Holley Carburetor

[George C.]

I am having hard hot restart/fuel percolating problems with stock a Holley carburetor on a 1970 LT-1. I tried a 1/4 phonetic spacer under the carburetor to reduce the heat transfer, but when I close the hood I hardly have any clearance between the air cleaner and hood. I don't want the engine to rock upon acceleration and bust the hood.

Has anyone else had this problem and how did you solve it?

[Duke W.]

Re: Holley Carburetor

Many are having problems with E10 percolation.

Two thing yous can do to mitigate the situation is wire the heat riser valve open and convert from ported to full time vacuum advance, and you will need to install a B28 VAC as part of the process. Tee into the choke vacuum break line... many threads on this subject.

Also, many have reduced fuel bowl measured temperatures by installing insulation sleeves on the chassis fuel pipe in the engine compartment. There are also threads on this issue with photos and IR gun temperature measurements.

Duke

[Joe L.]

Re: Holley Carburetor

I am having hard hot restart/fuel percolating problems with stock a Holley carburetor on a 1970 LT-1. I tried a 1/4 phonetic spacer under the carburetor to reduce the heat transfer, but when I close the hood I hardly have any clearance between the air cleaner and hood. I don't want the engine to rock upon acceleration and bust the hood.

Has anyone else had this problem and how did you solve it?

George------


You could also use the 1970 LT-1 with EEC insulator. This is an aluminum shield with an attached gasket. Overall, it will be thinner than 1/4" thick insulator gasket. Beyond that, it was used with your exact same intake manifold and hood in PRODUCTION for 1970 LT-1 with EEC (California) applications. So, whatever hood clearance there is using this insulator, it would be the same as GM originally supplied for those applications. The insulator was originally GM #3972156 and, later, GM #3999198. Both are long since GM-discontinued but I believe Dr. Rebuild offers an excellent reproduction.

One curious thing: 1970 LT-1 with EEC used the above referenced insulator. 1971-72 LT-1 (all were equipped with EEC) used the 1/4" thick insulator, originally GM #3989390 and later GM #3999259. However, and interestingly, 1970 LT-1 used a different intake manifold than 1971-72 LT-1. It's possible that, among other possible differences, the 1971-72 manifolds had slightly less height to compensate for the thicker insulator used for those years. I wonder?

[Larry E.]

Re: Holley Carburetor

FWIW-Picture of one discussed is below. GM made these for Holleys and Rochestor 4BBLS. Thanks-Larry

[David M.]

Re: Holley Carburetor

Along with the others advice Ill add this...If your not a numbers guy or going for top flight try this(its all reversible).
Remove the thermo stove flap in the exhaust manifold and weld up the shaft holes(or get another manifold to hack up and save the original)
Next block off the heat crossover in the intake. Both cast and aluminum intakes can have plugs welded into them in such a manner that they could be easily reversed if ever needed. I dont recommend installing the plugs into the heads.

Use the plugs along with the above mentioned tricks (insulator and timing tweaks) and you'll never have a hard start heat soak problem again.

Some suggest slightly lowering the float level too. 1 or 2, 32nds below spec. I did this to my Qjet as they are susceptible to burpin over into the power slots due to the fuel boiling over when static. It did respond favorably. But thats a non issue now that the heats been mitigated.

Verify your timing events and A/F mix is dialed in(use a vac gauge here). An adjustable travel vac advance canister will help to dial in vac adv at hot idle to where you want it. The adjustability allows you to super tune.
Also verify fuel pressure, floats, needle and seat condition(s). A leaky needle n seat can cause these symptoms too.

Never run anything but ethanol free gas in all carbureted machinery...period.

I did all of this to my original numbers 68 442. I solved a 20 year problem. I was tired of the burpin , fartin and smokin at startups at car cruses and shows. Its cold blooded now and needs time to warm up enough to get the choke to open, but who cares its a summer car. I had to tweak the divorced choke to get this to work satisfactorily. An electric choke conversion would solve this but Im going for that stealth OEM look.

Added benefits are nice cold dense charge air into the carb to enhance warm weather throttle response and no more burnt paint on the intake.