High Idle due to.. Air Leak?

Hey guys,

I just bought my 82 Yamaha Maxim last week and I started have some issues. It's a 82 650 XJMaxim. Pretty much everything is stock except I'm pretty sure the exhaust is aftermarket, which may be part of the problem.
When I bought the bike the owner had the carb intake boots epoxied to fill in the cracks because there was an air leak.
After warming up, the bike idles at a screaming 3500rpms.
But now, after taking it on a longer trip (50 min), it idles at about 4 grand and starts to overheat during riding. I've tried putting the gas setting on prime and that helps the running aspect but not the high idle.

Could it be an air leak? Needs to be rejetted for the exhaust?
What changed during the long ride that makes it run worse?

Any help or advice would be fantastic.

Thanks a ton!

 

the exhaust, if its more restricting, will cause it to run lean, but i dont think its gonna step up the idle like that. but i'm just learning my own yamaha (750 seca 82) and am repeating to you what i have been told cause i put a 4 to 1 exhaust on. you probably have tried turning the idler down already? make sure your choke lever is fully closing at the carbs, that would account for the faster idle on a warm machine as well as initial fast idle. and yes an air leak could do it, where the rubber boots go into the block spray some combustible liquid and see if it revs up. hope that helps.

 

Could be several things but have you tried to adjust the idle screw first?
Possibilities for a high idle are: idle screw set to high, sticking throttle cable, air leak, idle mixture, high or overfilling floats and more.
You should check the basics first, idle screw and throttle cable. Spray some starter fluid around the boots and throttle shaft seals to see if they leak.It is probably time to remove the carbs and rebuild them.

 

Yes i have messed with the idle screw and the choke is completely functional and does not stick or stay partially on. The exhaust is a 4 into 1. I'm pretty sure the main reason for the high idle is the carb boots issue. But, what could I have broken by riding the bike 50 minutes at 70mph? It started acting up and overheating to the point of shutting off after that trip.

Anything?

 

I've tried the starter spray trick looking for a leak. I have a similar problem with the idle rising from 900 to about 1400 as the bike heats up. At 1400 I tried to dial back the idle screw set to regain 900 but then the bike barely runs. So far I can't find aleak with the spray. Maybe because the spray is an atomized liquid rather than a gas and the leak is too small to suck it in? I'm going to try the unlit propane torch trick. Maybe as mlew says, it's not a leak and it's something else.

 

If your boots are leaking then it is running lean. A lean mixture means more heat. Test those boots with some starter fluid( most brake cleaners also work). Spray some around the boots and you'll hear a change in engine speed if there is a leak. You could have several carb problems compounding together to give you problems. I think ist time for a carb overhaul.

 

i have an aftermarket petcock on my tank. i cleaned my jets, needles and float bowls. since...idles all over the place, pours gas out the air intake filters when not running and fuel on, slow wind down, sometimes acts like it running out of gas...and sometimes it runs so good and so fast i'd put it up against the fabled gsxr. floats not stickin. carbs clean enough to eat off of..i feel your pain. i have sunk the three tree 1 1/2 inches for cornering, moved bars forward and using aftermarket clip ons. is now set up very like and performs very like honda's intercepters. WHEN IT RUNS! the mother f***** has the potential to be one of my favorite bikes ever but it hates me

 

3,500 rpm's is NOT Idle, ... that's a third of the way into the Power Curve.
Your Throttles are NOT Closing.

1.) Pull the Plugs. Line them up 1, 2, 3 & 4 and Post a photo of the Business ends ... In focus and well lighted.
(If you Pull those Plugs and they are CLEAN, ... Add 2-1/2 Ounces of Marvel Mystery Oil to your gas at every fill-up until we get this situation ironed-out.

2.) Perform a "Bench Sync" on your Carbs. Use Strips of 3X5 Card. You have to set the Linkages to allow the Throttles to CLOSE.

3.) Don't run Critically Lean. Air-cooled aluminum can't handle it.

4.) Prepare to remove the Carbs for Cleaning and re-jetting. You have to hve the Carbs working quiite well to alleviate all your present conditions.

 

Thank you for the replies and sorry for the late response.

I am currently rebuilding the forks and brakes. I had the engine rebuilt but am still have a similar problem but not near as severe. I replaced the carb to engine boots with used '82 boots and the problem almost doesn't exist. After long rides the idle does stay up (1500) for a while though. The carb cleaner test did yield leaky one time, but I can't replicate those results with warm or cold boots to save my life.

I am going to try and seal the boots with ATV sealant, the carbs are clean and sparkly and my plugs are fresh as can be. I will keep you updated.

It's riding season!

 

"Hanging idle" is the symptom of an out of sync condition.

It can only be cured with a running vacuum sync; once the float levels are accurately set AND the valve clearances in spec.

Otherwise you can fight with it forever.

 

Genius, I will get out the feelers and while I am at it give the carbs a good once over. I'm also going to seal the boots just for good measure.

Thanks for all the help! I will keep you posted.

 

Any update?

 

I sealed the carb air boots with RV Sealer and covered them with 1 1/2" bicycle tire tubing and the problem has not occurred since. I would recommend using some of the videos on this site to try and fix it. I couldn't see any visible leaks, but this worked and I've driven it at least 1k since then. Thanks all!