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Carb trouble?

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Carb trouble?

PostAuthor: tomblume471 » Tue Jun 12, 2018 8:51 pm

I have a 1992 virago 1100 that is having trouble running. When I first bought it it was completely stock and the only issue it had was back firing on decel so I took off and plugged the exhaust AIS. That fixed it. Then one of the bowls would overflow. Tore the carbs apart and found a needle seat o-ring had failed so I put a new one in.

Then I started to customize. I took the muffler off and put turn outs in it's place. I put a sigma6 jet kit in. Then I took 2 pvc elbows and put them in the intake boots and put some pods on the ends. It was running lean on the big end so I put some bigger main jets in. Ran much better on the big end but now it's fouling plugs but still pulls hard so I think I need a little smaller pilot jets. It was still running good but one day i didn't quite get it into 2nd under heavy acceleration and revved out the motor pretty good. Since then it's been on and off on how it runs. When I start it after letting it sit it idles ok but when I try to leave it will sputter and pop till it reaches about 3000 rpms then runs good. When I got home I was having trouble idling. I would start it up and try to give it some rpms and it would sputter and shoot flames out of the exhaust then idle for a couple seconds and die. I went through that a couple times. That says to me that is running lean but the plugs read rich. Am I wrong on that? What does this sound like? Any suggestions on what to check before pulling the carbs off again?

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Re: Carb trouble?

PostAuthor: Flyingdog » Wed Jun 13, 2018 12:01 am

In all likely hood, carb diagnosis over the net is pretty iffy..in the first place. First off..you'd definitely would think ya leaned it out. But not always the case. What it was, in the first place, is pretty critical. As in, was it (carbs) still all oem? Cuz, just because you changed out the exhaust, doesn't always necessitate re-jetting. The change to pods? Yea, you most likely let it breath easier, cuz pods are (usually) less restrictive than oem filter set-up. But that isn't always good, either. Lotta bikes need that restriction to balance out the A/F intake. Guess the first question to be: How big of a jump in jet size did ya go? Many people attack the jetting to change things up, when actually, they only need to change something in the needle setting. Either size and/or position (up or down), within the main jet holder (emulsion tube). Speaking of, even the emulsion tube can vary how the engine receives the correct A/F mixture. Lotta "what ifs" to begin with.
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Re: Carb trouble?

PostAuthor: bstig60 » Wed Jun 13, 2018 7:59 am

Sounds like the low speed circuit is plugged up partially or you may have a bad O ring in one of the pilot screws. With all the mods you have made on the carbs, did you change the pilot jet to a larger size?
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

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Re: Carb trouble?

PostAuthor: swtichblade » Thu Jun 14, 2018 7:33 pm

Maybe need to adjust the idle screws to suit your new mods. Maybe try syncing the carbs too. Both are done with carbs on and bike running. For your high end over richness you could always just try to add more air instead of downsizing jets.

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Re: Carb trouble?

PostAuthor: tomblume471 » Sat Jun 16, 2018 9:39 am

I believe I'm fouling out at idle because when I roll up in throttle it clears up and pulls. I was gonna go back to stock pilot jet and turn up my a/f screws and reclean everything. It's going to be the fourth time I have had them apart in the past year. What are your thoughts?

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Re: Carb trouble?

PostAuthor: bstig60 » Sat Jun 16, 2018 10:45 am

The pilot jet, pilot passage and pilot screw work together to allow the engine to get fuel to start and idle. They provide a bypass for low rpm fuel requirements thru a venturi port in front of the butterfly..... If this isn't clear or if the Oring is bad on the pilot screw or if the pilot jet is plugged or too large, it will cause the symptoms you are indicating.. BTW: the pilot screw regulates the amount of fuel to the venturi port, it does not have anything to do with regulating air.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

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Re: Carb trouble?

PostAuthor: tomblume471 » Wed Jun 20, 2018 8:32 pm

Well I have the pilot screw turned almost all the way in. That's why I think I have to put the stock pilot jet back in and crank the pilot screws out. Am I wrong in that?

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Re: Carb trouble?

PostAuthor: swtichblade » Thu Jun 21, 2018 12:23 pm

I am dealing with a similar issue where my rear cylinder only is fouling up very quickly and causing stalls. If I really hammer on the throttle it the fouling bogging down seems to go away. My research has led me to check the float height next. Supposedly if your fuel level is too high in the float bowl the gas can be more easily sucked up into the engine and this is over feeding at lower RPMS. But when the throttle is well opened up I guess it's is sucking enough fuel in and igniting fast enough to no longer make much of a difference (other than crappy fuel economy). Any how, this is what I am going to look into next on my bike. Maybe this will help you too.

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Re: Carb trouble?

PostAuthor: tomblume471 » Sat Jun 23, 2018 9:56 am

swtichblade wrote:I am dealing with a similar issue where my rear cylinder only is fouling up very quickly and causing stalls. If I really hammer on the throttle it the fouling bogging down seems to go away. My research has led me to check the float height next. Supposedly if your fuel level is too high in the float bowl the gas can be more easily sucked up into the engine and this is over feeding at lower RPMS. But when the throttle is well opened up I guess it's is sucking enough fuel in and igniting fast enough to no longer make much of a difference (other than crappy fuel economy). Any how, this is what I am going to look into next on my bike. Maybe this will help you too.
Ya I've checked my float height Everytime I took the carbs off. I will definitely be checking it again when I take them apart.

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