Idle speed high when warmed up

[RiskyBusiness]

Hey there. I am a new XS1100 owner. I have been working on my '79 Special through the winter and now have the brakes rebuilt and have it running thanks in no small part to the tech tips on this site.

My current quagmire is that the bike starts great, warms up, and idles pretty well around 1100 RPM. If I take it for a spin pretty soon it starts idling at around 3000-4000 RPM. Last night it was so bad that on my way home I started killing the engine at stop lights to keep it from revving so high. How should I go about diagnosing this?

Thanks!
James

[xssiveone]

Re: Idle speed high when warmed up

Originally posted by RiskyBusiness
My current quagmire is that the bike starts great, warms up, and idles pretty well around 1100 RPM. If I take it for a spin pretty soon it starts idling at around 3000-4000 RPM. Last night it was so bad that on my way home I started killing the engine at stop lights to keep it from revving so high. How should I go about diagnosing this?

Did you have the carbs off for cleaning? Sounds like it's either too lean or the carbs need to be syncronized. Check the tech tips for a method of bench syncing to get them close enough for smooth running.

[RiskyBusiness]

Re: Re: Idle speed high when warmed up

I should have mentioned that I did, indeed, clean the carbs and did a bench sync. I did not, however, check the float balance.

I am going to make a homemade 4 cylinder sync tool. After I build and try it I will post my results.

-j

[xssiveone]

By "too lean" I was referring to the mixture screw adjustment, not the float level. Once the floats are set, they very seldom go out of adjustment, altho it certainly won't hurt to check them.

When you take the carbs off to check the floats, clean them again. I know, you just said you cleaned them.... but there are so many small passages and corners in these carbs that it sometimes takes 2, or even 3 times, to get them truly clean. And if you, as so many people seem to, failed to remove the idle mixture screws to clean them and the passages underneath, then they are not truly clean.

Another thing to check is free movement of the slides, and also the diaphrams on the slides for holes.

[RiskyBusiness]

Thanks for the tip. I had stripped the carbs and cleaned even the most intimate pieces, but I agree that it sure can't hurt to do it again.

Help a newbie understand the lean issue. Why would a lean mix cause the bike to idle fine and then start idling high after taking her for a spin? I am new to cycle carbs so forgive me if this is obvious.

So on the topic of carbs, I am considering individual cap style air filters for each carb intake. I hear tell that I will have to re-jet. Anyone had experience with these? The filters are $10 at partsnmore.com



Anyone have good links on re-jetting?

-J

[bikerhawk]

Something else to check is to make sure the tips of the mixture screws haven't broken off in the carb body. I had the exact same problem with my XS750 several years ago and it absolutely drove me nuts until I finally figured it out. Take the screws out and examine the tips...they should all have a very sharp point to them. If they look kind of rounded off, then I would bet the tip is stuck down in the hole...you should be able to see just a pinpoint of light through the hole.

If this is your problem, my recommendation is to send them to Rob Reil in Atlanta...he's done many of these kinds of repairs. You could also try to press the tips back out yourself (tough to get a good angle), or some have even VERY CAREFULLY drilled them out with a 1.0mm bit, but it's so easy to slip and drill into the carb body instead, rendering it useless. I drilled mine out way back when and was probably more lucky than good...my problem was immediately fixed. If I had to deal with that again, I'd send 'em to Rob.

[Snow]

This problem sounds strangely familiar...

http://www.xs11.com/forum/showthread...&threadid=1780

Ended up being idle mixture wasn't correct, even though I was "idling" at 1000 before a ride, the idle was actually set at about 4k but the bad mixture was making the bike run at 1k.

And yeah, drilling the plugs out is a very dangerous proposition...I fubared my best set of carbs this past week or two.

[RiskyBusiness]

Originally posted by Snow
This problem sounds strangely familiar...

http://www.xs11.com/forum/showthread...&threadid=1780

Ended up being idle mixture wasn't correct, even though I was "idling" at 1000 before a ride, the idle was actually set at about 4k but the bad mixture was making the bike run at 1k.

And yeah, drilling the plugs out is a very dangerous proposition...I fubared my best set of carbs this past week or two.

Now that thread looks familiar! Thanks for pointing that out, Snow. Looks like the same type issue.

Here is my plan, correct me if this seems out of order:

1. Pull carbs and clean throughly
2. Install rebuild kits I just ordered from partsnmore
3. bench sync with bread tie wire
4. install and sync with homemade gadget
5. colortune
6. Ride happy with big grin

Anyone know a place in the US that sells colortunes? I hear that international shipping is slow right now. I have not bought a colortune yet but I would like one.

-J

[Snow]

There are a few places in the US, I got mine from a shop in Boca Rato, FL - some of the other guys got a better deal from another place, but I don't have either sites handy and cannot seem to find them through searching...make sure you get the 14mm motorcycle version and all should be good

Your attack order looks good, but I personally had to resync after colortuning as my idle mixture screws were waaayyy off...

[Yamamike]

been there

Hi, this sounds like a problem that I had this (spring) hint hint. The same thing would happen starts good,warms up, go for a ride and a few minutes in it idles around 2500-3000. On my #4 carb the coil spring on the throttle shaft was falling into a space between a shim and hanging up the throttle just a smidge on that cylinder only but it's enough to throw the idle speed off on a warm engine. I figured this out by pushing down on the syncronizing screws while idling the engine, sure enough, just a gentle touch on that one (between carb 3 and 4) would fix the idle speed, hope this helps.

Mike

[RiskyBusiness]

Re: been there

Originally posted by Yamamike
Hi, this sounds like a problem that I had this (spring) hint hint. The same thing would happen starts good,warms up, go for a ride and a few minutes in it idles around 2500-3000. On my #4 carb the coil spring on the throttle shaft was falling into a space between a shim and hanging up the throttle just a smidge on that cylinder only but it's enough to throw the idle speed off on a warm engine. I figured this out by pushing down on the syncronizing screws while idling the engine, sure enough, just a gentle touch on that one (between carb 3 and 4) would fix the idle speed, hope this helps.

Mike

Well that is easy enough to test for! Thanks. This weekend I will push on each carb's screw and see if it calms down. Thanks for the idea.

-j

[sixtysix]

Go to the links section for a link to carb jetting site.