There is a fellow on ebay that rebuilds several of the mid sixtes AFB carburetors and in his video he states that 3 pounds is the most pressure you would want to use because of the newer gas that is being used today. The reason I'm interested is my newly rebuilt 1963 AFB leaks fuel in the intake when off. It also runs rough I guess because of the extra fuel. Person that rebuilt my carb said I had a fuel pump pressure problem. I put a gauge on the fuel line and ran engine and it show 5 pounds. Is 5 pounds to much pressure or should I have pump built to 3 pounds. The pump is airtec purchased from one of the corvette parts dealers.
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Re: Fuel pressure for an AFB car 1963
I've seen that eBay video and examined the guys carbs - poorly rebuilt with incorrect screws and most converted to electric chokes (because manual chokes never work he says). I wouldn't believe anything he says. 5 pounds is near perfect for both WCFBs and AFBs (I run both)...
Your AFB may have percolation issue or perhaps the float level is too high....or trash in your needle valves; I don't see fuel pressure as being the culprit if your measurement is accurate... -
Re: Fuel pressure for an AFB car 1963
Five psi is nowhere's near enough pressure to unseat the needle. Your problem is internal to the carb if it's dripping fuel.
SteveComment
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Re: Fuel pressure for an AFB car 1963
agree with frank and steve.mikeComment
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Re: Fuel pressure for an AFB car 1963
Shop Manual says the fuel pump should put out 5 1/4 to 6 1/2 psi to function correctly.Comment
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Re: Fuel pressure for an AFB car 1963
Chester, I'm in agreement with all of the boys here......
When it's Off, the fuel pump is Off too, so it cannot be that causing it. You don't say when it drips when "off". Do you mean after a run at temperature, then "off"? Or at cooled temp and "off". I'd bet when hot.
If so, you have the common Heat Soak issue and percolation. Yes Ethanol can play a role as it boils at a lower temperature than the fuel. My 283 2x4 glass bowl filter will show bubbling after a hot run and heat soak. It's weird seeing that. In nearly 30 years of ownership, it only bubbles with the Ethanol fuels. I also get some dripping down the venturis when heat soaked. Next cool start clears it out.
RichComment
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Re: Fuel pressure for an AFB car 1963
Call your rebuilder back and tell him you measured the fuel pressure and its within specs and see what he says.
If he's honest he'll want the carb back to investigate further.Comment
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Re: Fuel pressure for an AFB car 1963
I could write a book about all the measures I've taken to reduce the hot soak effects on my 63 L-76 (340 hp). The most notable being the use of non-ethanol base gas (I can only get 90 octane near me) with Maxlead 2000 additive. I do agree with some of the eBay video in that I too could never keep a standard hot air choke working for very long. I went to electric, but mainly as part of my program to eliminate all metal to metal connections to the carb to avoid heat transfer. The L-76 is the worst case scenario what with the aluminum intake, steel fuel line to a steel filter mounted on the hot water manifold, etc. If the fuel pump is operating correctly it acts as a check valve to hold the fuel in the line, but then during hot soak, the fuel expands and percolates in that line and is able to push past the needle/seat to the point that if you are using standard float settings you will get fuel drip out of the primary clusters. Mine got so bad that my oil would get contaminated with fuel washing down the cylinder walls. My local auto parts store refused to accept my drain oil it was so bad. A lot of rebuilders are using new aftermarket fiats too that weigh in less on my gram scale.
Well, as you can see, I can go on and on about this subject. Suffice it to say I now have my situation developed about as best that can be without major reverseable changes. BTW, my electric choke is one I bought from J.C. Whitney years ago (don't laugh). It uses a thermal control mounted on the intake manifold to control the current to the heating element in the choke housing. It also effectively acts to close and open the choke valve with the assistance of the vacuum pull off. It's a beautiful piece, much better than Edelbrocks.
Stu FoxComment
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Re: Fuel pressure for an AFB car 1963
I simply wired open the heat riser on the passenger side exhaust manifold on my '63; then installed fuel injection intake manifold gaskets to block off the intake heat passages and I run all day long in Orlando heat with zero issues... Some also block off the "hot slot" passages in the intake - I didn't...
I've never had a minute problem with the hot air chokes on my '63 or '61 carbs...Comment
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Re: Fuel pressure for an AFB car 1963
Chet, I lowered my float level by 1/16 from the factory setting to stop the fuel drip and have no ill effects, Ethanol tends to perk the fuel from the heat when shut down.New England chapter member, 63 Convert. 327/340- Chapter/Regional/national Top Flight, 72 coupe- chapter and regional Top Flight.Comment
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Re: Fuel pressure for an AFB car 1963
Talked to the builder of carb and he said send it back and he would try to find the problem. Thanks everyone for your replies.Comment
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