carb (?) high idle problem

[warthogcrewchief]

I'm at a loss in trying to figure out what's wrong with my bike. The bike runs great, except for the fact that the idle seems to increase when it gets warm...even when I turn the idle adjust screw so low that I need to keep throttle on to keep it running. The idle screw seems to only do two things: either be too high or too low...no middle ground.

 

Occasionally, there will be a little popping from the exhaust when the idle is running high.

 

I'm thinking it could be a lean condition. Haven't been able to find any leaks using carb spray cleaner. For carb items, I've replaced:

 

air filter

main diaphragms

carb boots (w/ new o-rings)

 

 

I've also synced the carbs and there doesn't appear to be a single car that is way out of wack.

 

With that, I'm thinking it might be something above the carbs.

 

Any ideas??

[MiCarl]

Idle increasing hot is an indication of lean. A little of that is normal.

 

Your posts sound like you're having trouble dialing in an idle at any temp. If it wants to idle high, then you dial it back and suddenly the rpm drops like a rock and it stalls that is probably an air leak.

 

One place you might not have checked for a leak - the butterfly shaft seals. They are the seals on the throttle shafts where they pass through the carburetor body.

[warthogcrewchief]

Haven't thought about that. I'll have to get some carb-out again on the carbs tomorrow to see if I can determine if there is a leak (again).

 

If I can't find the leak, or unable to correct the leak, I will probably take the carbs off, and do a complete rebuild (again) and replace all the gaskets and seals (didn't do that last time).

 

It does sound like an air leak...

 

I can't seem to find the butterfly shaft seals. I've looked at carbcapital and bikebandit. Anyone know where I can find those small carb parts?

[Rocket]

I can't seem to find the butterfly shaft seals. I've looked at carbcapital and bikebandit. Anyone know where I can find those small carb parts?

 

I went to a Hydraulic shop & got Quad seals (that's what they called them) for the carb shafts on my 750 Maxim before. Take a sample one with you, when you go looking.

 

[MiCarl]

Yamaha doesn't sell the seals separately from the carburetor body. There is a guy (who specializes in XJ parts Rocket) I know that sells them. If you need some I'll get you his info.

[Rocket]

Yamaha doesn't sell the seals separately from the carburetor body. There is a guy (who specializes in XJ parts Rocket) I know that sells them. If you need some I'll get you his info.

 

Good to know, but that scoot is back at home, 1,000 miles away from me. I still have about 20 Quad seals in my desk drawer, back there. No problems with the carbs since I last did them, but I will need to work on the engine sometime.

 

Those seals I had previously used on the shafts, I got at a Hydraulic supply place in Victoria BC, which includes making new hydraulic lines, hoses & seals, parts to re-build pumps, controls.

[Condor]

I just went through that problem with the '91. I solved it by backing off all the sync screws on 4,1,3, plus the idle screw so they weren't effecting anything. Fired up the motor and readjusted the idle screw only to 1000rpm. Motor warmed up normally and the choke worked as it should. With the choke off and the engine warm I could rev the engine and it would settle back down to idle speed normally. I haven't resync'd the bike yet, but feel it will respond normally.

I'm no carb expert, but what I think is happening is if the the carbs other than #2 are sync'd too tight the idle speed is actually being controlled by #1, or #3, or #4, or any combination of them. When the motor is warm, and the choke is off, one or more of the carbs open up the main jet sooner and keep it open longer causing the idle to stay high.

Like I said I ain't no expert, but this worked for me.....

[warthogcrewchief]

I think part of my problem is that I synced the carbs....

 

I took the air cleaner off today and looked at the bare carbs as they ran. The number 1 (Left foward) carb slider doesn't respond to throttle and seems to stick. I had to use a rubber mallet to gently tap on the carb body to get it to return to the closed position.

 

I'm not sure if this is an issue from the diaphragms or I just need to clean up the slider.

 

I figure I'll clean up the slider first and see how it responds after that.... that is, as soon as the Mrs. gets off my case about cleaning up the place.

[warthogcrewchief]

I think I may have found the problem(s). I removed the air cleaner, and it appears that one of the air cleaner clamps was cockeyed a bit. I also removed the #1 carb cover and reseated the diaphragm, which solved the slider problem. With the diaphragm reseated and the intake installed correctly, the idle screw is a bit more responsive. I'll have to sync the carbs in a bit and see if, in fact, it did solve the problem.

 

EDIT:

 

I re-synced the carbs and they seem to be doing alright, as long as I have the carb tune pro hooked up to it. After the sync, I take the carbtune off and reinstall the three vacuum caps and the one vacuum line to the TCI/CDI.

 

I set the idle, and it stays at idle. If I rev up the engine to 3k-4k, and hold it there for a second, it usually will not return to the 1k I set the idle at unless I back the idle screw off...in case, is usually too low for the engine.

 

So, I figure I'll replace the caps (again) and replace the vacuum line, hoping this finally fixes the issue. I can't localize the leak using carb cleaner.

Edited April 4, 2010 by warthogcrewchief

[MiCarl]

If it's ok with the sync gauge attached then falls apart when you replace the vacuum caps and the line to the pressure sensor you problem is somewhere in those things.

[warthogcrewchief]

That's what I'm starting to think... I think the new set of vacuum caps might be incorrect. I need to find a new set or do what Nacho does -

 

get a piece of rubber hose (twice the length of the vacuum tube on the carb boot. Install the tube and fold it over, keeping it in place with two zip ties.

 

I'd rather get new caps. The stealership wants $4 a piece and can't go back into their inventory to find caps unless they have a part number...even though I told them that they're almost the same for any bike. So, I'll be looking at parts stores, hardware stores, and online.

[Condor]

I just did a search on Google and came up with this dealer.

 

http://store.qualitydist.net/piblrucavaca.html

[warthogcrewchief]

I replaced the vacuum line from the left front carb to the vacuum sensor. I also replaced the vacuum port caps and clamps from some I found at an auto parts store. Still having the same problem. I double-triple checked the carb mounting position on the intake manifold boots and the air box boots. Doesn't seem to be off on any of them. I did notice that the air box boots do rotate, but I don't think they'll cause a problem. Just to be safe, I'm going to use clear silicone or RTV to seal the boots to the air box. I plan on also removing the carbs this weekend, removing the boots and rechecking everything again.

 

For the butterfly shaft seals, some of you recommended a hydraulic shop? Well, I work on aircraft hydraulics every day. Would these seals that you all recommend be nothing more than a small o-ring? or are they something a little different than a simple o-ring?

 

Would a damaged paper gasket between the carb body and the jet body (inside the float bowl) cause a lean condition? I think I may have reassembled my carbs with one that may have been potentially damaged.

 

This carb issue is really getting on my nerves and am getting tired of working these $%$#@ carbs. I'm sure as heck not going to pay someone to work them when I have worked many carbs before in the past with great success.