m750 idle significantly faster when hot. help?

[live2ride]

hey guys.

i've noticed that my bike idles much higher when its already hot.  which only makes my legs hotter. 

I'd like to tell you how much faster but this is a 2000 monster 750 so i have no tach.

when the ambient temperature is cool, it idles regularly.  but when the temperature reaches 85+, the engine will idle much faster after it gets up to operating temperature. it idles at the expected temp for about 3 mins and then it idles fast.

its the worse thing to sit in traffic.  since this is aircooled, i understand it'll be hotter in traffic.  however, it's also runs faster/hotter after i come off the highway.

any suggestions?  the board has been very helpful with all the information i needed, but i searched this and got nowhere.

thanks in advance

[Autostrada Pilot]

My carb'd 900 does the same thing.  Once it's fully warmed up, it idles high.

If I let the clutch out just a tiny bit, it'll drop the idle back down.....for a few seconds or as long as there is a slight load on the engine.  I'd like to fix it, as I would think I'd get better gas mileage with the lower idle.

[supertjeduc]

You will have a leak between carbs and cilinder

[Javamoose]

My carb'd 900 does the same thing.  Once it's fully warmed up, it idles high.

If I let the clutch out just a tiny bit, it'll drop the idle back down.....for a few seconds or as long as there is a slight load on the engine.  I'd like to fix it, as I would think I'd get better gas mileage with the lower idle.

Mine does the exact same thing as the OP and responds the same to the slight slip of the clutch as above.  Also a 2000 M750...

[MongoReturns]

Mine does the exact same thing as the OP and responds the same to the slight slip of the clutch as above.  Also a 2000 M750...

Mine's done this for 10 years.  When it get real hot and the idle goes to 2.5k (just sitting there) I give the choke a quick pump & it drops down.  And I've always thought there must be something too that... needle jets? Emulusion tubes?  But if it's done it since new, odds of something being worn out are nil.  Or it could be the fuel infeed tube sits on top of the vert cylinder.

[Ddan]

My SS did the same thing.  Turning the idle down just a whisker made a big difference.

You will have a leak between carbs and cilinder

+1 Something else to look at.

[MongoReturns]

Yes, this stopped mine from doing it all the time as I recall.  It's a really fine line how much/little idle screw!

[Howie]

Assuming there are no vacuum leaks a throttle synch/ idle speed adjustment should fix things.  A slight increase in idle speed when hot is normal.  If your idle gets up to around 1400 RPM, the ignition advance kicks in and the engine speed can approach 3000 RPM.

[live2ride]

like a few have noted, i tend to let out the clutch a little to keep the idle down at stops but i dont want to b/c it will wear out the clutch more quickly.  so i only do so when the heat is unbearable.

check for leaks between carbs and cylinder
sync carbs
adjust idle speed screw

sounds like those are the possible remedies, and probably in that order i suppose.

i'll give it a shot.  good luck to the others with the same issue.

[Autostrada Pilot]

Any luck on this?  I've been out of town a lot and so I haven't had time to check things out.

[mojo]

My bike did this same thing while I was playing with the jetting in the carbs.  I turned the idle down about 1/8 turn and it made all the difference in the world.

[Privateer]

I've noticed this problem myself (04 620), idling around 1500 after highway speeds for 20-30 mins.  The solutions here are all about carb'd bikes.  

I looked in the service guide and it talks about hooking a DDS which I obviously don't have.  It was never a problem until I got new slip ons installed (by the dealer).  Any home solution for FI bikes?  

[Speeddog]

Not a 'home' solution... but a trim adjustment to richen it up a bit would likely fix it.

[needtorque]

Assuming there are no vacuum leaks a throttle synch/ idle speed adjustment should fix things.  A slight increase in idle speed when hot is normal.  If your idle gets up to around 1400 RPM, the ignition advance kicks in and the engine speed can approach 3000 RPM.

What Howie says here makes the most sense and I would lay money on him being correct.  The bike will always idle higher when warm.  When cold you should need the choke just to keep it running until it is warm.  If it is idling high enough to stay running when cold with little or no choke then when it is warm the idle will increase significantly enough to activate the advance.  The advance then takes over and runs the idle even higher. 

This all fits with the letting out of the clutch which temporarily idles the bike down under 1400 and stops the advance.   It also fits with those saying that a small adjustment to the idle made a big difference.  A small adjustment would stop the bike from reaching 1400 rpm and in turn stop the advance which would make it seem as though a very small adjustment knocked off about 1600 rpm (drop from 3000 rpm to 1200), when in fact it only shaved off the 100-200 rpm necessary to keep the advance from activating.