Hot bike, fast idle

I am having an interesting problem with my bike. It idles great when it is cold but really high sometimes when it is hot. When the bike is hot and has been run around 4500 - 5000 rpms for a while the bike will want to idle at 3000 at a stoplight. Not a consistent thing either, but happens a lot. I lower the idle by partly releasing the bike in gear. Of course when I pull the clutch in or put the bike in nuetral it will rev back at 3000.

I have just put a different set of used carbs in my bike recently (i did clean them). I did not touch any adjustments.

Also I have a (induction fuel petcock) fuel pump that will leak. I had to put a shutoff valve on the line.

Is it a problem with the fuel pump? Could I get by just rebuilding the fuel pump?

 

Mine does the same thing, I just turned down the idle screw, it'll idle really low when it's cold, but just leave the choke on a little longer than you would. Mine takes a little bit to warm up when it's cold, but, once it does, everything falls into place and the bike runs great and isn't screaming at everyone while im at the stop light.

 

First off, that is not a fuel pump (unless you actually added a fuel pump)
The vacuum hose to the fuel petcock pulls a diaphragm that pulls a little plunger, or stopper. this uncovers a passage that connects 2 of the 3 ports at the selector. The "prime" port goes straight thru.
I had a tiny piece of a leaf holding my plunger from seating, causing fuel flow all the time.

But that has nothing to do with a high, hot idle.
If you didn't have this problem with the other carbs, then the prime suspect is dry, worn throttle shaft seals (8 of them).

However. . . when you say you did not adjust your carbs. . .
Red Flag ! this raises all kinds of questions all over and inside the carbs, like, did you remove the "O" rings and washers inside the Pilot screw holes, and clean the little transfer ports?
That's just one example. My point is there would be many questions of what was skipped in a "quick" carb cleaning, and it might not be possible for someone to pin down the specific cause of your problem and have a "turn this screw" type of answer.

If it were me, I'd do a running sync, then I would see if the 4 Pilot screws are working using a ColorTune plug. If you don't have a colortune, you could listen to the idle change to verify that the idle circuit is working.
Then you can test each enrichment circuit individually if you loosen the "fork". You lift the plunger and hear the cylinder "choke out".
A non firing cylinder may fire up with the additional air/fuel.
You can use a spray bottle to see if a cylinder is firing at idle.
Spray water on the exhaust pipe.
Before taking the carbs back off, I would check the float levels.
You see- - you can diagnose the individual carbs while it's running.

Then use this information when going thru the carbs again to replace the throttle shaft seals, and some "O" rings. It often takes going thru the carbs three times.

 

Thanks for the education on the fuel petcock I never understood that quite right.

I did not have the high idle problem with the old carbs. The problem with them is that they would not idle with the choke off. You could check out my old posts from a long time ago. The throttle shaft o rings were completlely worn out on these and the carb boots were worn out. I bent the shaft where the butterfly goes in trying to change all the o rings. So I had to get some other carbs.

So when I got the other set of used carbs. I just took i cleaned the jets, fuel bowl, and made sure the carb passages was generally clean. I didn't change any adjustments on any of the carbs. I changed the the throttle shaft o rings that I could reach on these set of carbs without taking the shaft apart. The o rings are in much better shape on these carbs. So your right they have not been synced yet. I was wondering if this was my going to be my problem.

 

Just wanted to drag this up again because my bike is doing the same thing: hot bike = high idle.
I took my carbs apart and put them back together. No crap in the bowls, and all the jets look clean to me.
So what I did was to take off the plugs one by one to see if they affected anything individually.

Result: No difference between for any cylinder disabled.

I don't think its to do with mixture, because I played with that and it still sits high when hot. Any ideas would be great.

 

If you've checked for air leaks and/or sticking throttle cables and found none then when it's hot and acting up pull over, reach under and back off the idle screw in the middle of the carb racks. Should only take 1/4 or half turn to get it down. Your throttle blades are being held open too far. Again unless you have an air leak.

 

Ok, will look at the idle again tomorrow. I am so sure that I did, but it does explain it all.

If that fails, I will do some air leak tests. Another search on the forum for the best technique...

I have on me a can of WD40 and some deodorant! I think the deodorant should work nicely. Always did pretty well with the potato cannons all those years ago.

 

In both of your cases, you need to check and adjust your float levels, bench sync the rack; and do a running vac sync once installed. You should also check to ensure your slides pass the "clunk test" (do a search on the phrase.) THEN check for vacuum leaks using the unlit propane torch method.

There IS NO quick and easy "turn this screw" answer, unless you trapped the throttle quadrant under the fins on the back of the head when you reinstalled the rack.

 

Float levels are done.
Bench sync done.
Clunk test done.
Vac sync - pending...

I read the forums as much as I could before taking the things out, BUT
the Vac Sync needs to be done and I dont have the money to buy anything right now as I am sitting jobless.

I do have a question though.. when syncing are you adjusting the individual throttle screws or the mixture screws?

Or are the individual screws a "set and forget" after the bench sync?

As for the throttle quadrant I read about that way in advance so hooked it back with a bent paper clip! Getting those carbs onto the manifolds was the hardest bit so didnt want to do that again at all.

The carb inlet boots were easy after boiling them for a few minutes and pushing them through from the air filter hole. Well, the first was horrible till I came and read how others did it.

 

you adjust the three throttle screws,not the four mixture screws.

bench synq is just a starting point,but if done right the bike should
be pretty close. some can tune by ear, i use the "two bottle system".
i cant remember where i saw the post but you can make a set for
about $5.00, just check old forums/archives for the posting.
good luck.
ron

 

Here's a FREE YICS Tool.

http://xjbikes.com/Forums/viewtopic/t=4 ... +yics.html

Here's all you need for a Vacuum Sync.
(You can borrow the Tool from AutoZone)

http://xjbikes.com/Forums/viewtopic/t=2 ... +sync.html

 

I have now got my YICS tools (aka an old shirt and olive oil) and will get my Carb sync device sorted tomorrow.

An update on the idle...ah..yeah.. who left that idle adjuster so tight?

Oh and screwing in the mixture screw enriches right?

 

IN = Lean (Down)
OUT = Rich (Up)

 

RickCoMatic, parts, bigfitz52, iwingameover

You guys rock more than I could have ever imagined.

 

I have found the source of my air leak that I think is causing this fast idle. The choke plunger seals are leaking. The idle is raising when I spray WD 40 on two of them. Where do I get new ones? Or what is a cheap way of fixing them?

Carbs still need synced but they have the anti taper plugs on them so I haven't tried to do it yet.

 

Shoot Chacal a PM, XJ Forever.

 

The Rubber Surrounds on the Enrichment Circuit Plungers are not SEALS.

They are CAPS.
Dust Covers.

Spraying the Enrichment Valve Caps and having the RPM's rise is Normal.

As for treating them:
I always Brush-on some Armoral.
If you have them off for Cleaning Carbs ... Armoral the Inside, too with a Q-Tip ...
Or, just put them in the Palm of your Hand and bathe them in Armoral.

 

never thought about that rick, armor all is a pretty good rubber rejuvenator, I let my intake boots on my cb750 which felt as hard as plastic, soak them in armor all for a few days, noticed a difference in the flexibility of them, and it really makes plastic and rubber shine.

I have to say this now though- dont take the intake boots off the xj's just for that reason, the bolts are soft metal and like to break off in the head... the cb750 boots just slide over a large nipple..

 

Are you saying to put Armoral jut on the dust caps themselves?

Also is there any recommeded way to get the anti tamper plates off of the carbs?

 

Ah the saga of the high idle continues. IT IS DRIVING ME NUTS!!!!!!!! It also seems like it is getting worse. Here is what i have donee.

Put black gasket maker all over boots -no more cracks
Cleaned the carbs throughly
replaced throttle shaft o rings on the outside carbs
and screamed in frustration

I am about ready to get another bike. I am going to have someone help me sync the carbs Sunday after church. If that doesn't i am probably going to get a 96 seca II.

 

minnMaxim:

There are eight throttle shaft seals. They are a very common source for an air leak. If you only replaced two of them, there is a 75% chance that you didn't fix the air leak if the seals are the source of the leak. Breaking down the rack is the only way to replace all the seals. This will be the case with any bike that has 4 cv carbs.

To remove your anti tamper covers, VERY carefully drill a 1/16 inch hole in the center of the 4 covers. YOU MUST BE VERY CAREFUL TO NOT LET THE DRILL BIT GO IN FARTHER THAN THE BOTTOM OF THE COVER AND TOUCH THE TOP OF THE SOFT IDLE MIX SCREW BELOW. The covers are about 2mm thick and there is about a 1-2mm space between the bottom of the cover and top of the screw.. Then take a small screw that you can screw into the hole you just drilled and pull the cover out..... again being very careful to not let this screw go in too far and damage the top of the idle mixture screw. (If I use a drywall screw, I blunt the point of the screw tip so it doesn't dig into the air screw while your trying the get the threads to "bite" in the anti tamper cover.)

 

I took out the anti tamper plugs and have the bike at 3.5 turns out.

last time i tried to fix throttle valve seals i ended up bending up the throttle shaft. I bought another set of carbs on ebay and put them in. So I am a little hesitant to touch the other seals.

 

Finally fixed but no longer mine.

After a sync the maxim 550 no longer has an idling issue. It idles great now but not I have a new bike.

 

great to hear what kind of bike did you get

 

I got a 96 Yamaha Seca II. It only has 5000 miles on it!!!