RPM "creep"

[al_roethlisberger]

So, my bike idles a bit on the high side anyway, between 1200-1300 RPM. This started after my heads were ported, etc.... and although I think I can work it back down a bit with some more tinkering, I'm not worried about it right now since the engine is coming apart anyway for the case replacement.

 

 

But, to my question.... while I've gotten used to this relatively high idle, I've noticed that once the engine warms up, especially if for example sitting at long stoplight.... the RPM starts to "creep" up, sometimes almost to just a hair under 2k, so I'm guessing around 1700-1800 RPM.

 

This was also noticed by the folks at Hare Racing when they got the engine good and hot during it's last PCIII mapping.

 

But, after running the bike down the road a bit, and I'm guessing cooling it a bit after the long sit in the traffic light, the idle is back down nearer to it's original spot.

 

 

So.... is this normal? Does the ECU add fuel when the temp sensor detects that things are heating up, and thus bump the idle up?

 

Do your bikes do this?

 

My last bike was also air-cooled, but "dumb" and was carb'd and had no fancy computer monitoring things.... so things like idle just didn't vary all by themselves. So I'm just wondering.

 

Thanks

 

al

[Mr. Bean]

Mine seems to be the reverse of that. When it is in a normal temp range it idles at 1100 rpm +or- a bit. When it gets hot the idle actually seems to drop down to 900 to 1000 rpm. This is about the same when I come to a stop at the bottom of an off-ramp after a good highway run. It'll idle around 900rpm for a few seconds before slowly going back up to it's usual 1100. Once it really gets hot again though, it will drop back down to 900-1000 again.

 

Oh well, as long as it doesn't die anymore at lights (it doesn't) and it doesn't idle too high (again it doesn't) I'm happy

 

Randy

[Guest Brian Robson]

Since I added the Power Commander (and balanced the injectors at the same time), the idle, both hot and cold remains at ~1000 rpm, with maybe 100 revs increase when hot in traffic.

[Flatland Dan]

My idle tends to vary, but nowhere near as much as your's, Al. About 800 rpm cold and from 1000 to about 1300 hot. When it was brand new and having all sorts of engine problems-it was the computer-the idle was absolutely steady. Since replacing the computer, the idle has been a little unsteady. Later, Dan

[tomsp]

Al, after we got my tps and tb all set, my idle rose up to 1100. Before it was around 800-900 and was too low. This seems about right and does not creep. Maybe this is a heat thing and maybe related to where you box intakes are pointing (there was a thread on that I believe) - like maybe at lights the intakes are scooping more hot air from the engine and the sensor doesn't like that.

 

[al_roethlisberger]

Mine seems to be the reverse of that. When it is in a normal temp range it idles at 1100 rpm +or- a bit. When it gets hot the idle actually seems to drop down to 900 to 1000 rpm. This is about the same when I come to a stop at the bottom of an off-ramp after a good highway run. It'll idle around 900rpm for a few seconds before slowly going back up to it's usual 1100. Once it really gets hot again though, it will drop back down to 900-1000 again.

 

Oh well, as long as it doesn't die anymore at lights (it doesn't) and it doesn't idle too high (again it doesn't) I'm happy

 

Randy

 

...ahh yes, this inverse scenario you describe is related to valve lash, and is a common problem for North American bikes that have the "tight" lash specs to meet EPA noise limits.

 

Yours may not be too tight, but if really too tight, this will actually cause the bike to die during the scenarios you describe <_>

 

I fought this demon a little over a year ago, and the dealer seemed clueless. After a couple months of working with them, Mike Stewart came over and set my valve lash to Raceco Specs, and I've never had a low idle/dying problem again

 

 

al

[al_roethlisberger]

Al, after we got my tps and tb all set, my idle rose up to 1100. Before it was around 800-900 and was too low. This seems about right and does not creep. Maybe this is a heat thing and maybe related to where you box intakes are pointing (there was a thread on that I believe) - like maybe at lights the intakes are scooping more hot air from the engine and the sensor doesn't like that.

 

 

Well, my "base" high idle is definitely from two things, and maybe a third.

 

I was just curious about the "creep" issue...

 

But the causes of the high base idle are:

 

First, I had the heads Stage II ported last year, and that typically bumps the idle.

Second, I have Raceco Spec valve lash, and this typically bumps the idle a bit.

 

...and third, although I've tried everything else to lower the idle, I haven't checked the air bypass screws to see where the dealer set them when they were trying every trick in the book to get the bike to idle last Spring. I suspect if I set them correctly(assuming they aren't), I bet the idle will change too.

 

 

So, I'm not too worried about the idle being about 200-300RPM high, as I know the cause, and may have recourse to lower it if necessary.

 

BTW, thanks for the suggestion on the air inlets, but I haven't had an airbox since last Summer.... during the quest to duck the infamous "vapor lock"

 

Airbox Lid versus Pods Thread

 

 

al

[Guest erik]

Hi Al, my idle is only high on the revcouter. I noticed that after dual plugging at TLM the idle was 1500 in stead of the 1150 I was used to before dual plugging. But my revcounter gives 200 /300 too much. I only know that is gives too much after dual plugging, because I saw it on the monitor of the factory software. Mayby dual plugging does something too the reading of the revcounter?

Anyway, the bike idles great ant doesnt seem too idle too high.