Help Please with back fire problem - Star Motorcycle Forums: Star Raider, V-Max, V-Star, Road-Star Forum
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post #1 of 4 (permalink) Old 06-14-2010, 09:03 PM Thread Starter
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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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post #2 of 4 (permalink) Old 06-15-2010, 10:01 AM
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First I gotta say I can't see how changing the carbs could've changed your PSI. I'd say there was some other inconsistency. Try to get them again with the carbs n plugs removed. It is normal for the jetting to be different from the factory due to the airbox restrictions. This will help with the popping on decel. Mikuni has said that some popping in a well tuned engine on decel is normal. Is the stock airbox still in place? Here's a link to a chart on jetting just match your bike up. These sizes are in Mikuni Jets.

Here's a link to a dynojet to mikuni jet conversion. based on your numbers your jets are to lean. Go down to the second chart.

2005 1100 Custom
Speedster Slashdowns
ORKed 5/16" Lines
PODs K&N RU-600s W/PCV
PCS XXX/2 cams
Jetted & PMS Tweaked 20.0/152.5 3.0 turns
AIS Removed/Plugged
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TPS Connected
6" Fwd Control Extension W/Boards F&R
Memphis Shades Bullet Fairing
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post #3 of 4 (permalink) Old 06-15-2010, 04:33 PM
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Sounds like Fulltilt has got you covered for now.


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post #4 of 4 (permalink) Old 06-15-2010, 08:05 PM Thread Starter
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Thank you for your help. What I meant by switching the carbs was I turned them around and the the front started to pop and the back was ok. I sync'd the carbs today they were way off. The I put 4 1/2 turns on the PMS and it seems to be ok haven't got it on the street yet underload but at Idle /it will rev and decel nice and tight with no pops or backfires. If you don't mind me asking where do I get big jets like you were discribing. The kit I baught came with 112,110,108,106,104 that was it. Anyways I will take it out tomorrow and mess around with tweeking it. If there are any other ideas you have please I would be happy to try them, sound like you know what is up with bikes. I am a classic car guy so I am familiar with carbs and sync'ing just not were I can locate parts and dealing with 2 single carbs. A little different then a 4 barrel or so. Thanks again. Chris
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