BMW R1200R R1150R/T F800 K1200R R1100R/T R1250R RnineT Message Board

I have a Remus muffler on my 2002 R1150R

Techclusion fitted.

The bike runs good thru the entire range, idles at 1100 or so.

When closing down the throttle from a high speed, I get backfires.

It's a lot less since I timed it, but I'm curious as to the combustion in the muffler

Any comments?

Rags

Backfires happen or are made much worse by air leaks at the header attachment to the head, but most commonly it is an air leak at the header joint to the muffler inlet that is always the cause. To minimize backfiring, closing the throttle quickly and fully will activate the fuel cut circuit of the EFI fuel map, shutting off all fuel injection on engine decel until 1,800 RPM is crossed on the way down, leaving nothing to after-burn. That wonderful fuel cut circuit also gives the OilHead really strong engine braking on decel without wasting any fuel like carburetors did. As for the pipe joint, check for full engagement of the header pipe into the female split opening of the muffler. For a good fix that actually lasts in spite of its lowly 700 DegF rating, fully coat both metal mating surfaces with a very thin layer of high temp RTV gasket maker (available in Wal*Mart, AutoZone, AdvanceAuto, NAPA, etc) like this one:
http://www.amazon.com/Permatex-81878-Ma ... uto_text_z
It is an excellent performing hot oil gasket sealer, and easy to remove at engine service time. I used it to seal the muffler joint on my R1150R and it was still working great after years of use (NO backfires), without discoloration or charring, in spite of the normally high exhaust pipe heat.

Also in AutoZone or AdvanceAuto parts stores, a product made specifically for sealing muffler pipe joints:
http://www.amazon.com/Permatex-80335-Mu ... atex+80335

You should also be sure the muffler is SOLIDLY mounted and does not swing left/right or move around when the bike is ridden, so the joint sealer stays in place. Once you stop the air leaks, you will also notice the complete disappearance of all those little black (carbon) dots on the rear rim, caused by cold engine exhaust vapor condensates leaking past the muffler inlet joint.

Thanks a bunch Rob... much appreciated

Rags