M4's on, now.. how to tame the backfire and melted airbox

[Randew2U]

Finally put on my new M4 on my 04 BP yesterday. I took it for a test spin and noticed on downshifting the "popety pop" kind of backfiring, not excessive loud, like a firecracker, but objectionable. I have heard mention in here of an adjustment I can try before an all-out rejetting? I can do the rejet over the winter but would like to do a temporary adjustment to get through the summer. Will the backfiring damage the valves or exhaust if I do nothing for now? Any suggestions appreciated!

When I got home i noticed a melt spot on the airbox, where the two-two-one pipe passes close. I't didnt melt through though. I went to Wallmarts and picked up a black silicone sheet about 5" by 5" made by farberware for handling hot pots. I want to use this somehow as a heat shield, I'll post photos.

[jimc]

Couple of things..
Backfiring is sometimes just due to air leaks in the exhaust system rather
than jetting, I'd go through that first.
You might find that the 4" wide foil tape is a good heat shield retainer, and does a fair job of reflecting radiant on its own.

[DAVID THOMPSON]

i looked at past posts and fuel to air mixture screw seem to be
set at 5 turns out some as high as 7
but make a saftey wire so it can not fall out
read this post

http://www.mzriders.com/viewtopic.php?t=918

one on my rt125 fell out and i was lucky local shop had a carb in junk box
with proper parts to fix it

[kman.45]

I just fitted a D&D pipe, had a bit of pipe fabricated onto the stock 2into1 pipe. The pipe to exhaust can inlet fitting was not perfect. Had same popping on closed throttle decel. As others have posted and as a buddy told me, that is typically caused by an air leak in the exhaust. On his advice I went to an auto parts store and bought some exhaust sealer, Permatex and VersaChem make some. Apply liberally to joints and reassemble. Basically took care of mine, just some "burbling" now.

I did the following to carbs also:
1) air mixture screw 5 turns out (was at 5.5 it turns out, with stock exhaust on it).
2) replaced main jet in secondary carb with 135 Keihin jet (no 132 or 132.5 available at local dealers).
3) lifted main jet needle in secondary carb one notch.
4) set secondary carb to come on at 6 mm slide height of primary carb.

While this probably didn't result in much peak hp or torque gain. the throttle response and accel is noticeable better. Plus when that second carb opens up, the noise just "rips!"

I also noticed that the throttle stop on my bike was set to full "on." This was preventing full open of throttle, so I back it out to allow for full movement (prolly didn't do much, buy why limit it?).

kman

[phlat65]

go to your local MX shop, I bought some self adheasive exhaust heat sheeting. it came in 2 1ft square sheets, for $15.00 or so. I think it was MSR. I applied it to the airbox, and back of the side panel. my dual pipe headders are within 5mm of the airbox, and it stopped the melting.

[drj]

i did ab-so-lute-ly nothing...and after several hundred miles (maybe a thousand) enough soot collected in the nooks and crannies that it no longer does the decel POP POP...i think my way is cheapest...but certainly not the best!

i have no idea if the guy i bought it from did anything to the carb - but she runs great!!!

drj

[Randew2U]

ive had my M4 on for a few months now and so-far so-good. I like the bloop-bloop sound under load. The bike seems to vibrate more now, need to check mounting. I bought some sealant and want to adjust the positioning of it. I left the flexible bushing on the frame mounting point where i attached the steel bracket for the can. I want to look at removing that and making the bracket to frame connection rigid and the bracket to can connection flexible. make sense? Can i adjustthe