Carb puking gas
Pro
Joined: Jun 2009
Posts: 613
Likes: 3
From: Fleetwood PA
That fuel seems like it's under pressure some how to be spitting out like that. If it were heat ,I think you would see more of a flow out the vent tube. If you have a PCV hose going to the carb, make sure it's not gummed up causing back pressure in the carb.
Was it spitting like that with the electric pump or did that start after you put the mechanical on? ( just thinking it might be the mechanical fuel pulse)
I agree with lowering the floats a bit, and making sure they actually float.
Was it spitting like that with the electric pump or did that start after you put the mechanical on? ( just thinking it might be the mechanical fuel pulse)
I agree with lowering the floats a bit, and making sure they actually float.
Advanced
Joined: Apr 2008
Posts: 71
Likes: 0
You are confused about the heat shields. The aluminum shield keeps radiant heat from soaking the fuel bowls. They come with an insulating gasket that keeps the heat from passing from the manifold to the carb. This is where the extra height comes from. You can probably find the extra clearance under the hood, I did. It's usually not as tight as you think. If the clearance is absolutely not there you will have to run a fuel return line, which you might have to do any way depending on how bad your carb heating issue is. As far as the gas not being hot, gas is naturally cold to the touch. If you get over a hot engine on a hot day and touch the wet gas, yeah it's going to feel cold. If we keep this up one of two things is going to happen. 1. Lars finally chimes in and sets you straight. 2. It gets cold outside and your problem mysteriously goes away.
Burning Brakes
Joined: May 2008
Posts: 860
Likes: 0
From: Stratford Ontario
I tried to see what I could find on this and was wondering if Your sure Your metering block has the correct gasket and is not damged. I would also be tempted to lower the primary level slightly just to be sure level isn't too high. The sight plugs are not always in the perfect position for fuel level. This has got to be frustrating. I would pull sight plug out while idleing to see where the fuel level truely is. Use a rag to contain any fuel sepage. 
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
Set the float so that the fuel level is at the bottom of the hole, but not dribbeling out. This is where I set mine and I have to rock the car slightly to get any gas spilling out. Like I said, it cured my problems.
Thread Starter
Instructor
Joined: Oct 2008
Posts: 154
Likes: 5
From: Colorado Springs
I know you said you checked the float levels, but mine was acting very similar to yours. I have a 502 with an 850 DP. I had to lower the floats slightly below where you would normally have them and it completely cured all the problems.
The only way for fuel to shoot out of the vents is if the needle and seat allows fuel to get buy.
Have you checked fuel pressure?
Mine would do this after a while of driving and it would do it randomly.
I have a fuel pressure gauge mounted where I can see it while driving.
I disconnected the return line and ran without it for a while, this caused a my fuel pressure to become unstable. I ran two different fuel pressure regulators and they both did the same thing without the return line connected.
Does yours have a return line? If so check to make sure its connected and verify its not plugged.
Have you checked fuel pressure?
Mine would do this after a while of driving and it would do it randomly.
I have a fuel pressure gauge mounted where I can see it while driving.
I disconnected the return line and ran without it for a while, this caused a my fuel pressure to become unstable. I ran two different fuel pressure regulators and they both did the same thing without the return line connected.
Does yours have a return line? If so check to make sure its connected and verify its not plugged.
I don't have a return line.
I just watched the video again and was wondering if there is either a vacum or pressure build up in bowl. It seems like something is disturbing fuel in bowl. I was wondering what would happen if You placed Your thumb over vent and feel for pressure? Also have You tried running car with sight plug removed? But I would be leary about reving it with sight plug removed. I am going to look at My holley manual on primary side to see if I can see something that can cause that. I have a similar carb and it works great.
That fuel seems like it's under pressure some how to be spitting out like that. If it were heat ,I think you would see more of a flow out the vent tube. If you have a PCV hose going to the carb, make sure it's not gummed up causing back pressure in the carb.
Was it spitting like that with the electric pump or did that start after you put the mechanical on? ( just thinking it might be the mechanical fuel pulse)
I agree with lowering the floats a bit, and making sure they actually float.
Was it spitting like that with the electric pump or did that start after you put the mechanical on? ( just thinking it might be the mechanical fuel pulse)
I agree with lowering the floats a bit, and making sure they actually float.
You are confused about the heat shields. The aluminum shield keeps radiant heat from soaking the fuel bowls. They come with an insulating gasket that keeps the heat from passing from the manifold to the carb. This is where the extra height comes from. You can probably find the extra clearance under the hood, I did. It's usually not as tight as you think. If the clearance is absolutely not there you will have to run a fuel return line, which you might have to do any way depending on how bad your carb heating issue is. As far as the gas not being hot, gas is naturally cold to the touch. If you get over a hot engine on a hot day and touch the wet gas, yeah it's going to feel cold. If we keep this up one of two things is going to happen. 1. Lars finally chimes in and sets you straight. 2. It gets cold outside and your problem mysteriously goes away.
I tried to see what I could find on this and was wondering if Your sure Your metering block has the correct gasket and is not damged. I would also be tempted to lower the primary level slightly just to be sure level isn't too high. The sight plugs are not always in the perfect position for fuel level. This has got to be frustrating. I would pull sight plug out while idleing to see where the fuel level truely is. Use a rag to contain any fuel sepage.
Set the float so that the fuel level is at the bottom of the hole, but not dribbeling out. This is where I set mine and I have to rock the car slightly to get any gas spilling out. Like I said, it cured my problems.
Thanks everyone for the help so far.
Last edited by 68sting; Jul 27, 2010 at 04:18 PM.
Burning Brakes
Joined: May 2008
Posts: 860
Likes: 0
From: Stratford Ontario
Nice pic and nice car. It looks like a similar colour to My 73 vert. Any how I think Your gaskets and installation is correct. I see You have a "whistle" installed which makes it even harder for fuel to get out. When I asked about running without sight plug I meant in park and by hand move accelerator to see what happens. Dont forget the rag, You don't want any fires to add to the problem. I cant see how this is happening? Have You tried running without whistle? not that it should help. I keep checking My carb it is a similar setup and I can't see how this is possible.I know its not heat because mine gets real hot and I don't have a spacer or heat sheild on mine.Its so hot the fuel evaporates immediately after shutting off.Your going to be one of the carb gurus in no time.
Instructor
Joined: Mar 2002
Posts: 140
Likes: 1
From: east hampton ct
I know this is a long shot but do still have a baffle in the float bowl. They do make the long plastic extension version to eliminate this problem in the front bowl during hard acceleration.
Burning Brakes
Joined: May 2008
Posts: 860
Likes: 0
From: Stratford Ontario
I would also try running without the "whistle" it may be a shot in the dark but if it is against something on the end it may be closing the vent. So as you start to drive the fuel leaving creates a vacum until the needle opens and lets the fuel come in with enough force to splash it up and as the bowl fills it pressures enough to spit it out. I can't find any other reason if the float is close to where You say it is. Ive keep looking at My carb and the Holley manual and can't see any other reason for this. I never noticed in the pics but is Your carb the type with dual feeds, or center floats?
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Thread Starter
Instructor
Joined: Oct 2008
Posts: 154
Likes: 5
From: Colorado Springs
Nice pic and nice car. It looks like a similar colour to My 73 vert
asked about running without sight plug I meant in park and by hand move accelerator to see what happens
I know this is a long shot but do still have a baffle in the float bowl.
I would also try running without the "whistle" it may be a shot in the dark
Dumb question. Is this supposed to do this when you plug the vent tube? see video
Burning Brakes
Joined: May 2008
Posts: 860
Likes: 0
From: Stratford Ontario
Thats what makes Me think the whistle is affecting it. I will try that on My car in the morning and get back to You on that. You got Me thinking about that and Ive got to go look at some drawings inside carbs. I will try pluging My air vent and see what happens. Check this post Tommorow. We will solve this somehow.
Burning Brakes
Joined: May 2008
Posts: 860
Likes: 0
From: Stratford Ontario
I just tried covering vent tube and it had no effect on mine . Car ran the same and no fuel came out vent. I was wondering if You have center floats? I think You have vacum in the float bowl but I will have to do some investigating this afternoon I will get back to You.
Melting Slicks
Joined: May 2002
Posts: 2,717
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
Looking at the video your bowl became pressurized when you covered the vent, that's very odd. I've never seen that before. Fuel started flowing from the shooters and out the air bleeds.
We gotta figure out where that pressure is coming from.
Were did you have the electric pump connected?
In one of my earlier post I commented on a leak in the fuel line to the pump and it may be possible for the pump to pull air in, it sure looks like this may be whats going on with your system. I sure would have thought the pump would air lock before it would pressure the bowl up.
Can you snap a pic with the filter base off of the carb so we can see where everything is connected?
Neal
We gotta figure out where that pressure is coming from.
Were did you have the electric pump connected?
In one of my earlier post I commented on a leak in the fuel line to the pump and it may be possible for the pump to pull air in, it sure looks like this may be whats going on with your system. I sure would have thought the pump would air lock before it would pressure the bowl up.
Can you snap a pic with the filter base off of the carb so we can see where everything is connected?
Neal
Melting Slicks
Joined: May 2002
Posts: 2,717
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
watching the video again even after you remove your finger the fuel keeps flowing. Since liquid is not compressible there has to be air in the fuel system.
Neal
Neal
Melting Slicks
Joined: May 2002
Posts: 2,717
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
Don't see anything that jumps out at me as for as being out of place.
If you put your finger over the rear bowl vent will it do the same thing?
If not than it can't be the pump or it would be pressuring up both bowls.
Neal
If you put your finger over the rear bowl vent will it do the same thing?
If not than it can't be the pump or it would be pressuring up both bowls.
Neal
Pro
Joined: Jun 2009
Posts: 613
Likes: 3
From: Fleetwood PA
Definitely getting pressure in the float bowl. The fact that it's not running out the vent( more of a spirt) leads me to believe it's not the float needle or seat. Carbs actually work on differences in pressure(atmospheric) so something is causing the pressure to be way off. It's got to be a line or manifold pushing pressure back into the carb. I would take off and plug every single line going to it....even the big one on the back that I assume is going to you power brake booster. Hook up a vacuum gauge and see what you manifold vacuum is.
Burning Brakes
Joined: May 2008
Posts: 860
Likes: 0
From: Stratford Ontario
Do You know if the check valve is in the accelerator pump housing? When You put Your finger over the vent tube could You feel pressure or vacum? I felt nothing on mine. I would think it would be vacum to pull the needle off its seat. Pressure should hold it in place, and no fuel would get through.Right now the accelerator cuircut is the only thing I can see that could allow this to happen.
Pro
Joined: Jun 2009
Posts: 613
Likes: 3
From: Fleetwood PA
You shouldn't feel anything at the vent tube, it just keeps the float bowl at neutral atmospheric pressure. Ideally, if you plug the float bowl vent the car will eventually die because the fuel is not being allowed to flow out of the bowl( kind of like putting your finger over a straw and holding the soda in it). The problem you have is that when you take your finger off the end of the straw, it shoots out the top, meaning there is pressure at the bottom of the straw.
