if an engine back fires when shuting off throtle is it lean?

[illinoiskat]

I put a jet kit, new slip on, and GSXR cams in my bike. When I shut the throttle down at high rpms the bike backfires. I put the jet kit and the cams in my bike first. It only happened after I put a slip on the bike. The stock exhaust did not do this. I am thinking I need to go up a size on the jets in the carbs. Ideas?

[lucifers_ride]

Backfires thru the carbs or Fires Thru the exhaust??????? My SSR2 fires thru the exhaust, my bros Two Bros Racing does it, and buddies D&D does it....

[duff daddy]

if it back fires, that means its lack of back pressure, put the stock exhasut on it wont back fire because of the restriction, now put a full exhaust or just leave the headers there so it wide open, and youll get some nicee flames hahah but yea its just because of backpressure issues, you want backpressure in your bike i wouldnt say tis somethign to stress about

[ThAzKat]

back fire- Explosions of the fuel/air mixture that travel back through the intake

after fire-explosions in the exhaust track caused by too lean a air/fuel mixture

writen by Cyber

[The CyberPoet]

Re: if an engine back fires when shuting off throtle is it l

I put a jet kit, new slip on, and GSXR cams in my bike. When I shut the throttle down at high rpms the bike backfires. I put the jet kit and the cams in my bike first. It only happened after I put a slip on the bike. The stock exhaust did not do this. I am thinking I need to go up a size on the jets in the carbs. Ideas?

If you're getting after-fires (i.e. - out the exhaust) on decelleration, you may be able to cure them simply by increasing the pilot screw settings a quarter turn or a full turn (or somewhere in that range). If not, you'll need to go up a jet size and retest. Yes, it means that the mix goes to lean during the deceleration process (when the RPM's are still dropping, but only the idle circuit is fueling the carbs).

Want to know for sure: call the guys who make the jetkit -- they'll give you the answer
Hint: it'll be the same answer as I just gave you...

Cheers
=-= The CyberPoet

[ThAzKat]

Hi Marc! Sorry I didn't ask permission LOL

[illinoiskat]

ok, its an afterfire. I will play with the float bowl levels and the idle screw. It is still a little dead in the 2 - 3.5 k zone. Maybe the two will clean up the afterfire. The pipe helped the low end a bit. Thanks for the replys.

[trinc]

remove the 12.5 idle jets and install 15's - adjust the air-fuel mixture for a smooth idle. even when correct you'll get a little popping.

tim

p.s. of course you could put it on a dyno w/ a sniffer too

[Gripp]

I'll I did was back the mixture screws out half turn and all popping on decel is gone. I talk to a guy at my dealer and he said popping in the exaust is a lean condition, which can hurt the motor in the long run.

[illinoiskat]

I all ready have the screws backed out 4 turns. I will try a little more. Is the idle circuit allways on?

[arsenic]

4 turns is too many, the factory sets them at 1 1/4 turns for a stage on jet you should go to 2 1/2. Tighten the srew until it lightly seats then back it out 2 1/2 turns.

[illinoiskat]

I just followed the directions on the Ivans jet kit. I think the GSXR cams are making it more lean. hmmmmmm I think I will order the 15's and go one turn on them.

[The CyberPoet]

I all ready have the screws backed out 4 turns. I will try a little more. Is the idle circuit allways on?

I'm with Arsenic on this one -- 4 turns out is too many to go up further (Ivan's 600 kit for the 98+ sets his at 4 turns out for example; if you still get the problem, he'll tell you to go to a bigger main jet). If you need to go to more turns, up the main jet size one size and reset the turns down to 2-3/8, retest.

If you got the kit from Ivan, get him on the phone. He'll answer all your questions (and talk your ear off in the process).
PS - Ivan will send you new jets if you need them to get it "right", usually for free if you bought his kit. Seriously, talk to him about it!

Cheers
=-= The CyberPoet

[ThAzKat]

I just followed the directions on the Ivans jet kit. I think the GSXR cams are making it more lean. hmmmmmm I think I will order the 15's and go one turn on them.

Gixxer cams have more lift and duration than the Kat cams. Timing is also a issue, you should advance it. I would double check the carbs also.

[md86]

Um , I've read that if you're more than 4 turns out on the pilot to change the PILOT jet to one bigger ...