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Discussion Starter #1
I am a new guy but I got a deal on a 2002 Vstar 1100 with almost 30000 miles on it because the starter clutch was bad. I push started it and it ran but it back fires and shoots flames from rear cylinder exhaust pipe. The bike has the air pump system removed with Baron Plugs in the heads and a rubber cap at the intake boot, also has Vance and Hines slip on's I tore it apart and replaced the starter clutch and the bolts that hold starter together as they were bent from starter twisting. Now I am exploring the backfiring flame shooting issue.

Found cracking intake boots and replaced them, took carburetors all apart and cleaned all the passages and jets. Found spark plugs very black and obviously running rich. While carbs apart found the needles had six grooves and they were set on the third from bottom with snap ring. I moved up one groove hoping to lean it out a little. The main jets were marked front cylinder 112.5 and rear 110.0. Pilots were both 17.5. I reassembled the carbs reinstalled with the new boots and new fuel filter. NO CHANGE still back fires and pops with flames from rear cylinder pipe.

This is bad even at idle popping is obnoxious. I am at the end of my ideas. Anybody else have a cure?
 

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I am a new guy but I got a deal on a 2002 Vstar 1100 with almost 30000 miles on it because the starter clutch was bad. I push started it and it ran but it back fires and shoots flames from rear cylinder exhaust pipe. The bike has the air pump system removed with Baron Plugs in the heads and a rubber cap at the intake boot, also has Vance and Hines slip on's I tore it apart and replaced the starter clutch and the bolts that hold starter together as they were bent from starter twisting. Now I am exploring the backfiring flame shooting issue.

Found cracking intake boots and replaced them, took carburetors all apart and cleaned all the passages and jets. Found spark plugs very black and obviously running rich. While carbs apart found the needles had six grooves and they were set on the third from bottom with snap ring. I moved up one groove hoping to lean it out a little. The main jets were marked front cylinder 112.5 and rear 110.0. Pilots were both 17.5. I reassembled the carbs reinstalled with the new boots and new fuel filter. NO CHANGE still back fires and pops with flames from rear cylinder pipe.

This is bad even at idle popping is obnoxious. I am at the end of my ideas. Anybody else have a cure?
The cure for the back fire is to adjust the PMS out to 2 1/2 or 3 turns and see what happens. Also check for exhaust leaks especially where the slip-ons connect and at the front head.

Did you synch the carbs after you put them back on? That could also be a big part of your issue.

6 groove needles are not stock...and harder to tune. Most just toss 'em in the garbage and get a stock set. They are either 1 groove or 5 groove (use middle groove).

I used to lean out my PMS at night when I had a Thugstar pipe just to see the flames......that was fun...lol
 

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Discussion Starter #3
Flame on

I did remove the plugs and PMS screws are backed out 2.5 turns with no change. Synced the carbs and it idles better but no other changes. Problem seems to be with rear cylinder my next step is a compression test and valve adjustment if it needs it. I have looked the exhaust over real well and see no signs of leakage.
 

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I did remove the plugs and PMS screws are backed out 2.5 turns with no change. Synced the carbs and it idles better but no other changes. Problem seems to be with rear cylinder my next step is a compression test and valve adjustment if it needs it. I have looked the exhaust over real well and see no signs of leakage.
2 1/2 is probably not enough. I'd go to at least 3 1/2 or 4 and see what happens. If it stops the backfire, slowly turn them in until it starts again, then back out 1/8 turn.

Backfire on decel is a lean condition at idle. So it's either air getting in, or too little fuel. When you had the carbs apart...did you run something through all the small holes in the pilot jets? If those get plugged even slightly it will cause the same issue. I always run a stiff brush bristle through them when ever I have my carbs apart just in case.

Maybe I needed to read your post closer.....are you saying that while the bike is sitting still idling, it is throwing flames out?
 

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Discussion Starter #5
Flame thrower

I have now backed the screws out 3.25 turns and it is better. Will ride tomorrow if I get time.
 
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