Still backfiring 2003 Yamaha V-Star 1100 Custom - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 47 (permalink) Old 02-23-2017, 11:10 PM Thread Starter
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Still backfiring 2003 Yamaha V-Star 1100 Custom

Well, I've had this bike since March of 2015. It has won battles over and over again. I've put maybe 2 miles on it. Rebuilt/cleaned carbs(like 1000 times), rebuilt starter clutch, kremed the tank, new plugs, new ignition coils, oil change, the works. Still giving me hell.

The issues I'm having is when the bike warms up it backfires under load. I can ride 2 laps around my neighborhood and it doesn't backfire but once it gets warm it starts backfiring. The bike purrs at idle, no issues at all, but when I take off on it and it gets warm it will very very very loudly backfire. Equal to a shotgun blast easy as they are low boy shotgun pipes from Cobra.

When I rebuilt the carbs I put in Max Air PMS screws. I was told by someone they only control idle. But I can turn them in all the way and it doesn't affect idle at all. So I turned them out 3 turns each and went from there.

I'm so close to being able to ride it, it starts every time, runs everytime, but it's almost like it's loading up or something.

What would cause the bike to run fine for a couple minutes at idle and under load and then when it's warm backfire like that? Thoughts or tips? I haven't re-jetted the carb or anything as the bike came as is with custom pipes but it also wasn't running when I got it.

I'm looking for a savior. I dumped $176 on new ignition coils because I thought one might be heating up and breaking down but that proved to be a waste of money because I installed the new ones and still get backfire once its warmed up. On a tight budget so any help is appreciated.
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post #2 of 47 (permalink) Old 02-23-2017, 11:19 PM
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Sounds like the carbies haven't been jetted properly for the pipes to me.
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post #3 of 47 (permalink) Old 02-24-2017, 05:18 AM
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if you have stock intake and exhaust the pms screws should be 1 3/4 to 2 turns out.

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post #4 of 47 (permalink) Old 02-24-2017, 06:54 AM Thread Starter
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@nick57 I have custom exhaust on there, they are cobra low boy shotguns. I'm going to turn both in to two turns. Right now I'm at 3 on the rear cylinder and 2-1/2 on the front. When I rode it around at work my boss said it looked like it backfired through the front cylinder exhaust pipe.

@chedobean if they needed to be jetted then why does it run perfectly for a couple minutes then start backfiring?
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post #5 of 47 (permalink) Old 02-24-2017, 07:01 AM
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if stock is about 2 turns out and you put pipes on you will get popping on decelleration. so to get rid of the popping turn the screws out 1/4 turn or until the popping goes away.you say the bike has never run right. you have to determine the carb set up, what size pilot jets, the needle position.what octane fuel.
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Last edited by nick57; 02-24-2017 at 07:11 AM.
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post #6 of 47 (permalink) Old 02-24-2017, 07:11 AM Thread Starter
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@nick57 ok, right now I'm getting backing on acceleration. I'll turn them in to 2 on my lunch break today and work out from there and let you know how it goes. Thanks for the help
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post #7 of 47 (permalink) Old 02-24-2017, 08:08 AM
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Quote:
Originally Posted by Bike Merc View Post
@nick57 I have custom exhaust on there, they are cobra low boy shotguns. I'm going to turn both in to two turns. Right now I'm at 3 on the rear cylinder and 2-1/2 on the front. When I rode it around at work my boss said it looked like it backfired through the front cylinder exhaust pipe.

@chedobean if they needed to be jetted then why does it run perfectly for a couple minutes then start backfiring?
I'm not an expert on carburation, but I have managed to rejet and needle a few of my bikes successfully. I'm assuming that when you say it's fine initially, that it's starting to backfire when it gets to operating temperature?
It's been my experience that out of adjustment idle screws are most noticeable by popping and crackling on deceleration [ too lean]and problems just off idle. Sounds like you need a good mechanic to take a look and listen. [though I am one of those stubborn 'Bs' that likes to work things out for himself].
Another possible cause could be a vacuum leek in the manifold?
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post #8 of 47 (permalink) Old 02-24-2017, 10:21 AM
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I have to agree with chedobean; sounds like the jets don't match the pipes. I drilled out the pipes on my 1100 and it did a bit of popping and backfireing after that.
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post #9 of 47 (permalink) Old 02-24-2017, 03:41 PM
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On an 1100 with stock intake, you really don't need to change any jets....simply adjust the PMS out a bit like Nick suggested.

Please tell me you started this diagnosis by synching the carbs. When things aren't running correctly that is always the starting point. I wouldn't go any further until that is done. There is plenty of ground to cover afterwards if that doesn't solve it......but trying to diagnose an issue on a bike with 2 carbs and you're not sure if they are in synch is going to be a mighty futile excersize.
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post #10 of 47 (permalink) Old 02-24-2017, 07:21 PM
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Also the air injection system is notorious for causing popping and banging on the 1100s. I owned an 1100 vstar and mine popped a fair bit,[ but not loud shotgun bangs like you have described]. On advise from another owner I disconnected the air injection and it fixed that problem.
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