Backfire

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By Adrian on Sunday, September 15, 2002 - 04:01 pm:  View Adrian's Profile Search for other posts by Adrian Edit this post

Out for a ride yesterday the bike backfired a few times while compression braking after some liberal throttle applications. Any ideas about the possible causes? Should I be concerned? My bike has got 4000 miles and standard pipes.
I'm not sure the valves have ever been checked but don't know how this would affect backfires?  

By Tokas on Monday, September 16, 2002 - 05:33 am:  View Tokas's Profile Search for other posts by Tokas Edit this post

Hi Adrian. I never had any backfire with standard chip & cans.

But I just installed Renegade Highmounts & chip this friday. (Oh, how lovely they sounds!)
My first trip I took was too my MC-garage to get the 7500 km Service done. They tuned the CO-values, but the mechanics sad he made it a little richer than normal (5 something instead of 4) because i told him I was just about to mount free-flow sport air filter and an enlarged airbox.

Two days later when going some 320 km home from a classic motorcycle event my bike backfired, just as yours, sometimes after motorbraking. I first got worried but kind of like it, it sounds as a highly tuned competition bike!
It made me think about what it realy is. I'm not sure but my guess is that the backfire comes from not combusted gasoline in the headers exploding. And since this isn't inside the engine I don't think it would be harmful to the engine. Neither do my brother (car mechanics)think, but he sad it might damage the silencers...

Jorge! Are backfire a "feature" of renegade exhausts???  

By Befbever on Monday, September 16, 2002 - 06:00 am:  View Befbever's Profile Search for other posts by Befbever Edit this post


I've only had it once. Backfire is only normal considering the volume of air and fuel on this V-twin. But again, it only happened once.
Never had it with the stock stuff on it. 

By Adrian on Tuesday, September 17, 2002 - 04:43 pm:  View Adrian's Profile Search for other posts by Adrian Edit this post

So in general are backfires caused by too lean or too rich a mixture? Or are things more complicated than that?
thanks  

By Powermaster on Wednesday, September 18, 2002 - 05:16 am:  View Powermaster's Profile Search for other posts by Powermaster Edit this post

Adrian, where is the backfire comming from the exhaust or airbox?  

By Twowheels78 on Wednesday, September 18, 2002 - 09:39 am:  View Twowheels78's Profile Search for other posts by Twowheels78 Edit this post

Mine does it every once in a while through the airbox, or rather airkit. One time it was even enough to kill the engine. I can't say I ever remember getting any backfires through the exhaust. Any ideas Powermaster?  

By Adrian on Wednesday, September 18, 2002 - 10:38 am:  View Adrian's Profile Search for other posts by Adrian Edit this post

I'm not sure if its through the airbox or the pipes. However, both are standard. Does having a backfire coming from the airbox versus the pipes mean that the cause of the backfire is one thing versus another?
thanks again.  

By Andyjfalco on Wednesday, September 18, 2002 - 10:46 am:  View Andyjfalco's Profile Search for other posts by Andyjfalco Edit this post

Air box backfire can cause a loss of bollox. Not good My Falco backfires on the over run, Scorpion pipes, FP chip, and it sounds great! It's definatly from the pipes though.  

By Powermaster on Wednesday, September 18, 2002 - 01:31 pm:  View Powermaster's Profile Search for other posts by Powermaster Edit this post

Backfire through the exhaust on the up run is a sign of leaness the same aplies if through the airbox, on the overun it tends to be an airleak.
Regarding leaness, sometimes is a simple case of syncronising the throttle bodies or in plain English, balancing the carbs, more realy the Air to Fuel ration,as both cylinders tend to be out of sync.
It's funny you say that Andy, the usual complaints I get from the US is the bikes run rich, after reading some posts about people wanting to enlarge the throttle bodies (big mistake) I seem to have read that the US bikes are running on 48mm carbs. If this is correct a lot can be explained for their low BHP readings.  

By Adrian on Thursday, September 19, 2002 - 12:19 pm:  View Adrian's Profile Search for other posts by Adrian Edit this post

Thanks for the information about backfires. The only thing I don't get is where an air leak would come from? Air leaking into the exhaust near the headers? Anyway seeing how the usual cause is running lean I will derestrict the bike and go with the full power mapping (I think it runs richer). Ahh, I'm so happy that I have the last rationalization needed to take the choke collar off the tiger.  

By Twowheels78 on Monday, September 23, 2002 - 07:28 am:  View Twowheels78's Profile Search for other posts by Twowheels78 Edit this post

Powermaster you were right, the throttle bodies were out of sync, way out of sync! I had actually bought the throttle body synchronizer from evoluzione earlier this summer just never got around to doing it, lazy bum The air bleed screw for the front cylinder was 3.5 turns out There was also carmelized gas all over the throttle butterfly and velocity stack. That might explain why it wouldn't idle below 1700 rpm I set both cylinders to the stock 1.25 turns out and synchronized the throttles. No more backfires through the airbox, nice steady idle at 1400 rpm. It doesn't try to choke off in emergency stops, which I actually had to do yesterday, came within about five feet of hitting a deer If you haven't synced your throttles do it, it's well worth the time!

P.S. The throttle body synchronizer from evoluzione is only $20, a good set of carb stick would probably be better but this works. 

By Jcc273 on Monday, September 23, 2002 - 04:14 pm:  View Jcc273's Profile Search for other posts by Jcc273 Edit this post

Mine started backfiring on a trip round Nova Scotia. It took me a while to realize it was happening, always while engine braking, but then I'd get an occasional loud pop. We stopped for dinner, then checked out my bike. My buddy had the same thing happen to his ducati st2 and knew exactly what it was. I'd lost a f*cking plug from the rear exhaust header. In the dark, you could even see little blue flames shooting out under the seat! My buddy had a spare plug (he's lost two), so we were on the road again in minutes. There's one on each pipe, so check it out. I hope this helps.

-Jim  

By Tokas on Tuesday, September 24, 2002 - 04:55 am:  View Tokas's Profile Search for other posts by Tokas Edit this post

Thanks a lot JCC.

It makes sense. I didn't hear any backfire on my way to the service, but the day after there where backfires. During the service I noticed these plugs where removed due to CO-adjustment.

I'll go to the garage and see if this is the case! 

By Crmc33 on Tuesday, September 24, 2002 - 05:05 am:  View Crmc33's Profile Search for other posts by Crmc33 Edit this post

quick quick,

I dont like being left in suspenders

no matter what rumours youve heard 

By Tokas on Tuesday, September 24, 2002 - 10:18 am:  View Tokas's Profile Search for other posts by Tokas Edit this post

No more waiting Crmc, Jcc is right!

The "CO Intake Screw" and washer are missing. Parts number 8150488 & 8150489.

It says in the Spare Parts Catalogue for Falco that it should be secured with some Loctite 8150. I guess that's what the mechanics didn't do, and then of course they vibrated loose... 

By Befbever on Tuesday, September 24, 2002 - 10:50 am:  View Befbever's Profile Search for other posts by Befbever Edit this post


The intake screw?
Bloody hell!  

By Tokas on Tuesday, September 24, 2002 - 12:36 pm:  View Tokas's Profile Search for other posts by Tokas Edit this post

Yes, that's what it's called...

It's where you put the CO-probe to take in the CO... 


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