Exhaust "backfire"

[TennRT]

I have just started getting some exhaust "backfire" on my '99 RT, 17k miles. Any suggestions for most likely causes?

[Marek]

Mine does it as well - when I asked BMW service tech about it he said it's normal and nothing to worry about. It doesn't do it all the time but when riding in the mountains and getting on and off the gas all the time it's more noticable.

Mark

[upflying]

Along with surging, my '98 RT popped through the exhaust all the time. That is until I adjusted the valves and did a TB synch. I think a good tuneup will solve your problem.

[jemllc]

Out of sync carbs will cause backfire. If you are not doing your own, I think you will find it helpful. One usually has more time to get it near to perfect than the tech does.

Jimmy

[TennRT]

Thanks. This is what I was thinking, but appreciate the experience there.

[Cali Kid]

Dwight, welcome to the board. You will find many good suggestions and ideas here, but takes some of these tings with a grain of salt, including mine

 

With that said, backfire as you put it is really after-fire. That is, unburnt fuel collects in the exhaust system and then is suddenly ignited when the exhaust valve opens, typically after a slow burning cycle, and the fuel is ignited. So what do you do?

Yes, a throttle body synch (TBS) may help, (or plugs, or different gas, or CCP change) because one cylinder is probably a hair leaner than the other. Lean mixes burn a little slower creating the situation above. Then again, it may not help because most of these bikes are running lean to begin with. Since yours is an 1100 I won't offer any suggestion on changing that, but if you are only experiencing a few "pops" on deceleration it's not a problem of mechanical significance. You could end up chasing your tail if you know what I mean.

[Marek]

I went through the whole procedure of syncing the TB's according to instructions from our friens at IBMWR site using TwinMAx etc - starting at the zero=zero adjustment all the way through HIGH RPM sync. Bike runs good but it will surge at certain RPM ie just above 3000. I've it synced at 2500 and that produces good results at 4000 as well. Question now - shuld I be able to eliminate surgeing all together or is it one of those things you have to live with if you have 99 11RT?

What range or RPM do you sync your RT at?

 

Mark

[Ken H.]

What range or RPM do you sync your RT at?

That's kind of one of those "religion" questions.

 

FWIW, I do the high speed sync at about 500 RPM below where the worse surge problem is.

[ShovelStrokeEd]

I do mine just off idle. I eliminate the surge by never running the bike at that low an RPM. Even a cursury examination of the torque curve will show you the motor shouldn't be run under load there. Surge is just your bike telling you to downshift.

[philbytx]

Thus spoke the seraph....

 

Amen brother