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Post by rcq92130 on Aug 15, 2014 19:51:57 GMT -5
My brand new Gy6 (600 miles, well broken in) is getting only 9 or 10 psi vacuum at the intake manifold ... compared to 18 or so for a normal auto engine.
Anyone know if this is typical for these engines?
Due to the vacuum-driven fuel pump?
Anyone tried using an electric fuel pump?
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Post by geh3333 on Aug 16, 2014 3:35:47 GMT -5
" not good " I was going to use a different word but that will work ,LOL . Yeah many of these scoots use vacuum to open a fuel valve that allows for fuel to flow to the carb , and since the vacuum isn't the greatest there tends to be problems with the system . That's why others and myself remove this valve and added a regular shutoff valve . It's basically a backup safeguard anyway since the float in the carb will shutoff the flow of fuel when it fills with fuel . Like I said though many " not all have these " some are an actual vacuum fuel pump " depending on where the gas tank sits " . But yeah the vacuum is pretty weak.
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Post by geh3333 on Aug 16, 2014 3:45:56 GMT -5
To the electric fuel pump, if your tank is ubove the carb " behind and atop the seat " then u shouldn't need one , u can just get bigger fuel line remove the terrible vacuum valve and run it from the tank to a filter to the carb . If u need an actual pump u can switch to an electric one .
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Post by rcq92130 on Aug 16, 2014 9:22:37 GMT -5
Thx, GEH, for your replies.
The tank on my hog is under the floor (below feet), so the vacuum device is really a pump. I presume it uses vacuum to compress a spring ... then at some point the vacuum in the device is released & the spring pushes a diaphragm which pushes fuel. So vacuum is constantly being released as the 'pump' cycles --- maybe causing the low readings I see at the manifold.
But I don't know what is "normal vacuum" for these engines.
Wish someone here had actual experience with an electric pump on these beasts ....
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Post by rcq92130 on Aug 16, 2014 14:50:28 GMT -5
No one  |
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Post by alleyoop on Aug 16, 2014 15:24:08 GMT -5
What your not explaining is why do you believe its a Vacuum problem what is it that the motor is doing or not doing? You could be chasing the wrong problem. Fuel pumps work just fine, as long as they are always getting fuel from the tank and not have to try and sifon it out of the tank. Your tank is in the floorboards, where does the fuel come out of the top of the tank or from the bottom of the tank to the fuel pump. Also where is your fuel pump mounted, makes a big difference, if the fuel pump is mounted HIGHER than the outlet from the tank. You want gas to be flowing to the Fuel pump all the time so it has fuel to pump it to the fuel filter and or carb. My tank is up front and the fuel pump is on the bottom rail and then the fuel hose from the pump to my fuel filter is a run about 3 feet then it goes up to my carb about 1 1/2 feet no problems whatsoever. What also can makes a difference is how the Vacuum lines are hooked up especially if the scoot has emissions. Here is my Vacuum hooked up and the Vacuum line to the pump is also about 3 1/2 feet long. Alleyoop    |
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Post by rcq92130 on Aug 16, 2014 16:43:04 GMT -5
THANKS, Alley, for responding!
1. Re: "why".
Scooter was not behaving well since I removed all the emissions stuff - idle is rough & often stalls below 1,800 RPM or so, most often when cold. Could be many things (already have set the valve clearance) - incl. enricher, which is still there. Vacuum lines are minimal now, and all are tight --- yet I test and see what for larger engines is very low vacuum, so wondering why that might be. Maybe no one has yet tested for what normal vacuum is ...
Also had (for the first time) cut out at high speed last evening, so I began to wonder about fuel starvation. Looked at the new fuel filter just installed (below the level of the fuel) and saw it was only half full (it's clear, so you can see) - even though the outlet is below gas level. Even after removing the outlet hose - with gas freely coming out - the level in the filter remained at half. Got another new filter today and it seems better.
2. Tank is below floor, pump is 6 or so inches above the top of the tank, about at carburetor level (that's the OEM configuration). Have replaced all the OEM fuel and vacuum lines.
3. Vacuum lines: Very few now. Two nipples on the intake manifold - one goes directly to the fuel pump; the other to the side of the carb. That's all. Both are new hoses and clamped.
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Post by geh3333 on Aug 17, 2014 21:20:39 GMT -5
What your not explaining is why do you believe its a Vacuum problem what is it that the motor is doing or not doing? You could be chasing the wrong problem. Fuel pumps work just fine, as long as they are always getting fuel from the tank and not have to try and sifon it out of the tank. Your tank is in the floorboards, where does the fuel come out of the top of the tank or from the bottom of the tank to the fuel pump. Also where is your fuel pump mounted, makes a big difference, if the fuel pump is mounted HIGHER than the outlet from the tank. You want gas to be flowing to the Fuel pump all the time so it has fuel to pump it to the fuel filter and or carb. My tank is up front and the fuel pump is on the bottom rail and then the fuel hose from the pump to my fuel filter is a run about 3 feet then it goes up to my carb about 1 1/2 feet no problems whatsoever. What also can makes a difference is how the Vacuum lines are hooked up especially if the scoot has emissions. Here is my Vacuum hooked up and the Vacuum line to the pump is also about 3 1/2 feet long. Alleyoop I'm curious. Alley I see u have the 62mm bbk but what type of head do you have , and also are those pics of your scoot above " showing the pump and carb " ? |
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Post by tvnacman on Aug 18, 2014 4:56:50 GMT -5
10 to 15" at idle , then it drops to about 5" upon opening the butterfly , on the decell about 20" . working the a/f ratio you can get some more say 13 to 18" .
John
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Post by rcq92130 on Aug 18, 2014 8:54:43 GMT -5
THANKS, John !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
So mine (at 10, idle) isn't atypical. I wonder why these engines run so low (compared to car engines, which generally at 18 at idle).
Are you saying, though, that 10 @ idle is an indicator of improper f/a mixture?
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Post by tvnacman on Aug 18, 2014 9:11:50 GMT -5
I played around with the vac gauge a bit . I would imagine with a more restrictive air filter the vac would be higher .
I don't have a good fine feel for air fuel mix , but I did see a difference in the vac gauge while working the adjustment .
I'm thinking its a small piston , I notice sometimes the fuel system needs to be primed cranking vac is low or weak .
John
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..BAD TO THE BONE..
