89 Bayou 300 backfires & coughs above idle speed

[jguenthe]

Our 89 bayou 300 starts great, idles, but coughs, spits and backfires when you give it throttle over a fast idle. The carb seems to have some pressure blowing back out of it.

Here's the long saga.....
My son & I were given this 2x4 bayou and it had not run for some time, and the carb was in parts and it had no spark. I'm a fair mechanic, but have never worked on ATV's. We bought a Clymers manuel and after diagnosing the ignition module was bad replace it and got spark. We then throughly cleaned the fuel tank, tank shutoff valve, replaced gummy fuel hoses, added a fuel filter. Since the carb was in pieces when we got it, we compared all the pieces to the mauel diagram to check that no parts were missing. Then cleaned and reassembled the carb per the manuels diagram. I also filled the engine/transmission brim full of diesel, let it soak and then circulated it through a filter/pump to clean up and free any gumed up/stuck internals (this works excellent) We also checked the exhaust to be open, went over the wiring, and checked compression to be 130psi (marginal) .

The engine started and above fast idle coughed, backfired and seemed to be blowing back through the carb. Adjusting the carb needle seemed to have no effect of the rough running or even on the idle operation. The engine seems to be running very rich and smokes black when you give it throttle. After checking timing & several carb recleanings and float adjustments I gave in and took it to the local kawasaki shop. The shop put a new needle, seat and diaphram in the carb and it still ran the same, then they put a new carb on it and still no change. They finally told me it had a worn cam and I told them to remove the new carb and I picked it up.

I pulled the head, the cam checked out to be excellent per spec's, but the valves were very worn. After getting several recommendation for a different shop, I had the head rebuilt with new valves & seats, and they said the valve guides were OK. I also pulled the cylinder, and found the piston had been recently replaced with the next oversize one. We slid off the top ring and checked end gap in the bore and it was at new spec's. The cylinder appeared recently honed, and measured in spec, but about .002 - 003ths out of round. (I suspect someone honed the cylinder to meet the diameter spec of the oversize piston instead of having it machined)

After reassembly & checking timing ,the engine wouldn't start. After much troubleshooting I realized we had it timed 180 degrees out. We corrected this (compresion is 150 -160 psi) and it started right up, but still coughs, backfires and has blow back above high idle. The exhaust is clean at idle, but turns black as soon as you try to rev it up. Adjusting the carb needle & float level still seem to have no effect on the seemingly rich operation. (This is the original carb with the new nedle, seat 7 diaphram the shop installed)

I've moved the timing chain one tooth backwards and one forwards and it won't start, so this seems to confirm my timing is correct. I rechecked my valves and confirmed they are both closed (rockers loose) as soon as the piston starts on the up compression stroke.

What am I missing?
I've read some post that talk about a recall shim being aded to the carb? Does this apply to mine?
Could the new ignition module be faulty.
I haven't pulled the flywheel (don't have the special pulle rthe manuel shows) cover, could the key be slightly sheared, throwing timing off very slightly?

Thanks for any suggestions.

[QKENUF4U]

welcome to the world of ****ty bayou's. im a mech. and was never able to figure out a customers quad for this same problem. the only solution ive seen on here is the guy got a new carb. i did everything i could do to solve that problem.
good luck

[olbooker]

I'm curious as to the ignition module. Is this a NEW OEM module?

I had an older Bayou 300 come in with similar symptoms. The customer wanted it re-jetted, since he brought it up from a lower altitude. He had already replaced the carb with a different model, trying to get it running... went from a CV to a standard Mikuni.

After fixing his incorrect cable housing length and getting the slide to fully close, I was able to get it started. After about half throttle, it would start to cough and die. No amount of jetting changes helped. I had him bring me the original carb and it was quite worn out. Must have been without an air filter for some time... the slide was trashed.

This Bayou smoked horribly as it warmed up. Obviously in bad condition and the customer didn't seem to want to spend any money on it. It ran at low altitude, but not after bringing it up here. I finally tracked it down to a bad ignition module. I found one wire that, if barely touched, would cause the engine to die. It happened to be the coil wire. Wire in the module was broken, not allowing enough current flow to sustain higher RPMs. Seems that this module had been replaced before with a used one and wasn't even the correct module. It was mounted all wrong, with a hose clamp, putting the wiring in a strain. Haven't heard from the customer in months now after telling him how much a new module costs.

When you say that you timed it 180 out, I'm concerned that you may have nicked a valve and possibly bent it. It wouldn't take much to cause a little backfire out the intake.

I don't have a manual available at the moment, but 150ish compression might not be up to par on a fresh engine. Not sure if the out of round cylinder is contributing to it. How did you measure this? Honing is not an incorrect method of resizing the cylinder. We used to have problems using our Sunnen automatic honing machine on small cylinders, previously bored or not. It would hone out of round. The old fashioned Sunnen hand hone would hone perfectly.

I almost want to rule out carburation. IF a new carb was tried and didn't affect the operation, you should be able to rule it out. The carb to head boot is good... no cracks? Is it running exactly like it did from the start? A lot of things have happened here since you started this project. Sometimes it is easy to say "it does exactly the same thing" when it doesn't. Sure sounds like you have checked it out thoroughly.

What a long-winded reply. So sorry. Sometimes I feel like Q above me, but it isn't always ****ty Bayous that frustrate me. So you want to be a motorcycle mechanic, eh!

[jguenthe]

I replaced the ignition with a OEM module I bought off the internet. It looked new, in a clean box, so I think it was the real thing. I measured the cylinder with a set of snap gauges. I tkow thats a little tricky, bit I took the measurements several times to be sure I was consistent.

It really does seem to be running exactly the same as when It first started after I replaced the ignition module. The one thing that baffels me about the carb, is no amount of adjustment seems to change it at all. I can run the pilot jet complete in or several turn out and nothing changes. Any body have a more detailed carb adjustment procedure than in the Clymers manuel?

You mention I might have bent a valve. Can I use compression tester hose and a compressor with air regulator & a valve to check the engine?

my son rechecked and wiggled all the wiring and even used a wire with aligator clips to jump from point to point to rule out a bad connection this weekend ..none found.

As far as wanting to be a motorcycle mechanic...I'll nominate my 19 yr old son for that. As a pre-engineering college student these old engines are good training to go along with the books.

As for me, I'm just an old dad keeping up with 3 boys, and having the time of my life doing it.

Merry Christmas, and I don't mean Happy Holidays!

[zedx11]

did you check to see if the timing chain was still within spec? the book should give you a length for a certain amount of links then the tolerances.

[jguenthe]

This evening I checked the timing chain and it's well within spec's. Also confirmed the tensioner is working properly.

Any suggestions for a replacement carburator for the klein.

[olbooker]

You could use regulated air pressure in the cylinder to check the valves. Put it at TDC compression, in gear and hold the brake. Shouldn't be any air escaping from the intake or exhaust. 80 - 100 psi should be good.

You have had the carb apart. Are the jets open and clean? What altitude are you at? When you have std jets at high altitude, the pilot adjustment doesn't effect the idle much.

The only problem with using other than stock carburetors is that they don't always match up with the current air box. A carb was tried by the dealer... yes? And it didn't fix the problem.

Is this your carb?: http://www.kawasakimotorcycle.org/fo...d=116607246 6

I wonder if the enrichment valve is stuck open or damaged in some way... Of course, a new carb was already tried.

[Mace_46]

I have a 1995 Bayou 300 and I have the exact same problem.... I notice the last thread was in 2006, any new news on how to fix the problem? I have a new cylonder, piston, carb rebuild, new sparkplug, air cleaner, timing chain, tensioner, and ?gas? .... I am at a loss on what is the problem... I have adjusted and readjusted the carb with no luck..

[elr658]

That's because the valves are too tight. Adjust them to LOOSE side of the tolerance.

[mybabyhimi]

i also have a 94 bayou 2x4 mine runs fine untill i run over a small tree or rock just enought to bounce the rear tires off the ground and then it starts backfiring and won't take fuel it will idle fine i let it set there for about 30-45 sec. then it go just fine seem like the more oil i put in the bike the less it does it only calls for two quarts i put in 5 and it don't do this any help would be great

[mr351clevland]

mate i know this may sound stupid but check the plug on your rectifier make shure its not curoded that can cause them bayous to run crap aswell

[phillbus]

I have a very similar problem with my 86 bayou 300. Runs fine at idle but when you give it gas it sputters and backfires through the carb, and makes a ton of blue smoke (burning oil??) and stalls. At idle everything's fine.

I took off the intake valve cover and the intake valve didn't seem to be seating right. When it was closed you could push it open slightly. I took the head off and sent it to a machine shop, they said it needed an intake valve and valve seals. I had both valve seals and the intake valve replaced (spent about $65)

So I got the head back today, and now I'm trying to time it... I thought there would be timing marks on the crank and the cam sprockets to match up but I'm not seeing anything on the crank.

I don't want to just wing it and ruin my new intake valve.

I was reading on here and seen it can be off 180* can someone explain that a little more? When the piston is at TDC that just means at the top most position right? Then at TDC where should the cam be? Whats the timing mark on the cam sprocket? There's 2 little lines on the sproket 180* apart, are these it? or is it the key on the camshaft?

[mr351clevland]

hi mate i know it seems very confusing trying to time thes things but it is realy very easy ahhhh ok it does have timing marks on the crank at the top of the gear box just under your hi low range shift bar ther is a big flat head screw just below and to the side of the barrel on the left take it out and turn it over till you see 2 lines then f then t t is top dead center just to the side of the t is a line .line it up to a little notch in wer you unscrewed the fat head screw then thats set move up to the top now now on the cam your right it does have 2 lines with writing beside them find the 1 that says lf 300 i think it is. if that is a bit confusing 4 ya its just easer to just make shure your cam lobes are facing down towards the bottom off the motor wen they are put your cam sproket on and line it up the line in the top off the head cas the cam sproket will only go on 1 way like i sed just make shure your lobes are facing down line up the line on the spoket the the 1 on the head make shur your lining ip up to cep tention on the left side of your timing chane with out turning the motor then wen its all done put your timing chane tentioner in turn the motor over a couple of times and re chek every thing if you need anny thing els just let me know