Topic: Gas coming from velocity stacks

[robdrobd]

When I really nail the throttle I gas gas spitting out of the stacks. My air screws are seated all the way in. Should I turn them out a half turn or will that not solve anything. Plugs show that I am running rich. Ideas from stack users?

[Nortstudio]

I'm not a stack user, but the only time I have had gas moving in that direction was from the float level being off/float needle not working properly.

Good luck.

[robdrobd]

Hmmm. I think I might try to turn the screws out first. I adjusted the floats to spec. Anybody with stacks out there...out there.....out there...

[Nortstudio]

As far as I understood it, the air mixture screw, for most carbs, determines the mix between air and fuel.  Usually used to adjust that mix for low idle conditions.  Also, speaking out of turn here, because I ride a 550, but turning out the screw allows more air in, not less gas out the stack.  Also, I should have mentioned that it could be a float getting stuck, not just incorrect height.

The Stacks are no different from any other air filter system, in terms of them NOT regularly seeing gas flow.  It stands to reason that since it offers less restricted air flow, that the pull through them would slightly help prevent gas flowing the wrong way, not make it worse.  This is just an assumption, and not scientific of course.  Then again, maybe there is some weird rearward suction from stacks I don't know about...

Either way, it really does seem that the carbs need to come off.  Something is preventing the gas from flowing in the opposite direction of you stack/air filter, or allowing too much gas to pool up in there to be healthy.  maybe post a question in the performance section where more people tend to run stacks?

Hoping a pro chimes in here any minute...

[robdrobd]

You make a good point. The bikes is running really well other than that. It seems if I had gas coming out from the bowls my overflow tubes would have some gas coming out as well. I didn't even know we had a performance section. I will check there too.

[Nortstudio]

I think you are probably right, you would most likely see gas at the drain hose, but stranger things have happened.  After having my carbs off 9 times in 2 weeks, I now don't rule anything out

I'm sure it's got to be something simple (and possibly annoying).  Carbs are going to be the death of me....

[rm56]

Your floats are either out of adjustment or sticking open. When a float sticks instead of the needle stopping fuel flow it just starts pissing out your overflow and everwhere else such as your stacks, after the bowl fills up. Put your bowls, adjust the floats, and clean the main needles, to do it right you should use a float guage. Z-1 Enterprises sells them. Oh and I would not recommend you smoke around your bike unless your don't mind loud explosions.

[TerryK]

Float level has nothing to do with fuel backfiring out of the stacks. On carbs without accelerator pumps, when you whack the throttles open you create a momentary low vacuum condition causing a "backfire" that will spit fuel out the intake bell of the carb until the vacuum gets high enough to handle all the fuel. Also if you have your air screws all the way in which means there is no air being fed to the pilot/low speed circuit causing a rich condition. Factory setting for the air screw is 1-1/2 +/- 3/8 turn. Start there.

Keep in mind, no matter how well you have them set up, round slide, non-accelerator pump carbs rarely allow you to crack the throttle wide open without the engine stumbling at least a bit. You have to roll the throttle on. 

[robdrobd]

Ahhhh Terry, that is the simple fix I have been looking for. If 1 1/2 is factory shouldn't it be quite a bit less with all the air coming in from the stacks?

[Nortstudio]

Float level has nothing to do with fuel backfiring out of the stacks. On carbs without accelerator pumps, when you whack the throttles open you create a momentary low vacuum condition causing a "backfire" that will spit fuel out the intake bell of the carb until the vacuum gets high enough to handle all the fuel. Also if you have your air screws all the way in which means there is no air being fed to the pilot/low speed circuit causing a rich condition. Factory setting for the air screw is 1-1/2 +/- 3/8 turn. Start there.

Keep in mind, no matter how well you have them set up, round slide, non-accelerator pump carbs rarely allow you to crack the throttle wide open without the engine stumbling at least a bit. You have to roll the throttle on.

There's the expert we were waiting for   Glad it's something simple.

[robdrobd]

Yep, can't ride today in the east coast anyway. It's a little rainy:)

[Nortstudio]

I'm right there with you!  but Brooklyn got hit WAY less than expected.  I think it might be a good day for me to do some work on the new project

[robdrobd]

I think it's a good day to lay around and watch all the lame chopper shows on cable

[Nortstudio]

I think it's a good day to lay around and watch all the lame chopper shows on cable

not when I could take the carbs apart for the 10th time

[robdrobd]

Ha, good luck with that.

[Nortstudio]

If only turning the air screw would solve the issue I'm having, I would be a happy camper.