Click on image for the lowdown. 
====
| | | Forums66 Topics128,034 Posts1,055,544 Members48,425 | | Most Online14,466
Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
| | THANKS!
For helping keep this great
old truck web site
on the Internet for over 30 years! and not clogged down
with Ads!  Again, thanks!
| | | | Joined: Jul 2003 Posts: 38 Apprentice | | Apprentice Joined: Jul 2003 Posts: 38 | Hey bolters,
I have a 39 GMC, 228 with the orginal Zenith caburetor. When the engine is hot, 180 degrees, the engine floods.
This will happen about 10-15 minutes after the engine is shutdown. I varified this by waiting and looking down the carb.
The engine is timmed correctly and has a steady 18 inches of vacuum at idle.
How can I solve this percolation problem?
Thanks, Jim
Jim
| | | | | Joined: Jul 2004 Posts: 5,708 'Bolter | | 'Bolter Joined: Jul 2004 Posts: 5,708 | Jim,
I missed class the day they studied '39 GMC's, but most old Chevrolet's has a phenolic spacer located between the manifold and carburetor to act as a thermal insulator.
This kept heat from crawling up and doing exactly what you describe. Does your truck have one of these insulators under the carburetor?
Stuart | | | | | Joined: Jul 2003 Posts: 38 Apprentice | | Apprentice Joined: Jul 2003 Posts: 38 |
Stuart,
I do have an insulator block. I was also thinking, perhaps the float is too high.
The carb was professionally rebuilt and the truck runs great. So I'm not sure about changing the float level.
Thanks for your input,
Jim
| | | | | Joined: Mar 2002 Posts: 9,115 'Bolter | | 'Bolter Joined: Mar 2002 Posts: 9,115 | Does your heat riser valve work? It could be just a flooding carb and I guess in that situation, full throttle position is the way to clear it until it starts. | | | | | Joined: Jul 2003 Posts: 38 Apprentice | | Apprentice Joined: Jul 2003 Posts: 38 | E. Gabster
The heat riser valve works good.
To get it started after sets awhile is to keep the throttle full open.
Thanks, Jim
Jim
| | | | | Joined: Aug 2005 Posts: 6,377 Ex Hall Monitor | | Ex Hall Monitor Joined: Aug 2005 Posts: 6,377 | I had a hard starting hot problem. The solution was a combination of things. High amp battery (Optima Redtop 6v), 1 gauge cables (no body had 0 gauge) and learning to not step on the gas pedal when starting hot. They all have some heat transfer because of the way the manifolds are made so there's a tendency for a carb to percolate some. Stepping on the gas pedal only squirts more gas into a rich condition. It usually only takes a few seconds of cranking when hot to fire up now.
Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.
| | | | | Joined: Nov 2000 Posts: 582 Shop Shark | | Shop Shark Joined: Nov 2000 Posts: 582 | I also had a hard starting problem when hot. Increased the gauge of the battery cables to heavy duty to the starter. No more problems. Didn't seem to be associated with the crappy Rochester. | | | | | Joined: Mar 2005 Posts: 1,513 'Bolter | | 'Bolter Joined: Mar 2005 Posts: 1,513 | Scroll down this page until you see the "hard starting-hot " paragraph. Also look and see if your fuel line is making contact with a heater hose. http://www.thecarburetorshop.com/Troubleshooting.htm
1952 1300 Canadian 1/2 ton restomod You Tube | | | | | Joined: Jul 2003 Posts: 38 Apprentice | | Apprentice Joined: Jul 2003 Posts: 38 | Thanks for the info on the gasoline. I will try to start the engie using that method.
No, the gas line does not touch any hoses, and clears the engine block.
Jim
| | |
|
|
