Popping or spitting out of carbs

Hey guys. My 78 KZ650B is running, but has developed a new problem. When throttling up (or down) from about 1/6 throttle up (only under load or in gear) I get a popping, backfiring or "spitting" out of the carburetors. This was not happening and is new. Before you ask, I have pods but stock jets and I do not own an airbox. The valve clearance and timing have been checked and adjusted. I have no idea what the cause or solution to this particular problem is.

Lean or air leaks. When I do jetting, I tell the client or myself to run it for at least 100 miles. Sometimes it will lean out. That just means the engine is breaking in and wants more fuel.
Steve

Running pods with stock jetting is a bad idea. The engine will run lean and hot - not a good thing. Either rejet or get a stock airbox & air filter. Ed

What I've seen here is guys putting on pods, 4/1 exhaust all at the same time and wondering why the bike won't run for SHT. Go one size up (pilots and mains), see how that works with one item only, then add the exhaust or pods and start again.
Steve

Steve has this bang on- just did this same thing great result.
I had to go up an extra pilot size for mine- buts that's probably unique to my setup.
I was having trouble with idling.

Also- make sure your carb boots are creating a really good seal and you retorque your head nuts after the heat cycle.

17.5 pilots, nettle up a notch and 117.5 mains are about perfect for mine. Ran the same only with 112.5 mains before I went with the 700 kit and 750 cam.

Air screws out 1 and 3/4 a turn too ....... will get them closer this summer with the color tune hopefully. make sure you have good carb holders too, new ones were money well spent I feel.

Yup.
Steve

Is there an online source for jets? I've got 102.5 mains that need a bump and no one seems to have anything local. Tempting me to get out the drill index.

Twilightoptics wrote: Is there an online source for jets? I've got 102.5 mains that need a bump and no one seems to have anything local. Tempting me to get out the drill index.

Jets R Us

ewolpert wrote: Hey guys. My 78 KZ650B is running, but has developed a new problem. When throttling up (or down) from about 1/6 throttle up (only under load or in gear) I get a popping, backfiring or "spitting" out of the carburetors. This was not happening and is new. Before you ask, I have pods but stock jets and I do not own an airbox. The valve clearance and timing have been checked and adjusted. I have no idea what the cause or solution to this particular problem is.

Would also double-check the intake valve clearances, as insufficient clearance can result in backfiring through the carb.

And assure proper ignition timing and functioning of the advancer unit.

Good fortune!