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After fuel pump number 3 it's finally running (1978 403 V8), took it for a short drive and among other issues I noticed it is seeping some fuel on the top of the airhorn coming out of the accelerator pump stem. I had noticed this issue before I parked it to deal with bad heads, I thought it was flooding but it wasn't. The fuel pump at the time was starting to die. I adjusted the float down a bit to see if that would do anything, apparently it hasn't except to cause another fuel delivery issue. Regardless, this isn't because of flooding, and the accelerator pump doesn't seem to be the original. Would putting an O ring help it to stop seeping fuel or do I just replace the pump assembly?
No. Don't add an inappropriate O-Ring. Buy a brand spanking new Accelerator pump. Note in the Quadrajet manual(s) & CSM the various adjustments which you should perform on the accelerator pump linkage - be meticulous, little adjustments make a difference. Mike (Mike's Carburetor Parts) provides an excellent image tutorial.
The pump on a Q-jet is not a tight fit. A little seepage wont hurt a thing but there really should not be fuel anywhere near it. Are you sure the bowl vent isnt clogged somehow ? Allowing pressure to build up ? Are you sure your float isnt sinking ?
No. Don't add an inappropriate O-Ring. Buy a brand spanking new Accelerator pump. Note in the Quadrajet manual(s) & CSM the various adjustments which you should perform on the accelerator pump linkage - be meticulous, little adjustments make a difference. Mike (Mike's Carburetor Parts) provides an excellent image tutorial.
The pump on a Q-jet is not a tight fit. A little seepage wont hurt a thing but there really should not be fuel anywhere near it. Are you sure the bowl vent isnt clogged somehow ? Allowing pressure to build up ? Are you sure your float isnt sinking ?
It had been seeping out and running slightly down the front of the carburetor. Since this is a driving car I'd rather it not leak fuel onto a hot engine, over time it will build up. Is the bowl vent that open slot behind the primary choke flaps? I'm not sure how that can be clogged unless I'm missing something. The float is 100 percent not sinking, it might be sticking occasionally and is definitely misadjusted but it does float. This seepage was a problem before I parked it because of bad heads, I'm trying to get all the carburetor issues knocked out in one go.
Ok the model number is 17058253. So generally what circumstance is occurring in a non-flooded carburetor to cause fuel to come out the stem when the accelerator pump is being used?
Ok the model number is 17058253. So generally what circumstance is occurring in a non-flooded carburetor to cause fuel to come out the stem when the accelerator pump is being used?
Generally, they don't leak fuel from the accelerator pump stem, if they do it's: (1) incorrect float level; (2) high fuel pump pressure (overcoming needle & seat); or, (3) faulty accelerator pump piston - as in the accelerator pump itself is not centered in the bore likely the result of a poorly manufactured accelerator pump (piston). Degraded accelerator pump components is another possibility.
If you're 100% sure on the float level you can eliminate that issue. You stated the accelerator pump was replaced. That's not surprising since the components wear over time. However, if you buy a new accelerator pump (my suggestion) purchase a high quality accelerator pump from a reputable carburetor shop e.g. Cliff Ruggle's, Mike's Carburetor Parts, Quadrajet Power.
I am curious to know about something though. With the car not running, if you work the accelerator pump (throttle) does fuel begin to leak WITHOUT the engine running i.e. eliminating the possibility it's fuel pressure related? If so, you can most likely eliminate excessive fuel pressure since the fuel pump isn't running.
Finally, a clogged vent (debris) could be suspect and the worst-case scenario would be warped/fatiqued bowl assembly or bowl cover assembly. If you inherited this issue, I'd suspect faulty accelerator pump as my 1st option. If that fails, move to next level of remediation (gunk/debris restriction fuel flow is a possibility.
Some later Qjets have a lip seal where the accelerator pump comes out of the air horn. I'm not sure if this 78 carb has one or not. I know the 1980s CCC carbs have them. These seals are nearly never replaced during a rebuild since they are staked on the underside of the air horn.
I had a q-jet professionally rebuilt that leaked badly from the accelerator pump less than a year later. Apparently the cup wasn't ethanol resistant (I run 93 with ethanol) because it was mush.
Generally, they don't leak fuel from the accelerator pump stem, if they do it's: (1) incorrect float level; (2) high fuel pump pressure (overcoming needle & seat); or, (3) faulty accelerator pump piston - as in the accelerator pump itself is not centered in the bore likely the result of a poorly manufactured accelerator pump (piston). Degraded accelerator pump components is another possibility.
If you're 100% sure on the float level you can eliminate that issue. You stated the accelerator pump was replaced. That's not surprising since the components wear over time. However, if you buy a new accelerator pump (my suggestion) purchase a high quality accelerator pump from a reputable carburetor shop e.g. Cliff Ruggle's, Mike's Carburetor Parts, Quadrajet Power.
I am curious to know about something though. With the car not running, if you work the accelerator pump (throttle) does fuel begin to leak WITHOUT the engine running i.e. eliminating the possibility it's fuel pressure related? If so, you can most likely eliminate excessive fuel pressure since the fuel pump isn't running.
Finally, a clogged vent (debris) could be suspect and the worst-case scenario would be warped/fatiqued bowl assembly or bowl cover assembly. If you inherited this issue, I'd suspect faulty accelerator pump as my 1st option. If that fails, move to next level of remediation (gunk/debris restriction fuel flow is a possibility.
Fuel pressure is 100% not the problem. I confirmed with a friend that I had watching the vacuum gauge and he told me the reading was 5-8, only I didn't realize until now he meant 5-8 inHg as this was on the suction side. Which translates to 2.5-4 psi. Better than the 1.5 psi the last one was pulling but now I'm not confident fuel pump no 3 is good enough. Still, clearly the carburetor has problems too so I'll readjust the float back up to stock as well as replace the accelerator pump with one I have from Quadrajet Power. It never occurred to me the one that's in there could just have been Chinesium junk.
I had a q-jet professionally rebuilt that leaked badly from the accelerator pump less than a year later. Apparently the cup wasn't ethanol resistant (I run 93 with ethanol) because it was mush.
Anyone remember when the cups were leather? Seems like eons ago.
Well put the new accelerator pump on, hosed down the carburetor pretty good including idle circuits. Made no difference at all, there's still fuel leaking out the pump stem. I'm at a complete loss......
As said, a small leak is not that big of a deal. It won't build up - it'll evaporate extremely quickly. It just makes a smear because oil and dirt will get swept up in the gas and then deposited when it evaporates. It's extremely unlikely to cause a fire unless it's a constant stream of fuel. If this is the only problem then it might be best to just ignore it.
The plunger is usually the problem because if it doesn't make a good seal then the fuel can spray back up towards the air horn instead of being squirted out the pump holes. Did the new plunger have a blue seal? Those tend to be better. Some of them also have a garter spring to keep the seal spread open. Take a close look at the bore for scratches/gouges.
It really does sound like high fuel level to me. A float that isn't completely sealed will fall a bit. Or a float set too high. Or a needle/seat that's slightly worn will still let fuel pass until the float gets forced up high enough to close it. Or a fuel pump that's putting out more than 7 PSI on the outlet. I've never head of anyone testing a mechanical fuel pump by checking the amount of vacuum on the suction side. Definitely a good method, but sounds like a PITA to set up.
If it was me, I would do a full rebuild with a new float and new needle/seat. But I'm also a firm believer in the Unnecessary Parts Cannon Philosophy. I very specifically do not advise anyone to follow my faith.
As said, a small leak is not that big of a deal. It won't build up - it'll evaporate extremely quickly. It just makes a smear because oil and dirt will get swept up in the gas and then deposited when it evaporates. It's extremely unlikely to cause a fire unless it's a constant stream of fuel. If this is the only problem then it might be best to just ignore it.
The plunger is usually the problem because if it doesn't make a good seal then the fuel can spray back up towards the air horn instead of being squirted out the pump holes. Did the new plunger have a blue seal? Those tend to be better. Some of them also have a garter spring to keep the seal spread open. Take a close look at the bore for scratches/gouges.
It really does sound like high fuel level to me. A float that isn't completely sealed will fall a bit. Or a float set too high. Or a needle/seat that's slightly worn will still let fuel pass until the float gets forced up high enough to close it. Or a fuel pump that's putting out more than 7 PSI on the outlet. I've never head of anyone testing a mechanical fuel pump by checking the amount of vacuum on the suction side. Definitely a good method, but sounds like a PITA to set up.
If it was me, I would do a full rebuild with a new float and new needle/seat. But I'm also a firm believer in the Unnecessary Parts Cannon Philosophy. I very specifically do not advise anyone to follow my faith.
Yes the new plunger did have a blue seal. I thought like you the issue was a high fuel level, but since this also occurred when I was tracking what turned out to be a bad fuel pump and I knew the fuel level in the carburetor was low I'm pretty sure that's not the issue. I even adjusted the float down anyway and it made no difference.
One thing that comes to mind is I noticed the air horn gasket does seem to like wicking up fuel like a sponge, any ideas on how to prevent that?
Well got it up and running with the double air horn gasket, I did notice a difference as far as seepage out the front. However it's still leaking quite a bit out the accelerator pump stem, no change. I'm wondering if putting on a small o ring or lip seal will solve it.
