back firing

[speedracer33]

predator 212 with .36 jet, 140 etube, and exhaust... I've lost 5 mph at my top end and back fires like crazy at full throttle... will the high flo intake take care it? if not what is the cause? at the top end of throttle it feels like it still has more to go but like I said starts back firing like a machine gun...

 

[Poboy kartman]

OK.....FESS UP!!!!! What else did you do??????

 

[speedracer33]

nothing... that's it I swear... I just removed the governor just tonight but it did it before... right after I rejetted the carb. I hoping it's just the air fuel mixture but I'm not sure.... exhaust, .36 jet and 140 etube... runs good at half throttle but back fires at full throttle

 

[BirdFanatic]

nothing... that's it I swear... I just removed the governor just tonight but it did it before... right after I rejetted the carb. I hoping it's just the air fuel mixture but I'm not sure.... exhaust, .36 jet and 140 etube... runs good at mix throttle but back fires at full throttle

that could be the valve float or your valve lash stinks and needs to be set .

 

[landuse]

Did you rejet the carb because you wre told you needed to, or did you do it after letting your kart tell you that it needs it. There is no point in rejetting if it is not needed. The old spark plug test is what tells you if it is needed

 

[Denny]

Have you tried firing back?
Denny

 

[speedracer33]

I was told if you add a high flo intake and a high flo exhaust you need to rejetted the carb to keep the air fuel mixture correct

 

[DaveP]

that tends to be true,,, BUT,,,, you need to let the engine tell you if it is so. What does the plug look like now?

Pull plug and take pic and post.

 

[speedracer33]

here's the plug

 

[justinlogue5_0]

Don't quote me on this but I was told on some year model predators, they had the coils with built in rev limiters?

 

[speedracer33]

What would the Rev limiter do?

 

[justinlogue5_0]

Limits the rev's (RPM"S) by cutting the fire causing the back fire issue. Example would be a drag car sitting at the line full throttle and the motor going pop-pop-pop-pop.

Again, not sure if this is your problem.Just a thought out loud.

 

[speedracer33]

I didn't get the back fire till I rejetted... I hoping it's the air fuel mixture because I'm still running stock intake... my new intake will be in the mail today...

 

[justinlogue5_0]

Your getting to much fuel, basically flooding the motor and the motor is trying to burn it off which causes the pops and black spark plug. If you went to big on the jets, the new intake won't help you either. Once you put your new intake on, if it still pops then you need smaller jets. How small is a trial in error.

 

[speedracer33]

I had a .37 jet in it and I noticed the back fire so I went don't to the
.36 jet... if it still back fires after the new intake I throw the stock jet on top of the 140 etube and see how that goes...

 

[speedracer33]

that is still the stock spark... what is a good aftermarket spark plug?

 

[justinlogue5_0]

IMO just stick with a autolite or something similar. I spent the money on a fancy "Racing" plug and didn't even get a tank of gas on it and it fouled out. Put a regular autolite in it and have been running every since.

Also on the jetting. You can go bigger than stock jet size with your current mods. When I did mine I went a little bit over kill which caused small puffs of black smoke at idle but cruising and wide open runs were perfect. Unfortunately I can't remember what size that actually was since I changed mine again after adding cam, rod, etc......

 

[speedracer33]

thanks for the info...

 

[speedracer33]

new intake came in

 

[speedracer33]

I can't tell a difference between a modded predator 212 and stock... is that possible? what kind of gains am I supposed to be seeing with intake, 140 tube, stock jet took out the back firing and hi flo exhaust... my mph stock was 40.65... after mods I'm running 39.76