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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: leecow on October 11, 2012, 06:31:06 PM

Title: Running a little rough at low RPMs / little throttle
Post by: leecow on October 11, 2012, 06:31:06 PM

Noticed the #2 cylinder dropping in and out the last time I did a carb sync which correlated well with some on-road observations. Not quite as forgiving when colde and the miss tends to get worse as the operating temp goes up. Things are fine above 3500 rpm though it may feel a little down on power. Effecting gas mileage by a percent or two and can a little disconcerting when rolling back onto the throttle in a corner. New plugs and wires didn't alter the behavior. Gunked injector and bad rubber somewhere in the intake seem likely candidates but was wondering if there were other typical culprits.

Title: Re: Running a little rough at low RPMs / little throttle
Post by: jetpoweredmonkey on October 11, 2012, 08:27:48 PM

Have you checked the valve adjustment?  Harbor Freight has a $40 leakdown tester if you don't feel like pulling off the valve cover.

After a recent expensive episode with my Vanagon, I'll be checking for cylinder leakage very early in the troubleshooting process from now on!

Title: Re: Running a little rough at low RPMs / little throttle
Post by: frankenduck on October 11, 2012, 10:11:45 PM

Try some starter fluid around the boots between the TBs and head.

Difficulty synching one or more cylinders is a typical symptom.

As the RPMs increase so does the vacuum which can temporarily seal cracks in the TB boots.

Title: try wife swapping around the coils to see if it follows
Post by: kennybobby on October 12, 2012, 06:07:56 AM

Quote from: leecow on October 11, 2012, 06:31:06 PM

Noticed the #2 cylinder dropping in and out ... Not quite as forgiving when colde and the miss tends to get worse as the operating temp goes up.

Had a friend with a K100 doing this.   ignition coils--one was misfiring, hard to troubleshoot.

Title: Re: Running a little rough at low RPMs / little throttle
Post by: leecow on October 13, 2012, 12:21:24 PM

Thanks all. Will start with the simplest and move on from there. It was in the winter plan to refurb all the rubber around the TB and have Mr. Injector do his thing so hopefully the source of this issue is in that neighborhood.

Title: Re: Running a little rough at low RPMs / little throttle
Post by: frankenduck on October 13, 2012, 01:40:59 PM

Yeah, if you're going to keep it then redoing the rubber and an FI job is a good idea.