the cam gear? I also checked the woodruff key and its good. I honestly cant figure out how it would have jumped timing with the timing chain being tight and the key not being sheared. Any insight or advise would be great. thanks again Scott
×
×
  • Create New...