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Topic: Can't prime the carb

in Forum: C3 Fuel, Emission Control, and Exhaust Systems

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Can't prime the carb (1/9)
4/7/19 2:44pm

Christian
Former Member
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Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 193

Some guidance would be appreciated here. I can't fire up the engine because, apparently the gas does not make it to the carburetor. The carb stays dry. The first time, I suspected the fuel filter. I checked it: It was soaked with gas and looked fine (neither clogged nor dirty), so I put it back. Tried again to start the car: It fired up like a charm. Once, the engine starts, it runs fine and does not seem to starve from gas. Obviously, the fuel pump works. If I start the engine shortly after shut it down, it starts fine. After a night however, I am back in the same situation. It looks I can't prime the car when cold/fry. Can't figure out why.

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Re: Can't prime the carb (2/9)
4/8/19 11:31am

Norsky

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Burke, VT - USA

Vette(s):
SOLD - "The Toy" - '70 Convertible
SOLD - "The Beast" - '90 ZR-1 (#682)
SOLD - "Betty" - '28 Ford Model A Tudor
Still have - "BLKBRRD" - '78 Pontiac Trans Am

Joined: 1/23/2002
Posts: 7190

What carb is it? Holley, Q-Jet, ??? Has it been rebuilt recently? When a friend and I rebuilt the Q-Jet on "BLKBRRD" during the "putting it back together" process we forgot to do one tiny little step that stops the float bowl from slowly draining. So I have had a similar problem with starting the car after it has sat for a bit. Same day starting has not an issue. When the car has sat it takes a bit of cranking (it usually takes several 10 second cranks) to get fuel back into the carb but it has always started.

Many, MANY years ago I had a fuel issue with my daily driver. Most of the time it would start and run fine but it would occasionally just die. Then after a bit it would start up and run fine. Not wanting to get stranded somewhere I took it in to get checked out (the car was still under warranty). Everything in the fuel system checked out fine but the mechanic had a hunch. He pulled the fuel pump off and opened it up. What he found was one of the internal valves had come apart so pieces were floating around inside. He theorized that occasionally a part would lodge itself blocking off the fuel flow. A new fuel pump solved the problem.

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Jim Olson

"The Toys"...!!! Save the Wave!

Where I've been in a Corvette...!!!

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Re: Can't prime the carb (3/9)
4/8/19 5:40pm

Christian
Former Member
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Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 193

Norsky said: What carb is it? Holley, Q-Jet, ??? Has it been rebuilt recently? When a friend and I rebuilt the Q-Jet on "BLKBRRD" during the "putting it back together" process we forgot to do one tiny little step that stops the float bowl from slowly draining. So I have had a similar problem with starting the car after it has sat for a bit. Same day starting has not an issue. When the car has sat it takes a bit of cranking (it usually takes several 10 second cranks) to get fuel back into the carb but it has always started...

Thank You Norsky for sharing this.

It is a Q-Jet. And Yes, it has been (professionally) rebuilt recently.

It sounds like your experience is VERY similar to mine.

What exactly is the "one tiny little step that stops the float bowl from slowly draining"?

My fuel pump is fairly new (a year or two), so I would not expect it to be the problem.

|UPDATED|4/8/2019 2:40:43 PM (AZT)|/UPDATED|

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Re: Can't prime the carb (4/9)
4/8/19 10:35pm

F4Gary

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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
Posts: 1409

What do you mean by "prime the carb"? Accelerator pump?

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Re: Can't prime the carb (5/9)
4/9/19 1:19am

Norsky

Many years ago "Zen-Master Ken" (kstyer) had put together a most excellent step-by-step how-to rebuild a Q-Jet and it was published on another member's web-site but unfortunately the article is no longer there. If I remember correctly when you're about halfway through putting it back together the float bowl plugs need to be checked to make sure they are properly sealed. If they're not the float bowls will keep draining. To correct the problem with my carb meant having to partially tear it down (again), fix the issue and then put it back together again. At the time I didn't want to fool with it and have just lived with the problem. (I'm now in the process of replacing the carb with a TB EFI unit so...)

Someone with more carb rebuilding experience than I can chime in on what to do but I just did quick Google search for "how to rebuild a rochester quadrajet carb" and several things to look at popped up.

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Jim Olson

"The Toys"...!!! Save the Wave!

Where I've been in a Corvette...!!!

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Re: Can't prime the carb (6/9)
4/13/19 12:32pm

daveo76
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Vancouver, WA - USA

Vette(s):
1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.

Joined: 8/25/2005
Posts: 857

I would recommend two books for all those running q-jets.

1. Cliff Ruggles. https://www.amazon.com/Rochester-Carburetors-Revised-Doug-Roe/dp/0895863014/ref=sr_1_fkmrnull_2?crid=RX2H7OY1CPLD&keywords=cliff+ruggles+quadrajet&qid=1555172390&s=gateway&sprefix=cliff+ruggles%2Caps%2C192&sr=8-2-fkmrnull

2. Doug Roe. https://www.amazon.com/Rochester-Carburetors-Revised-Doug-Roe/dp/0895863014/ref=sr_1_fkmrnull_2?crid=RX2H7OY1CPLD&keywords=cliff+ruggles+quadrajet&qid=1555172390&s=gateway&sprefix=cliff+ruggles%2Caps%2C192&sr=8-2-fkmrnull

In that order. I rebuilt my q-jet myself step-by-step with Cliff's book. And used his rebuild kit that is designed for ethanol fuel. I used it untested after the rebuild to start and break-in the cam on my engine that I rebuilt at the same time. Wasn't the smartest idea in the world and I was pretty nervous about it, but it worked out fine. Both engine and carb are running fine 7 years later. I haven't even really had to touch the carb. Engine fires very consistently after 3-4 seconds of cranking when cold. And hot starts are no problem either.

|UPDATED|4/13/2019 9:32:29 AM (AZT)|/UPDATED|

______________

1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.

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Re: Can't prime the carb (7/9)
4/13/19 9:43pm

F4Gary

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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
Posts: 1409

Christian, you should PM Lars over on Corvette Forum. That's his handle and he is the go to guy on rebuilding and tuning QJets.

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Re: Can't prime the carb (8/9)
4/15/19 8:28am

Christian
Former Member
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Houston, TX - USA

Vette(s):
1971 LS5 Convertible 4 sp

Joined: 2/25/2003
Posts: 193

Thank you guys for your insights.

The problem is now crystal clear for me indeed: It is just that the bowl drains when the car sits for 24 hours or more. If I put some gas in the carb before cranking, it fires up like a charm. Otherwise, it takes 40 seconds, which is a lot for the battery. But it starts eventually.

I keep the information regarding rebuilding the carburetor which was just rebuilt. It works fine beside this issue. SO, I guess I willl live with it for now, until I am tired of it.

Thanks y'all.

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Re: Can't prime the carb (9/9)
4/15/19 12:56pm

Adams' Apple

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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 20128

The well plugs on the bottom of the main body are leaking. MOST carb kits come with a small rubber-like sponge to insert under the plugs before bolting on the carb base, to stop the leak. They don't really stop it, just slow it down. The real fix is to clean the area, and use a small mount of JB Weld on the plugs to seal them. Some have gone as far as removing the plugs(soft lead plugs), tapping the holes, and inserting screws/bolts into them to seal the leak. That's a bit much, for me. The JB Weld will fix it for much longer than the rubber band-aid in the kits, and costs less than having the main body machined for screws/bolts.

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