Backfire
04-24-2007, 07:25 AM
#1
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Squid
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Join Date: Mar 2007
Posts: 12
Backfire
My first post here so let me introduce myself.
I acquired 1998 super hawk recently with 38000km on gauges.
Bike seem to be running fine with decent power and pull good handling as well, not what I am used to my last bike was 2005 ZX10R so I am running short for some 60-70 ponies, but bikes performs much better than what I was expecting, Still getting used to all the vibrations this thing produce.
I had K&N air filter installed and set of brand new Kerker carbon pipes (awesome sound)
Problem I am experiencing now is backfire a lots of backfire at low RPM on deceleration, city driving first, second & third gear.
Is the DynoJet stage 1 solution ?
Also I am new to V-Twin is it good idea to use full synthetic as engine oil ?
Any ides solving this problem will be appreciated
Thanks
I acquired 1998 super hawk recently with 38000km on gauges.
Bike seem to be running fine with decent power and pull good handling as well, not what I am used to my last bike was 2005 ZX10R so I am running short for some 60-70 ponies, but bikes performs much better than what I was expecting, Still getting used to all the vibrations this thing produce.
I had K&N air filter installed and set of brand new Kerker carbon pipes (awesome sound)
Problem I am experiencing now is backfire a lots of backfire at low RPM on deceleration, city driving first, second & third gear.
Is the DynoJet stage 1 solution ?
Also I am new to V-Twin is it good idea to use full synthetic as engine oil ?
Any ides solving this problem will be appreciated
Thanks
04-24-2007, 07:44 AM
#2
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SuperSport
Join Date: May 2005
Location: North Wales, PA
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its your PAIR valve. its completely normal. you can remove the pair valve and get blockoff plates. that will fix it. or you can just leave it alone, it won't hurt anything. I'm getting mine done this week. if your bike hasn't been rejetted since you got the airfilter and the pipes, you're probably running a bit lean too. might want to rejet. I have a stage 1 dynojet kit and I've never had a problem. some people say that the dynojet kit is harder to install than the other brands. full synth oil is fine. I run partial synth myself. I use honda oil, but some guys on here just use mobil 1. and it will slowly eat oil over time. don't worry about it. its normal for big twins.
05-14-2007, 10:44 AM
#4
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its your PAIR valve. its completely normal. you can remove the pair valve and get blockoff plates. that will fix it. or you can just leave it alone, it won't hurt anything. I'm getting mine done this week. if your bike hasn't been rejetted since you got the airfilter and the pipes, you're probably running a bit lean too. might want to rejet. I have a stage 1 dynojet kit and I've never had a problem. some people say that the dynojet kit is harder to install than the other brands. full synth oil is fine. I run partial synth myself. I use honda oil, but some guys on here just use mobil 1. and it will slowly eat oil over time. don't worry about it. its normal for big twins.
Do not run you bike like this because it will scorch your exhaust valves and seats and eventually build up carbon on one side of the exhaust valve seats and bend all your exhaust valves. Think of the popping as explosion right near the exhaust valves while they are open.
05-14-2007, 06:23 PM
#7
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Squid
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Ok, I guess I got a question then? I'm having issues with backfire thru the carbs when riding around town at/or between 3500-4000 rpm. I changed my plugs, which had 10k on them, and that seemed to help a little but it is still happening. I have MIG exhaust that are now wide open, Dynojet kit installed and everything that can be done to the carbs as per Greg's website. What do I do?
05-14-2007, 06:32 PM
#8
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Squid
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Than problem I have is popping on exhaust not backfiring, I disabled pair valves it reduced popping for I can say 80%. Its still pops when decelerating from 3000-4000 rpm.
Also second problem I have is when driving at same rpm range 3000-4000 at study speed (not moving throttle) after 10-15 sec engine will start to cut off and occasionally strange noise will be emitted from engine.
I search form and find that this can be caused if carburetors are not synchronized, which is not a case I had them checked and vacuum gauge shows they run even trough all the rpm.
Also engine will occasionally quit at traffic light
Any ides what it can be?
Thanks
Also second problem I have is when driving at same rpm range 3000-4000 at study speed (not moving throttle) after 10-15 sec engine will start to cut off and occasionally strange noise will be emitted from engine.
I search form and find that this can be caused if carburetors are not synchronized, which is not a case I had them checked and vacuum gauge shows they run even trough all the rpm.
Also engine will occasionally quit at traffic light
Any ides what it can be?
Thanks
05-14-2007, 06:40 PM
#9
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SuperSport
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Location: Victoriaville, Quebec, Canada
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Than problem I have is popping on exhaust not backfiring, I disabled pair valves it reduced popping for I can say 80%. Its still pops when decelerating from 3000-4000 rpm.
Also second problem I have is when driving at same rpm range 3000-4000 at study speed (not moving throttle) after 10-15 sec engine will start to cut off and occasionally strange noise will be emitted from engine.
I search form and find that this can be caused if carburetors are not synchronized, which is not a case I had them checked and vacuum gauge shows they run even trough all the rpm.
Also engine will occasionally quit at traffic light
Any ides what it can be?
Thanks
Also second problem I have is when driving at same rpm range 3000-4000 at study speed (not moving throttle) after 10-15 sec engine will start to cut off and occasionally strange noise will be emitted from engine.
I search form and find that this can be caused if carburetors are not synchronized, which is not a case I had them checked and vacuum gauge shows they run even trough all the rpm.
Also engine will occasionally quit at traffic light
Any ides what it can be?
Thanks
If so back up the needle one notch, if you haven't installed it yet, time to do it. Get the needle backed one notch from the instruction settings, it will save you some time
That goes for gmoney too lean outs induce backfires.
05-14-2007, 07:01 PM
#10
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Squid
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Join Date: Mar 2007
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Too lean, did you get that dynojet kit in ??
If so back up the needle one notch, if you haven't installed it yet, time to do it. Get the needle backed one notch from the instruction settings, it will save you some time
That goes for gmoney too lean outs induce backfires.
If so back up the needle one notch, if you haven't installed it yet, time to do it. Get the needle backed one notch from the instruction settings, it will save you some time
That goes for gmoney too lean outs induce backfires.
05-14-2007, 08:25 PM
#12
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Squid
Join Date: May 2007
Location: Sacramento
Posts: 5
Popping or gun shot style backfire?
[first post - quasi-n00b here]
When I bought my VTR (used '98) in 2000, it had wicked gunshot sounding backfires going on. Blue flames out the back and all. It also reeked of gasoline after shutting it off. It turns out that the float valves in the carbs were sticking open, so fuel was still dumping in to the engine when the throttle was cut, then detonating in the hot headers.....
It from the discussion that you may be dealing with popping, not full on explosions in your exhaust, but what the hell I'll throw my $0.02 in to the mix.
-Jon in Sacto, CA
'98 VTR1000
When I bought my VTR (used '98) in 2000, it had wicked gunshot sounding backfires going on. Blue flames out the back and all. It also reeked of gasoline after shutting it off. It turns out that the float valves in the carbs were sticking open, so fuel was still dumping in to the engine when the throttle was cut, then detonating in the hot headers.....
It from the discussion that you may be dealing with popping, not full on explosions in your exhaust, but what the hell I'll throw my $0.02 in to the mix.
-Jon in Sacto, CA
'98 VTR1000
05-14-2007, 10:09 PM
#13
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Backfire through the carbs is a classic symptom of out of sync carbs. If they're in sync then the next course of action will be to check/adjust the TPS to ~500Ω. Then, if that still doesn't work adjust mixture screws to 2 - 2.25 turns out and check for intake/vacuum leaks.
05-15-2007, 12:54 AM
#15
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I have owned many bikes with this system and know 1st hand what it does. First it scorches the exhaust valves and then over time builds up carbon on the valve seat more often than not unevenly. In time the valve bends with the carbon buildup (takes between a couple to ten thousand miles). In the end you have to rebuild the head and if the valves are bent you will need new ones and if you have ever rebuilt a shim and bucket cam head you will know how much of a pain it is to get the clearances right. If your pair is malfunctioning either fix it or block it off right away.
05-15-2007, 01:42 AM
#16
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Well, I agree with what you say on the operation of PAIR, but there's a couple things I don't agree with. For one, I think that it's pretty rare for the system to malfunction. I've not once heard of a VTR PAIR valve going bad and mucking up an engine. Second, the most violent explosion occurs in the combustion chamber, where high temperature combined with atomized, compressed mixture is ignited. I think the relatively mild combustion that occurs in the head is not going to damage the valves. The rapid velocity of the exhaust out of the head precludes the flame front moving back towards the valve(s). Lastly, the carbon buildup is most likely due to an overly rich condition, causing carbon buildup on the back side of the valve, probably in a low flow region. Carbon buildup on valves is most likely seen on intake valves, however, and is rare on exhaust valves due to the heat and lack of fuel. The purpose of the PAIR system is to burn any unused fuel in the exhaust and thus the lack of fuel precludes any carbon buildup.
Tell me if my reasoning is AFU.
Tell me if my reasoning is AFU.
05-15-2007, 07:19 AM
#17
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Huge exhaust explosions won't hurt the exhaust valves, yuo can basically dynimite your exhaust pipe and no damage will be done to the valves, for starters, I nuked my CF pipe because of thousands of blasts in it until the rivets gave way. Pin the throttle, then hit the kill switch on and off, can't do worst than that and my exhaust valves are quite healty. The only thing that really can damage an exhaust valve is improper valve adjustement. The force needed to lift the valve from it's seat is way greater than what the poping can generate.
05-15-2007, 07:48 AM
#18
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Hmm I got myself a DynoJet stage 1 but after reading threads at this and other forums I find that that if not done using dyno at the shop it can cause lots of problems. I thought putting back the OEM air filter would be a better solution I do not know, what do you guys think?
05-15-2007, 09:10 AM
#19
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I myself am no authority on the inner workings of 4 valve twins but the guy I talked to at my dealership used to race RC-51's and before I had the pair valve blocked off, he told me not to worry about the popping and gurgling on the decel. he said it was very common among twins and it wouldn't hurt anything. he was kinda surprised that I was going to the trouble of having the pair valve disabled at all.
05-15-2007, 12:04 PM
#20
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Well, I agree with what you say on the operation of PAIR, but there's a couple things I don't agree with. For one, I think that it's pretty rare for the system to malfunction. I've not once heard of a VTR PAIR valve going bad and mucking up an engine. Second, the most violent explosion occurs in the combustion chamber, where high temperature combined with atomized, compressed mixture is ignited. I think the relatively mild combustion that occurs in the head is not going to damage the valves. The rapid velocity of the exhaust out of the head precludes the flame front moving back towards the valve(s). Lastly, the carbon buildup is most likely due to an overly rich condition, causing carbon buildup on the back side of the valve, probably in a low flow region. Carbon buildup on valves is most likely seen on intake valves, however, and is rare on exhaust valves due to the heat and lack of fuel. The purpose of the PAIR system is to burn any unused fuel in the exhaust and thus the lack of fuel precludes any carbon buildup.
Tell me if my reasoning is AFU.
Tell me if my reasoning is AFU.
The problem is that these extra explosions are happening when the exhaust valves are open. When closed combustion is fine but when open the seating surfaces are left unprotected. Its just like when an engine (car or bike) has a leaky header gasket. It is very hard on the exhaust valves. Until you have seen the damage its hard to contemplate. I'll try to find some old pics I had illustrating this.
As far as the system malfunctioning it is very common. Here are a few scenarios.
1. vacuum hose from carb/intake becomes blocked, disconnected, pinched, or cracked. Result is valve not closing under vacuum creating popping.
2. air supply hoses are cracked or disconnected between the pair supply valve and pair intake cap, or pair intake cap gasket leaking resulting in sucking air. Result is popping under vacuum.
3. stuck pair supply valve not closing. Result is popping under vacuum.
If hooked up correctly you should not have popping unless you have leaky header gaskets or poor jetting coupled with a very open exhaust. The valve is there for a reason and it closes the air supply under vacuum for a reason. In my experience every time a friend's bike has these symptoms and the bike uses an emissions valve like the pair it is always the problem. Check the operation of the valve buy using a vacuum pump and blow through it. It should be closed when vacuum is applied then make sure all your hoses are hooked up and in good shape. After seeing the damage and without emissions tests in my area I usually install block-off plates.
05-15-2007, 12:11 PM
#21
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Huge exhaust explosions won't hurt the exhaust valves, yuo can basically dynimite your exhaust pipe and no damage will be done to the valves, for starters, I nuked my CF pipe because of thousands of blasts in it until the rivets gave way. Pin the throttle, then hit the kill switch on and off, can't do worst than that and my exhaust valves are quite healty. The only thing that really can damage an exhaust valve is improper valve adjustement. The force needed to lift the valve from it's seat is way greater than what the poping can generate.
05-15-2007, 12:17 PM
#23
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I myself am no authority on the inner workings of 4 valve twins but the guy I talked to at my dealership used to race RC-51's and before I had the pair valve blocked off, he told me not to worry about the popping and gurgling on the decel. he said it was very common among twins and it wouldn't hurt anything. he was kinda surprised that I was going to the trouble of having the pair valve disabled at all.
05-15-2007, 12:36 PM
#24
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Let me brake it down. The harder you pull on the throttle the more air volume enters the engine resulting in a bigger boom. Compression under throttle = 110-180+ depending on the engine. With the throttle closed compression is much lower (about 40psi lower but varies). Compression with high vacuum (24-29in) during engine decel is almost nothing. Compression is key for ignition and efficient combustion. Without sufficient compression pressures much of the fuel is not burned and the hot mixture exits the exhaust and then should not be mixed with an excess of fresh cool o2. That is why the valve closes under vacuum.
05-15-2007, 07:44 PM
#25
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The very first alteration we made with an aftermarket exhaust is causing the problem, the cam is tuned for stock restriction, by opening up the exhaust more unburnt gases make it out of the exhaust port before the valve closes, this is the price to pay for the better filling of the unswept volume during overlap.
I agree that there is other ways to kill a valve(money shift for example), I'm just skeptical on how a valve can be damaged by exhaust afterburn, I have a tendency to put this on the myth category, the unlikely scenario I can think of is that the exhaust valve is blasted open and bounce back on his seat or get hit by the piston(unlikely since the pressure on the exhaust would need to beat the pressure inside+spring) ; very unlikely, the spring force is just too great and the poping pressure tends to rush to the open end.
I don't question that some people have seen damage, I will question the cause/effect relation ; most destroyed valves are from lean burn and detonation, a lean condition will create misfires and some afterburn, the poping is induced by the lean condition as well as the engine failure, not the engine failure from the afterburn. So the guy takes his engine apart and says "the damn thing was like a shotgun" and find his valves and maybe the whole engine banged up and goes"see, the backfires killed my engine..."
I agree that there is other ways to kill a valve(money shift for example), I'm just skeptical on how a valve can be damaged by exhaust afterburn, I have a tendency to put this on the myth category, the unlikely scenario I can think of is that the exhaust valve is blasted open and bounce back on his seat or get hit by the piston(unlikely since the pressure on the exhaust would need to beat the pressure inside+spring) ; very unlikely, the spring force is just too great and the poping pressure tends to rush to the open end.
I don't question that some people have seen damage, I will question the cause/effect relation ; most destroyed valves are from lean burn and detonation, a lean condition will create misfires and some afterburn, the poping is induced by the lean condition as well as the engine failure, not the engine failure from the afterburn. So the guy takes his engine apart and says "the damn thing was like a shotgun" and find his valves and maybe the whole engine banged up and goes"see, the backfires killed my engine..."
05-16-2007, 12:30 AM
#26
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I agree that there is other ways to kill a valve(money shift for example), I'm just skeptical on how a valve can be damaged by exhaust afterburn, I have a tendency to put this on the myth category, the unlikely scenario I can think of is that the exhaust valve is blasted open and bounce back on his seat or get hit by the piston(unlikely since the pressure on the exhaust would need to beat the pressure inside+spring) ; very unlikely, the spring force is just too great and the poping pressure tends to rush to the open end.
I don't question that some people have seen damage, I will question the cause/effect relation ; most destroyed valves are from lean burn and detonation, a lean condition will create misfires and some afterburn, the poping is induced by the lean condition as well as the engine failure, not the engine failure from the afterburn. So the guy takes his engine apart and says "the damn thing was like a shotgun" and find his valves and maybe the whole engine banged up and goes"see, the backfires killed my engine..."
I don't question that some people have seen damage, I will question the cause/effect relation ; most destroyed valves are from lean burn and detonation, a lean condition will create misfires and some afterburn, the poping is induced by the lean condition as well as the engine failure, not the engine failure from the afterburn. So the guy takes his engine apart and says "the damn thing was like a shotgun" and find his valves and maybe the whole engine banged up and goes"see, the backfires killed my engine..."
Anyways believe me or not but thats my .02... Actually that was about a buck fifty.
Good brainstorm session though I don't get to wax intellectual about bikes too often. Most people I ride with can barely change their oil.
One more thing...
BLOCK-OFF PLATES ARE GOOD!!!!!!!!
05-16-2007, 05:12 AM
#27
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I agree that this is a good discussion, well I'm the scientific kind, since I'll tear my engine apart next winter and I abused my bike a lot in this kind of way on purpose, I will simply check them for trueness. The leakdown tests are very good tough 2 % on both.
05-17-2007, 01:17 AM
#29
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The dirty explosion blasts toward the valve and can directly hit part of the seat while the protected side gets minimal coating. It has to do with the exhaust exit angle relative to the valve seat. The whole valve seat gets coated but usually one side gets it worse and builds over time. Its hard to explain but if you saw it you would agree. Its like spraying paint into the exhaust exit, one side of the seat would get a good coat while some would get a light fogging. I wouldn't of guessed this as a result if I hadn't seen it on two different bikes.
05-17-2007, 02:08 AM
#30
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Carbon buildup is soot. Soot comes from incomplete combustion. The whole purpose of the PAIR system is to ensure complete combustion (no unburnt fuel out the exhaust). This is the problem I am having with your explanation.
