Idles high when warm

My bike runs ok, but after riding it for a while it starts idling high at 2000 to 2500 RPM.

What do you all think? Could it be that my boots are leaking?

 

My limited knowledge from my experience with the same problem was with the carb gaskets and seals (not sure if that's what they're called).
When the engine warmed the plastic/rubber would expand or contract letting air in and messing up the balance in the carbs etc.
Just an idea...

 

Probably needs a carb tuning. This forum has some instructions, just do a quick search. You will need a YICS tool of some origin and vacuum tool.

That's my guess. My 83 XJ750 did this and that's what it needed.

 

I agree with the above:

You could check for false air intake by ligthly spraying starter-spray on boots, around diaphragm covers, at the vacuum intake rubber caps, the throttle shaft seals and maybe a few other places - and watch for increase in revs.

Apart from my carbs needing cleaning and syncronisation I had false air intake in 3 of the mentioned places: http://xjbikes.com/Forums/viewtopic/p=33586.html#33586

Also a syncronisation and maybe a colortuning would be a good idea (can be done without taking the carbs off the bike).

 

Try the Idle adjuster or the cable tension adjustment???

 

Did this just start happening or has it been like this for a while?

Have you fixed the problem?

 

It's been happening since I got it last year. The idle is set at 1500 rpm when it first starts up. After it really warms up it idles at 3000 rpm.
My tach also doesn't move until it warms up also.

I notice on the XJ750, there is no tach cable but it connects to one of the coils. Could that be the problem?

If not, then I have 2 annoying problems.

 

Well I spoke to soon in my reply...
After having the carbs professionally cleaned/tuned after my own 5 attempts, my idle still rides high after a good 30 mins of driving.
idles at 1500 then upto 2500-3000 after a nice ride.
If I engage the clutch slightly it brings it back down again.
I resealed my boots and checked for leaks there, my carb has all new seals and rubber etc. It's an oldie though so I think I can tolerate this problem after solving most of my others.
Good luck in your search for a cure, I'll let you know if I find one as well.

 

You (both) really do want to solve your fast idle problem. It is a dangerous condition. It makes the bike hard to control under breaking and deceleration. Low speed manoeuvring is affected as well requiring having to play with the clutch friction zone which is not good for the long life of your clutch.

Start back at the start again checking the obvious, air leak, idle speed adjustment setting, cables binding, choke stuck or not closing etc.
Keep going you will find it eventually and it is a great feeling when you do!

 

You have tried setting the idle speed, via the large adjustment knob in the centre of the rack, when the bike is hot?

Can you bring the idle down with it?

Basic question I know but it pays to check the obvious to aviod months of trouble for a 5 minute fix

 

I hope I'm adding a positive comment here.

I've been playing around with mine. My uncle accidentally bumped mine up to 3000 once it was warm. I backed it down so now (when hot) it idles around 1300. Now, keep in mind this is when it is hot. When the engine is cold it will just stall unless the choke is on?

Unless there is something wrong with my method. Why don't you guys set your idle to optimum when the engine is hot by adjusting the screw. It will of course probably not idle when the engine is cold without choke... but isn't that pretty much the way it is? Maybe its a bad example, but I remember all the Yamaha XT225's at motorcycle training did not want to idle without choke until they were good and hot. Thats just the way they had them set. Its the way mine is set.

 

Of course you are . Never be afraid of making a post on XJBikes that is what the site is here for and what makes it the great place it is .

Spot on as I had pointed out, but you managed to phrase it better than I. Set ya idle at operating temp!
All engine running (mixtures, sync, idle speed) fine tuning should be done when at normal operating temperature.
Gotta get the obvious seen to first. 8)
It will stall with no choke cold, maybe not even start, that is what the choke is for! 8O

If idle has been set when hot and the problem persists it means that there is something else amiss.

 

Starting from DEAD COLD should require ENRICHMENT.
Starting warm shouldn't need it.
Reasons for High Idle:
Tight cable.
Air leaks.
Mixture screws too rich.

Test for Air Leaks by introducing Propane Gas near suspected leaks.
A spike in rpm when Propane Gas is introduced will help find leaks.

 

I color tuned my bike last year when it was cool. Should I now recolor tune my bike when it warm? Carefully of course.

Also, would the tach not working until it's warm and the high idle when warm have anything in common?

 

Did you set the idle speed when the bike was warm and at normal temperature?

Go for a ride, 10 - 15 minutes down the road stop and set your idle?

Normal operating temperature.
Are you meaning the weather was cool or that the bike had not been warmed up by going for a ride first?
Have the gear you need ready, use a shop fan pointed at the engine. Take her for a ride, 20 minutes or so. Home and working quickly do the colour tune, use that fan to keep engine temperatures down. Think about the times you have sat idling in traffic for several minutes. As you say carefully, use common sence and if it is taking too long switch off and have a cuppa while she cools down a bit.

Do the same as above to sync the carbs (first) then go for another ride get home and colourtune. Hay any excuse to go for a ride eh? Then you can also see what affect your changes make too.

I don't know, but it might pay to have a general inspection of the electrical system looking for signs of damage and corroded plugs and connectors. Can't hurt.