Backfire

[Patch]

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

 

It's not so much the number/ it is about the whole picture!

 

In troubleshooting theory is a crucial element; that is what saves time and money.

 

When I'm wrong but contribute something/ then, that becomes a growth point for me.

[wrscomncents]

It's not so much the number/ it is about the whole picture!

 

In troubleshooting theory is a crucial element; that is what saves time and money.

 

When I'm wrong but contribute something/ then, that becomes a growth point for me.

 

Patch

 

I really appreciate your response and your time, along with all the others who have responded. That being said, respectfully, I'm not sure exactly what you are referring to as far as the number 2 cylinder being the problem with the backfire on the number 4 cylinder. I can certainly understand the concern with the number 3 cylinder being at only 150psi but number two is at 200psi. I have thought all along that this bike sat for a long time and I intended to perform the fogging on it after reading your post, as soon as the riding season ends. I had never heard of fogging before reading your post. So I'm not sure how that relates to the backfire. It appears that the problem revolves around the number 4 carb and it looks like I will be pulling the carbs off again. I had a problem with this cylinder after the first time I rebuilt the carbs with number 4 not firing at all. When I pulled the carbs off for the second time I replaced the needle and seat thinking that the first one may be faulty. So I found that if I close the fuel mixture valve on that carb (#4) the backfire stops. If I open it slowly the backfire will start after about 3/4 of a turn. I may be missing what you are referring to and if so please let me know. I am trying to learn as much as possible and I appreciate your thoughts.

 

Another question as far as carbon on the valves. I can see how the fogging procedure will clear the rings but I'm not sure how the valves would be cleaned since they are above the cylinder. Am I missing something?

[Patch]

maybe I crossed the numbers when I transferred them to my work sheet? Let me check.

[Patch]

Patch

 

I really appreciate your response and your time, along with all the others who have responded. That being said, respectfully, I'm not sure exactly what you are referring to as far as the number 2 cylinder being the problem with the backfire on the number 4 cylinder. I can certainly understand the concern with the number 3 cylinder being at only 150psi but number two is at 200psi. I have thought all along that this bike sat for a long time and I intended to perform the fogging on it after reading your post, as soon as the riding season ends. I had never heard of fogging before reading your post. So I'm not sure how that relates to the backfire.

​While researching yesterday on page 3-20 we find a different set of kPa numbers; the minimums are very important! That page says that 188.5 is the minimum. @ 190 you are knocking at the door.

In a 10:1 we expect to take advantage of the heat that CR level offers. If we can't reach the expected heat range then we will have unburnt fuel pumped through the exhaust, all the while we are also evacuating fuel still in the process of ignition. It gets hard to understand but the fuel charge is separated combined and then separated, and all the while happening at very high speeds. Still we always have to contend with ignition duration and is why 10:1 works well and the complete circuit is designed around that choice.

At 190 psi no. 4 should meet expectations, then where do we look next..

It appears that the problem revolves around the number 4 carb and it looks like I will be pulling the carbs off again.

I had a problem with this cylinder after the first time I rebuilt the carbs with number 4 not firing at all. As in no spark or pilot circuit?

When I pulled the carbs off for the second time I replaced the needle and seat thinking that the first one may be faulty.

So I found that if I close the fuel mixture valve on that carb (#4) the backfire stops.

If I open it slowly the backfire will start after about 3/4 of a turn. For you to note this as you have we again see fuel not ignited or completing ignition. If its not spark at low rpm then there is something else in the history. 1st to come to mind outside of spark is mismatch jetting, pilot tip broken, may have been removed from cast leaving an enlarged port, also check for proper spring washer and O-ring order, main jet leaking (needle or worn jet tube)

I may be missing what you are referring to and if so please let me know. I am trying to learn as much as possible and I appreciate your thoughts. We get that and we really enjoy the questions, problems and your engagement!

 

Another question as far as carbon on the valves. I can see how the fogging procedure will clear the rings but I'm not sure how the valves would be cleaned since they are above the cylinder. Am I missing something? That is why we call it creep as in creeping

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Yep I mixed 2 & 3, which tied it into the firing order and the piping! So That throws off some of the other stuff on my work sheet, I'll need to start it over.

 

Masking the backfire isn't a reasonable fix in this case. If as you describe a very load backfire/ is something I know all to well and is too often an eerie part of jetting when pushing the stick off the envelope;)

Meantime I'll go through the notes and compare again to see how far off I am.

Now no. 3 will likely continue to carbon mainly on the exhaust side, which includes the back of the valve, stem and seat,,, not sure your resistance to just dealing with it while the bike is down anyways..

[wrscomncents]

Patch

 

I really appreciate your response and your time, along with all the others who have responded. That being said, respectfully, I'm not sure exactly what you are referring to as far as the number 2 cylinder being the problem with the backfire on the number 4 cylinder. I can certainly understand the concern with the number 3 cylinder being at only 150psi but number two is at 200psi. I have thought all along that this bike sat for a long time and I intended to perform the fogging on it after reading your post, as soon as the riding season ends. I had never heard of fogging before reading your post. So I'm not sure how that relates to the backfire.

​While researching yesterday on page 3-20 we find a different set of kPa numbers; the minimums are very important! That page says that 188.5 is the minimum. @ 190 you are knocking at the door.

In a 10:1 we expect to take advantage of the heat that CR level offers. If we can't reach the expected heat range then we will have unburnt fuel pumped through the exhaust, all the while we are also evacuating fuel still in the process of ignition. It gets hard to understand but the fuel charge is separated combined and then separated, and all the while happening at very high speeds. Still we always have to contend with ignition duration and is why 10:1 works well and the complete circuit is designed around that choice.

At 190 psi no. 4 should meet expectations, then where do we look next..

It appears that the problem revolves around the number 4 carb and it looks like I will be pulling the carbs off again.

I had a problem with this cylinder after the first time I rebuilt the carbs with number 4 not firing at all. As in no spark or pilot circuit?

When I pulled the carbs off for the second time I replaced the needle and seat thinking that the first one may be faulty.

So I found that if I close the fuel mixture valve on that carb (#4) the backfire stops.

If I open it slowly the backfire will start after about 3/4 of a turn. For you to note this as you have we again see fuel not ignited or completing ignition. If its not spark at low rpm then there is something else in the history. 1st to come to mind outside of spark is mismatch jetting, pilot tip broken, may have been removed from cast leaving an enlarged port, also check for proper spring washer and O-ring order, main jet leaking (needle or worn jet tube)

I may be missing what you are referring to and if so please let me know. I am trying to learn as much as possible and I appreciate your thoughts. We get that and we really enjoy the questions, problems and your engagement!

 

Another question as far as carbon on the valves. I can see how the fogging procedure will clear the rings but I'm not sure how the valves would be cleaned since they are above the cylinder. Am I missing something? That is why we call it creep as in creeping

-------------------------------------------------------------------------------------

Yep I mixed 2 & 3, which tied it into the firing order and the piping! So That throws off some of the other stuff on my work sheet, I'll need to start it over.

 

Masking the backfire isn't a reasonable fix in this case. If as you describe a very load backfire/ is something I know all to well and is too often an eerie part of jetting when pushing the stick off the envelope;)

Meantime I'll go through the notes and compare again to see how far off I am.

Now no. 3 will likely continue to carbon mainly on the exhaust side, which includes the back of the valve, stem and seat,,, not sure your resistance to just dealing with it while the bike is down anyways..

 

Okay thanks for checking over again. I guess you're right that I should go ahead and do the fogging since I am going to have to pull the carbs again. The problem I have now is I'm not sure what else to do with that carb once I have it off. I have already cleaned it twice and replaced the needle and seat. The float is set exactly as all of the others which are working fine. I feel like I am pulling it just to pull it. Is there anything else that could be causing the problem such as the main jet?

[wrscomncents]

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..

 

snyper

 

I have changed the exhaust gaskets on both pipes and when I hold a lighter by them I show no signs of a leak. There is a spot where the chrome shield is welded to the pipe that actually blows out the lighter. I have felt that area while the bike is cold and I cannot feel a hole or a crack so not sure how big it is. Its also very hard to see that area. Don't know if that would be enough to cause this backfire.

[snyper316]

snyper

 

I have changed the exhaust gaskets on both pipes and when I hold a lighter by them I show no signs of a leak. There is a spot where the chrome shield is welded to the pipe that actually blows out the lighter. I have felt that area while the bike is cold and I cannot feel a hole or a crack so not sure how big it is. Its also very hard to see that area. Don't know if that would be enough to cause this backfire.

What I had thought exactly. Worth a try to get that area fixed. Can you get a picture of this crome cover your talking about? My gaskets didn't seem that bad either when I replaced them but there is no more back fire.

 

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[wrscomncents]

What I had thought exactly. Worth a try to get that area fixed. Can you get a picture of this crome cover your talking about? My gaskets didn't seem that bad either when I replaced them but there is no more back fire.

 

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Yeah I can try to.

[wrscomncents]

Yeah I can try to.

T

 

The leak is right in the area where the metal bracket connects from the shield to the pipe but I cannot see it.

[Patch]

snyper

 

I have changed the exhaust gaskets on both pipes and when I hold a lighter by them I show no signs of a leak. There is a spot where the chrome shield is welded to the pipe that actually blows out the lighter. I have felt that area while the bike is cold and I cannot feel a hole or a crack so not sure how big it is. Its also very hard to see that area. Don't know if that would be enough to cause this backfire.

 

If you take this root and the backfiring stops, has the problem been addressed?

 

Certainly fix the exhaust leak but the source of fuel leak should be dealt with as well.

 

Is there any chance you can measure the pipe temperature at the exhaust port at the rpm when it usually goes off? You mentioned earlier that you could almost time it I think?

[wrscomncents]

If you take this root and the backfiring stops, has the problem been addressed?

 

Certainly fix the exhaust leak but the source of fuel leak should be dealt with as well.

 

Is there any chance you can measure the pipe temperature at the exhaust port at the rpm when it usually goes off? You mentioned earlier that you could almost time it I think?

 

Patch

 

I agree with you. I'm definitely going to do the fogging. I'm just not sure if the backfire is related to the leak in the exhaust or a problem with the carb. Could it be that the carb is okay and the problem is the exhaust leak?

[snyper316]

Patch

 

I agree with you. I'm definitely going to do the fogging. I'm just not sure if the backfire is related to the leak in the exhaust or a problem with the carb. Could it be that the carb is okay and the problem is the exhaust leak?

It actually can be a number of things. Ignition timing, fuel and exhaust.

 

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[snyper316]

But since you do have exhaust leak I would fix that too. But as he said your fuel issue too. Another crazy thing too could be a short in safety features that causes an intermittent kill. Like you drive your vehicle down the road and turn the key off with the engine still turning and turning it back on to create a backfire. I used to do that with my 76 ford pu I was young and dumb. But it is funny when it sounds like a big gun shooting. I wouldn't do that stuff now days tho.

 

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[wrscomncents]

It actually can be a number of things. Ignition timing, fuel and exhaust.

 

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Yeah I know. It's like when someone asks you why their car is making that funny noise. I'm just trying to pick everyone's brain here because I have run out of ideas.

[Sylvester]

Look for air coming through the diaphragm covers. Just had this on my 02 RSMV at #4 carb.

 

[wrscomncents]

Look for air coming through the diaphragm covers. Just had this on my 02 RSMV at #4 carb.

 

 

Sylvester

 

I will check that out. Were you getting a backfire. I have lightly blown air into the carb to check the slide movement and all appeared to be working fine but it can't hurt to check.

[BlueSky]

Checking the compression with the engine cold makes a difference. Checking it without the throttle wide open makes a difference.

[wrscomncents]

Checking the compression with the engine cold makes a difference. Checking it without the throttle wide open makes a difference.

 

BlueSky

 

Checked compression with all plugs out and throttle full. Engine cold. Like I said I had to check with a compression tester that had to be held in the plug hole so it may not be exactly accurate but should be close enough.

[Patch]

Was just rereading the original complaint, a LOUD backfire has a completely different direction to popping which was also mentioned.

 

If we suspect the backfire is unburnt fuel then that can be from 2 or 4 correct?

 

Load test the coils using the gap test, then we can just rule it out.

 

About your question on what can cause it from carb 4 and reading your other responses, have you checked that the enricher is not leaking, the needle jet is in proper working condition?

 

I think you said 3/4 or 7/8 of a turn starts the backfiring not popping? So the post I wrote has the suggestions for this as a cause. This means that you need examine each piece carefully to make sure you can rule it in or out.

[wrscomncents]

Was just rereading the original complaint, a LOUD backfire has a completely different direction to popping which was also mentioned.

 

If we suspect the backfire is unburnt fuel then that can be from 2 or 4 correct?

 

Load test the coils using the gap test, then we can just rule it out.

 

About your question on what can cause it from carb 4 and reading your other responses, have you checked that the enricher is not leaking, the needle jet is in proper working condition?

 

I think you said 3/4 or 7/8 of a turn starts the backfiring not popping? So the post I wrote has the suggestions for this as a cause. This means that you need examine each piece carefully to make sure you can rule it in or out.

 

Yes it is a LOUD backfire not just a popping. And it does it at an idle and as soon as the bike starts. Really not much time for the exhaust to get hot.

 

I'm not sure how you go about load testing the coils. I have had a spark tester on each wire and the spark does jump a considerable distance. Well past one.

 

The needle valve and seat are both new and appeared to be working properly. At the risk of sounding stupid I'm not sure what the enricher is.

 

Once again appreciate all your time and input.

[snyper316]

Sounds like my bike when I first got her she was all stock and very lean setup. The enricher is the choke.

 

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[wrscomncents]

Sounds like my bike when I first got her she was all stock and very lean setup. The enricher is the choke.

 

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Okay duh. Thanks

[snyper316]

How does she run off idle?

Okay duh. Thanks

 

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[snyper316]

3000rpm and above

 

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[Patch]

Yes it is a LOUD backfire not just a popping. And it does it at an idle and as soon as the bike starts. Really not much time for the exhaust to get hot.

 

I'm not sure how you go about load testing the coils. I have had a spark tester on each wire and the spark does jump a considerable distance. Well past one. Then that is a pass/good

 

The needle valve and seat are both new and appeared to be working properly. Ok I thought there was some confusion there. At the end of the vacuum slide there is a needle, remove the cap, there is a very long spring (not a stiff one) then slip out the black diaphragm attached to the slide piston. That needle needs to be checked and it should move a little as there is a spring at the rear end, so it just moves a little which permits it to center down the main jet tube!

At the risk of sounding stupid I'm not sure what the enricher is. Look at the manual

 

Once again appreciate all your time and input.