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Discussion Starter #1
Hey everyone,

I have a 2002 V-Star 1100 that is backfiring. The front pipe is becoming discolored so I can only assume the front cylinder is running too hot, not sure if that is related to the backfire or not as I don't really know anything about engines.

In order to try to remedy the problem I rebuilt the carb, cleaned all the airbox parts, and replaced the spark plugs. I checked all the fuel lines and the fuel filter, everything looked good there.

Can anyone help me figure out why it's backfiring?

 

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Welcome from Atlantic Canada. Sounds like you've tried everything I can think of but we have some more knowledgeable members here who I'm sure will have some thoughts on it.
 

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Are both pipes getting the same temp? Just feel to the quick touch. Sounds like you been thru what i would think. Did you let it run too long with enricher? Maybe look at plugs to see if you can isolate wich cylinder.
 

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Discussion Starter #5
Are both pipes getting the same temp? Just feel to the quick touch. Sounds like you been thru what i would think. Did you let it run too long with enricher? Maybe look at plugs to see if you can isolate wich cylinder.
Hey, thanks for chiming in! Front pipe gets much hotter, which is why it is discolored. Only start it on the enricher and turn it down as soon as the bike will let me, which is usually right away. Bike will actually run with it all the way off, it was all the way off in the video actually. And I shot that video after it had run for a while with it turned all the way down.
 

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If the front pipe is hot and discolored it sounds like it might be lean. You can pull a plug and check, but i believe it is usually hotter. I am sure more guys will have more ideas.
 

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Normally the popping you are experiencing is from a lean condition. In a lean condition the cylinder runs much hotter. When you back off the throttle and RPMs quickly drop a certain amount of unburned fuel enters the exhaust bike. The heat from running lean has heated the pipes enough to ignite the unburned fuel. Easy fix, turn PSM screws out about 1/8 to 1/4 turn at a time till the popping stops. If your PSM screws have gotten way out of whack, screw them in till they gently seat, then back out 3 turns as a starting point. You should not have to turn out more than 3.5 turns out, if so you have other carb issues. Another cause of exhaust popping is a loose exhaust pipe to head. Could just be a little loose or gaskets could be bad. Good luck and keep us posted.
 

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Discussion Starter #8
Normally the popping you are experiencing is from a lean condition. In a lean condition the cylinder runs much hotter. When you back off the throttle and RPMs quickly drop a certain amount of unburned fuel enters the exhaust bike. The heat from running lean has heated the pipes enough to ignite the unburned fuel. Easy fix, turn PSM screws out about 1/8 to 1/4 turn at a time till the popping stops. If your PSM screws have gotten way out of whack, screw them in till they gently seat, then back out 3 turns as a starting point. You should not have to turn out more than 3.5 turns out, if so you have other carb issues. Another cause of exhaust popping is a loose exhaust pipe to head. Could just be a little loose or gaskets could be bad. Good luck and keep us posted.
Hey lesblank. I tried to find some adjustment screws on the carbs when I rebuilt them, the only screws I found were to drain the bowls and one to adjust the idle (I think?) with a big plastic knob on it. Where are the PSM screws located?
 

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Hey lesblank. I tried to find some adjustment screws on the carbs when I rebuilt them, the only screws I found were to drain the bowls and one to adjust the idle (I think?) with a big plastic knob on it. Where are the PSM screws located?
There is a plug on the bottom of the carb you have to drill carefully, run a screw in the hole and pop the plug out.
Might want to search that. I am not sure about the 1100. You will have to remove the carb(s)? Again.
Yamaha makes these bikes lean for emission standards.
 

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Discussion Starter #11
So when I checked the front exhaust I just made sure it was tight. I decided to take it off to see if there were any problems.

It looks like there was an air leak around about half of it, but since I'm a noob at this I'll defer to the experts. It definitely needs a new gasket though lol.

Going to fix this first and see if I have any success, and move to installing adjust PMS screws if it doesn't solve the problem.

92586
92587

92588
 

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Yes, the gaskets were leaking and need replacing. Hopefully this will fix most of the popping. Keep us informed.
 

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other causes of running lean:

running on premium / hi octane fuel (1100 is tuned for regular)
vacuum leak
carbs not synched
 

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As KCW stated above, Carbs not Synced. On these bikes and, more importantly, these carbs, any time you do anything with the carbs, they need to be synced. You can get them close with sound, but unless you use a carb syncronizer (which you make at home), you'll always be just a little off.
 

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Hey everyone,

I have a 2002 V-Star 1100 that is backfiring. The front pipe is becoming discolored so I can only assume the front cylinder is running too hot, not sure if that is related to the backfire or not as I don't really know anything about engines.

In order to try to remedy the problem I rebuilt the carb, cleaned all the airbox parts, and replaced the spark plugs. I checked all the fuel lines and the fuel filter, everything looked good there.

Can anyone help me figure out why it's backfiring?

Did you set you air fuel mix screws back to where they were ? If the bike is too lean or too rich it will backfire.
 
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