The hotter she gets...

Ok. So i was out riding my bike as usual yesterday and i noticed something odd. I usually only dive my bike about 5 miles to/from work everyday. And i have rode her on the weekends some too. But yesterday i rode for about an hour and a half. And as i rode and the engine got warmer the idle speed climbed. When i first cranked her up she was idleing right on 1500 rpms as usual. But about 20 mins later i stopped at a light and she was idling at about 2300. Then about 30 minutes after that she was up to 2800. By the time i got home to the garage she was idling at a steady 3500. So my two questions are #1. What could cause this? and #2 Am i damaging my bike by letting her run at that high of an idle speed?
Thanks!

 

First off, by 20 minutes of riding it should be as hot as it's going to get.
In my experience, engines will idle higher in an overheat condition.
A 1050 RPM idle (warmed up) is " the standard" . If you are idleing at 1,500 on start up, you are set too high. Cold motors idle at 800, IF they even idle cold !

Also, check the snugness of your intake boots. Vac leaks. A little throttle cable slack. What do your plugs look like?

 

I'd check for a vacuum leak around the carb boots. Things expand as the heat up and it's possible you have a leak when the bike gets to operating temperature that is not apparent when cold. Use some carb cleaner and spray around the boots to see if you get a surge in RPMs. If so, you may need to get with Chacal for some replacement boots.

 

I LOVE this board....I was just wondering if that was true...mine idles at about 800 RPMs when I first start it and as it warms it climbs up to a steady 1100 RPM.

This board has to be FULL of psychics...everytime I wonder about something...its answered on here within the day.

Maybe I missed it...but have you bench synch'd your carbs?

 

any chance you left the choke on? Don't laugh, its been done before....

 

according to my maxim 400 manual my idle should be set at 1200 rpms after warming up.

 

I was going to ask the same thing.

 

Mine climbs too, but not that high. Mine does idle at about 800-900 RPM when cold (it was a chilly 45 degrees F this morning) and then to about 1200 RPM when "warm" during a commute to and from work and when driving in temps below 75 or so (most of the summer this year...damn global warming lol), but when nice and hot and in temps above 80 or so, the idle creeps up to about 1600 RPM. We'll see how she runs next year after a bunch of defered maintainance but she's good enough for this year.

 

Ok....so i did not leave the choke on....and yesterday while riding she got up to 3500 rpms........my biggest question is "Am i damaging my bike by letting it idle so high?".......i havent checked out the carb boots yet but i called the local yamaha dealer and they are $200.00 for four of them.....anybody know of a cheaper way to replace/repair them?......

 

No. 3,500 is a high idle that says you have a problem, but it won't actually hurt your engine. Folks on this site have claimed 12,000 RPM during a missed shift! Driving at hi-way speeds with 1 carb running too lean can blow a hole in a piston, but that won't happen with no load.

Chacal sells boots, you can paint on "liquid electrical tape" on cracked boots for a tacky looking fix, or buy used ones.

 

35-Hundred is not Idle.
3,500 rpm's is at the low end of the Power Band.
You're getting extra Fuel and Air from someplace.
Manifold leaks, loose clamps, Carb Seals and Stuck Diaphragm Pistons and Carb linkage issues are usually to blame.

Begin by probing for an Air leak with Propane Gas or Carb Cleaner.
Also be sure that there is sufficient slack in the Throttle Cable.

It doesn't take a very big Air leak to cause the engine to increase revolutions by several hundred rpm's and more.