It sounds like perhaps over fuelling. Have you tried running it without the power commander connected?
Frustrated With Backfiring
Yea yea, I know we all need another backfiring thread. Yes I've used the search function...
07dl1k with 2bros, k&n and pc5, PAIR delete
I bought the bike with these mods already done, but I added dB killer tips to quiet it down. The bike did not backfire at that point.
Bought new upper TB boots thinking they might be old. They looked fine, but I replaced them anyway. Removed TB's, checked/cleaned lower boots and all TB surfaces. All boot clamps very tight and seated correctly. I even replaced all the exhaust gaskets and double checked all the clamps and hardware etc.
Fuel injector seals looked good, no cracks or damage. TPS correctly adjusted, TBS good, idle 1300rpm.
Backfires ONLY on decel and ALWAYS at ~4200 or 4000rpms. It goes from a medium pop of a backfire, to sounding like a gun going off. I am afraid of getting a ticket, and honestly it's very obnoxious.
My understanding is that these bikes cut all fuel at around this point, if that's true than the PC5 tune shouldn't matter. Is that correct? I have not played with the tune at all since owning the bike, which IMO rules the tune out. Backfires out the exhaust 100%, not through the intake.
I've been chasing this issue in circles and I'm irritated. Bike runs absolutely great with this one issue.
Could an injector be leaky?
07dl1k with 2bros, k&n and pc5, PAIR delete
I bought the bike with these mods already done, but I added dB killer tips to quiet it down. The bike did not backfire at that point.
Bought new upper TB boots thinking they might be old. They looked fine, but I replaced them anyway. Removed TB's, checked/cleaned lower boots and all TB surfaces. All boot clamps very tight and seated correctly. I even replaced all the exhaust gaskets and double checked all the clamps and hardware etc.
Fuel injector seals looked good, no cracks or damage. TPS correctly adjusted, TBS good, idle 1300rpm.
Backfires ONLY on decel and ALWAYS at ~4200 or 4000rpms. It goes from a medium pop of a backfire, to sounding like a gun going off. I am afraid of getting a ticket, and honestly it's very obnoxious.
My understanding is that these bikes cut all fuel at around this point, if that's true than the PC5 tune shouldn't matter. Is that correct? I have not played with the tune at all since owning the bike, which IMO rules the tune out. Backfires out the exhaust 100%, not through the intake.
I've been chasing this issue in circles and I'm irritated. Bike runs absolutely great with this one issue.
Could an injector be leaky?
1 - 16 of 16 Posts
That kind of backfiring is usually (always?) excess fuel that gets ignited in the exhaust system by a hot spot in the exhaust or maybe on the exhaust valve. It would be worthwhile to try it without the magic tune box just to see what happens. Would you describe your riding style as "spirited"? Stated differently, lots of throttle followed by zero throttle?
No I havent unplugged the tuner, mainly because the bike wasnt doing this when I bought it and the tune hasnt changed. Other than the backfiring the bike runs great.It sounds like perhaps over fuelling. Have you tried running it without the power commander connected?
Yea I do ride spirited for sure. The bike does backfire at ~4000rpm on decel pretty much no matter what, but it is definitely worse when the throttle was high before fulling letting off. Sometimes even medium throttle, followed by zero throttle produces a pretty loud backfire.That kind of backfiring is usually (always?) excess fuel that gets ignited in the exhaust system by a hot spot in the exhaust or maybe on the exhaust valve. It would be worthwhile to try it without the magic tune box just to see what happens. Would you describe your riding style as "spirited"? Stated differently, lots of throttle followed by zero throttle?
It would be helpful to have specific information on what rpm (s) the fuel is cut by ecu... I read it's right around 4k...so that makes it hard to know if this is an overly rich condition or lean condition. If I was a betting man, it sounds like unburnt fuel exploding in the exhaust to me. I should also add new plugs were added less than 4k miles ago.
Backfiring on throttle off decel is usually A) excessive unburnt fuel or B) fresh air entering exhaust and re-igniting unburnt fuel.
B) is hard to check for with the engine running because the leak can either blow out the exhaust or create a venturi and create vacuum at the leak. Take a leaf blower or air gun and blow air up the (cold) exhaust to create positive pressure. Spray a soapy solution on cold exhaust joints while blowing the air and you'll see bubbles at air leaks. Worth double-checking since you just worked on the exhaust system. KISS method.
If that doesn't bear fruit, you could lean out the PCV settings or temporarily delete it all together. May need to trim fuel from mid throttle and WOT.
B) is hard to check for with the engine running because the leak can either blow out the exhaust or create a venturi and create vacuum at the leak. Take a leaf blower or air gun and blow air up the (cold) exhaust to create positive pressure. Spray a soapy solution on cold exhaust joints while blowing the air and you'll see bubbles at air leaks. Worth double-checking since you just worked on the exhaust system. KISS method.
If that doesn't bear fruit, you could lean out the PCV settings or temporarily delete it all together. May need to trim fuel from mid throttle and WOT.
When was the last valve clearance check done?
Ok things to check so far:
Spray bottle exh leak test
Unplug PC5 and see what happens
Lean PC5 tune out from 4Krpm to 4.2Krpm
I'm planning on checking the valves for this winters project. The PO wasn't sure when they were last done (always the case!). It doesnt make noise or have starting issues, so I think it's safe until then. Ive been doing tons of work on my bike so I want to enjoy this CA riding season as long as possible.
Spray bottle exh leak test
Unplug PC5 and see what happens
Lean PC5 tune out from 4Krpm to 4.2Krpm
I'm planning on checking the valves for this winters project. The PO wasn't sure when they were last done (always the case!). It doesnt make noise or have starting issues, so I think it's safe until then. Ive been doing tons of work on my bike so I want to enjoy this CA riding season as long as possible.
Pushing your hand against the exhaust outlet at idle should stall the motor, if it won't you have a exhaust leak.
If you think you are running rich looking at the spark plugs will give you the answer.
Due to valve timing and overlap there will be some raw fuel let past into the exhaust, raw fuel in a hot exhaust with a open end can cause the fuel to detonate, the length of the system and how open it is will play a big part.
I guess you don't want to spend the cash but I would recommend you put the bike on a dyno, the performance gains can be huge and well worth the cost.
I fitted a PCFC to my V2, the result was OK but I wanted more, I spoke to my dyno guy and told him I wanted to shred rear tires and loft the front wheel with a twist of the grip, he got that for me.
If you think you are running rich looking at the spark plugs will give you the answer.
Due to valve timing and overlap there will be some raw fuel let past into the exhaust, raw fuel in a hot exhaust with a open end can cause the fuel to detonate, the length of the system and how open it is will play a big part.
I guess you don't want to spend the cash but I would recommend you put the bike on a dyno, the performance gains can be huge and well worth the cost.
I fitted a PCFC to my V2, the result was OK but I wanted more, I spoke to my dyno guy and told him I wanted to shred rear tires and loft the front wheel with a twist of the grip, he got that for me.
Supposedly the PO had my bike dyno tuned, however I am in doubt that they attempted to properly disable the PAIR system for proper AFR ratio. The PAIR system artificially raises the AFR due to the O² being introduced to the exhaust.Pushing your hand against the exhaust outlet at idle should stall the motor, if it won't you have a exhaust leak.
If you think you are running rich looking at the spark plugs will give you the answer.
Due to valve timing and overlap there will be some raw fuel let past into the exhaust, raw fuel in a hot exhaust with a open end can cause the fuel to detonate, the length of the system and how open it is will play a big part.
I guess you don't want to spend the cash but I would recommend you put the bike on a dyno, the performance gains can be huge and well worth the cost.
I fitted a PCFC to my V2, the result was OK but I wanted more, I spoke to my dyno guy and told him I wanted to shred rear tires and loft the front wheel with a twist of the grip, he got that for me.
I'll see if the bike shuts off with exhaust blocked aa well. Checking the plugs can tell you how an engine is running over all for sure, but trying to judge momentary AFR from plugs is difficult unless you can keep an engine in the desired/questioned range for a short period and immediately kill the engine before the 'real' AFR changes. One day I would like to have my bike tuned, I've also tosses around the idea of installing an 0² sensor in the exhaust and buy the auto tune module from dynojet.
I had this problem and tried EVERYTHING! Turned out I had an injector that wasn't shutting off completely. I could smell the rich condition from the exhaust. Just another thought of a place to look.
If I'm still backfiring after the above recommend tests, I would pretty much be ready to send the injectors off for a rebuild/flow match. Thanks.I had this problem and tried EVERYTHING! Turned out I had an injector that wasn't shutting off completely. I could smell the rich condition from the exhaust. Just another thought of a place to look.
Unless you have a local shop, I was impressed with price and service from The Injector Shop: Fuel Injector Parts, Rebuild Kits, o-rings, seal kits,If I'm still backfiring after the above recommend tests, I would pretty much be ready to send the injectors off for a rebuild/flow match. Thanks.
Try smelling the oil.
If a injector is not shutting off it can pass into the cylinder each time the motor is shut off this leads to raw fuel sitting in the cylinder and leaching down to the crank case.
If a injector is not shutting off it can pass into the cylinder each time the motor is shut off this leads to raw fuel sitting in the cylinder and leaching down to the crank case.
Update: Bike failed the soapy water test in multiple exhaust junctions. Ordered new pipe gaskets, and used exhaust sealant like the manual says.
Soapy water test passed, except for a super small leak at the tailpipe junction. I can easily remove and reseal those so that's no biggie.
But flames!!? Whaaat? On decel, around the same rpm there is a much more minor backfire now (so there was improvement) but I witnessed blue flames shoot out both tailpipes! This has never happened, even on my initial exhaust testing when I watched carefully.
I know that the minor leak at the tailpipes is letting 0² in which combusts the unburnt fuel, and yes I'm going to reseal the pipes with more sealant BUT to me this pretty mich guarantees the engine is running rich.
When I bought the bike the PO, who struck me as trustful and backed that up to me (another story), said it was dyno tuned. I'm betting the tuner did a crap job, and didn't pinch the vacuum feed to the PAIR valve thus getting an artificially lean reading on the sniffer.
Next step after tailpipe reseal is unplug the PC5. If that helps and eliminates the flames/pop, I will try the existing tunes that are out there. If unplugging doesn't work, than maybe its an injector issue. At this point though, I don't think it's the injector(s) since the flames were pretty equal on both sides which I don't think would happen if one injector was leaky or spraying poorly.
I will update this as I have time.
Soapy water test passed, except for a super small leak at the tailpipe junction. I can easily remove and reseal those so that's no biggie.
But flames!!? Whaaat? On decel, around the same rpm there is a much more minor backfire now (so there was improvement) but I witnessed blue flames shoot out both tailpipes! This has never happened, even on my initial exhaust testing when I watched carefully.
I know that the minor leak at the tailpipes is letting 0² in which combusts the unburnt fuel, and yes I'm going to reseal the pipes with more sealant BUT to me this pretty mich guarantees the engine is running rich.
When I bought the bike the PO, who struck me as trustful and backed that up to me (another story), said it was dyno tuned. I'm betting the tuner did a crap job, and didn't pinch the vacuum feed to the PAIR valve thus getting an artificially lean reading on the sniffer.
Next step after tailpipe reseal is unplug the PC5. If that helps and eliminates the flames/pop, I will try the existing tunes that are out there. If unplugging doesn't work, than maybe its an injector issue. At this point though, I don't think it's the injector(s) since the flames were pretty equal on both sides which I don't think would happen if one injector was leaky or spraying poorly.
I will update this as I have time.
Nicely done!
Alright so I think I am on the right track. I was going to unplug the PC5 until I saw that some body disassembly would be required. In the 'do whats easiest first' principle, I decided to look at the existing tune. I saved it for later if needed, and decided to try the dynojet 2 bros tune since it seemed to make people happy.
No more flames which is great, the bike is getting better mileage for sure, seems to be running well overall. Now I think I am getting your average decel popping instead of a loud backfore which again is improvement.
One area of potential improvement is from about 3k rpm to 4k rpm around 50-70% throttle where the bike feels a bit rattley, but this is a minor concern as I seldom open the throttle that much in that range. I honestly can't tell of the bike has more or less power at WOT but that's a good thing.
My plan is to make 2 copies of the same dynojet 2bros tune, with the only difference being the 0% column at 4000, 4250, 4500 set to (-5%) to determine if it's actually normal decel popping or if its just much more minor backfiring still.
I have to say it's pretty neat to be able to tune a fuel injection machine with a computer!
No more flames which is great, the bike is getting better mileage for sure, seems to be running well overall. Now I think I am getting your average decel popping instead of a loud backfore which again is improvement.
One area of potential improvement is from about 3k rpm to 4k rpm around 50-70% throttle where the bike feels a bit rattley, but this is a minor concern as I seldom open the throttle that much in that range. I honestly can't tell of the bike has more or less power at WOT but that's a good thing.
My plan is to make 2 copies of the same dynojet 2bros tune, with the only difference being the 0% column at 4000, 4250, 4500 set to (-5%) to determine if it's actually normal decel popping or if its just much more minor backfiring still.
I have to say it's pretty neat to be able to tune a fuel injection machine with a computer!
1 - 16 of 16 Posts
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