Phenolic insulators
 

Has anyone used the phenolic insulator kit our host sells? I'd like to know if it actually improves the hot start situation and also if you can still use the ram air pan since it raises the carbs 3/8"

I fought the hard start when engine was HOT years ago when I first got my car(65 GTO). It got a little worse when I went with 2 1/2" exhaust. A mini starter cured the problem. I later put phenolic spacers under all three carbs, but 1/4" ones. No problem with ram air pan. I do not think it will cure hot start problem , but just a guess. Easy enough to try however.

Dave

Dave, thanks for the input. The mini starter definitely took care of the hot crank problem. I'm reading about the fuel in the carbs heating up, making it hard to start and was curious if the phenolic insulators helped at all.

Good to know they clear with the ram air pan, I'd hate to give that up.

The spacers should help as their purpose is to isolate the carbs from the manifold and prevent the heat from boiling away the fuel in the bowls. There was a good article on this in Hemmings Muscle Machines, January 2015 and I believe this was also covered in HPP.

Ethanol is hygroscopic which means it attracts water out of the air so ethanol based fuels have a lower boiling point than non-ethanol fuels. That makes it more susceptible to vaporizing in the float bowl (or in other parts of the fuel system) causing vapor lock, especially after a period of heat soak. The author ran a series of tests at different temperatures and the car started without hesitation. It took about four to five seconds to start at the very high temp test but was considered acceptable as it wouldn’t start under those conditions prior to the install of the spacers.

Other users are happy with their results. As long as there are no clearance issues with your current set you have nothing to lose by giving them a try.

Info from Jon Hardgrove:

FUEL LEAK BY THROTTLE SHAFT(S)
A common complaint today is fuel dripping out of the throttle body by the throttle shaft AFTER the engine is switched off. While a number of issues may cause this problem, by far the most common issue is the volatility of modern fuel. Mechanical fuel pumps have a check valve which prevents fuel from moving back to the fuel tank. The problem is as follows:

(1) After the engine is switched off, heat from the engine heats the fuel in the fuel line.

(2) The expanding fuel (increased volatility) creates pressure in the fuel line from the pump to the carburetor.

(3) The check valve prevents the fuel backing up through the fuel pump.

(4) The pressure increases to a point the float/fuel valve combination in the carburetor cannot withstand the pressure.

(5) An amount of fuel (usually from a teaspoon to a couple of tablespoons) flows into the fuel bowl of the carburetor.

(6) This raises the fuel level in the bowl above the main discharge nozzle(s).

(7) Fuel flows through the main discharge nozzle(s) and drips onto the throttle plate(s) which is/are closed, and exits out beside the throttle shaft(s) dripping onto the intake.

Possible solutions:

(1) IF POSSIBLE, AVOID ETHANOL LACED FUEL! Sometimes you can buy real gasoline at a marina

(2) Buy the lowest octane name-brand fuel that does not ping or detonate in your engine (the higher grades often have more ethanol)

(3) Install a “vapor return line” (take a look at return lines used on many factory air-conditioned cars)

(4) Learn to live with the issue.

HARD STARTING, HOT

Difficult starting of a hot vehicle from 5 minutes to an hour after the engine has been operated, can be caused by the volatility of modern fuel. If you have this problem; try using the following method to start the engine: DON’T touch the footfeed (VERY important). Crank the engine over from three to 5 seconds (different vehicles will respond to different times); and then GENTLY (so as not to activate the accelerator pump) press the footfeed approximately 1/3 of its travel. The engine should start, and may run rough. Run the engine at a high idle for about 10 seconds. This issue is caused by volatility of modern fuel. Once the engine has been shut off, the gasoline is heated by the latent heat of the engine, and percolates the fuel from the bowl into the throttle area, forming a mixture that is too rich to fire. If you push the footfeed to the floor (as has been the traditional method of “unloading” a flooded engine) the gasoline continues to flow into the engine (again due to the volatility). By not touching the footfeed, you do not open the throttle plates, and the engine will pump the overrich mixture out of the tailpipe. Once the overrich mixture has been alleviated, gently opening the throttle will allow the engine to start.

THROTTLE BODY GASKETS

Beginning with the 1957 carburetors, Rochester started using throttle body gaskets (the gasket between the throttle body and the bowl assembly) that have slots in the sealing surface, thus not making a complete seal of the two castings ON CERTAIN CARBURETORS ONLY! Not all carburetors use them. This is only one of the reasons we want a tag number when we supply a kit, as our kits are manufactured (by us) to the original Rochester bill-of-material. The correct gasket will be in the kit. The slots were provided to allow pressure in the venturi area to be bled to the outside of the carburetor during hot city driving thus helping to prevent stalling during hot city driving. For all you die-hards (or hardheads) – there is no vacuum leak! These slots are above the throttle plates!! Are you still a die-hard? Here is a link to a reproduction of the original Rochester bulletin introducing the slotted gaskets. ROCHESTER BULLETIN Here is another link showing a slotted gasket, a regular gasket (often used for marine carbs) and some other hot idle compensation devices HOT IDLE DEVICES.

Link:
http://www.thecarburetorshop.com/Troubleshooting.htm

I put these spacers on my tripower this summer. But first i drove it for 2 hours and then used one of those lazer thermometers, the after effects were 18 degree drop in temp on the fuel bowls.

That's a significant drop in temp. Did it improve the hot start problem?

It never happened again, but my problem was it would boil after sitting then when i started it and hit traffic it would try and die on me, running a dead head electric fuel pump doesn't help, i'll run a return line once i don't feel lazy.

ahnuld,
By any chance, are you using a ram air pan along with the insulators? If so, are there any hood clearance issues? Thanks

I have no clearance problem with 1/4 inch spacers. don't think there would be a problem with 3/8 spacers. Providing you have the hood bracing cut properly.

wrong pic. , can't fix