low end missfire

[herbie]

Had some problems last winter with a low end miss fire. When giving the bike throttle from low speed it stuttered and missed but ran fine above 3000 rpm and revved out as high as I wanted to take it. On a steady throttle at low speeds it also ran a bit rough and wooly. I suspected the carbs and stripped them. One diaphrahm had a small hole. I replaced this and she ran fine...

Out the other day with the wife and kid (sidecar) the problem returned. Stripped the carbs again and everything looked fie exept one pilot jet slightly blocked. Slapped it back together after a good clean and...no change.

Checked out the dreaded pick ups. They seem fine - no change to resistance readings or engine note when they're pulled and wiggled. The coils seem fine too - cant see any arcing from the HT leads when sprayed with water either.

Any ideas? I still suspect the carbs.

Herbie.

[fxrer]

Yeah, I'd still think carbs, too. The fact that it runs fine above 3000 rpm would seem to eliminate electrical problems.

Mid range fuel metering is controlled by the needle height in the main jet - hence the problem when you found the hole in the diaphragm. I keep looking closely at this interface, ie, needles in jets, on the other carbs.

[John]

Pull the main nozzles, (emulsion tubes) and check that the small holes in the sides of them are not stopped up.

[MAXIMAN]

Before you pull the carbs run a couple tanks of seafoam through it.

Also check you air filter. When I first rolled Zilla out of the old gals garage in Californ...it was doing the same thing. It would miss and sputter until it hit about 2500 or 3000 rpms then it would launch like a rocket.

I ran a couple tanks of seafoam through it an that help alot but it still had a slight missing problem. Then it dawned on me to check the air filter. It looked bad. Dunno if it was that bad....but I replaced it. Wow...it solved the problem.

G'day

[Thumper]

I'm having that bother to it's really annoying. Have replaced all 4 diaphragms (3 had holes in and the third one wasn't that hot either) replaced all 4 float valves (some were worn and sticking flooding the engine) have cleaned the carbs several times (i'm gonna try cleaning the main nozzle, i didn't know it came out that easy was scared of doing more harm than good). I'm supposed to be goin to XS rally in Belgium next month but this problem just won't go away.

[skids]

The condition might be caused by the idle circuit of a carb being too rich. If you can start it without the choke, i.e. it was run earlier and let cool down, feel the pipes after you start it as it warms-up. A cooler pipe may be too rich.

Originally posted by Thumper
I'm having that bother to it's really annoying.