Maxwedge

iTrader: (1)

I changed carbs this weekend and while the new setup runs much better everywhere in the rev range, I have lots of backfiring on decel. My old carb was jetted richer and I would only get a pop if I ran it hard and turned it off as soon as I parked.

With the new carb the engine revs up smoothly instead of choking on the secondaries, and the exhaust doesn't stink like before. But it pops, pups, or booms every time I let of the throttle, at any rpm between 3 - 6k. On long downhills, using engine braking, it will pop numerous times, I made no changes other than the carb. So why the sudden pop-fest? I thought it was the rich nature of rotaries that caused afterburn, but again, this carb is leaner than the old didn't have the issue.

Jeff20B

iTrader: (13)

Maybe it's letting MORE air in on decel, and this air is igniting inside the exhaust causing afterfire. Think of it like you have an unintended exhaust leak, which can also cause afterfire.

Can you tell us which carb you were using, and then which carb you switched to? You didn't mention it in your post.

t_g_farrell

iTrader: (1)

Jetting between carbs is not really comparable. I bet you are actually a little richer than before and when the carbs loaded up either from revving it up or sustained acceleration and then letting off the gas, that rich mixture doesn't burn all the way and gas ends up in the hot exhaust which further ignites it for the wonderful backfires. Does it shoot flames as well?

If you have an AFR meter to use it would help you diagnose it or you can do it old school and check you plug color at various points to see if its rich.

Also, make double sure there are no exhaust leaks, thats always a recipe for backfire as Jeff mentioned.

I think you went from Holley ot Edlebrock or something like that right?

Maxwedge

iTrader: (1)

Thanks guys. T_G_ yes, I went from an Eddy 500 to a Holley 465 this past weekend. The with the Eddy my exhaust reeked of gas and it stumbled on the secondaries, which is why I assume it was too rich. With the Holley it doesn't stink and the secondaries come in buttery smooth. But I don't have an AF meter hooked up yet, so I'm guessing. I don't know if it's shooting flames, I haven't had anyone follow to watch. I had a bike that did that though, which I could see.