Constant Backfiring

I've had my 426 for two years now and have had little time on the bike. I just recently noticed that it backfires just as much on the track than when I start it up between seasons. Does anyone else have this problem. If so what's the fix?

Backfiring is usually a sign of lean-ness.

If its popping on deceleration (throttle closed) then your pilot circuit is probably lean. Richen the circuit slightly by tweaking the Kouba T that you just bought via NH Kevin. What??? you didnt buy one..shame on missed out.. so try the old fiddly method with a short screwdriver in the correct orifice! If you get to more than 2 turns out on the screw you will need a larger pilot jet or smaller Pilot air jet. See the thread Jetting Qs for Taffy's table of PJ to PAJ matches.

If its popping all over then you have other problems which is sort of out of my leagues to deal with, but basically.... Smaller MJ will lean, Larger MAJ will lean and vice versa.

Raising the needle will richen mostly the top end but will also influence the bottom soemwhat, lowering it will lean it. Needle fatness will influence pretty much the whole shebang, but more down at the lower end.

You may want to post your complete jetting for additional help from the pros






Fuel Screw #turns

Also, are you deoctopussed ? This makes a difference on what you PAJ should be to compensate.

Whatever you do, do it step by step.

You may want to consider that:

You may have an exhaust leak between the header and barrel or header and silencer.

Your starting to foul a plug.

You have an intake leak. This would normally show as an irregular or high idle speed.

Your jetting is off.

Change the plug and tighten the pipe connections and go try it.


you've probably got some crud build up in your carb if you're not using the bike that much.

check when you give the carb a thorough cleaning that the jets look clean and don't look like the side of an old ship.

if you've changed nothing else and you do this you'll be fine. there is one more thing you can do and that is change the plug at the end.


I started having backfiring when I installed a "Terry Cable" type hot start remote button. I would suggest this this got bad enough that I fouled my first plug, so check your hot start whether or not you have a remote.


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