My 09 with 351 top end and Mikuni 33/34 pumper idles with stutter and surging (100-400 rpm fluctuations). When running at 3500 in gear, it's just ragged. In gear at anything between idle speed and 4000 rpm, it's annoyingly jerky.It's hard to increase throttle from idle without sudden jerk (as when slowing for hard turn then throttling up), Throttle Tamer installed, new clutch and throttle cables last summer, well lubed.

Bill just rebuilt the carb about 3 months ago, jetted for Atlanta altitude. Nothing but ethanol free gas for the last 16 months.
New IMS tank, new fuel lines, was too rich, but new plug is now the right color (brownish, no deposits), decel pops on downshifting / rev matching with occasional slight backfires on upshift. FMF Q4 exhaust.
New airbox with K&N air filter. Valves checked last summer. Bike runs strong right up to 80 mph, no dead spots in power, starts easy hot or cold never stalls. 50 mpg.

Could this ragged (surging and missing) be caused by a bad ECU or some other electrical problem? It's bumming me out.
I'm mystified.

 

You've checked for vacuum leaks?

 

yes I have. Carb cleaner, Both sides of carb and at manifold

 

checked at both boots and the airbox, no leaks

 

Did you adj your air screw?
IMO, Bill (and others) sets everything up too rich.

 

Yeah it was too rich. Got that dialed back and replaced the spark plug. I'll post a vid from my phone

 

The vid starts with choke at 1/2, then I turn the choke off

 

here's the link to Dropbox

Video, with half and then no choke

 

Ignnore the crackling when off the throttle. It means nothing unless it is big pops. Mikuni points out that a properly tuned carb will pop and crackle on decel with throttle off. Slighly cracking the throttle will usually take it out. It is a normal lean condition that allows a bit of fuel mix to collect in the cylinder and exhaust until it fires - the pop and crackle.

Wish I could help on the carb. What you're describing is the range affected by the pilot/pilot needle and the cutaway of the slide. I believe if you go below one full turn out on the idle mix you need to go a size down on the pilot jet. If past 3 turns out on the idle mix you need to go up a size on the pilot jet. I believe that's correct.

 

Thanks, I've been willing to accept the popping, it's not bad, I just mentioned it as part of a general description of the bike's behavior.

I get the concept of when you're at an extreme with the mix, it's time to sort of recalibrate by replacing the jet so that the proper air/fuel ratio falls closer to the mid point of the mix screw... sound right? I'd be more interested in doing this if I didn't have to push the bike from my illegal living room garage, about 60 yards to a place where I can actually start it.

Every mechanic I've showed it to is reluctant to start on it, probably because of the 351cc/mikuni combo (that's under an IMS tank that takes an hour to get off and on). I would think a mechanic with a shop could use any damn tank with longer supply tubes, and crank it right there on the lift. But I'm talkin out my *** cause I'm not ever sure where the pilot jet is located. Still, I'm surprised at the reluctance, and the "just get used to it" attitude, even tho I wave hand fulls of money at them.

This bike is super strong in that low rpm range and it just galls me that it runs so ragged right where it should pull best. Frustrating.