Backfire

I need some help. I have a backfire that is coming from the number 4 cylinder. It occurs when at an idle mostly although it will also occur at times when riding. It is a very LOUD backfire that occurs about every five to ten seconds while at an idle. I know it is the number four cylinder because when I pull the plug wire on that cylinder it stops. I had a problem earlier with that cylinder not firing at all. I removed the carbs and re-cleaned and rechecked the floats then reinstalled them. Now the cylinder is firing but I have this terrible backfire problem. I did a compression test on all cylinders and number 4 is 190 psi. I recently checked and reset all the valves. On number 4 the intake valve is currently at .006 which is the outer limit (.004-.006) recommend and the exhaust is also at .006 which is the inner limit (.006-.008) recommended. I have used a lighter to try to find any leaks in the exhaust and the only thing I have found is an area where the chrome cover piece is welded to the pipe will blow out the lighter when I pass by it. Would that be enough to cause this type of problem? It is before the Y connection to the number three cylinder pipe. I am getting great spark to all cylinders. I have tried adjusting the fuel/air mixture screw out from two turns to three and a half with no change. Any ideas would be greatly appreciated. This is driving me crazy, one because I can't find the problem and two because I can't ride.

A very loud backfire sounds to me like intermittent ignition. I would check the ignition components for that cylinder. Just wild guessing here.

Couple of things come to mind. Check your choke and make sure when it is pushed all the way in that carb number 4 plunger is in correct position. You can compare number 4 to the other 3 for a reference. The other thing is your float may be getting hung up. May have gotten a little bit of dirt in bowl when you had it apart. You can drain carb using drain screw and tap on side of carb with screw driver handle to see if you can free up float. YOu can also check drain hose in front of air filter housing to see if any gas is leaking out of it. Number 4 carb would leak out opposite side of bike.

A very loud backfire sounds to me like intermittent ignition. I would check the ignition components for that cylinder. Just wild guessing here.

BlueSky

Thanks for the response. It is a very loud popping backfire. I have had a spark tester attached to the wire and I am getting a very strong and steady spark. Have also tested using the spark plug attached to the wire and same results. It did not appear to be intermittent. Any suggestions on other ways of checking would be helpful. Thanks again.

Couple of things come to mind. Check your choke and make sure when it is pushed all the way in that carb number 4 plunger is in correct position. You can compare number 4 to the other 3 for a reference. The other thing is your float may be getting hung up. May have gotten a little bit of dirt in bowl when you had it apart. You can drain carb using drain screw and tap on side of carb with screw driver handle to see if you can free up float. YOu can also check drain hose in front of air filter housing to see if any gas is leaking out of it. Number 4 carb would leak out opposite side of bike.

sldunker

Thanks for the response. I will check the choke again. I did check them all before reinstalling the carbs but I will check again. I have had the carbs off twice now so I may have to pull them again. I just don't want to do that unless I have to. What would be the main cause of the back fire if it were carb related. I'm just trying to wrap my head around the problem. For instance I can understand why the cylinder was not firing before if the carb was dirty and no fuel was getting to the cylinder but what would cause the back fire? Too much fuel? I did not see any fuel leaking from the overflow tube but I will definitely check that again. Appreciate any ideas.

I have had backfiring two time. They both happened the first year I had bike. Both times it was fuel related. The first time it was really bad and it would pop all the time and I also had gas coming out vent. I had to turn off gas valve and let bike run tell it stopped. I was afraid it would fill up one of the cyclinders. I took carbs apart and could not find a problem. I put it all back together including checking for a pinched vent line. It ran fine afterwards. There must have been a bit of dirt under the needle and it fell out when I had carbs apart.

The second time I had intermittent popping and I resolved this by tapping on carb. I did not have gas coming out of vent this time.

When float sticks the carb overfills with gas and floods the cylinder. Excess gas gets into the exhaust pipe and it gets ignited by hot exhaust gases and you have an unwanted explosion.

I have had backfiring two time. They both happened the first year I had bike. Both times it was fuel related. The first time it was really bad and it would pop all the time and I also had gas coming out vent. I had to turn off gas valve and let bike run tell it stopped. I was afraid it would fill up one of the cyclinders. I took carbs apart and could not find a problem. I put it all back together including checking for a pinched vent line. It ran fine afterwards. There must have been a bit of dirt under the needle and it fell out when I had carbs apart.

The second time I had intermittent popping and I resolved this by tapping on carb. I did not have gas coming out of vent this time.

When float sticks the carb overfills with gas and floods the cylinder. Excess gas gets into the exhaust pipe and it gets ignited by hot exhaust gases and you have an unwanted explosion.

Okay that makes sense. Looks like I may have to pull the carbs again. I'll try banging on it a bit first. I think I may have a problem with that particular carb. I rebuilt all of them and only this one has been giving me problems. I didn't even realize it at first the bike was running so well on just three cylinders and this is the first Venture that I have had. I noticed that it was just a little sluggish when I accelerated at high speed and I decided to check the cylinders. It was then that I discovered that the number 4 cylinder was cold and not firing. At least now I know it is firing. If there is anything specific that you can think of that I should look for when I open them back up please let me know. Thanks for your help.

I need some help. I have a backfire that is coming from the number 4 cylinder. It occurs when at an idle mostly although it will also occur at times when riding. It is a very LOUD backfire that occurs about every five to ten seconds while at an idle. I know it is the number four cylinder because when I pull the plug wire on that cylinder it stops. I had a problem earlier with that cylinder not firing at all. I removed the carbs and re-cleaned and rechecked the floats then reinstalled them. Now the cylinder is firing but I have this terrible backfire problem. I did a compression test on all cylinders and number 4 is 190 psi. I recently checked and reset all the valves. On number 4 the intake valve is currently at .006 which is the outer limit (.004-.006) recommend and the exhaust is also at .006 which is the inner limit (.006-.008) recommended. I have used a lighter to try to find any leaks in the exhaust and the only thing I have found is an area where the chrome cover piece is welded to the pipe will blow out the lighter when I pass by it. Would that be enough to cause this type of problem? It is before the Y connection to the number three cylinder pipe. I am getting great spark to all cylinders. I have tried adjusting the fuel/air mixture screw out from two turns to three and a half with no change. Any ideas would be greatly appreciated. This is driving me crazy, one because I can't find the problem and two because I can't ride.

You bought the bike in 17, had 24000 miles.

This is a 10:1 with a standard of 220 psi min 175.

Why haven't you posted all the readings?

190 is low for this mileage in my opinion. If you wish to fix it once and for all lets build a complete picture.

Patch

PS I'm not back in town till late tomorrow, meaning I can't respond quicker..

remove the needle and inspect tip closely. Look for anything abnormal. Also look closely at seat. Make sure float moves freely. When needle is closed you should not be able to blow from gas feed inlet to bowl

Ok. Thanks

[/color]

You bought the bike in 17, had 24000 miles.

This is a 10:1 with a standard of 220 psi min 175.

Why haven't you posted all the readings?

190 is low for this mileage in my opinion. If you wish to fix it once and for all lets build a complete picture.

Patch

PS I'm not back in town till late tomorrow, meaning I can't respond quicker..

Patch

Thanks for the response. The only reason I only posted that cylinder is because it seems to be the only cylinder that is having a problem. All of the other three have been running fine. So here is the compression on the other three. #1 210 #2 200 #3 150 #4 190. I know that number three is below normal but at the same time I get the lowest drop in RPM when I pull the plug off of that cylinder. Also I am using a compression gauge that has to be held down on the spark plug hole to get a reading so I'm not sure how accurate those reading are. All of the valve readings are pretty much the same. All intake valves are at .15mm except #1 and #2 outside valves are at .13mm. All exhaust valves are at .16mm. All plug wires have been checked and all are getting good spark. The backfire occurs as soon as I start the bike. I have had it on the road and it will back fire once every so often at cruise but very little. It does not seem to increase much when decelerating, only a little. It seems to occur mostly at idle and as I said it is a very loud popping type of backfire out the exhaust. Hope that is helpful.

When you did the carbs, did you sync them?

If you run a higher octane fuel...still get back fire?

When you did the carbs, did you sync them?

If you run a higher octane fuel...still get back fire?

XV1100SE

Yes I have synced them. I have not tried running a higher octane fuel but the problem is only occurring in the number 4 cylinder so I don't believe it is a fuel grade problem. Appreciate the response though. Looking for anything that may help. By the way I had a 1979 XS1100 for many years. Loved that bike.

Patch

 

Thanks for the response. The only reason I only posted that cylinder is because it seems to be the only cylinder that is having a problem. All of the other three have been running fine. So here is the compression on the other three. #1 210 #2 200 #3 150 #4 190. I know that number three is below normal but at the same time I get the lowest drop in RPM when I pull the plug off of that cylinder. Also I am using a compression gauge that has to be held down on the spark plug hole to get a reading so I'm not sure how accurate those reading are. All of the valve readings are pretty much the same. All intake valves are at .15mm except #1 and #2 outside valves are at .13mm. All exhaust valves are at .16mm. All plug wires have been checked and all are getting good spark. The backfire occurs as soon as I start the bike. I have had it on the road and it will back fire once every so often at cruise but very little. It does not seem to increase much when decelerating, only a little. It seems to occur mostly at idle and as I said it is a very loud popping type of backfire out the exhaust. Hope that is helpful.

Thanks, I see a couple of things.. Easy stuff! So I'm back a earlier than anticipated, I'll work out a plan for you and you can decide which way is best for you.

XV1100SE....By the way I had a 1979 XS1100 for many years. Loved that bike.

I had a '99 1100 "Special Edition". Great bike and an easy step to the 2nd Gen Venture. Riding position very similar, shaft drive....

Couple of things come to mind. Check your choke and make sure when it is pushed all the way in that carb number 4 plunger is in correct position. You can compare number 4 to the other 3 for a reference.

Very well thought out sldunker! And because we only had no. 4 190 to work through in my opinion you were on the right track. There is of course one other likely that we would add especially knowing the carbs had been disassembled, which is the needle jet. We would look for proper reassembly shims springs and washers; often we find that the needle is stiff and so can't slip through the main jet, binds/not seating/ wearing....

OK so 4 is not the problem as I read it. 2 is the problem 4 is the igniter!

I can write this up for you but it gets a bit techy. I will with and if no objections elaborate on the fogging thread?

So this is in short a thermal efficiency problem on no. 2!

Because this is a 10:1 the circuit is designed to take advantage of this CR heat. Because no. 2 is at the moment more like a toaster than a high compression performance engine she is well beyond her limits!

All the results you post are below my expectations for the listed mileage. This is going to cost at least $12.00 to correct and if it were me I would follow the fogging thread for instructions on how to. I would do all 4 jugs, I am guessing you will end up around 215 or 218 but no. 2 will be a little slower as she is well stuck. The important thing to remember is that Deepcreep does not burn and will continue to work at very high temperatures. This is one engine I would also spray down through the the carbs venturi to clean the valve seats 2 second burst there.

1 3 2 4

when I overlaid the results it confirmed my suspicions...

Let me know if you have any questions

Patch

I need some help. I have a backfire that is coming from the number 4 cylinder. It occurs when at an idle mostly although it will also occur at times when riding. It is a very LOUD backfire that occurs about every five to ten seconds while at an idle. I know it is the number four cylinder because when I pull the plug wire on that cylinder it stops. I had a problem earlier with that cylinder not firing at all. I removed the carbs and re-cleaned and rechecked the floats then reinstalled them. Now the cylinder is firing but I have this terrible backfire problem. I did a compression test on all cylinders and number 4 is 190 psi. I recently checked and reset all the valves. On number 4 the intake valve is currently at .006 which is the outer limit (.004-.006) recommend and the exhaust is also at .006 which is the inner limit (.006-.008) recommended. I have used a lighter to try to find any leaks in the exhaust and the only thing I have found is an area where the chrome cover piece is welded to the pipe will blow out the lighter when I pass by it. Would that be enough to cause this type of problem? It is before the Y connection to the number three cylinder pipe. I am getting great spark to all cylinders. I have tried adjusting the fuel/air mixture screw out from two turns to three and a half with no change. Any ideas would be greatly appreciated. This is driving me crazy, one because I can't find the problem and two because I can't ride.

I chased a backfire on tinker, Rbig1 and Yammer kept telling me it was exhaust if it was on decel, but sometimes it did it on idle too... I replaced the exhaust gaskets and it went away, anything extra close to the engine will creat a back fire I went thru my carbs and finally went with what i was being told and it indeed fixed my problem..

I chased a backfire on tinker, Rbig1 and Yammer kept telling me it was exhaust if it was on decel, but sometimes it did it on idle too... I replaced the exhaust gaskets and it went away, anything extra close to the engine will creat a back fire I went thru my carbs and finally went with what i was being told and it indeed fixed my problem..

So if there is no o2 there can be no ignition. That does not solve the problem tho, it masks it, at least in this OPs case.

Very well thought out sldunker! And because we only had no. 4 190 to work through in my opinion you were on the right track. There is of course one other likely that we would add especially knowing the carbs had been disassembled, which is the needle jet. We would look for proper reassembly shims springs and washers; often we find that the needle is stiff and so can't slip through the main jet, binds/not seating/ wearing....

 

OK so 4 is not the problem as I read it. 2 is the problem 4 is the igniter!

I can write this up for you but it gets a bit techy. I will with and if no objections elaborate on the fogging thread?

 

So this is in short a thermal efficiency problem on no. 2!

 

Because this is a 10:1 the circuit is designed to take advantage of this CR heat. Because no. 2 is at the moment more like a toaster than a high compression performance engine she is well beyond her limits!

 

All the results you post are below my expectations for the listed mileage. This is going to cost at least $12.00 to correct and if it were me I would follow the fogging thread for instructions on how to. I would do all 4 jugs, I am guessing you will end up around 215 or 218 but no. 2 will be a little slower as she is well stuck. The important thing to remember is that Deepcreep does not burn and will continue to work at very high temperatures. This is one engine I would also spray down through the the carbs venturi to clean the valve seats 2 second burst there.

 

1 3 2 4

when I overlaid the results it confirmed my suspicions...

Let me know if you have any questions

Patch

Umm what...

Umm what...

I give, whats the question?

I give, whats the question?

you lost me, if you got back fire on 4 how is 2?

you lost me, if you got back fire on 4 how is 2?

In time I'd like to add how I go about my trouble shooting by adding hints to the fogging thread.

Snyper I could be wrong but it is what my worksheet shows me. I haven't worked on this model, therefore I have to rely on the specs and graphs provided in the manual, after which I just put my experience to the plow.

I can also add that no. 2 is slowing the complete firing chain down. The longer this persists the shorter the life of this engine.

Without the compression test there would have been too much missing information and,,, this would have just been another backfire issue. Is also why slunker(not sure I spellt it..) deserves credit, he nail the problem just not the source! This is where I sometimes have advantage, I'm hooked on combustion.

This engine ran on 3 jugs and at times 2!?! Not because of 4 tho/ it still has the same ignition hardware/ it likely powered up over 1/4 throttle which made the bike feel OK. But no. 2 was and is still not contributing to torque because it lacks thermal expansion. 323.5 cc at 10:1 which should read 220 psi static, and should output about 1000 pounds of force at peak diminishing at BDC say maybe

Now you know why;) and if I'm right then all you have to do is follow the logical path, and please if I'm wrong let me know.

Steven G. I agree with your analysis of a possibility of stuck rings. We could also have a problem with carbon around the valve heads and maybe the valve stems. I would encourage the OP to follow your instructions of fogging of the engine. I have never tried Deep Creep to free rings. I usually use Yamaha's ring free or Amsoil's PI. Have had good luck with both of these.

The op should do this after he gets his carbs clean.

Steven G. I agree with your analysis of a possibility of stuck rings. We could also have a problem with carbon around the valve heads and maybe the valve stems. I would encourage the OP to follow your instructions of fogging of the engine. I have never tried Deep Creep to free rings. I usually use Yamaha's ring free or Amsoil's PI. Have had good luck with both of these.

The op should do this after he gets his carbs clean.

100% agreed%

The reason I didn't mention it but covered it under engine life is because it gets kind of techy for the guys without training.

The carbon for those that don't know is a result of the missed thermal properties.

Not sure what first introduced me to to deepcreep but it has certainly been a great addition to my games. In almost all cases where I've used it for soaking rings I've also seen it creep up, around and through carbon, and is why I often suggest applying it down the venturi.

Sometimes it takes several applications but, cost effective and non harmful.

Truth is I didn't even know they sold a stuck ring products. Goes to show the size of my world;)

190 psig is great compression. Thinking there is a problem with 190 psig is wrong in my opinion.