hard starting when warm

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ccockrell
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Joined: Tue Aug 04, 2020 5:20 pm

hard starting when warm

Post by ccockrell »

I have a 63 with a 80 hp engine. When I first start the car it starts immediately and drives well. At take off and when shifting up and accelerating I get a hesitation with a little bit of a popping noise through the exhaust while driving. When the engine is warm the engine is very hard starting but will ultimately start. When I park the car in the garage after driving it, I notice a strong smell of gas with possibly a small amount of fuel on the outside of the carburetor. I haven't been able to track it down 100% but it appears to be coming from the top of the carburetor. Is it anyone's opinion that these are all separate issues or issues that cause my hesitation and hard warm starting? I hope this all makes some sort of sense to you all. Thanks in advance.

joelsplace
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Re: hard starting when warm

Post by joelsplace »

Make sure the accelerator pumps both squirt.
Check the float level.
Check the fuel pressure - it is often too high.
113 Corvairs, 5 Ultravans and counting
Northlake, TX

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bbodie52
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Re: hard starting when warm

Post by bbodie52 »

The purpose of the thick plastic spacer and gasket pair between the hot air-cooled aluminum heads and the aluminum carburetors is to block some of the heat transfer that would otherwise take place. That heat could cause gasoline to boil and vaporize in the carburetors, which would disrupt engine operation. You may want to remove the carburetors and inspect the gaskets and spacer that should be there. Sometimes a previous owner may remove and reinstall the carburetors and simply install a single gasket. Or it may be that a reinstalled plastic spacer was inadvertently cracked or damaged upon installation, which could cause a vacuum leak. If you have a vacuum leak, or an overheating carburetor body with possibly boiling/vaporizing gasoline in the carburetor body, this couldbe the cause of your poor operation and hard-starting issues.

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bbodie52 wrote:I wanted to make sure that some important insulators were not accidentally omitted when your car was worked on in the past…

Carburetor rebuild kits often contain a thin gasket to seal the underside of the carburetor where it mounts on the intake manifold. The Corvair carburetors need a plastic insulator to isolate the base of the carburetor from the intake manifold, which prevents the gasoline inside the carburetor from boiling or vaporizing if excessive heat is allowed to transfer from the hot aluminum intake manifold on the cylinder head to the carburetor body. These plastic insulators can be easily damaged when removed. Clark's Corvair Parts bundles gaskets and insulators together. They are listed near the top of page 56 in the catalog http://www.corvair.com/user-cgi/catalog ... ow_page=56.

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:angry: If the insulators are not present, and only a single gasket is being used under each carburetor, the fuel may be close to boiling when the car is driven. The use of fuel may allow some effective cooling of the fluid in each float bowl as fuel is consumed and replaced with cooler liquid from the tank. But when the engine is shut down the remaining heat from the heads may continue to heat the gasoline in the float bowls of the idle engine, causing the gasoline to percolate and appear as it drips from the venturi cluster in each carburetor. :evil:
This diagram may be of help in confirming your vacuum connections. The vacuum advance MUST be connected to the vertical "spark port" on the right carburetor. The vertical port only applies vacuum to the vacuum advance mechanism as the throttle is opened, to bring the vacuum advance timing into play at low to medium throttle settings. The horizontal vacuum port is directly connected to full intake manifold vacuum, and is intended to activate the choke pull-off diaphragm to partially open the choke butterfly the moment the cold engine starts. Connecting the horizontal port to the distributor vacuum advance would engage full vacuum advance at engine idle, which is too much timing advance at the wrong time.

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The attached carburetor service manual is a useful and informative supplement to the shop manual...

:chevy:
Attachments
DELCO ROCHESTER - Models H, HV Carburetor Service Guide.pdf
DELCO ROCHESTER - Models H, HV Carburetor Service Guide
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Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible

joelsplace
Posts: 1163
Joined: Wed Oct 13, 2010 12:51 pm
Location: Northlake, TX

Re: hard starting when warm

Post by joelsplace »

Brad's info is good. Besides insulator problems you could be overheating. Have you looked inside the top shroud for rags or mouse nests?
The vacuum balance tube connectors in Brad's illustration are rubber hoses and a very common source for vacuum leaks because they get cooked being connected directly to the heads.
113 Corvairs, 5 Ultravans and counting
Northlake, TX

ccockrell
Posts: 4
Joined: Tue Aug 04, 2020 5:20 pm

Re: hard starting when warm

Post by ccockrell »

Thank you very much for the priceless info! I don't see anything that could be blocking airflow and I don't see or hear any signs of overheating. I will take each piece at a time to see what I can come up with. Thanks again!

66vairguy
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Re: hard starting when warm

Post by 66vairguy »

Hot starting (within about 20 minutes of shutting off the engine) is not uncommon on a 62-63 carburetor. GM received a lot of complaints and in 64 added the vapor vent at the bottom of the carburetor (hugely misunderstood as it lets cool air in to vent fumes up into aircleaner NOT OUT INTO ENGINE COMPARTMENT). Either go with the 64 carburetor, or let the engine cool off before re-starting it.

The other issue is today's gasoline. When the lead was removed (a long time ago) octane dropped and so did engine performance and economy. The gasoline refiners finally got the octane back up by changing the refining process. This made the gasoline more volatile (not an issue with fuel injection). On a hot day after a long drive I've heard the gasoline in the bowls literally boiling!!! Of course after a few days the carburetors are dry. This is why many have gone to electric fuel pumps to prime the carbs and avoid vapor lock at the fuel pump.

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