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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.
 

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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....
 

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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....
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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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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Discussion Starter #5
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
 

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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.
 

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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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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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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.
 

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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. :thumbsup:
 

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I've looked at a number of options and at this point in time I am going to focus on other matters. I was going to apply the DEI gold heat tape to the carbs, but thought that would look like crap and not yield too much benefit. Then I tried mocking up a heat shield (similar design to the quadrajets), but the challenge is all the linkage connecting the tri powers gets in the way.

Then I thought about the issue more and realize even if I am able to block the majority of radiant energy, the ambient temperature in the engine bay (after running with the hood closed) will still be well over 150* (guess) and the carbs will get heat soaked regardless. According to the www, gasoline has an initial boiling point around 95*F and final boiling point of 200* F and vaporizes at 140*F.
 

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I've looked at a number of options and at this point in time I am going to focus on other matters. I was going to apply the DEI gold heat tape to the carbs, but thought that would look like crap and not yield too much benefit. Then I tried mocking up a heat shield (similar design to the quadrajets), but the challenge is all the linkage connecting the tri powers gets in the way.

Then I thought about the issue more and realize even if I am able to block the majority of radiant energy, the ambient temperature in the engine bay (after running with the hood closed) will still be well over 150* (guess) and the carbs will get heat soaked regardless. According to the www, gasoline has an initial boiling point around 95*F and final boiling point of 200* F and vaporizes at 140*F.
Nothin' but negativity. :yesnod: How 'bout rigging up a carbon dioxide fire extinguisher and giving it a shot on the carbs/top of the engine to cool things off? Could rig it up with some duct tape, bailing wire, and a pull cable. :thumbsup:

I don't think it is the underhood temps that are of the biggest concern, its the direct heat applied to the carbs from the engine as the engine temps go up once you shut the engine off and water circulation stops in the cooling system - so all cars with carbs would experience heat soak and we would all have starting issues.

Think about it. Boiling point of 95 degrees? Don't know of too many cars that would not have that number when thermostats are 160-195 degrees. I think what you are trying to do is minimize the direct heat under the carb to minimize the boil-off and make starting quicker - not necessarily right off the key at first turn. A fully charged battery & good spinning starter is also a plus - it'll get the fuel pump pumping faster.

I was told by one guy that this is one of the reasons why the aftermarket add-on fuel injection set-ups are becoming more and more popular - they don't have the start-up problems like a carb does with the ethanol fuel. Don't know how true this is.
 

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Discussion Starter #13
I was told by one guy that this is one of the reasons why the aftermarket add-on fuel injection set-ups are becoming more and more popular - they don't have the start-up problems like a carb does with the ethanol fuel. Don't know how true this is.
Fuel injection setups use a high pressure setup from the tank, thus increasing the effective boiling point quite a bit. As such, fuel injected setups don't experience vapor lock like a carb setup, nor do they experience the gas boiling (which is what most of us have).

My setup works fine as long as i keep the throttle ~1/3 down as I crank the hot motor - it will fire right up.

Chris
 
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