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Confounded BACKFIRING


SyntorX

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I have a 94R1100RS with a Staintune exhaust. Every time I release the throttle (from 3k rpms and up) to decelerate, the bike backfires popPopPOPPOppop. I read a value of .585 volts on the TPS red and white wire. I tried lowering it to the spec. .340-.400 volts but the bike wouldn't stay running so I put it back.

The bike runs ok. It gets upper 40's mpg. I just backfires and has a unsteady idle at times fluctuates from 800-1100rpms.

What needs to be done? anyone?

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russell_bynum
I have a 94R1100RS with a Staintune exhaust. Every time I release the throttle (from 3k rpms and up) to decelerate, the bike backfires popPopPOPPOppop. I read a value of .585 volts on the TPS red and white wire. I tried lowering it to the spec. .340-.400 volts but the bike wouldn't stay running so I put it back.

The bike runs ok. It gets upper 40's mpg. I just backfires and has a unsteady idle at times fluctuates from 800-1100rpms.

What needs to be done? anyone?

 

1. Some backfiring is fairly normal with an aftermarket exhaust.

2. You can't just monkey around with the TPS randomly to get a value you want. It needs to be calibrated with the throttle butterfly. Go to the Oilhead Tech page on the iBMWr's website and read all the articles that mention the "Zero=Zero" procedure.

 

Follow the procedure to the T and you should wind up with an appropriate idle speed and the TPS voltage within spec.

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I have a 94R1100RS with a Staintune exhaust. Every time I release the throttle (from 3k rpms and up) to decelerate, the bike backfires popPopPOPPOppop. I read a value of .585 volts on the TPS red and white wire. I tried lowering it to the spec. .340-.400 volts but the bike wouldn't stay running so I put it back.

The bike runs ok. It gets upper 40's mpg. I just backfires and has a unsteady idle at times fluctuates from 800-1100rpms.

What needs to be done? anyone?

 

SyntorX, I can’t say for sure on the 94 as I don’t have the specs on that early Motronic unit but on the 95 & up you do need the TPS (low cal) voltage under .400v at base idle.. Did you do a computer reset after the TPS adjustment? If not try disconnecting the battery for about 30 seconds after the TPS re-setting so the computer can adapt to the new values.. Make sure you are using a GOOD CLEAN solid ground for your voltmeter as a ground resistance can skew the readings..

 

I’m not sure of the wire colors on the early TPS units so makes sure you are measuring the low (0 tp1/2 throttle) side of the TPS & not trying to set the high (1/2 throttle to wide open) side..

 

As far as popping in the exhaust,, if you have little or no baffling in the muffler most will pop on over-run or decel.. If it bothers you try a fuel controller like the Techlusion then add fuel on the decel as that will usually stop or lower the popping.. If the richer doesn’t help then try going leaner on decel (depends on if it’s popping in the muffler or starting the after burn in the pipe close to the cyl head then traveling to the muffler..

 

Twisty

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Thanks russell. You are right about the IBMWR website it is full of useful info. Before doing the Zero=Zero I wanted to get with you all and post the situation to acquire auxillary points of view.

Bad thing is, the bike was at the dealer 2500miles ago (it has 44,000mi) for full service to the tune of $550!!!

Indiana has only one dealer and I am riding to Kentucky from now on.

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Right on, Twisty. No I didn't reset the Motronic.-oops

 

I did notice that if I slowly decel the throttle and use brakes to slow I can keep it from backfiring. But, just las week I was at Deals Gap, Cherohala Skyway, Blue Ridge Skyway and there were plenty of times where I wasn't afforded the time to "slowly decel the throttle".

 

I will look into the techlusion system tho, thanks

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russell_bynum
Thanks russell. You are right about the IBMWR website it is full of useful info. Before doing the Zero=Zero I wanted to get with you all and post the situation to acquire auxillary points of view.

Bad thing is, the bike was at the dealer 2500miles ago (it has 44,000mi) for full service to the tune of $550!!!

Indiana has only one dealer and I am riding to Kentucky from now on.

 

Before you do anything like a Techlusion or a PowerCommander, you need to get a good baseline.

 

Your bike should be able to idle just fine with the TPS within spec.

 

My advice is to do a really good valve adjustment, then the 0=0. You can not be too anal retentive about these two things.

 

The good news is, once you get the 0=0 done, you should never have to touch the TPS ever again unless it fails or you have to remove it for some reason.

 

Do the 0=0 and get the bike running properly, then let's see what's going on with the backfiring and if there's anything we can do about it.

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10-4 one of my buddies just bought a TwinMax sync tool so I will do the 0=0 and accurately sync the throttle, oh yeah and check the valves and will like you said ..Go from there.

Regards

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Right on, Twisty. No I didn't reset the Motronic.-oops

 

I did notice that if I slowly decel the throttle and use brakes to slow I can keep it from backfiring. But, just las week I was at Deals Gap, Cherohala Skyway, Blue Ridge Skyway and there were plenty of times where I wasn't afforded the time to "slowly decel the throttle".

 

I will look into the techlusion system tho, thanks

SyntorX, that popping on decel is a burnable mixture in the exhaust that finds oxygen then lights off..

 

Basically two ways to stop it.. Make the exhaust too rich to burn (that is how most applications stop the popping) ,, or make it too lean to burn (very difficult to accomplish without total injector control)..

 

Like I said above, somewhat normal on a performance exhaust as the exhaust reversion pulses pull the air back into the exhaust system farther.. On a production exhaust the muffler design keeps the mixture in the muffler from igniting & even if it does it quiets the popping so it isn’t a problem..

 

If your TPS is out of adjustment it could add to your problem.. On over-run or dropped throttle the fueling computer should shut the fuel injectors off until down around 1500 RPMs or so.. It bases it’s assumption of when you are decelerating on TPS voltage & engine RPM.. If your TPS voltage is out of whack it might not see a dropped throttle as a decel event..

 

You can do the 0=0 if you want but I never put much stock in that operation.. I always just set the idle RPM using the brass screws then set the TPS voltage to about .385v at that point.. You want the TPS voltage as high as possible at idle but still under .4 volts.. You really can’t set it to .4 volts as that doesn’t leave any room for slight creep due to engine heat or wear so .385 volts seems to work as good as anything & leaves a little wiggle room..

 

The only time I can see a real advantage to the 0=0 is if someone has diddled the factory set base throttle plate stop screws & you have no idea of what your typical base throttle plate angle is,, or there is a large difference in brass screw settings side to side after a TBI balance..

 

One good point of those fuel contollers is they allow some extra fuel to be added at above 1500 RPM decel & if a performance pipe is installed they usualy go leaner somewhat from the pipe..

 

Twisty

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russell_bynum

You can do the 0=0 if you want but I never put much stock in that operation.. I always just set the idle RPM using the brass screws then set the TPS voltage to about .385v at that point.. You want the TPS voltage as high as possible at idle but still under .4 volts.. You really can’t set it to .4 volts as that doesn’t leave any room for slight creep due to engine heat or wear so .385 volts seems to work as good as anything & leaves a little wiggle room..

 

The only time I can see a real advantage to the 0=0 is if someone has diddled the factory set base throttle plate stop screws & you have no idea of what your typical base throttle plate angle is,, or there is a large difference in brass screw settings side to side after a TBI balance..

 

 

The bike wouldn't idle, and he mucked with the TPS. We don't know if that means he adjusted the idle stop screws or if he physically moved the TPS itself, but either way...that's a problem. If the bike doesn't idle with the TPS voltage within the spec, then there's a problem and a 0=0 is the only way to make sure you have everything in order.

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You can do the 0=0 if you want but I never put much stock in that operation.. I always just set the idle RPM using the brass screws then set the TPS voltage to about .385v at that point.. You want the TPS voltage as high as possible at idle but still under .4 volts.. You really can’t set it to .4 volts as that doesn’t leave any room for slight creep due to engine heat or wear so .385 volts seems to work as good as anything & leaves a little wiggle room..

 

The only time I can see a real advantage to the 0=0 is if someone has diddled the factory set base throttle plate stop screws & you have no idea of what your typical base throttle plate angle is,, or there is a large difference in brass screw settings side to side after a TBI balance..

 

 

The bike wouldn't idle, and he mucked with the TPS. We don't know if that means he adjusted the idle stop screws or if he physically moved the TPS itself, but either way...that's a problem. If the bike doesn't idle with the TPS voltage within the spec, then there's a problem and a 0=0 is the only way to make sure you have everything in order.

 

Russell, if he messed with the factory idle throttle plate stop screws then yes a 0=0 is probably in order.. I don’t see where he said he did..

 

I say not to mess with the factory set idle throttle plate angles as you gain nothing (unless they have been messed with or there is a gross difference in brass screw setting after a TBI balance ) ..

 

You say he should mess with them..

 

I guess he will just have to chose to believe one of the other of us & go with that..

 

Twisty

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russell_bynum

He said he changed the TPS voltage.

 

I read a value of .585 volts on the TPS red and white wire. I tried lowering it to the spec. .340-.400 volts but the bike wouldn't stay running so I put it back.

 

You either do that by adjusting the idle stop screws or by moving the TPS itself.

 

Either way, the bike doesn't idle when the TPS voltage is where it should be at idle. We don't know what's out of whack, but we know the TPS was adjusted in some way. 0=0 gets us back to a known-good setting and we can go from there.

 

Or am I missing something?

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