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backfire through carb

3232 Views 18 Replies 5 Participants Last post by  CUZMOTEEFOOSWA
i did the scar mod and pair removal. I have no vacuum leaks and I followed all directions with adding three washers. I'm running a velocity stack and open exhaust.The plugs look perfect according to the picture chart. The more I turn the a/f screw out to richin it up, the worse it gets.It idles and starts perfect but as soon as you put a load on it the carb starts popping.I'm at the end of my rope.
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Well, here's what I would do---if it runs good and the plugs indicate you're A/F is correct, keep an eye on your plugs. If the continue to look good over the next tankful or so and it's running the way you want it--I'd leave it alone. Any pics of your set-up? That would give me/us a better idea and ballpark estimate of what type of air your pulling. If it starts to indicate lean on your plug checks, then you'll want to look into moving up in jet size.
Agreed GG; I looked at your pics Mike, with that set-up I think a stock 195 main would be rich, even shimmed. That V-stack will pull as much air, if not more, than most aftermarket airkits out there. What type of filter are you using on it? Even with a foam or oiled gauze element it wouldn't indicate to me that it would run rich from that little bit of air restriction (from the filter) with a stock main and pilot in there.
Do you mean it should run lean with that much air?I'm using an oil foam from Thunder cycles.

Yes, sorry--typo error. That much air and a 195 stock main and stock pilot should be really lean IMHO. I don't see how it could run rich with that type of set-up; with those pipes you're putting on with no baffles, you will most likely be lean. My guess, you'll want to go with anywhere from a 200 Keihin up, probably a 205 or 210 is my guess since you probably have little to no restriction on intake or exhaust. I'd order all three mains, then start to experiment.

You have a Keihin CV carb, you want a 393 series Main Jet. I'd call Factory Pro (go to website to get their number), you can buy individual main jets from them for like $3-4/each and shipping them is cheap since they have miniscule weight. Rage Performance was my other resource, but they had trouble getting a 200 for me and don't get anything bigger than that anyway.
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