2009 KX250F No Start after Rebuild

Hey, I have a very puzzling and now frustrating project on my hands and looking for some advice. I have a 2009 KX250F that will not start after I have rebuilt it. For a little history, I bought this bike and it wouldn't start as it had no compression. I did verify that. This bike sat outside for a while too, chain & sprockets all rusted even head bolts were rusted. Muffler was mounted on the wrong side of frame... long story short, it was in rough shape.

 

I have put in a new piston & rings, cylinder had some were but was not scuffed & crank was good. head was tested and I replaced 2 bent exhaust valves. I now have 85-90 psi of compression. I rebuilt the carb, took all the jets out and cleaned. Had to replace the hot start plunger was seized in the carb. I had the magneto cover off and I had to clean out some metal filings out of the base. Not sure what they are from but it was metal. I put a new spark plug in. I tested the coil and was in spec and I just had test leads into the plug for the coil and my spike voltage was approx. 130 VDC. I now have the bike together so it should run but I can even get to sound like it wants to start even jump starting.

 

I'm running out of things to check but I almost to the point to start over and recheck what I have done. I do live in the maritimes so weather isn't that warm yet in the garage so I don't know if it could be as simple as the outside temperature making it hard to start. Anyway, any advice or tips would be greatly appreciated. Thanks in advance.

 

Mike

hey mate, I am in the same boat as you!

 

Check out my thread!

 

http://www.thumpertalk.com/topic/1130294-2011-will-not-start-after-a-rebuild-plz-help/

 

Maybe we can help each other.

 

I am gonna do a leak test on the valves, and if that comes back good I really don't know. It's my last hope lol

 

To leak test my valves I just bought a regulator and extended blow gun with rubber tip with the head installed, regulated it to 20 psi and the rubber tip sealed in the spark plug port and tested it that way. after I found exhaust valves were leaking. I took my head to a engine repair shop and found my exhaust valves were bent. So I replaced the bent ones and they grinded the seats for me. I just put it back together yesterday, made my valve adjustments and my timing is good... it doesn't even want to try to start is the frustrating part.

To leak test my valves I just bought a regulator and extended blow gun with rubber tip with the head installed, regulated it to 20 psi and the rubber tip sealed in the spark plug port and tested it that way. after I found exhaust valves were leaking. I took my head to a engine repair shop and found my exhaust valves were bent. So I replaced the bent ones and they grinded the seats for me. I just put it back together yesterday, made my valve adjustments and my timing is good... it doesn't even want to try to start is the frustrating part.

Thanks for the tip!

 

Have you tried to bump start it?? 

 

Same as mine. Not even a splutter. Good spark compression and fuel. What the &%$#@!!!! :(

A little advice. bet way to set cylinder head leak down is with no cams installed. I brazed up an old spark plug with air fitting. run thru a regulator and put 40-60 psi in the head and listen in the intake or exhaust port.

If that checks ok then install the cams, check the lash or gap to the valve buckets and make sure you have the correct clearance. The distance is very small .003 to .005.

if that checks out then you need to make sure of your timing marks. at tdc the cams should line up with exhaust cam mark on 9:00 right in level with the head valve cover mating surface.The other mark o the cam should be almost straight up. same deal on the intake cam just opposite sides, so one mark on the 3:00 ( right in line with the valve cover mating surface and the other straight up.

Make sure the magneto mark is on the recommended mark, some models have two very close together. A trick I use is to use a breaker bar an 17mm socket, find the mark insert the tool and zip tie or tape it to the foot peg if engine is still in the bike. That will keep your tdc on the mark when you install the cams. Do the exhaust first and keep the tension on the leading edge of the chain, meaning no slack or close to it on the exhaust side, then install your intake. then chain tensioner.

Rotate the engine after this and make sure your marks line back up after a few rotations. If they don't you will have to reset the cams.

if electrical is good and have spark, and still does not start. it has to be a fuel problem. Carbureted bikes are a bit finicky, I found with some jet changes or plugged jets it is very difficult to get it fired up.

Thanks for the tip!

 

Have you tried to bump start it?? 

 

Same as mine. Not even a splutter. Good spark compression and fuel. What the &%$#@!!!! :(

I have tried to jump start it. still the same... doesn't even sounds like it wants to start.

A little advice. bet way to set cylinder head leak down is with no cams installed. I brazed up an old spark plug with air fitting. run thru a regulator and put 40-60 psi in the head and listen in the intake or exhaust port.

If that checks ok then install the cams, check the lash or gap to the valve buckets and make sure you have the correct clearance. The distance is very small .003 to .005.

if that checks out then you need to make sure of your timing marks. at tdc the cams should line up with exhaust cam mark on 9:00 right in level with the head valve cover mating surface.The other mark o the cam should be almost straight up. same deal on the intake cam just opposite sides, so one mark on the 3:00 ( right in line with the valve cover mating surface and the other straight up.

Make sure the magneto mark is on the recommended mark, some models have two very close together. A trick I use is to use a breaker bar an 17mm socket, find the mark insert the tool and zip tie or tape it to the foot peg if engine is still in the bike. That will keep your tdc on the mark when you install the cams. Do the exhaust first and keep the tension on the leading edge of the chain, meaning no slack or close to it on the exhaust side, then install your intake. then chain tensioner.

Rotate the engine after this and make sure your marks line back up after a few rotations. If they don't you will have to reset the cams.

if electrical is good and have spark, and still does not start. it has to be a fuel problem. Carbureted bikes are a bit finicky, I found with some jet changes or plugged jets it is very difficult to get it fired up.

Yeah I followed everything in the manual to spec. Timing is on and both cams ex is at 9 & 12 o'clock & in is at 12 & 3 o'clock. Valve clearance is in spec. I do have spark. ohm'ed out coil and is in spec. Tested the plug to the coil. (test leads into the plug to measure the voltage) and my voltage spike is 130vdc kicking it over and spark plug still in. I had the carb all apart. Cleaned all the jets & ports with carb cleaner & compressed air. Fuel is fresh, and I know the carb is getting fuel. I just don't know if the spark is hot enough to light the fuel or could be jetting... I'll have to look into the manual to check the diagnostics about the jetting.

Can you try to push start it then pull the spark plug? If fuel is being sucked in then it should be wet if no ignition is happening.

Can you try to push start it then pull the spark plug? If fuel is being sucked in then it should be wet if no ignition is happening.

So here is the latest. It would not start by jump or bump starting but I did run propane through the air box as a clean fuel source. It will start only when I pull the hot start lever in. It runs for about 3 secs then quits so to me that would eliminate any electrical issues. I made adjustments to the floats and they are now in spec but still the same thing.

Turn on the fuel tap , lie the bike over to the side and see if fuel comes out the overflow pipe on the carb, then turn the throttle twice, full quick turns , pull the choke and try start it.

 

Doesnt work then take out the carb and make sure all jets are clean, needle is in correct position and the slide plate is in the correct way around and not upside down.

 

Make sure the pilot circuit is clean and that both pilot circuit entry points into the carb are clear, one under the slide and one in front of the slide on the engine side.

 

Check that the air screw is in and it has its oring and washer still on the end of the spring, or it wont seal.

 

Make sure the accelerator pump is still spraying fuel when you open the throttle.     

Turn on the fuel tap , lie the bike over to the side and see if fuel comes out the overflow pipe on the carb, then turn the throttle twice, full quick turns , pull the choke and try start it.

 

Doesnt work then take out the carb and make sure all jets are clean, needle is in correct position and the slide plate is in the correct way around and not upside down.

 

Make sure the pilot circuit is clean and that both pilot circuit entry points into the carb are clear, one under the slide and one in front of the slide on the engine side.

 

Check that the air screw is in and it has its oring and washer still on the end of the spring, or it wont seal.

 

Make sure the accelerator pump is still spraying fuel when you open the throttle.     

So I tried the first step to your advice not thinking it would work and surprising it started... ran for about 10 secs then quit. it seems to start a lot easier with the hot start lever than choke. I am going to pull the carb to make sure that no jets or carb ports are clogged. When it does start, it doesn't idle high with the choke on. I tried playing with the idle screw but it didn't make a difference. Once I have the carb fully cleaned and back together, I will update. thanks for the info.

I took apart the carb and found the pilot air screw spring was missing. Surprisingly I found the spring... I now it seems to start almost everytime but it still stalls after 10 secs of idle with choke. I played with the idle screw again and it did help but it seems hard to kick now the engine has a hard time turning over. I'm going to let it sit for the night and check it in the morning.

Did you turn the fuel screw out about 2 turns ?

 

Is the pilot circuit clear ?

 

Does the hot start plunger work smoothly , and close when you release the lever ?

 

Sounds like its not getting fuel from the pilot circuit so the 2 bursts of fuel from the accelerator pump is priming it to run a couple seconds. 

 

Is the slide plate the correct way round ?

Did you turn the fuel screw out about 2 turns ?

 

Is the pilot circuit clear ?

 

Does the hot start plunger work smoothly , and close when you release the lever ?

 

Sounds like its not getting fuel from the pilot circuit so the 2 bursts of fuel from the accelerator pump is priming it to run a couple seconds. 

 

Is the slide plate the correct way round ?

I have the manual. I turned the pilot screw 2-1/8 turns. everything with the hot start is new except the actual lever on the bars and works smooth. all the carb ports are clean & when I sprayed carb cleaner through the jets, I had a nice steady stream spraying through the jets. the slide plate is in the correct position. I started it again today but it stalled after 5 secs. I tried kicking it again but it really hard to kick over. I took the plug out to roll it over by hand and it doesn't feel smooth like it is binding up. I took out the spark plug thinking maybe hydro locked but same result.. I checked the oil through the sight glass but oil level is in range. I'll probably have to valve cover off and check make sure nothing is binding up under there. Thanks again for the carb advice. It helped me find the missing spring on the pilot screw.

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