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Jetting Questions

3518 Views 11 Replies 7 Participants Last post by  TinyBear
I just put a Cobra 2-1 HP exhaust in and a Max air preditor pro (with ais removal on my 2008 Yamaha V-Star 1100.

And it is quite the difference power wise normally, quite shockingly actually. BUT i am having issues with at random times the bike looses all power spits coughs and back fires as if it was running out of fuel (BUT its got a fresh full tank of good fuel, done it with fuel from two different places).

I am a diesel mechanic for a living so i good with my hands but carburation is not my strongest point (ALL Diesels are fuel injected). So i kinda at a loss as to what could be causing this issue. Bike was running just fine prior to the upgrades so i assume it has to be something too do with the fuel jetting i am thinking but being as its randomness its not making any sense to me. The proplem presists with the fuel pet cock on or on reserve too.
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Sounds good on the 2 into 1 and Max Air.

Don't have much help but, sounds like you are loosing both cylinders so doesn't sound like one carburetor. wonder if you have checked the fuel filter?

Double check to see if you might have traped or pinched a wire, maybe loosened a connector that might affect the ignition. Even though you worked on exhaust and carburetors you may have gotten something else in the way.


Cut and paste this link to your browser. Check the table, you'll have to scroll way down. Match your setup to the table and check your jetting and needles. Backfiring out the exhaust is a sign of an overly rich condition. Mark your throttle handgrip to see at what throttle position (idle, 1/4, 1/2, 3/4, full). There is also a picture to help you isolate where the problem is and lots of pictures about all things carburetor.
Did you sync your carbs? Did you replace the stock needle screws with the Maxair adjustable ones? Float levels have to be right on. As with diesel fuel system adjustments, the ones on carbs must also be precise. Next check for vacuum leaks at the carb bases, this can be done with the bike running and spraying carb cleaner around the bases.Any rpm change will indicate a leak.
Hope this helps.
Thanx for the help so far guys.

yeah took it to a dealer to sync the carbs. The stock needle screws were replaced with the max air ones. I try checking for leaks at the carbs.

Its just bogeling my mind cause i cant see a pattern to it. The ONLY thing im seeing now is it only really does it at higher speeds 80-100+ km/hr and when ya give it the lots of the throttle. BUT most times it works just fine witch is why i cant understand.

Talking to the older guys at work they saying i may have the floats adjusted too low and the bikes starving for fuel. But that dont make sence to me cause other times i can go WOT and it just GOES.

See on a diesel things are ALOT different. When ya hit the gas on a gasoline engine you control the air intake and the carb or injection deals the fuel to match. On a Diesel the throttle directly controls the Fuel injection and as much air as possible is dumped in. So with diesels you dont really ever see this kinda deal. Their are adjustments for your injectors in some cases but they dont affect things as much as messing with a carb on a gasser.

Regardless i do like haveing a carburated motorcycle cause even though i apprently not much good at fiteling with em they do fasinate me and i am enjoying the learning proccese.

That being said i probly send it to the dealer to play with if i cant figure it out soon as i taking the bike on a trip soon so i kinda need to get it running. Worst case though i just steal my old 650 vstar back from my mum for the week.
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Just a guess but you may have a sticking slide as it is actuated by vacuum and not mechanical linkage it could be intermittent. Also these main needles regulate at the higher RPM as your problem indicates. So check that the diaphragms are seated properly in the housing and the slides are both moving freely through their entire travel.

It could be that with the increase in power you now have. You are hitting the fuel cutoff. Solenoids that shut off the fuel around 6000 rpm. Try unplugging them and go for a ride see if it helps. Becarful that you don't over rev the engine. This will also cause the Check Engine light to come on. Maxair makes a kit that eliminates these solenoids. I did this when I added the Maxair kit, quite a while after I added a tach and after market pipes. I thought that there was a problem with the engine.
Hopes this helps.
No i already have the fuel solinoid cut off bypass from max air as well.

And it happens at lower rpms as well as higher rpms. Only happend so far at 80-100+km/h (so like 50-60+mph).

Got a appointment booked at my local dealer they pretty good with these bikes and are willing to let me into the shop to kinda see whats going on.

I just rebuil my old bike to like new (its now my mothers) but i can take that a bit till i sort mine out.
Re:-Jetting question

Check your'e float levels just incase you set them too low when you changed the jets also make sure the fuel bowl vents are clear.
Hay TinyBear next time it does it open your gas cap and see if that makes a differences. Maybe a vacuum on the gas tank? Cap vent clogged?
Farmalldanzil has a good point. It could be a plugged gas cap vent. I would not have thought of that. But sound very possible. Nice thing about this forum, someone always has a differant thought.
Hmm somethings funny. The bikes been running like a top for the last few days. No hicups TONS of power and just runs prefectly fine no matter how i ride. Getting 41mpg riding it pretty hard and around 48 taking it easy.

IM thinking something was jamming up the floats or something but i gona tear it down to be sure. Its been two full tanks of fuel since it last had a issue so i not really sure what to think but man if it keeps running like this i am one very HAPPY camper.
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