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Hot start/ heat soak issues. Carb guys help out

COCHEV

COCHEV

1/2 ton status
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Jul 9, 2002
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Washougal WA
So the ol' burb starts great every morning, but she hates to start say 20-30 min after being shut off hot. Shut it off and start it again right away. No prob. Wait a bit longer and I have to give say 1/4 pedal and she rumbles to life, idles a bit rough for a bit then good to go.

The research I've done only leads to people talking about remote selenoids n such. She doesn't turn over any slower in the heat. I think its a fuel thing.

Carb is a q-jet. Rebuilt. New float set to spec. Plugs epoxied. Thick gasket, etc. Stock tired 350 no headers.

Any suggestion besides fuel injection. I've had this issue on my last 2 carbed rigs. Is this just the joys of carburetion? Ive had tons of carbed rige tho. I've also heard that the ethanol can cause these issues too...I think we are 10% eth up here

Thoughts...
 
I have to do the same thing with my stuff. Virtually all my trucks have been like that. I think it just has to do with the carb not having a "light choke" feature. The carb is designed to start cold via the choke. And then after its "not cold" anymore, it dont need no choke. But really, the engine has cooled down a bit, and as such, doesnt light off correctly without that perfect fuel mix. At least thats my theory on it.
 
Vapor lock maybe? I had the same exact issue with my '70 Challenger (383). Same exact time frame too - after 20 mins of sitting hot, it would be extremely hard to start and run terrible for 5 mins, got worse in warm weather. Tried high volume mechanical fuel pumps, inspected the lines for kinks or leaks and tore into the sock on the end of the fuel pick up tube. I even tried a plastic spacer under the carb thinking that keeping it cooler would prevent it. None of it worked until I stumbled upon a $70 repo fuel filter for the 440 Six Pack models which came with a built in vapor separator. Hmm...since my car didn't have a return line, I decided to make the 5/16 primary fuel line that was already in the car the return line and added a larger 3/8 line for the feed. I also installed a bigger pick up tube and found a fuel filter that had the vapor separator built in ($3, I think it was for a Taurus) and hooked it all up. Problem pretty much went away 90%, I still get a little vapor lock when the tank is less than 1/4 full.

I always wondered why our factory stock '86 Blazer (350) never vapor locked. Found out that there's a separator built into the mechanical fuel pump (return line looks small like it's only a 1/4). It's been pretty effective since it's never given any problems even in 100 deg weather.
 
My only advice is don't by an edelbrock performer to fix the issue. I have one with an electric choke on the truck and it seems to do the same thing. I also have a edelbrock performer with a manual choke in the blazer, but I can't remember if I have had the same issue. Haven't really driven it enough to remember.
 
Hmmm, I thought all fuel filters were pretty much the same. I took the in carb fuel filter out and have an inline one just before the carb. I've never looked to see if my return line has a vapor separator....

I don't remember any of my older carbed rigs doing this in the past . its only been in the past few years. And yes even a couple rigs with edelbrocks did it too.
 
The new ethanol laced gas definatly increases the tendency for this to happen ...alcohol makes the mixture leaner to begin with,as it has less BTU's than gasoline,and vaporizes at a lower temparature..so when its hot it'll tend to boil away in the carb bowl faster than gas will..the vapor can also make the liquid gas not want to get pumped into the carb bowl,kind of an air lock situation..

A thick gasket or phenolic insulator block under the carb will help this,but might cause grief next winter when temps dip below 50 and its damp out,frost can form on the venturi and cause carb icing and stalling..

If the vehicle still has the stock heat riser or EFE valve,be sure its in the open position when its hot,its rare for the vacuum operated ones to stick open though,due to a return spring being built into the diaphram to make it return to the open position should the diaphram fail...but the vacuum supply hoses or rhermal switch could let vaccum activate it when it should be open too..some guys use the block off plates in Fel-Pro gasket sets to block off the heat riser passages in the intake manifold so no heat gets under the carb to prevent vapor locking and fuel from boiling off in the carb bowl..in colder climates this might cause carb icing though..

The return line setup does help prevent this trouble too,if your vehicle lacks this it might pay off to add one to it..most vehicles built after 1968 or so had the charcoal canister and return line to the fuel tank,so even if the canister is missing the line should still be there to hook a return line to--if the fuel pump has only an in and out fitting and no provision for a return line,you can get a metal fuel filter that has a third nipple for vapor return,they used them on old 60's Buicks and AMC cars,if I had my WIX book handy I could list the part number ,but its in the garage..

Older Q-jets sometimes had the well plugs leak badly and that can flood a hot engine easily..there are foam plugs and epoxy kits to seal them up to prevent that too...

I dont know if any fuel additives might help this condition,but a few old timers I waited on in the parts stores claimed a little marvel mystery oil in the gas or even diesel or kerosene made the gas less likely to vaporize as rapidly and they swore it cured their hard hot start problems in their motor homes..
 
I knew this was ethanol related, but hadn't looked into any cures. My buddy is having the same troubles with his VW Thing... This ethanol is ruining all things that I have been messing with this summer. Cars, trucks, boats. It's BS.
 
E-P-A !!.


....if we still had the same gasoline formulation we had back when we had carbs I'm willing to bet 99% of all issues with them would vanish...but we might be swimming in smog too though..:rolleyes:..

The guys who added Marvel Mystery Oil used to put a quart in a full tank of gas--but their motor homes probably had 50+ gallon tanks,I'd say a pint would be more than enough in a 20 gallon tank...might make a little smoke,but it'll do more good than harm keeping the valves and top end clean..

You guys should see the troubles the air cooled engines on mowers ,tractors and weed whackers have on this ethanol crap--especially the 15% formulation...I'm lucky to mow all my yard before the tractor starts sputtering and dying when its hot out,I have to keep pulling the choke out and leave it in the "sweet spot" to keep it running,and often it wont run under a load like with the blades on..a lot of water can stay dispersed in this ethanol gas so no doubt thats half the problem!..

I have to nurse it back to a shady spot and go for a cold drink--once it cools off some it runs great again--for another 5,15,or 30 minutes...sometimes it'll run great all day,other times it acts like the fuel boils away before it gets to the carb or something...
 
diesel4me said:
E-P-A !!.


....if we still had the same gasoline formulation we had back when we had carbs I'm willing to bet 99% of all issues with them would vanish...but we might be swimming in smog too though..:rolleyes:..

The guys who added Marvel Mystery Oil used to put a quart in a full tank of gas--but their motor homes probably had 50+ gallon tanks,I'd say a pint would be more than enough in a 20 gallon tank...might make a little smoke,but it'll do more good than harm keeping the valves and top end clean..

You guys should see the troubles the air cooled engines on mowers ,tractors and weed whackers have on this ethanol crap--especially the 15% formulation...I'm lucky to mow all my yard before the tractor starts sputtering and dying when its hot out,I have to keep pulling the choke out and leave it in the "sweet spot" to keep it running,and often it wont run under a load like with the blades on..a lot of water can stay dispersed in this ethanol gas so no doubt thats half the problem!..

I have to nurse it back to a shady spot and go for a cold drink--once it cools off some it runs great again--for another 5,15,or 30 minutes...sometimes it'll run great all day,other times it acts like the fuel boils away before it gets to the carb or something...
Click to expand...

Sounds good to me,I'll try it out.
 
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