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Posted by: Gint Mar 21 2004, 08:15 PM

It's been a looong time since I had a good old fashioned 'murican carb'd V8. My 72 Chvy truck has had an ongoing hot start issue. After running it to full temp and shutting it off and coming back to start after 10 minutes or longer (until it cools off anyway, then everything is fine), you have to open the throttle at least half way to get it to start. And then it runs like crap for a few minutes. Then all is well again. I've suspected fuel boiling for a while now, so I rebuilt the Edelbrock 600 carb today to verify float settings and general health of the carb.

Today after I finished it and drove it and warmed it up, I waited 10 minutes and then tried to restart. The problem still exists. I pulled the air cleaner off and I could hear fuel bubbling. There was fuel leaking from the secondary throttle shaft on the right side of the carb as well. Taking the carb top off revealed fuel in the right side bowl still bubbling a tiny bit. The float bowl is dumping fuel into the secondary cavity and causing the leak at the secondary throttle shaft and dumping fuel into the manifold. So root cause is determined. I have a buddy that is going to give me a phenolic spacer and gasket that I will install later this week.

Is this fairly typical?

Posted by: rick 918-S Mar 21 2004, 08:24 PM

Sounds like a fair assessment. Fuel will expand when hot. But check the needle and seat again and power valve for leaking. I seem to recall a blown power valve will allow fuel to leak through passages in the metering block into the venturies.

Posted by: Gint Mar 21 2004, 08:27 PM

Thanks Rich. But everything is good as I just rebuilt the carb today and measured everything, including the acclerator pump valve.

Posted by: PatW Mar 21 2004, 09:30 PM

Holley's like to blow the f'in power valve. Another is the plate warping makes the thing impossible to seal. Alaways had bad luck with Holley's.. Some people swear by them. My cars ran better with Q-Jets, but not faster. Get a Q-Jet and save yourself a lot of headaches. IMHO.

Pat

Posted by: Gint Mar 21 2004, 10:50 PM

I forgot to mention it's an Edelbrock Performer 600 (square bore). Not too old either. It's on a Performer aluminum intake as well. Q-Jet copy yes?

Posted by: PatW Mar 21 2004, 11:36 PM

All Q-Jets are spreadbores. What you have likley is a Carter AFB copy. I've known folks that have gone through a whole shelf of Holley's before they got one that would work right. Maybe you just have a bad one?.

A Q-Jet.. AKA Rochester Quadra-Jet


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Posted by: Gint Mar 21 2004, 11:41 PM

Now I'm more confused. Mine doesn't look like that.

It's a http://www.edelbrock.com/automotive/carb_square.html


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Posted by: PatW Mar 21 2004, 11:49 PM

Yup, that be Carter AFB copy.. Never took one of those apart, don't know my sh!t about that. <_<

Sorry about the Holley thing. I should have paid more attention in your orginal post.

Pat

Posted by: Gint Mar 21 2004, 11:53 PM

No sweat. Thanks for the replies. You made me think and actually look into my carb a little more. I should have done that first anyway.

But the original question still stands. I'm wondering if anyone knows if this is typical behaviour or if there is a problem that needs fixin'.

Posted by: Gint Mar 22 2004, 04:33 PM

Anybody? All you V8 guys awake?

Posted by: John2kx Mar 22 2004, 04:58 PM

Gint,

I run the same carb you have in my 914. Was concerned with vapor lock due to no airflow in engine bay but have not had that problem in 18 months car has been on road. Had a 1" spacer installed between carb and intake from engine builder but removed it to clear engine cover with my choice of air filter.........still no vapor lock or fuel boil issues.

Sorry, but can't offer any help.

John

Posted by: John2kx Mar 22 2004, 05:02 PM

Gint,

Sorry for the confusion but I'm running a 600 Holley and not the 'brock as you show in pic. They look identical from the pics..........I've got to get back on the rum : )

John

Posted by: rick 918-S Mar 22 2004, 07:10 PM

Don't know the Carter that well. I know the Q-jet had an internal leak they designed a repair kit for. I think I remember it consisted of a funny shaped piece of sponge! Does the Carter copy have a metering rod setup? If so they were easy to damage and then caused an internal leak.

Posted by: DuckRyder Mar 22 2004, 07:26 PM

Q-Jets are bad about leaking from the well plugs on the bottom.

WEBER/CARTER/EDELBROCK dont have similar plugs AFIK.

I'd put the spacer in and maybe lower the float level slightly.

If you look at the side of the carb, you will probably find a Weber emblem...............

Posted by: Rgreen914 Mar 23 2004, 03:24 AM

Ran a couple of small blocks with Q-jets and never had any real problems; it's been way too long since I took an AFB apart to remember much about them. You might try some sort of insulation on the metal fuel line from the mechanical pump (if you have that sort of stock set-up); in the old days guys at the drag strip would wrap aluminum foil around the metal line. Probably an under carb spacer (phenolic) would help.

Posted by: Rgreen914 Mar 23 2004, 03:34 AM

Just remembered, back in the 70's, some drag racers used to run these aluminum sheets under the carbs as heat sinks; they sat under the carb, were about twice the size of the carb base gaskets and were sandwiched between two gaskets. They were considered part of the "hot set-up" for Super Stock/Stock racers.

Posted by: Gint Mar 23 2004, 08:46 PM

1/2" phenolic spacer went on this evening. Preliminary results look good. Tomorrow will tell after I drive it home from work.

Thanks all.

Posted by: andys Mar 23 2004, 09:53 PM

Gint,

I'm assuming intake and exhaust manifolds are stock. Check first to see if your heat riser valve is stuck closed, as they often can in an older vehicle. If stuck closed (or partially closed), it will send exhaust gasses through the intake manifold under the carb, and heat it up real good. A phenolic spacer might cure the symptom in this case, but not the cause. Might also check the EGR valve to see if it perhaps isn't stuck open, as well as a closed thermal valve in the air cleaner horn. If fuel is boiling in the carb, I'd look for a heat source.

Andy

Posted by: Gint Mar 23 2004, 09:56 PM

Thanks Andy. Intake is an Edlebrock Performer aluminum unit, exhaust are stock manifolds. 72 Chevy truck didn't have an EGR though. But that little block on the manifold under the carb could be a heat riser of some type. I'll look closer at it tomorrow.

Posted by: andys Mar 23 2004, 10:14 PM

Gint,

I don't know for sure about this particular manifold, but many after market street manifolds have provision for the heat riser system (warms up the manifold durring cold start to help atomize the fuel). The heat riser valve is usually located at or near the junction of the exhaust header and the exhaust pipe. It is a spiral wound bi-metal spring which operates a butterfly valve to choke off the exhaust on one side. If the small shaft at the center of the spring doesn't move (or move freely), then it's stuck. Some performance intake manifold gaskets have a knock-out for the heat riser passage in case you choose not to use it.

Andy

Posted by: Gint Mar 23 2004, 10:18 PM

You're talkin about an exhaust heat riser. Gotcha. I know what that is. Don't have one of those either. The intake has a little box on it with a cover just under the carb. Coincidentally, right under the right side of the carb where the issue mainly is.