Carb Boots

[snark]

My '81 GS450L has been popping, backfiring, and stalling lately, especially when it is cooler than about 50 degrees out and usually at about 3000 RPM. I can sort of fix this be riding with the choke part way on. I talked to a friend of mine who said that he thinks the carb boots probably need to be replaced. For a 24 year old bike I can believe that part. My question is...do both sets of boots need to be replaced or just the ones between the carb and the head? Do I need to start looking at another possible cause?

Thanks

[Anonymous]

Most likely you only need to replace the ones between the carbs and the air box. Usually the ones on the manifold start to leak gas when they go bad. It is also possible that the problem is in the carburetors themselves. Sounds like it's not getting enough gas through the needle jet. When you put the choke on it actually feeds it more gasn and not less air (technically it's not a choke then, but they still call it that). If one of your main jets is plugged up this would explain why turning on the choke seems to solve this. The carb clean up series on the front page of this site is a big help (under the technical tab). Check it out

[UncleMike]

I was under the impression that the boots between the head and the carbs were the major problem. This would save me a lot of money if it isn't the case as the one's I'm finding are looking to run me around $25-30!

[Anonymous]

Ya. Sorry about that. What I meant to say (kind of came out wrong ) was that usually when the ones on the monifold go bad they leak gas. That can cause the kind of problem that you're having. If they start to crack between the carbs and air box your bike will most likely still be running. It's not terribly good for it, but it will run better that you are describing. What carbs does your bike have on it. I have a spare set of manifold boots for an '83550. It is the weird kind that had two 2barrel carbs. I doubt yours has those, but if it does I'd be glad to send them to you with just shipping costs.

[UncleMike]

Oh, man. If he doesn't want 'em, I'll gladly pay you for them. I'm in the process of doing a complete re-build on mine as well and that's been the most elusive part.


Not sure if we share the same carbs though. Since I've got two cylinders and you have four, correct?

[Anonymous]

Ya. It's a 4. It only has two carburetors, but there are four holes in the intake boots (each carb has two boars in it). Kind of a cute idea, but finding parts for those carbs sucks! :x If you want the boots for your 2 then you might have luck with the wanted forum. You see people selling all sorts of stuff. Good luck 8)

[snark]

Thanks for the offer but I have different carbs. I'm not seeing anything leaking around the boots...that was a suggestion from a friend of mine. I think I may lean towards a good carb cleaning. Thanks for the help.

[earlfor]

Boots are intakes. Leaks will not be visable.

Earl

Thanks for the offer but I have different carbs. I'm not seeing anything leaking around the boots...that was a suggestion from a friend of mine. I think I may lean towards a good carb cleaning. Thanks for the help.

[bradleymaynar]

The best way to see a "leak" on the intake is to spray WD-40 or similar around the intake boots. If they are leaking the engine should bog depending on which side, if not both. As Earl said, they don't "leak" because the engine is pulling/vacuuming from the carbs.

Brad tt

[snark]

OK...here's a dumb question. My boots look fine...solid and not dried out. Could just the O rings be bad? I don't need much choke to make it happy and if the bike and the weather is warm enough it runs fine.

[Anonymous]

If you have the bolt on intake manifolds the o-rings should be checked and then replaced anyway.

Steve

[KEITH KRAUSE]

OK...here's a dumb question. My boots look fine...solid and not dried out. Could just the O rings be bad? I don't need much choke to make it happy and if the bike and the weather is warm enough it runs fine.

Does the bikes idle rpm rise significantly when fully warmed up? This is the classic symptom of an intake leak.

[snark]

I think you may have found my problem. She runs a little high when warmed up. That's also when the popping and backfiring stop.

[KEITH KRAUSE]

I think you may have found my problem. She runs a little high when warmed up. That's also when the popping and backfiring stop.

The most common cause of an intake leak that results in a "high idle" once warmed up, is the o-rings in the manifolds get hard/brittle and leak. Replace them and apply some hi-temp bearing grease to help them last. I also suggest replacing any stock manifold Phillips screws with Allens so you can torque to 6 ft /lb.

[snark]

Thanks for all the help. The O rings are replaced and all is well. One thing I did learn from this...when it has the old phillips screws and not enough room to fit a screw driver, a pair of channel locks work quite nicely!