No start when hot- '62-340 hp

[Rob Edwards]

I have about 100 miles on a rebuilt 327-340 and am running into problems with hot starting. I read thru the archives and came up with some culprits, but I thought I'd ask your thoughts on some things.
Without any basis for comparison, she seems to take more cranking than I would expect when cold, but she will start and runs fine (especially after setting the timing correctly yesterday!) The problem is, if I shut her off I'd better have something to do for 20-30 minutes before she'll start again. Temp gauge doesnt work but the upper rad hose is right at 195-200oF (with an IR therm) after a 10 mile drive. (Has the correct repro Harrison aluminum rad and a NOS waterpump) When cranking hot, the starter does not seem as strong, so either the starter is par-boiled or it's a tight, new motor (Brand new battery, with Battery Tender on it at night). Another issue is this gas percolation I've read about. She has the stock #3795397 aluminum intake and 3269S carb, but the PO put an aftermarket fuel pump and plumbed it with flexible rubber hose and some clear plastic inline fuel filter.

OK- so what's going to make the most significant difference in beating the heat-soak issue?
1) I have ordered the pump-to-filter stainless fuel line, filter and filter-to-carb nipple in hopes that moving the fuel line away from the block might help (though now I'm worried that I won't be able to hook it up given the location of the outlet on the non-stock fuel pump).
2) Should I pull the intake and block off the crossovers (maybe helps with percolation in the carb bowl?) What gasket does one use for that?
3) Is there any way to put a heat shield over the starter or solenoid that'll actually do anything?
4) Is this just a 'tight' newly rebuilt engine and I just need to go out and drive the thing?

I'm trying to keep this car as original/correct as possible (with the knowledge that there are about a million little things wrong with it), so I'd like keep these fixes as minimally invasive as possible.

Thanks and sorry (again) for verbosity!

[Wayne Pope (722)]

Re: No start when hot- '62-340 hp

Put some miles on it before you get too excited. Do you see a perculation problem or are you guessing?

[Terry Deusterman (11486)]

Re: No start when hot- '62-340 hp

Agree with Wayne, put some more miles on it. Also check the archives about setting the timing correctly for this car, it is very important. John Hickley wrote an excellant article in the Corvette Enthusiant a couple months back.

Usually hard starting when hot is weak starter, weak battery or bad connections. Recheck all your cables and wires, pulling the starter to have checked is not that big of a job. Just my 2 cents.
Terry

[Mark Hedberg (30810)]

Same Hot Starting Issue - '64 327/300

I have about 500 miles on the rebuild of my L75. Cold she fires up immediately. Hot, I have to crank and crank it with my foot pressing the accellerator all the way to the floor. I have a stock engine, including the proper three pieces between the intake and the carb, but the carb is a new Edelbrock 600 CFM w/electric choke (search for an original Carter is another story). Edelbrock suggested adding another insulator right under the carb and even sent me one for free. About 3/8". Could that actually help?

I have not blocked anything on the intake other than the two carb preheat holes.

[Stephen Phillips (38702)]

Re: Same Hot Starting Issue - '64 327/300

I'd be interested if you find a solution. I've also got an Edelbrock 600 cfm on my L75 and have to depress the gas pedal all the way to get it to fire up when hot. The car turns over fine, but doesn't want to fire up. I formerly had the problem with the starter acting as a heat sink and solved that with a remote solenoid. I know it's not original but my car is a driver. I figured that the current problem is the electric choke, but haven't taken the time to try changes there.

[Duke Williams (22045)]

Re: Same Hot Starting Issue - '64 327/300

If you have to floor the throttle to allow hot starting you might have a flooding problem, which could be caused by too high a float level or a leaking needle and seat.

When the engine is good and warm after a drive, remove the air cleaner prior to shut down, then shut down the engine and carefully observe the fuel discharge nozzle in the primary venturi. If you observe fuel dribbling out after shutdown, either the float level is too high or the needle and seat is leaking.

Duke

[Clem Zahrobsky (45134)]

Re: Same Hot Starting Issue - '64 327/300

if you see what duke posted drop the float level about 1/16" to 1/8" and see what happens. having owned these cars with aluminum intakes when they were new i always blocked the heat riser cross over for better performance.

[Rob Edwards]

Clem: A question:

Clem-

Keeping in mind I'm younger than the car and a chevy SB newbie, could you indulge a stupid question and let me know what one uses to block those crossover passages? Is it a different gasket, or sheet aluminum cut to fit, or ??? Thanks!

[Clem Zahrobsky (45134)]

Re: Clem: A question:

the way i did it was to drain down the rad,loosened all the manifold bolts,used a screwdriver to pry up on the intake and installed stainless steel shim stock plates in between the 2 intake bolts where the heat riser passages are located on both sides of the intake. you must use .005/.007 thick stainless steel shin stock because any other material will burn thru from the hot exhaust gasses. you can also buy special intake gasket with the crossovers blocked but make sure they use stainless steel as anything else will burn thru. make sure that your heat riser valve on the exhaust manifold is also blocked open.

[Rob Edwards]

Re: Clem: A question:

Great, Clem, thanks for the response. I'll give it a shot when I get her back from the tranny rebuild.

-Rob

[Duke Williams (22045)]

Re: Clem: A question:

Many years ago I blocked the heat risers on my '63 340 HP and found performance to be unsatisfactory. After the choke was off the engine would stumble badly on initial start from a dead stop until the engine had been running for at least twenty minutes. I pulled the shims out within a few days. The heat riser is there to evaporate the liquid fuel, and without it the mixture can go lean because some of the fuel puddles in the plenum below the carb and will not evaporate quickly enough.

Check that your heat riser is free and consider wiring it open. This is what I ended up doing.

These cars didn't flood when new. Find and correct the source of the flooding before you block the heat riser.

If you do block the heat riser, just block one side, but BE SURE TO WIRE THE VALVE OPEN. By blocking on side some exhaust heat can migrate up under the carb, but it will be considerably less than with both sides open. If you block one or both side of the heat riser passages and do not wire the valve open, the RH exhaust will be completely blocked when the valve is cold and closed.

Duke

[Clem Zahrobsky (45134)]

Re: Clem: A question:

duke you may have been having carb icing which can happen up certain conditions with no manifold heat. i ran all of my aluminum intake engined cars with no heat and never had any problems except when near freezing temps so i just let them warm up for a few minutes. some of these cars even had the cold air intake thru the plenum in front of the windshield. NEVER do this with a cast iron intake because there is not enought heat transfer for street driving. the gas now days is the problem because you can hear it bubbling in the carb after shut down. GM fixed part of this problem with the return line to the tank from the fuel pump so there was no pressure on the needle/seats after shutdown.

[Rob Edwards]

Re: Clem: A question:

Guys-

This car is in Laguna Beach,CA and will never see temps below 40oF. The PO cheaped out on the fuel lines, which are rubber from the aftermarket fuel pump, with a clear plastic fuel filter about 3" before the carb, with another rubber hose going to the carb. I drove her about 25 miles this morning to Anaheim (4,000 rpm at ~75 mph- how restful!) and 5 minutes after shutoff the upper rad hose was at 225oF and the gas was literally boiling in the filter housing. (She puked a bunch of coolant, I'm having the cheapo octagonal Stant cap pressure tested, a correct 13-pounder is on its way) Now I'm worried that between bad percolation and the cheapo aftermarket fuel pump (maybe too much pressure?) that I'm going to hurt the carb somehow. For what it's worth, I have been running her on 100 octane pump gas from 76 Unocal with some CD-2 lead substitute.
I have the correct stainless fuel line, fuel filter, and carb nipple coming from CC, so hopefully that'll buy me a little bit of heat sinking for the percolation issue. Next dumb newbie question: How best to wire wire open the heat riser valve? Thanks!

[Duke Williams (22045)]

Re: Clem: A question:

I don't think it was carb icing - just lean mixture due to fuel puddling.

When the engine is cold simply open the heat riser vavle and use some stainless steel safety wire to hold it open - weight down.

The '62 340 HP engine does not have vacuum advance, which will increase operating temperatures. Suggest you run 16 degrees initial advance. With 100 PON fuel it should not detonate, and you don't need any additives.

Duke

[Stephen Phillips (38702)]

Re: Clem: A question:

Rob, Instead of wiring the heat riser valve open, you can buy the spacer for the fuel injection model and it provides an open passageway. If you're lucky, someone used brass nuts on the exhaust header bolts or this may be difficult.