low speed stumble

darnold · 06-01-2009, 06:59 AM

We have a 2000 1100s that runs really rough between 2,500 and 3,500 rpm. The motor is completely stock and is low mileage. The bike idles and will pull cleanly at higher rpm.

We have replaced the fuel filter and plugs. The fuel is new and the air filter is clean.

A simple plug test by holding the rpm range while the engine is rough running shows a lean mixture with white spark plugs.

Any suggestions for a fix?

Thanks,
-dan

jpalamaro · 06-01-2009, 07:09 AM

Dan, I'm a relatively new member on this board so not meaning to preach. But, filling in your profile, location, etc. might get a better response. In fact someone might be near you and willing to help. Just a suggestion, certainly not mandatory.

Sorry I can't help.

SergioK · 06-01-2009, 08:48 AM

My bike had a weird idle and displayed the same symptoms - odd since it ran fine at higher rpms. It turned out to be a very minute crack in the shielding around the spark plug wire. New wires and the problem went away. Are those the original almost 10 year old spark plug wires on the bike?

wood-d · 06-02-2009, 03:22 AM

+1 for SergioK. I'd check the spark plugs too.

darnold · 06-08-2009, 07:48 AM

The bike has new OEM plugs.

In addition to the fuel and air filter I have now checked valve lash, checked the tps voltage, sync'd the throttle bodies, and reset the idle bypass screws.

Bike is still runs like crap above 2,500 rpm.

Any suggestions?

SergioK · 06-08-2009, 08:22 AM

You sync'd the TB's at idle and at 4k rpm? Idle set via bypass screws, 4k set via cables.

darnold · 06-08-2009, 08:43 AM

I have followed the online methods for tps and throttle sync. The OEM "paint" is still present on the tps mounting screws and the left side throttle stop screw. The tps voltage is .380 volts.

I set the idle screws and the right side throttle cable to sync using a mercury vacuum gauge.

jduke · 06-08-2009, 12:59 PM

Check your spark plug wires and then the coil.
I'll bet that's where your problems are.

R111S · R111S's Garage

Run some Chevron Techron Fuel System Cleaner through a couple tanks.

sgoodwin · sgoodwin's Garage

Maybe it's just getting old like Bill's dad, that happens more then!

darnold · 06-12-2009, 06:36 AM

Still no luck.

Last night I disconnected the battery to clear the adaption table and reset the cpu. Then unplugged the o2 sensor from the harness. The bike still will not run between 2k and 3k rpm. It idles at 1k and will run above 3k.

Any ideas?

SergioK · 06-12-2009, 07:00 AM

I'd go back and resync the TB's at idle. Confirm you have no spark plug ignition leaks (read-bad spark plug cables). Adjust the throttle cables at 4k rpm. Check fuel injectors for correct spray.

roger albert · 06-12-2009, 07:36 AM

+1 on above, but if your hole in performance is from 3-4k, then sync your cables right at the start, or in the middle of that (3000-3500rpm) The problem with syncing up at 4k, where many people intuitively believe is correct (but isn't ideal) is that the butterflies are open far enough that tiny differences have little effect anyway, and are lost in the noise of other intake/head/exhaust flow differences. Note, plenty bikes sync well there, but you should experiment with the sync point here, perhaps going as low as 2500-3000 if need be (which will work fine, if your idle sync is truly good.

Sparkplugs DO need to be checked, but they don't often cause such a truly severe, but narrow and well defined (both in terms of rpm) dropout. Still worth checking though.

SergioK · 06-12-2009, 09:05 AM

Thanks for that adjustment tip Roger. Gonna make a mental & paper note of that for my next TB sync.

RBMann · 06-12-2009, 10:37 AM

When I first read this it sounded like the classic lean surge we know and hate. Solved mine with the Power Commander. Recently I have been messing with the PC map to try and get back the gas mileage I lost in solving the surge problem.

Good luck with your issue, whatever it turns out to be.

R111S · R111S's Garage

Quote:

Originally Posted by darnold

Still no luck.

Last night I disconnected the battery to clear the adaption table and reset the cpu. Then unplugged the o2 sensor from the harness. The bike still will not run between 2k and 3k rpm. It idles at 1k and will run above 3k.

Any ideas?

Whenever you disconnect the Battery you must rotate the Throttle between Min and Max a few times with the key On BEFORE cranking to start.