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KLX 351 idle problems

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Here's the long scoop of it. Sorry for going long winded, but I tried to answer in advance any questions I'm sure you guys would think of and ask:

What would act like a vacuum leak that isn't a vacuum leak? *headscratch* Idle wanders, gets worse as bike warms up, eventually bogging and dying. Sometimes easy to fire right back up, sometimes you have to wait a few minutes and use full choke (even when you've just been riding for an hour). Runs better when cold. I've checked oil, coolant, gas. I've checked for vacuum leaks and cannot find one for the life of me. It used to run great. This started "all of a sudden" one day. Runs almost perfect when it's running. It's the sitting around with clutch in or just idling where it gets all crazy-like. Throttle response also doesn't seem to be quite what it used to, and it sometimes seems to have these slight momentary hiccups and surges at speed. They're difficult to detect, though.

351 big bore

FMF Q4

132 main jet

42 pilot jet

dynojet stage 2 needle jet and spring (already updated before big bore kit)

snorkel removed

It ran unbelievably excellent with this set up- including steady, reliable idle and easy starting- until a few days ago. The first "scare" happened when I developed a kink and a small split in the hose from my reserve tap to my petcock (sounds like a personal problem). I assumed the worst, but filling it back up and it ran great. So, I drained the tank and replaced the bad fuel line. Bingo. Seemed to fix it.

But, it quickly developed the erratic idle after that. Is it possible some gunk just got loose, made it somehow past the fuel filter (or gunked up the fuel filter, even) and is clogging my jets? This is my DAILY rider, so in the past 25,000+ miles I have never had any issues with gunked up jets.

There is a slight exhaust leak, but it's always been there. Bill Blue (351 developer) put the kit in with me and noticed it on the rebuild. It had been there before the rebuild and he said it was slight enough that it shouldn't make a difference. And, for the first 500 or so miles after the rebuild (oil changed at 350), it didn't seem to matter.

There is popping at decel pretty severe, but that's been there ever since the pipe change and doesn't seem to go away or get any better or worse with each successive rejetting. Until the bike started recently idling like crap, I never gave it any thought, except a thought of annoyance when my right sock and boot smells like exhaust after a long ride. LOL

Also, there is definitely top end noise now. A clicking/knocking like the valves are off a bit. Hoping it's not the cam chain (yet again... stupid Kawasaki). It does seem to get a bit better once the bike is warmed up. I'm just praying there isn't damage done to my precious new piston. I did have one brief instance of overheating and I pulled over straight away and found I was low on coolant. Added water to make it the rest of the way home and had no issues, even at 75mph (stupid interstate. I hate "cruising" that fast). I had done a track day that same day and this was during the ride home. I noticed no overheating issues all day at the track, but I only ran 3 or 4 sessions, as people kept crashing due to cold tires from a cooler day and that would end sessions early.

I went up 2 teeth in the front sprocket before the track day and really took it pretty easy (especially with all the crashing going on... I have to ride home, you know?). I didn't push past 80mph, averaged about 55-65 through the turns and basically just cruised around the track and had fun throwing it around the corners. For 20 minutes. And then the bike would sit for an hour until the next session. Repeat for a total of 4 times. Not much different than a 20 minute highway commute, honestly, but with more lean angle. Was fun and chill.

But, at the end of the day, just after the second to last session, was when it first died on idle. I mean, DIED. Instantly. Almost as soon as I pulled the clutch in and began to coast back into the paddock. It had done this once before the day before and left me baffled, but it bogged for several seconds first. This time it was basically an instant drop in RPM.

It took a few tries, but I got it to restart and made my way quickly back to the garage, where I tried playing with the idle screw. But, that didn't seem to make a difference. Sometimes the idle would race, sometimes it would bog. But either way, it would wander until it bogged and eventually killed itself.

On the ride home, this got so bad that I kept stalling at every light. I made it about 20 minutes from home before giving up, calling a friend (whom I seriously owe a beer or 12), and towing it the rest of the way in his pickup. Does it run? Sure. But I can't stop or it will die. And that's not a good enough reason to give a cop. :smashpc:

It sure seems like a vacuum leak, like something probably just came a little loose on the track (something that was already coming loose), but I cannot find a leak for the life of me. Also, what's with the top end noise? It used to run so awesome and without any clicking. Would the new piston affect valves? Is one of the valves bad? Compression testing seems to give a lot of false diagnoses, from what I've read and heard, so I don't want to go chasing my tail down that expensive path. I would, however, like to check and adjust valves.

I do know that an exhaust leak can mimic the sound of valves or cam chain. But I'm just confused here. There was always an exhaust leak (a slight one), but there wasn't always the top end noise. In fact, it ran awesome after the big bore kit, because part of my top end noise before was ringslap and I knew it was getting time for a new piston (ergo, "Why not bore it out?").

I just have this horrible sense of dread that something very expensive is wrong and something terrible happened to my brand new top end... You know how your mind goes there. I've been up since 5am. I am losing sleep over this. I don't want to go shelling out hundreds of $$, you know?

If the float level was bad, why would it get worse as the engine warms up, and why would it run great but not idle. Wouldn't a low float bowl do the opposite? Idle great, but not accelerate? That's what was happening before, when my reserve tap line was pinched. It was getting *just* enough gas to idle smoothly and start great, but then on acceleration it would bog, buck, and die.

Now I have the opposite problem. It's hard starting once warm, accelerates decently, but bogs and dies on idle, especially once warm. *headscratch*

I went from one problem to the other, but all I did was replace a fuel line.

I am in way over my head here. This machine is my daily rider, my only vehicle, and I just put a ton of money into it to improve it and now it's barely running. This is very frustrating and sickening. I'm praying it's an easy fix, something obvious that I'm missing.

Oh, as for hours... The first 300 miles took over 8 hours. I was careful to break it in properly. Lots of gear changing, engine braking, cruising at various speeds and various gears, roll ons, roll offs, rofls (just kidding). It was a LONG ride back from Topeka to KC and the bike seemed to handle it like a champ. Ran awesome to work the next morning. Changed the oil. Riding home, I hit reserve and that's when the pinched reserve line came into play. That was a cheap and easy fix/find. But not more than a couple days after that, this whole erratic idle business started. It's getting rapidly worse and worse.

👍

Help!

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Sounds a little like you got water in the tank, or maybe a piece of fuel line in the float valve maybe that's causing a lean run condition. Have you cleaned the tank and carb out? Also, there is a tank vent, make sure that is clear and working properly. Set up a a fuel line going into a gas can and turn on the petcock and see if it runs continuiously without stopping.

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It's gone through a couple gas tanks since this started, but I can still check for water, I guess. Good call on checking fuel flow from the petcock. I was hoping to avoid having to pull, disassemble, and clean the carb as that means being without transportation for at least a few days (and work is a 2 hour walk away), but I may be out of options at this point. Guess I'll pick up some carb cleaner at work today (I work at a dealership). Might as well pick the mechanics' brains while I'm there. And maybe pick up an air filter and spark plug while I'm at it. Even if they're fine on inspection, at least I'll have them ready once I start pulling parts.

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Question: Wouldn't interrupted fuel flow get even worse under load than idle, as there is more demand? I really do want to understand the dynamics behind this, assuming that's the issue (once I check flow). It seems to me that as the demand for gas goes up, a gas clogging issue should make itself more apparent, not less. That's what happened last time there was an interruption in fuel flow. It would idle fine, but die under load as the float bowl would empty. This opposite thing has me confused. I do sound engineering, so I understand the concept of troubleshooting signal flow, but I only know the "rules" and "symptoms" of audio engineering, not small combustion engines.

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Definitely take your carb out and make sure all jets are clean.

I had similar on an older bike and it was a clogged pilot.

And it shouldn't take you more than a couple hours to remove the carb and clean it thoroughly, don't worry about down time!

Good luck

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The top end noise, quieting when warmed up, sounds like classic cam chain tensioner problems. Consider the Krieger adjuster. But that shouldn't be the cause for idle problem.

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The top end noise, quieting when warmed up, sounds like classic cam chain tensioner problems. Consider the Krieger adjuster. But that shouldn't be the cause for idle problem.

Yeah, no, I was mentioning it as an "oh, by the way..." And this isn't the first cam chain/tensioner issue I've had with this bike, so that's why I thought I recognized the noise. If someone is finally coming out with an aftermarket tensioner for the 09+ models, I could just kiss them.

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How interesting. I put a Bill Blue 331 kit in my klx300 early last summer. My break-in was very meticulous, probably way overboard. First trip and hard riding was in August in Colorado Mountains. First day out it ran great throughout power band. Second day it ran great but was beginning to have off idle issues. by mid third day I was unable to come off idle under any kind of load without engine dying. Screwing in the fuel screw until it was completely seated made the bike idle best. Have not had a chance to pull the carb off and check it out. I did forget to tighten the air boots on each end of the carb so maybe some dirt got in. I also experimented with some av-gas blended into regular fuel on second day. I am pretty sure that it has nothing to do with the kit itself as i was very pleased with the increased power. Any thoughts ?

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Yeah, no, I was mentioning it as an "oh, by the way..." And this isn't the first cam chain/tensioner issue I've had with this bike, so that's why I thought I recognized the noise. If someone is finally coming out with an aftermarket tensioner for the 09+ models, I could just kiss them.

I believe Krieger has a tensioner (adjuster) model that will fit your '09+ model. He doesn't update his web site very often, and doesn't even show one for the KLX250 on his site that I can find. But I and many others have one made for our bike. He collaborated with TNC (a member on this site) to build one. Give him a call or email. http://www.kriegercamchaintensioners.com/

Kind of sounds like KAWBOYBILL needed to lean out his BBBB after some break-in. This could be something to check for the idle issue.

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Ah, gasket leak, too. Had to put more than 8 oz. in the radiator twice in the past 4 days. :smashpc: The poor guy was almost bone dry and gave an overheating warning once. Bah.

It's in the back of an Enterprise van now and I'm heading back to Wichita. Bill's a stand-up guy and we're going to replace the head gasket tomorrow morning. Since I'm heading back, I'm going to just swap out the carb for the Mikuni. The stock carb hasn't been the greatest since mile 1. I'm kinda done trying to "make it work." I've heard nothing but good things about the TM carburetor, except for the gas consumption.

But if I had to choose between gas mileage and performance/reliability, I'll pass on the gas mileage. That's just fun tax.

Report to come...

(Even before the 351, I have rejetted this thing more than once. Cold starting sucks and throttle response is never more than "acceptable.")

Edited by lauriejennifer
added more info

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I have always had decent performance out of my stock carb especially with the dyno jet kit in it. Fairly easy to tune for both low and higher altitudes when it was a 300. I hear good things about the mikunis and am contemplating a switch. Not sure if I want to stay with a 34 or go to the 36. I also am not fond of having to virtually remove the carb to reset it for the altitudes. Oh well decisions to be made over the off season.

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by mid third day I was unable to come off idle under any kind of load without engine dying. Screwing in the fuel screw until it was completely seated made the bike idle best. Have not had a chance to pull the carb off and check it out. I did forget to tighten the air boots on each end of the carb so maybe some dirt got in. I also experimented with some av-gas blended into regular fuel on second day. I am pretty sure that it has nothing to do with the kit itself as i was very pleased with the increased power. Any thoughts ?

It's NOT the 331 kit that is causing your carburation problems. Why would you put AV gas in it, and, was it clean? My FIRST guess would be Pilot Jet clogging. The dirt you may suck in from not tightening the boots would potentially cause high wear in your engine, but, not necessarily anything with your carb function. Again, Pilot Jet clogging is where I'd look first.

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I am sure it is not the 331 kit. I do agree that the pilot is most likely the issue and that is where I will start. I have owned the bike since new and have never had any problems with contamination in the fuel bowl. Since I have the fuel bowl off twice a year I make sure everything is clean. That is why I would be surprised to have a clogged pilot. Forgetting to re-tighten the air boot clamps was dumb on my part. I experimented with AV gas as a method to get the octane up a bit. The information I have says 91 octane minimum for the original 300 motor at 11:1 compression ratio. Since the 331 kits are 12:1, I was looking for a way to get the octane value up a bit.

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Got the bike back yesterday. Went with the Mikuni carb while I was at it. Heck, if it was having idle problems, why not just go ahead and upgrade anyway, right?

*sigh*

It ran great for about 2 miles, and then it started doing it again. Wandering, erratic idle, and it dies quickly on idle once the engine is warm. I recorded a video of it idling in my garage from cold to warm:

VIDEO:

The "it dies on idle" is much more dramatic when actually riding it (it's almost as soon as you pull the clutch in and begin to stop), but it's raining and crappy outside at the moment. I'll demonstrate that in the near future.

This is very, very frustrating. I literally cannot take this thing anywhere, unless I don't have to stop at any lights or stop signs. I just put $$$ into this upgrade, and now it won't hold idle.

Four months ago-ish, Kawasaki had to warranty a bunch of repairs on my wiring harness that had prematurely corroded. It has been a steady decline in idle performance ever since then. In other words, this started before the big bore kit and is just now getting rapidly worse, to the point where the bike is honestly unrideable. I hope that if it is electrical, it would still be under warranty, since my only upgrades have had nothing to do with electrical. The sudden, most rapid decline started at the same time as the cracked sleeve.

The valves were also just checked and adjusted. When I mean JUST, I mean less than 20 miles ago.

Edited by lauriejennifer

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UPDATE: Bike idles *slightly* better with a/f screw completely in. It still hiccups, falters, and eventually dies as the engine warms up, though. If I try to back out the A/F screw even just 1/8th of a turn, it will stall IMMEDIATELY.

It sure seems like a vacuum leak. Why can't I find one ANYWHERE? *tearing hair out*

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UPDATE: Bike idles *slightly* better with a/f screw completely in. It still hiccups, falters, and eventually dies as the engine warms up, though. If I try to back out the A/F screw even just 1/8th of a turn, it will stall IMMEDIATELY.

It sure seems like a vacuum leak. Why can't I find one ANYWHERE? *tearing hair out*

Is there an o-ring on the AF screw? Loosening it richens the mixture....surely you're bike isn't so rich it's killing it...so, if there is an o-ring there that allows a vaccuum leak, maybe that could be part of the problem?

That's just a wild guess. Still think it sounds like fuel delivery problems due to a carb vent line being welded nearly shut, or kinked, or full of dirt, or a bug or spider web in it.

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I have had issues with the cam chain before. It may just be a bit stretched and time for a new one. Still might be something as simple as a failing ignition coil, though.

I've pretty much narrowed it down to ignition coil, igniter (aka, CDI box), or loose cam chain. Or, perhaps a combo of all of the above.

I also think it's a timing issue, because I think it's wandering past TDC on sudden decel... not if I just let off the throttle and let it engine brake, but if I pull the clutch in and let the RPMs drop suddenly, it will stall. Every time, once warm. Intermittently, if cold.

I can now get a fairly steady idle otherwise. And if I just keep giving it a bit of throttle while coasting to a stop with the clutch in, it won't die. Then, if I ease off the throttle slowly, it won't die. It's going from half-throttle to clutch in and coasting that seems to be killing it... but only after the engine is warm.

Also, it is becoming increasingly hard starting. It also doesn't like to stay started initially. It turns over freely, but doesn't "catch" (a chick's term for "fires up, or 'actually starts'"). Or, it will often catch briefly and with quickly rising RPMs... only to drop back off and die immediately. $((*#&$@(*& %)(

#$O(#$&*%#$*( !!!!!

So, in conclusion:

-Hard starting

-Fairly steady idle. Probably just some more minor jetting and a/f screw adjusting as far as that goes.

-Once warm, the engine will stall IMMEDIATELY if you let the RPMs drop suddenly. For example, cruising at 35mph. Red light ahead. Pull clutch in to coast. RPMs drop off completely in less than 3 seconds and engine is "dead." Hard restarting.

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Yeah, no, I was mentioning it as an "oh, by the way..." And this isn't the first cam chain/tensioner issue I've had with this bike, so that's why I thought I recognized the noise. If someone is finally coming out with an aftermarket tensioner for the 09+ models, I could just kiss them.

I just read this... if you are a Laurie or Jennifer I appreciate the sentiment, but my wife wouldn't like it...

Mark - Krieger Cam Chain Tensioners

By the way, ever get the problem fixed? I had a wandering idle and a problem with stalling and hard starting when I had the valves too tight, cam chains worn out, bad OEM tensioner in my KLX650. Worked great after that... for the next 30,000+ miles since the rebuilt top end and manual tensioner. It's still going strong and I check the valves a bit more frequently.

Edited by KLX678

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