Single Massive Backfire

[weehe]

I have been slowly fixing up my FZ since I bought it. It has 37500 miles on it, so I know there is some work to be done. On to the next problem, on decelerating I get a single massive backfire. This is shotgun level loud, people freak out if they are next to me. This happens easier when cold (needs less time of decel) , but always happens when warm too (like coming off the highway). My next step is to do a TB sync which I have read might help. But I wanted to see if there is something else I should look into (besides buying a PC3). I just replaced my plugs and they appeared to indicate I'm running rich (they were decently black). This makes sense to me since I'm only getting low 30 mpg with all highway riding. I am 100% stock to the best of my knowledge. Really hoping to get this bike running near perfect, eventually.

 

[TownsendsFJR1300]

Are the valve clearances in spec? Its well overdue if it hasn't been checked yet..

With the richness, did you check the air filter yet?

I'd hold off on the PC until you get the engine running normally. You don't need to add more fuel from what you posted.

Do a search as well to hotwire and check the CO settings. Someone may have messed with them and bumped the #'s up...

 

[Serzedo]

After what I have read, I would rather do an ECU flash instead of buying a PC.

But that seems something related to valves or mixture of fuel.

"V"

 

[FinalImpact]

Or an exhaust leak. If no exterior leaks are found, maybe the AIS valves are stuck open with debris or the solenoid has failed and is stuck open?

It doesn't explain 30mpgs tho. Make sure the gap doesn't exceed 0.028" max.
And yes, all other things mentioned could be a factor.
Air filter condition, valve adjust, CO settings...

 

[weehe]

Are the valve clearances in spec? Its well overdue if it hasn't been checked yet..

With the richness, did you check the air filter yet?

I'd hold off on the PC until you get the engine running normally. You don't need to add more fuel from what you posted.

Do a search as well to hotwire and check the CO settings. Someone may have messed with them and bumped the #'s up...

I am not planning on getting a PC, I guess I worded that bad. I was afraid it might be the valves. I have no history besides what I have done and the previous owner replacing the fuel pump. I will look into the CO, have no clue what that is. I replaced the air filter abiut 500 miles ago, but will take a look.

 

[FinalImpact]

Look up C01/C02 CO settings. A function you enter like diagnostic mode and alter fuel offsets to cylinders 1&4 and 2&3....

Scott,
My fuel map is like 50-50 taking away fuel in many places to maintain a 13.0:1 AFR... In doing so these plugs have 3000mi on them....

CR10E (one range cooler than stock).

 

[TownsendsFJR1300]

Can't get much cleaner than that. ^^^


I think, (now, having learned of the UNKNOWN service history), there may be two issues..

Obviously the "rich factor"- perhaps in permanent choke operation?- poor mileage, excess fuel, black plugs, etc.

The above other points should also be checked for the back fire, (good points)

But with no knowledge if the valves have been checked, a partially open exhaust valve, coupled with the excess fuel could cause that problem and SHOULD BE DONE ANYWAY as the Op simply doesn't know..

In any event, the valve check should be done. I think I'd be doing that ASAP before possibly burning a valve..


**Weehe, can you post a short video (with the best audio) of the bike running from cold, let it warm up, then some more video? Mine sounds very different once warmed up. if yours sounds about the same both cold and hot, that'd help confirm perhaps that part of the system is clogged (where coolant runs thru-frgot the name)..;





Randy, I think you have a better image with where the coolant runs, etc for warm up....

 

[Serzedo]

I have a video of mine with the engine cold and hot.
[video=youtube_share;y4o-Mz4LLLc]https://youtu.be/y4o-Mz4LLLc[/video]

"V"

 

[TownsendsFJR1300]

Its doesn't sound bad at all.. I gather cold, the RPM's are a little higher and they maybe 200 or so once warmed up??

Any excessive black that comes out the exhaust when revved up??

 

[weehe]

Thanks everyone for the recommendations, I didn't realize this might be a big problem. I will look into the CO1/CO2 programing. I believe I remember seeing something about it while confirming my TPS had been replaced (it has). I currently average 35 mpg, but have seen close to 30 with more traffic. Here are the plugs I pulled out the other day. The previous owner said he replaced them right before I bought it, if that is true they have less than 1500 miles on them.


I would say the first plug (on the left) shows how all the plugs really look. I used my phone so the pics are not great and the other three plugs look better than they should.

My cold start and warm idle sound pretty much the same as the video above. My idle on cold start is around 1800 rpm then settles to 1400 and stays smooth. I figured I would eventually have to check the valves, but your responses have made me want to do it as my next step. I will try and get a video tomorrow.

 

[TownsendsFJR1300]

Those plugs don't look bad at all... Re-installing with the gap on the tighter side of spec's would be a good idea (it opens up as it wears).

I'm leaning more towards a valve not closing fully(valve adjustment) for your backfire.

Were you able to check those other items?

 

[FinalImpact]

The backfire is a product of the high idle 1400rpm. As a test, go to a location, make it happen, then set idle to speed to say 1200 or so and see if it changes it.

Its a product of reburn from air being introduced!

MPGs... May effect that ever slightly if your in town in low gears all the time. Run some fuel cleaner through it.

 

[weehe]

I have not had a chance to do anything. I'm looking up about CO now. Hopefully will have time tonight or tomorrow to get the video and check CO settings.

 

[FinalImpact]

Also, it looks like your plugs have anti-sieze on them. Be careful when torque is set, as you could pull threads by having a lubricant on the washer and threads. With a used plug and the crush washer crushed, stop tightening when the plug quits turning!

As for the CO setting. US bikes have to ground an add-on wire to the ecu to access it.
Once grounded, press both set/reset, turn key and while holding them down until it enters diag mode. Push both buttons to toggle from diag to CO mode.

Many of the US S2s have matching numbers and often times are 0/0 C01/C02.
S1s have been all over the map with +/-15 variants between the two values.

There are instructions in my build thread if you need them. Finalimpacts build thread...

 

[FinalImpact]

I have not had a chance to do anything. I'm looking up about CO now. Hopefully will have time tonight or tomorrow to get the video and check CO settings.

Post #10 here....
08 FZ6 Condensed build thread ~FinalImpact~

 

[weehe]

The backfire is a product of the high idle 1400rpm. As a test, go to a location, make it happen, then set idle to speed to say 1200 or so and see if it changes it.

Its a product of reburn from air being introduced!

MPGs... May effect that ever slightly if your in town in low gears all the time. Run some fuel cleaner through it.

So my idle should be 1200, not 1400? Im guessing there is an idle screw i can adjust.

 

[weehe]

Also, it looks like your plugs have anti-sieze on them. Be careful when torque is set, as you could pull threads by having a lubricant on the washer and threads. With a used plug and the crush washer crushed, stop tightening when the plug quits turning!

As for the CO setting. US bikes have to ground an add-on wire to the ecu to access it.
Once grounded, press both set/reset, turn key and while holding them down until it enters diag mode. Push both buttons to toggle from diag to CO mode.

Many of the US S2s have matching numbers and often times are 0/0 C01/C02.
S1s have been all over the map with +/-15 variants between the two values.

There are instructions in my build thread if you need them. Finalimpacts build thread...

Thanks, i remember seeing the diag mode when checking my TPS values. I'll see if maybe the previous owner did the ground already. If not I'll try and get that done asap.

 

[FinalImpact]

Thanks, i remember seeing the diag mode when checking my TPS values. I'll see if maybe the previous owner did the ground already. If not I'll try and get that done asap.

I think its really as simple as your idle being higher. That added amount of air makes it all possible. It also explains why bikes with real low idle settings backfire less. There is less air to create the "reburn" effect in the exhaust.

FWIW: from cold to hot I would guess mine has 300 RPM variation.

Also; methanol in the fuel typically hurts MPG's. Although it shouldn't be drastic (maybe 3 - 5% reduction), worse with lower compression engines. I think its part of why my plugs are so clean. Yesterday rode about ~200 miles and averaged ~45 mpg and thats with ignition advance, fuel controller mapped for power, and open exhaust.

 

[TownsendsFJR1300]

So my idle should be 1200, not 1400? Im guessing there is an idle screw i can adjust.

It's on the left side of the bike, between the frame and fuel tank. Kind of a large star shaped screw. Counter Clockwise to lower the idle.

Do you have the dual headlight mod?

I agree with FI, lowering the idle should help and its really not needed that higher. I have mine at about 1050, but I don't do much city riding. Absolutely no backing firing at all, even with a hard decell...

 

[weehe]

I think its really as simple as your idle being higher. That added amount of air makes it all possible. It also explains why bikes with real low idle settings backfire less. There is less air to create the "reburn" effect in the exhaust.

FWIW: from cold to hot I would guess mine has 300 RPM variation.

Also; methanol in the fuel typically hurts MPG's. Although it shouldn't be drastic (maybe 3 - 5% reduction), worse with lower compression engines. I think its part of why my plugs are so clean. Yesterday rode about ~200 miles and averaged ~45 mpg and thats with ignition advance, fuel controller mapped for power, and open exhaust.

I guess i always assumed idle was fine because it was smooth. It does drop 300-400rpm from cold to warm. But i do know that after riding on the highway it hangs up higher, around 1600rpms, for the first stop light, it does lower eventually. I will lower idle down to 1100 and see how it does.

I think you mean ethanol hurting mpg. And its normally 5-10% here, but is consistent so im not too concerned. Im sure everything that has been brought up will help increase my mpg, but im more concerned about the backfire. I will eventually get everything back to proper.