Another hot start (not starter solenoid) - Pontiac GTO Forum
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post #1 of 13 (permalink) Old 08-05-2018, 11:03 PM Thread Starter
 
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Another hot start (not starter solenoid)

My car starts wonderfully when cold (with just two taps of the throttle) - fires right up. The car runs great and pulls hard. After driving for a bit and if I come out and want to start it again, I need to hold throttle / gas pedal partially in (car cranks fine).

Setup - 1965 Tri power, with headers, remote starter solenoid, pertronix ignition and phenolic spacers.

I am guessing this means my choke is not set properly (too rich) ? Thanks in advance for your help.

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #2 of 13 (permalink) Old 08-06-2018, 07:07 AM Thread Starter
 
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A quick update from reading last night....Many seem to believe this problem is related to ethanol in the gasoline, which reduces the boiling point, thus causing vapor lock on a hot engine. I'd be curious if people had these problems back in the 60s & 70s, as this data point would substantiate or negate this hypothesis....

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #3 of 13 (permalink) Old 08-06-2018, 05:00 PM
 
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Originally Posted by cij911 View Post
A quick update from reading last night....Many seem to believe this problem is related to ethanol in the gasoline, which reduces the boiling point, thus causing vapor lock on a hot engine. I'd be curious if people had these problems back in the 60s & 70s, as this data point would substantiate or negate this hypothesis....
Had the same problem with my Tripower as well. It would run like crap when the outside air temp was very hot. I did two things, first, installed phenolic spacer between the three carbs and the intake manifold. I got those from Tripower.com, they worked well and stopped most of the heat soak, when the car was stopped. The second thing I did was block off the center carb crossover, in the intake. I don't drive her in the winter, so didn't need the center carb to be heated by exhaust gas running underneath, in the intake. Those things basically solved my problems of fuel boiling.
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post #4 of 13 (permalink) Old 08-06-2018, 07:28 PM
 
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Originally Posted by cij911 View Post
A quick update from reading last night....Many seem to believe this problem is related to ethanol in the gasoline, which reduces the boiling point, thus causing vapor lock on a hot engine. I'd be curious if people had these problems back in the 60s & 70s, as this data point would substantiate or negate this hypothesis....
Yes, the ethanol in the gas seems to cause problems with the hot engine. Some will install an electric fuel pump at the tank to help deliver the fuel better to the fuel pump. The other solution is what Joe's Toy has provided.

In one of my 1960's car magazines where Milt Schornack is wringing out one of the GTO's at the track, he mentions adding an electric fuel pump to the car at the tank to help with the fuel boiling off. Many track runs were done back to back and the engines got hot. Often to get the best times, he would have to let the engine temps cool down, then make a blast down the track.
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post #5 of 13 (permalink) Old 08-06-2018, 09:46 PM Thread Starter
 
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Thanks guys!

Joe - I already have the phenolic spacers from John @ Tri Power (he's great). Unfortunately I failed to block the crossover ports when I installed the intake manifold (ughhhh), so now I either live with burnt paint and hard hot starts or remove , paint, and block the ports. Thanks

Jim - I also read about electric pumps being added to the mix, as well as a return line. The problem I am having though really is the fuel boiling in the bowl and I don't think an electric pump would remedy that problem. Talking to Lars and a few others (non- GTO board guys), the suggestion was to make a heat shield and try to block as much of the radiant heat from the bowls as possible.

And in other news, it looks like my clutch is on the way out......Sigh

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #6 of 13 (permalink) Old 08-08-2018, 09:14 AM Thread Starter
 
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To help reduce the boiling of the fuel while the car is sitting (radiant heat), I will test some Gold Leaf reflective tape on and around the carburetors. I have used this product with high horsepower turbo'd cars before and it helped quite a bit. No idea how good / bad it will look or how it will perform.

I will update the post in a few months after testing and pictures.

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #7 of 13 (permalink) Old 08-08-2018, 05:34 PM
 
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Are you using the Ram Air tub and open hood scoop? The Ram Air set-up was not really about ramming air into the carbs, but rather, allowing cooler outside temp air into the carbs while keep the hotter under hood temps away from the carbs. Might be an option?
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post #8 of 13 (permalink) Old 08-09-2018, 11:52 AM
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Fuel percolation (boiling off in the float bowls after the vehicle is shut down hot) is not the same as vapor lock (fuel vaporizing in the fuel line during operation). That said, spacers will help, but not always cure the percolation situation. An electric fuel pump won't. It'll only help with vapor lock. My '65 GTO (tripower 389) with no spacers never boils off for some reason. Lucky I guess. My '61 Corvette, with dual WCFB 4 bbl carbs boils the gas on hot days at shut off, even with the spacers. Before I installed them, it was much worse, though. Guys on the Corvette forum who drive cross country complain about this problem all the time, and it always seems to go away as soon as they get to another city or state that sells non-ethanol gas. So yes, ethanol gas is super volatile and doesn't like carburetors on hot days.
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post #9 of 13 (permalink) Old 08-09-2018, 02:51 PM Thread Starter
 
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Are you using the Ram Air tub and open hood scoop? The Ram Air set-up was not really about ramming air into the carbs, but rather, allowing cooler outside temp air into the carbs while keep the hotter under hood temps away from the carbs. Might be an option?
I do have the Ram Air tub, but it doesn't act as a heat shield as it rests on top of the air horn.

1965 GTO Convertible 3 speed tri-power drum brakes originally

Current setup:
400 cu in with tri-power
4 speed Muncie
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post #10 of 13 (permalink) Old 08-09-2018, 07:53 PM
 
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I do have the Ram Air tub, but it doesn't act as a heat shield as it rests on top of the air horn.
OK, realize it would not act as a heat shield, was just thinking the cooler outside air above the carbs might help.

The Quadrajet carbs on the late 60's early 70's Chevy's had a heat shield from what I have read - looks like a big plate that goes under the carb and then extends over the intake manifold to keep heat from rising. Looks kind of funky, but supposedly worked. You can still buy them on Ebay.

I suppose you could make something similar out of aluminum plate that would go under the carbs and be large enough to shield the carbs from the intake/engine heat.

Blocking the heat crossover would be on my list. You can get the gaskets that have the block off plates included. While you had the intake off, this may sound silly, why not put a thermal barrier sheet/insulation between the intake and engine on top of the valley pan? I got this catalog in the mail and it offers all kinds of items for heat & sound control. There is a muffler wrap, among other things, that might be cut to fit or check out their other products. There is a downloadable PDF catalog: DEI Introduces 2018 Product Catalog - Design Engineering, Inc Some Mopar big block engines actually used an insulation under their intakes that was said to minimize engine noise coming up from the valley pan, but my guess is that it also reduced temps from the engine getting to the underside of the intake manifold as Mopar under hood temps get quite high.
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