Hard starting after the car is at operating temperature - Pontiac GTO Forum
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post #1 of 14 (permalink) Old 10-25-2019, 07:03 PM Thread Starter
 
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Hard starting after the car is at operating temperature

Hey guys
I have a low mileage 67 gto ho that’s pretty much all stock ..original motor ,carb,distributor etc .the car runs strong and fantastic. Brand new battery also . .the starter cranks the motor over strong and fast also . It’s starts first crank very easy when it’s cold ,but when it gets up to operating temperature and I go to start the car it cranks quiet a bit and then finally starts but maybe sounds like it’s kind of loaded up . But when it starts it runs very strong .
Anything I should look at to fix the problem?

Salinas ca
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post #2 of 14 (permalink) Old 10-25-2019, 07:24 PM Thread Starter
 
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The Spark plugs are dry but I’m gonna replace them later

Salinas ca
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post #3 of 14 (permalink) Old 10-25-2019, 07:36 PM
 
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My '66 came with a Carter carb, but now has an Edelbrock. I had similar problems. When the car was shutoff, the gas would heat up and boil over into the intake manifold causing a very rich mixture at startup. I removed the carb and found a thin mounting gasket. I ordered a FELPRO 13834 gasket which is 2 layers fastened together, and is around 1/4" thick. That solved my problem.
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post #4 of 14 (permalink) Old 10-25-2019, 10:31 PM Thread Starter
 
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So a thicker gasket fixed it ...interesting

Salinas ca
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post #5 of 14 (permalink) Old 10-26-2019, 12:11 AM
 
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So a thicker gasket fixed it ...interesting
No it won't ....there are several root causes for hot start problems. Most likely try holding the gas pedal down ~ 1/4 the way when cranking and see if that helps....most likely the fuel has boiled into the intake / car is flooded.

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 14 (permalink) Old 10-26-2019, 12:16 AM Thread Starter
 
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Thanks
How do fix that problem ?

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So a thicker gasket fixed it ...interesting
No it won't ....there are several root causes for hot start problems. Most likely try holding the gas pedal down ~ 1/4 the way when cranking and see if that helps....most likely the fuel has boiled into the intake / car is flooded.

Salinas ca
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post #7 of 14 (permalink) Old 10-26-2019, 09:27 AM
 
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Thanks
How do fix that problem ?
Well depending on which carb you have, you can buy a reflective shield and phenolic spacers (you'll need to get the longer studs too). I have the tri power setup and there is no readily available heat shield, but I do have phenolic spacers. I am fabricating heat shields to see if they help.

While I have seen an improvement with the phenolic spacers, after driving hard and parking the car I can literally hear the gas boiling in the carbs...

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 #8 of 14 (permalink) Old 10-26-2019, 09:28 AM
 
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The thicker gasket will help insulate the carb from the hot manifold, which causes the fuel to boil over into the manifold. On some of my big block Mopars I had to install a 1/2" phenolic insulator between the carb and manifold to prevent the fuel boiling problem. I had considered doing the same thing to my GTO, but the thicker gasket solved my problem. I'm just putting it out there for your consideration.
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post #9 of 14 (permalink) Old 10-26-2019, 12:40 PM
 
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Originally Posted by Raptor View Post
Hey guys
I have a low mileage 67 gto ho thatís pretty much all stock ..original motor ,carb,distributor etc .the car runs strong and fantastic. Brand new battery also . .the starter cranks the motor over strong and fast also . Itís starts first crank very easy when itís cold ,but when it gets up to operating temperature and I go to start the car it cranks quite a bit and then finally starts but maybe sounds like itís kind of loaded up . But when it starts it runs very strong .
Anything I should look at to fix the problem?
When I read this - I interpreted as similar to a hot start issue I have.

So to clarify - is the engine cranking rate the same when cold has hot?

If the heat from the engine transfers to the starter wiring and starter motor - this dramatically increases the resistance in the circuit causing slower cranking. On very hot days (~90) and driving for ~25 mins, mine will not crank at all for ~15mins. I have to pop the hood and wait it out.

DK

<)))>><

"Pray as though everything depended on God. Work as though everything depended on you." - Saint Augustine
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post #10 of 14 (permalink) Old 10-26-2019, 12:59 PM
 
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Yes, it sounds like heat soak. When the car is shut off heat reaches the carb 3 ways....

Conductive, Radiant and Convective...

The fix for Conductive heat transfer to carb is a phenolic spacer under the carb...

The fix for radiant heat is radiant heat shields between the carb bowls and the intake

The fix for convective heat is to open the hood or install a fan system of some sort

You can also wrap your fuel lines with DEI Fire sleeve wrap...

First start with a phenolic spacer, it may fix it and get more
If needed...

We are in winter blend gasoline now and it has a very low distillation curve...boils fast

If you have a hood blanket remove it they hold way too much heat
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

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