Backfire From Carbs ?

[Robert Corrie]

I have rejetted stock carbs on my 1150 with pods and a header, on start up it backfires from the carbs. Causes? Solutions?

[Billy Ricks]

A couple of things to check would be carb synch and valve clearances. Did you check the float levels when the carbs were apart?

[Carter Turk]

Carbs backfiring

You're not alone, mine did that too with a pipe, jet kit and pods. Hardly at all with 90 GSXR carbs.

Kevin Cameron writes about this in his Sportbike Performance Handbook. I think he mentions Cam overlap causing some of the pulse to get sucked back thru the intake tract causing the backfire. Carter

[KEITH KRAUSE]

The cause, in my experiences, seems to be a lean mixture. I call it "spitting". It gets worse as the temperature drops and is most common at cold start ups. It can also happen at cruising speeds. I have tried various ways to eliminate it, larger pilot jets, adjusting the carbs pilot/air screws, even raising the jet needle. I have seen this on several bikes, some of which I know have correctly set valve clearances and ignition timing and perfectly clean carbs with a good synch' job. In some cases, the spitting does'nt happen just by giving extra choke at start up. But this results in a high rpm which is'nt good either. That's another reason I feel it's mixture related, but who can say?
I've had good success minimizing it on several bikes, in some cases almost completely except for cold start ups in the 30's. But never been able to completely stop it. I called Dynojet and they say they are aware of it and it's one of those "driveability" problems that re-jetting can cause.
I can say for sure that richening the mixture helps, as long as that does'nt cause other problems. If it's minimized, it's easy to live with.

[Anonymous]

I have a 98 Bandit as well that has been rejetted with pod filters and it also does the same thing. It gets worse when it's cold but goes away after a minute of so of idling. I have found that it's not as bad if I give the throttle a twist before starting. I have checked with other guys on Bandits on the Maximum Suzuki forum and it seems that I am not alone.

[Hoomgar]

My 1000 has always done that. It was rejetted when I bought it and has been redone again since I have owned it. It is rare, but it happens. I find it disturbing when it happens but has never caused a problem to date.

[Anonymous]

so if my bike "spits" it must be jetted

[KEITH KRAUSE]

so if my bike "spits" it must be jetted

If your bike spits, then you do have some degree of over lean mixture.
It could be dirty jets or dirty passages, intake leaks, incorrect float level, incorrect jet size, valve tappet clearances, poorly synch'd carbs...