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Discussion Starter · #1 ·
Hello everybody, just wondering if back firing is bad for the 9. Been having lots of it after de-baffling the exhaust. As we are in the Equator and the whether is hot most of the time, lots and lots of back firing. What is the best spark plug for our kind of whether? Thanks in advance.
 

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Did you block the pair system?

That should take care of most of your backfiring issue.
 

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Sure, if you search pair valve you may end up with something, but I can just tell you here.

There is a line from the front of your air box that runs to the top of both heads.

That is the Pair system. It is an emissions thing and allows filtered air to enter the head on the exhaust cycle to cleanly flush the cylinder for the next cycle.

However, when you open up the exhaust, the lower back pressure acts with the pair system to actual suck out the new fuel being fed to the head during the brief overlap of the valve openings. Thus, unburnt fuel is sucked into you exhaust where it ignites from the heat of the pipes and makes a nice backfire.

There are several fixes.

The easiest is to pull your throttle side intake and remove the pair line from the air box, plug it with a marble or bolt or anything you can fit in there, but is snug enough to block the line, then reconnect the hose to the air box to plug that hole.

If you happen to be taking your bike apart for another reason, you can use the other method which is to pull the pair line off all together, plug the hole in the air box and block the pair inlets in the heads with a metal plate. (I cut my own from aluminum roofing flashing, but you can buy them from dlp.)
 

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Aren't we so lucky to have access to these brilliant minds on this forum? What did people do before the Internet?
 

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Aren't we so lucky to have access to these brilliant minds on this forum? What did people do before the Internet?
Nothing brilliant about it.

Just been there.

After doing it, you will be the next guy giving the same advice.

Briliance is easy when you stand on the shoulders of giants.
 

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Doubt I could do that. I dont have the tools or mechanical ability, thats why its so amazing to me, how good you guys really are.
 

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Discussion Starter · #8 ·
Thanks squarerounder. Looks like a handful to me. I will keep this in mind and do it one day with the help of a friend. Would be fun. Thanks again.:bigthumbsup:
 

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Just a Thought. If you took the exhaust off the bike to debaffle, go back and make sure you torqued the header bolts down good. Use a torque wrench so you dont break them though. If you are sucking in air there it will have serious decell popping.
 

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That is the Pair system. It is an emissions thing and allows filtered air to enter the head on the exhaust cycle to cleanly flush the cylinder for the next cycle.

However, when you open up the exhaust, the lower back pressure acts with the pair system to actual suck out the new fuel being fed to the head during the brief overlap of the valve openings. Thus, unburnt fuel is sucked into you exhaust where it ignites from the heat of the pipes and makes a nice backfire.
SR, excellent advice on how to fix it, but the purpose and operation of it is slightly different.

It is an emissions device. It does admit air into the head, but it admits it after the exhaust valve. It doesn't help in flushing out the cylinder. It does add air to the exhaust so any unburnt fuel in the mixture can burn off when it hits the catalytic converter. It only operates on closed throttle.

The reason you hear the popping more with a more open exhaust is just because the exhaust is more open. It actually does it even on a stock exhaust, but you can't hear it as much due to the baffling. The decrease in back pressure may help contribute to it, but it's mostly due to the extra air being added to the unburnt fuel that is already present and an open exhaust allowing it to be heard more easily.

And any area that can allow air into the system can cause popping, whether it be at the heads, one of the connections in the exhausts, or the PAIR valve.

To the OP, is it popping out the exhaust or backfiring through the intake? Most stock exhausts don't backfire even when debaffled unless you fully gut them. But running one really lean will make it backfire through the intake.
 

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SR, excellent advice on how to fix it, but the purpose and operation of it is slightly different.

It is an emissions device. It does admit air into the head, but it admits it after the exhaust valve. It doesn't help in flushing out the cylinder. It does add air to the exhaust so any unburnt fuel in the mixture can burn off when it hits the catalytic converter. It only operates on closed throttle.

The reason you hear the popping more with a more open exhaust is just because the exhaust is more open. It actually does it even on a stock exhaust, but you can't hear it as much due to the baffling. The decrease in back pressure may help contribute to it, but it's mostly due to the extra air being added to the unburnt fuel that is already present and an open exhaust allowing it to be heard more easily.

And any area that can allow air into the system can cause popping, whether it be at the heads, one of the connections in the exhausts, or the PAIR valve.

To the OP, is it popping out the exhaust or backfiring through the intake? Most stock exhausts don't backfire even when debaffled unless you fully gut them. But running one really lean will make it backfire through the intake.
I will take your word for it.

Like I said, I obtained my understanding of the pair system from prior posts on the forum, so I am basing my description on nothing more than my memory of those post.

So, I am happy to accept a better description of what it is intended to do.

All I know for sure is that blocking the pair system cured my back fire problems.

Thanks for clearing that up for.
 

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SR, if you're family with the old air injection systems they used on cars and trucks in the 70's and 80's it works the same way. Those had an air pump that pumped air into the exhaust manifolds, ours just uses the vacuum created by the escaping exhaust gases to draw air in. I had an old Datsun 240 Z that used a similar system, and several different Japanese and European brands used one like it. IMHO, it was a much better way to induce air into the exhaust than the air pumps that had carbon vanes in them that required replacing or froze up often.
 

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Discussion Starter · #14 ·
SR, excellent advice on how to fix it, but the purpose and operation of it is slightly different.

It is an emissions device. It does admit air into the head, but it admits it after the exhaust valve. It doesn't help in flushing out the cylinder. It does add air to the exhaust so any unburnt fuel in the mixture can burn off when it hits the catalytic converter. It only operates on closed throttle.

The reason you hear the popping more with a more open exhaust is just because the exhaust is more open. It actually does it even on a stock exhaust, but you can't hear it as much due to the baffling. The decrease in back pressure may help contribute to it, but it's mostly due to the extra air being added to the unburnt fuel that is already present and an open exhaust allowing it to be heard more easily.

And any area that can allow air into the system can cause popping, whether it be at the heads, one of the connections in the exhausts, or the PAIR valve.

To the OP, is it popping out the exhaust or backfiring through the intake? Most stock exhausts don't backfire even when debaffled unless you fully gut them. But running one really lean will make it backfire through the intake.
I guess the backfiring is from the intakes. Could have to double check on that. Can't be riding for another 2 weeks as I have a swollen knee out of the blues. Can't seems to stand up properly without pain in the joint at the right knee. Getting old really sucks.:verymad: Thanks for the detailed explanations.
 

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Not sure anyone is still active on this thread but here goes. I just installed roadburner 3inch drag pros to my c109. Quite a bit of backfiring and an ocasional pop or two as I ride. I have a Cobra 2000r fi controller which I have not installed yet. Will this be the fix I need? or do I need to block the pair valve as well?

Dan
 

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Not sure anyone is still active on this thread but here goes. I just installed roadburner 3inch drag pros to my c109. Quite a bit of backfiring and an ocasional pop or two as I ride. I have a Cobra 2000r fi controller which I have not installed yet. Will this be the fix I need? or do I need to block the pair valve as well?

Dan
Since you are going to have the tank and air box off to instal your FI controller anyway, go ahead and block the pair valve hoses. As mentioned before, if your head to exhaust pipe leaks, from being too loose or a bad gasket, which could happen when changing the exhaust, this will also cause backfiring. Just don't strip the threads in the heads trying to overtighten the bolts!
 

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Not sure anyone is still active on this thread but here goes. I just installed roadburner 3inch drag pros to my c109. Quite a bit of backfiring and an ocasional pop or two as I ride. I have a Cobra 2000r fi controller which I have not installed yet. Will this be the fix I need? or do I need to block the pair valve as well?

Dan
Blocking the PAIR valves will do more to fix the backfiring than anything you can do on the fuel tuning. All you can do with the tuner is add more fuel, which will just aggravate the problem. The reason it pops is because air is being admitted into the exhaust, either through a leak or because of the PAIR valve, and once the air is in there with the fuel it ignites and pops or backfires. Stop the air and you stop the popping, almost 100%.
 

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I'm showing my ignorance here but I'll let fly - if you put on after market pipes don't you have to block the pair valves because of their design?:dontknow:
 

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I'm showing my ignorance here but I'll let fly - if you put on after market pipes don't you have to block the pair valves because of their design?:dontknow:
Nope. The PAIR valves dump air in after the exhaust valve but before the exhaust port. Aftermarket exhausts don't interfere with the way they work at all.

The only reason you may need to block them is because the extra air can mix with and cause any extra fuel in the exhaust to ignite, causing the backfiring you hear. If you have no popping in the exhaust there's no reason or benefit to blocking them at all.
 
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