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Help Reading Spark Plug? 04xr400

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Any thoughts on this plug? I re-jetted to 160/58 and am running full AM exhaust. When I re-jetted, (from138/48 if I recall correctly) I also moved the needle clip down 1 slot. 

Bike runs strong. But.... has a weird hiccup when abruptly tapering off of hard acceleration. If I'm running WOT and then back off just enough to sustain RPM's, the bike is hiccuping for a second and then starts thumping again. 

Here's the plug. I plan to tinker with it this weekend until I figure this out. I'll be checking/adjusting valves while patiently awaiting your expert replies. 

To my novice, automotive trained only eye the plug looks good but I'm new to bikes. 

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Plug looks ok. What plug is it?

What's your elevation?

Aftermarket air filter too?

While you're checking the valve clearances, check the cam chain auto tensioner too. You want to get an idea of how close the chain is to the end of its service life. If you can remove the tensioner, extend its plunger fully and then re-insert the tensioner fully back into the cylinder, the chain wear/stretch is at the limit of the tensioners ability to compensate. With too much slop in the cam chain, I can see it causing a momentary hiccup when rolling off the throttle.

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Thanks for the replies - I checked and adjusted the valves. .004 intake .005 exhaust. To be honest, I don't think they needed any adjustment. I put it all back together and I am pretty sure I have my valves a touch tight now as it was pretty dang hard to start and it's usually a 1-2 kick start. 

I'm going to re-adjust the valves, try to figure out what the heck the cam chain auto-tensioner is and follow the advice given, and might put the needle clip back in the middle/stock slot to see what occurs. I'll read about the cam tensioner in my manual. 

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7 hours ago, JKTrevecca said:

Thanks for the replies - I checked and adjusted the valves. .004 intake .005 exhaust. To be honest, I don't think they needed any adjustment. I put it all back together and I am pretty sure I have my valves a touch tight now as it was pretty dang hard to start and it's usually a 1-2 kick start. 

I'm going to re-adjust the valves, try to figure out what the heck the cam chain auto-tensioner is and follow the advice given, and might put the needle clip back in the middle/stock slot to see what occurs. I'll read about the cam tensioner in my manual. 

Curious, what did the clearances measure before you adjusted them?

If you didn't know, you should bring the engine to TDC for every one of your starting kicks. Kicking from anyplace else in the stroke is a wasted effort. And a cold engine doesn't usually like ANY throttle input during the kick.

The tensioner is on the right side of the cylinder under the intake manifold. Pay no mind to that bolt sticking out of mine. That's a field repair I made so I could keep riding for the weekend, when it's internal spring broke on me. Originally it has a center screw that acts as a cover screw for the retract mechanism.

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Valve clearances before first adjustment were dang close to .004 and .005. I snugged em up thinking "i'm sure the adjustment is usually to tighten them b/c they become loose with use" so, like an idiot, using the .004 and .005 feeler guages, I adjusted them to the point the guage was snug and locked em down. Then... after it took about 20 kicks to start it I got to thinking "i bet I over-adjusted the valves and they're sticking open" so I re-adjusted them loosening them up to the point the .004 and .005 barely drags and she started right up. On to much worse things....I am either the worlds worst mechanic or I'm having a TON of bad luck today. Likely a little bit of both.

After re-adjusting the valves, a little bit of fuel began to pour out two of the small hoses that come off the carb and terminate just in front of the rear tire into the atmosphere. Since I just re-built the carb I proceeded to remove it again to find out why the needle wasn't closing/sealing. Turns out there was a random piece of black rubber between the needle and it's seat. I removed the debris. Then... after putting that all back together and replacing the fuel line/hose which I suspect is where the shard of black rubber came from, the bike started right up like it's supposed to, ran great, but then a TERRIBLE sound occurred at idle like something was inside the cylinder and the bike died. This is the first time I've ever heard anything like this. Having just read TR42's suggestion about the cam-chain tensioner I proceeded to check that. We're in good shape there. There is at least 1/4, maybe 3/8 of an inch gap when the tensioner is fully extended. I had to do a two handed maneuver to retract the tensioner while tightening the two 8mm bolts by hand before releasing the tensioner to apply it's tension.

So... The noise I had just heard nor the whole reason I started this mess today which is the hiccup when rolling off the throtte are due to the cam tensioner. In the process of all of this I've screwed up something or there has been a coincidental failure at the same time. Something is either in the cylinder/combustion chamber or down in the crankcase and is physically stopping the engine. It will start right back up (yes I know this is dumb and in hindsight, now that I realize what might be going on I wish I hadn't) but after a few seconds whatever is in there will smack against something at idle and the engine will die. 

Here is a video. This was taken right after I checked the cam chain tensioner and triple checked the valves in hopes this noise might be me forgetting to tighten one of the valves. You can hear something ticking that isn't the valves and then from about 2:15 - 2:20 until about 2:30 - 2:50 you'll hear it 3 distinct times and the last time you hear it, it kills the bike. I *could* re-start it but at this point I realized, this is only going to make things worse. 

Please help! Sorry for the terrible video. What do you suggest I do first? My thoughts are to remove the plug and stick a camera/scope down into the cylinder to see if I let something get in there while the carb was removed. (If I did, I am dumb and deserve the consequences). Man I'm just sick to my stomach right now!! I'm hoping like crazy that no damage has been done and that I can remove whatever this is w/o disassembling the engine. I should have just been content with my 83 xr350. 

 

Edited by JKTrevecca

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Your thinking on the valve clearances is backwards. They get tighter with wear. So a loose .004" and .005" is better.

You didn't turn the engine over while the tensioner was out did you? That would be bad.

Before you adjust the right exhaust valve, you must make sure you have 3/16"-5/16" manual decomp lever free play as measured at it tip when the engine is set to TDC on the compression stroke, as you would have it set for checking the valves. And you must still have that amount of lever play after any adjustment of the valve clearance.

Be sure you got the tappet nuts tight.

But I will tell you that the valve ticking you're hearing is normal. It's when you hear nothing at all that you should be concerned, means they're too tight. Slappy valves are happy valves. They're probably looser than they were before you adjusted them the first time, so they're going to make more noise than they did before.

If the manual decomp mechanism is misadjusted, it may be causing the bike to die, as it activates the right exhaust valve to dump compression.

I'd set the engine back to TDC on the compression stroke and see what kind of lever free play travel you have. You adjust it at the cable end at the mechanism on the head.

You can also feel the mechanism while the engine is running and see if you can feel the valve bumping it. Don't want that. When all that is adjusted properly, then, with the engine running, turn the bars side to side fully and make sure that doing that doesn't pull on the decomp cable and activate the mechanism, making the engine die or stumble. If it does, you need to work on cable routing.

If you thing you got the tensioner re-installed ok, then fine, but just for the heck of it, I'd remove the center cover screw again, and use a screwdriver to retract the plunger, then release it and make sure it's spring back out. Don't have to remove it from the engine again for this. This verifies the units torsion spring didn't break when you reinstalled it last time.

Edited by Trailryder42

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Well... I confirmed what I was fearful of. There was a small brass screw in the cylinder. I know exactly where this screw was "supposed" to be because I couldn't find it when I took the carb apart the second time. DANG IT! The "normal" ticking sound I understand. It may have been difficult to hear in the video but there is/was an intermittent and very abnormal ticking sound coming from the engine that was foreign and that noise coincided with the engine stalling. 

Here it it. Since it still ran well and the screw was soft brass I'm going to re-assemble and hope for the best. The valves all hold paint thinner in the intake/exhaust chambers and there is no scoring on the cylinder walls. In fact, the original honing hash marks are still quite visible. The screw knocked off some carbon and I'm REALLY hoping that's all it did. I think the sound I was hearing was the screw sticking a valve open and causing the engine to stall. We shall see. 

First, I must extract a broken bolt in the head. One of the cylinder head/valve cover bolts was siezed and broke. then, as luck/skill would have it, the first drill bit I used to drill out the middle of what was left also broke. I'm off to the store to get a micro-drill bit to drill a lot of tiny holes around the 1 broken drill bit and finesse this out before re-assembly. 

Learn from me guys. I'm an idiot! The only good thing I've learned today is that if I end up keeping this bike, it's pretty straight forward to re-build/work on the top end of this engine. Pretty simple design. 

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Curious, how did a screw from the carb get inside the cylinder? Cough up the story. lol

Glad you figured it out. I'd have never guessed that.

Sounds like you might have lucked out with little to no damage.

Edited by Trailryder42

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Have you cleaned the carb? The air diverter valve under that funny looking round cover under the choke lever has a diaphram and tiny passages that may need cleaning. It effects fuel delivery when you roll off the throttle.

It's always best to adjust 1 fuel circuit at a time, get it dialed in, then move to the next. Pilot system, main, then needle last. When you make more than 1 at a time, it's hard to judge what result was caused by what move.

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So you need to buy a drill bit to extract a broken drill bit to extract a broken head bolt  :banghead:

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Well it's all back together and runs exactly like it did before the screw-episode. I've been messing with the carb for the past week. At one point, I moved the clip on the needle while the car was still on the bike. The screw is/was one of the two screws that hold the throttle linkage plate to the throttle cylinder inside the carb. I don't recall exactly when but at one point after that, I had the carb off and apart again and recognized that I was missing one of those two screws. Well... I found it. No clue how/when it got into the carb and how long is was above the intake valve before making it's way past and into the cylinder but it surely did just that. I hated to tear into a virgin engine! But... I learned that it's a pretty easy engine to work on. If it hadn't been for the broken valve cover bolt I would have had it apart and back together in about 3 hours. Add 7 to that to get that broken bolt *and* broken dill bit out and the hole re-tapped. Gees.

So... Now I'm back to square one. Bike hiccups when rolling off the throttle slowly. I had a thought TR42. Tell me if there could be any truth to this. The air diverter valve you mentioned. First of all yes, I cleaned it. However, does it operate off of back pressure in the exhaust when rolling off the throttle? My understanding is that it injects fuel into the carb when rolling off the throttle to prevent backfire. Is that correct? Would/Could an AM header and un-restricted AM pipe reduce the backflow pressure enough to cause this to no longer work as intended and cause the hiccupping I'm experiencing?

Anyway... My last needle clip adjustment was to move it to 1 below the middle but that is too lean as the bike is backfiring a touch when decelerating so I'm going to get into the carb yet again to move that clip back to middle or 1 above middle.

I really wish I could figure out this hiccup. Perhaps I'm just being too picky and wanting the bike to run like a fuel injected Lexus but I don't think I'm asking for too much. Thanks for the help and for giving me a place to share my screwy story.

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Need to be clear, "backfiring" and popping out of the exhaust on decel are 2 different things. Backfiring is a KA-POW ! Popping is a more subdued pop pa pop pop pop. They're caused by 2 different things.

Yes, the air diverter valve is supposed to provide a rich condition during negative throttle positions. We had a long discussion on this some time ago. Could probably do a forum search for "air diverter valve" and my name and find it. I'd say your theory has merit.

I have no doubt that an AM exhaust systems flow is different than stock. When you say "full" AM exhaust, that includes muffler too?

A larger diameter header and freer flowing muffler than stock will decrease back pressure in the system over that of stock, having the effect of lower bottom end  torque in slow speed riding and throttle positions, and more flow/less restriction to over rev at higher speed riding and throttle positions.

You never answered the question of your elevation or if the air filter and cage is still the stock unit.

I ask about the air filter because when you alter the exhaust but leave the airbox and filter stock, it becomes a bottleneck to flow for the whole system. You get screwy jetting problems that's hard to dial in. Increase flow of one, you have to increase flow of the other.

You understand the relation in raising and lowering the needles the clip position, right?

And with all this messing with the needle, be sure you don't get the slide arm turned around 180* when re-installing and cover the hole in the bottom of the slide.

 

Edited by Trailryder42

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2 hours ago, Trailryder42 said:

Need to be clear, "backfiring" and popping out of the exhaust on decel are 2 different things. Backfiring is a KA-POW ! Popping is a more subdued pop pa pop pop pop. They're caused by 2 different things.

Yes, the air diverter valve is supposed to provide a rich condition during negative throttle positions. We had a long discussion on this some time ago. Could probably do a forum search for "air diverter valve" and my name and find it. I'd say your theory has merit.

I have no doubt that an AM exhaust systems flow is different than stock. When you say "full" AM exhaust, that includes muffler too?

A larger diameter header and freer flowing muffler than stock will decrease back pressure in the system over that of stock, having the effect of lower bottom end  torque in slow speed riding and throttle positions, and more flow/less restriction to over rev at higher speed riding and throttle positions.

You never answered the question of your elevation or if the air filter and cage is still the stock unit.

I ask about the air filter because when you alter the exhaust but leave the airbox and filter stock, it becomes a bottleneck to flow for the whole system. You get screwy jetting problems that's hard to dial in. Increase flow of one, you have to increase flow of the other.

You understand the relation in raising and lowering the needles the clip position, right?

And with all this messing with the needle, be sure you don't get the slide arm turned around 180* when re-installing and cover the hole in the bottom of the slide.

 

This is *not* backfiring. This is popping. It did this popping a LOT before jetting change. Didn't again until I moved the needle clip to 1 click lean away from middle. That's not too concerning to me except that I understand it means it's too lean so I plan to lower the needle clip back to middle or 1 below middle. (Correct?)

I'm running full AM exhaust meaning a free flowing header and muffler. "Bills Pipes" brand to be exact. When I bought the bike it came with 3 exhaust systems. The one that is on it, the stock pipe and muffler and a slip-on that is open w/ no spark arrestor that works with the stock pipe. I might put the stock set-up back on to see if that changes the hiccup under deceleration. Too many variables!

I'm also running an AM air filter. I believe it is a UniFilter on a plastic cage. There is a picture of it in my previous thread. The air-box hasn't been modified, however.

I understand the raising and lowering, yes. Raising = Leaner Lowering = Richer.

 

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Correct, raising or lowering "the clip" on the needle = those results.

Still no info on your elevation. I want to know your elevation to determine if your current 58/160 jetting with that exhaust and UNI filter combo is proper.

At the WOT position you described in your first post that this is happening, you're on the main jet system, not the needle. You are probably seeing an effect, but not elimination, in the degree of popping with clip adjustment because of overlap between the 2 systems. I'd set the needle back to middle and increase the main jet size. If you're near sea level in elevation, with that exhaust and air filter combo, a 160 is often too lean. In this case, I'd recommend a 162-165.

Are you riding street, trail or both with this bike? Ratio of each?

The stock header is no slouch, plus it's stainless steel. I never understood some folks need to swap it out. Some could use a little work inside the mounting flange area to relieve excess weld (one of the Gordon mods) but that's it. And the stock muffler ain't bad either, once Gordon modded, and you keep its arrestor intact.

 

Edited by Trailryder42

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1 hour ago, Trailryder42 said:

Correct, raising or lowering "the clip" on the needle = those results.

Still no info on your elevation. I want to know your elevation to determine if your current 58/160 jetting with that exhaust and UNI filter combo is proper.

At the WOT position you described in your first post that this is happening, you're on the main jet system, not the needle. You are probably seeing an effect, but not elimination, in the degree of popping with clip adjustment because of overlap between the 2 systems. I'd set the needle back to middle and increase the main jet size. If you're near sea level in elevation, with that exhaust and air filter combo, a 160 is often too lean. In this case, I'd recommend a 162-165.

Are you riding street, trail or both with this bike? Ratio of each?

The stock header is no slouch, plus it's stainless steel. I never understood some folks need to swap it out. Some could use a little work inside the mounting flange area to relieve excess weld (one of the Gordon mods) but that's it. And the stock muffler ain't bad either, once Gordon modded, and you keep its arrestor intact.

 

I'm in Nashville, TN. Google tells me the elevation is about 600 feet above sea level. Most of my riding is off road trails/adventure/discovery/woods with a jump or two here and there with the occasional trip on road.

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In that case, I think I'd be putting the stock header back on it, that is if it's not crushed. Take a look at the posts for cleaning up its flange welds and you can try mating it with the AM muffler or with the stock muffler with Gordon mod. Experiment with both, but I think it would do better for the riding you're doing.

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