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Discussion Starter #1
Bought me a 2005 VStar 1100 this spring with 5000 miles. It was bone stock and had always been serviced by Yamaha.

The only thing I did to it was to drill out the end of the factory pipes with a 1 1/2" hole saw. After that it sounded great and ran just as well as it had before. I would have described the sound as a smooth rumble with occasional light popping on decel. which is normal as i understand.

1200 miles later I'm riding on a hot day. Have lunch and come out and start the bike and there's a loud pop from under the gas tank, like a backfire, (only a frontfire?). My buddy said he saw a puff of smoke coming out from the left side, somewhere around the carbs. After that my exhaust now sounds raspier and there is significant popping and backfireing on decel. at all speeds. The idle sounds lower too.

Any ideas on what might have happened. Did something get damaged when it frontfired? Thanks!
 

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i had that happen on my vstar 1100 when i took the baffles out and what it was is that my carb had fallen lose of the boot it would still run but like you said at low idle. just look closely at it, it might be off just a little bit.
 

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Sounds like the boot to the manifold (between the carb and the head) might hahe cracked. This will yield a lean condition that will pop at carb and lower your idle. Get some WD-40 and spray around boot with the bike running when the idle changes you found your leak.
 

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Well I took the air cleaner off and the carb had indeed come partially away from the front cylinder. Hope that cures the problem. Your help was much appreciated!
 

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Discussion Starter #6
No, actually I didn't even know the 1100 had an AIS until yesterday. My previous bike was a 650 vstar and the AIS was pretty obvious up front. After riding around for the day after putting the carb back on right the backfiring has cleared up immensely, but is still there. And I really don't remember it doing it at all previously. Makes me wonder if something got damaged?

Anyway, AIS disable is scheduled this afternoon to see how it runs then. Probably remove the unit shortly thereafter.
 

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My AIS has been removed for the past 63k miles with no issues. I think it was put there for emissions for use with catalytic converters. The extra air is needed to burn off any fuel in the exhaust pipe before it gets to the muffler/catalytic converter. Raw fuel mixed with the material in the catalytic converter cause excessive heat.
 

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Help Please with back fire problem

I just bought a 05 1100 custom it has the hard krome exhaust on it. I noticed a backfire from the rear cylinder from the pipe and the carb pops too. I jetted the carb with dyno jets. I also compressioned tested it it was about 105 PSI while the front was 120 PSI. I turned the carb around and the problem followed to the front cylinder then. I also checked the plugs and wires. the plugs are brown which is good. The AIS is totally removed and the applicable items are plugged. I am running a 112 jet on the front and a 110 on the rear. 2 1/2 turns on the PMS screw. I also frabicated a restrictor in which I installed just to see if it would work on the rear exhaust still no work then tried one on the intake to see no luck also. I have also tinkered with the PMS screw to see if tht helps but it doesn't. I can't think of anything else to do. It pops on decel, idle, and when reving it up. Any help will be appricated, I am spent.
 

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2003 Vstar 1100 Custom. Did the final baffle removal (1.5" hole saw) this weekend. Backfires like crazy while engine braking. Bypassed AIS system and still backfires. Plugs are brown, runs fine. ???
 

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Open up your PMS screw about 1/2 turn
 

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Mikuni says on a properly tuned bike with an open exhaust some popping is considered normal, you have opened the exhaust. It is due to the sudden leaning of the mixture when you shut the throttle. Opening your PMS screw enrichens the mixture at this point and lessens the popping, and yes this is the same for the 650.
 

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Sweet, preciate it!
 

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I Left you another tidbit on one of your other posts. I edited it in, you may have looked at it already.
 

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Problem may very well be the Dyna Jet kits are no good, go with mikuni 147.5 and mikuni 20 pilots and original needles with c clip then plastic spacer and two .5 washers 3 turns out on pms screws to start
 
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