Rich or lean?

I have a 65 Metra kit and a big Mikuni 19 or 20 I think. When I get the bike started it runs great but at full throttle bogs down. It prefers about half throttle where it really rips. It also is a bitch to start, but when it gets going it's fine. A new spark will make it start up no problem, and it generally does seem dirty (leading me to think rich) but I'm also thinking it might be lean causing it to not want to start and be a wuss at full throttle. Any thoughts and opinions would be greatly appreciated.

Re: Rich or lean?

sookia sookia /

sounds rich, what jet is in it?

Re: Rich or lean?

I would swing toward lean. Cold starts are easier when too rich and going full throttle will allow more air in than fuel if you have reached the maximum flow of a too small jet. Backing off the throttle gets back in a usable range. Too rich tends to simply cut out hard due to fouling the plug breifly until you back off and the plug clens off. Lean will just seem weak and unresponsive.

Re: Rich or lean?

I'm not sure. That's my next step. Any idea what a Mikuni might like with that kinda kit?

Re: Rich or lean?

The symptom of backing off the throttle and then it perking back Up is EXACTLY what it's doing. What perplexes me is the dirtiness of the plugs, but I guess that could be my gas.

Re: Rich or lean?

A dirty plug does not mean rich, just a dark one. Dirty with deposits is an uneven burn, contaminated fuel and if the deposits are pure carbon it would be rich running. If it is a dirty reddish brown, that is rust in your tank.

Re: Rich or lean?

I will report back with a jet size. Thankyou everyone!

Re: Rich or lean?

OK so there is an idle jet with no discernible markings on it that I can see (I have good eye sight) and the main jet is an 80. Sound like a combo to make a 65 metra run lean?

PS I know there is no rust and the gas is clean

Re: Rich or lean?

Jet sounds pretty low for a 20. There is no mikuni VM19, and if it is, it's a clone and likely all of your problems.

The pilot jet has no effect on your problems aside from difficulty starting possibly.

Re: Rich or lean?

It must be the VM20 then, and both jets were clear and the thing is basically brand new so It must need a bigger jet. Mikuni's go up by 5's I believe, any clue what it would like? I'm planning on getting several to cover the seasons.

Re: Rich or lean?

I would start over a hundred. People run a HUGE range though, from 160s to 110s.

Re: Rich or lean?

Cool, I just got a 135-140-145 recomendation from the performance page, I'll start there this has been a big help!

Re: Rich or lean?

Well,it sounded too rich to me,but..............? don-ohio (:^)

Re: Rich or lean?

Lean does explain me having to pedal it three blocks down the street even with a basically new spark plug, when immediately changed out it will fire right up but just after a short ride it gets finickay about starting again.

Re: Rich or lean?

Could be fouled from being or or contaminated. Without seeing the plug it's a coin toss. Could also be your condenser acting up and by the time you change the plug it has cooled down and starts again.

Re: Rich or lean?

Yea condensers do kinda go slow like that, but it idles perfectly once it gets fired up. I'm thinkin it just needs the up jetting and more gas, I hope Thats all.

Re: Rich or lean?

So I ordered my new jets and in the mean time pulled the head just to take a look and there was a LOT of build up on the piston, I spent 20 minutes scraping all the shit off to see silver again. Is this caused by it running lean or something else?

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