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Old 10-27-2008, 11:55 AM   #1
1970heavychevy
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runs great, at first

My 70' 350 with Edelbrock carb fires right up. Takes off with a lot of power. Then after about 3 miles, it bogs, surges a little. I have to give light throttle just to barely get home. WOT and it just barely goes. It's a blast to drive up to that point.

List of what I've done in the past month.

New fuel lines, filters, pump, put in a regulator.
New distributor cap, button, module, coil, plug wires and plugs.
New battery, alternator and rewired engine compartment with new wire.

Does it sound like its time to rebuild the carburetor?
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Old 10-27-2008, 12:00 PM   #2
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Re: runs great, at first

Are you running a heat spacer between the carb & manifold. I was told that is an issues with the Edelbrocks. I forgot what exactly it's technical name is, but I know I was told to get one for mine as that would be an issue, the heat effecting the carb.

Otherwise, the only other thing I can think of is a choke issue.
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Old 10-27-2008, 12:02 PM   #3
1970heavychevy
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Re: runs great, at first

Yeah it has the heat spacer.
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Old 10-27-2008, 12:26 PM   #4
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Re: runs great, at first

Is your fuel tank vented?
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Old 10-27-2008, 12:32 PM   #5
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Re: runs great, at first

Is there crud in your fuel tank? I bought a 79 gmc and the fuel tank was full of rust and such, it would clog the fuel filter in bout 5-10 minutes. Pull over, take filter off, clean, and it would run another 5-10 minutes, then repeat the process.
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Old 10-27-2008, 12:35 PM   #6
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Re: runs great, at first

Might check your fuel filter again, sounds like once the bowl runs out its starving for gas.
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Old 10-27-2008, 12:40 PM   #7
1970heavychevy
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Re: runs great, at first

Both the filter near the tank and the one next to the carb are clean. The sock in the tank was changed out about 3 years ago.
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Old 10-27-2008, 12:41 PM   #8
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Re: runs great, at first

But is the tank vented? Drive without the gas cap on (if the tank ain't near full and stay away from the twisties!) and see if it still dies.
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Old 10-27-2008, 12:48 PM   #9
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Re: runs great, at first

Did you do a compression check?
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Old 10-27-2008, 01:53 PM   #10
1970heavychevy
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Re: runs great, at first

I'm not sure if the tank is vented. There is no charcoal canister or vent tube so I think not. The cap that's on it is a twist on, old school look. Maybe original. Compression check is next in line. Just have to by the gauge.
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Old 10-27-2008, 01:54 PM   #11
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Re: runs great, at first

Twist on that didn't make since. Their all twist on.
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Old 10-27-2008, 02:07 PM   #12
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Re: runs great, at first

Drive w/out the gas cap in, but put a rag in it to keep gas from spilling out. Then it can ventilate.
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Old 10-27-2008, 02:16 PM   #13
1970heavychevy
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Re: runs great, at first

I really don't think any of it is vented. The cap is solid (no holes in the top). And there is no charcoal canister. I will try that, it seems to simple of a fix.
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Old 10-27-2008, 05:39 PM   #14
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Re: runs great, at first

The old cap is vented. I went ahead and put a new one on anyways. I guess carb or compression. Just not sure any more.
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Old 10-27-2008, 05:50 PM   #15
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Re: runs great, at first

Wire open the choke if you have one.
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Old 10-27-2008, 05:54 PM   #16
1970heavychevy
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Re: runs great, at first

It's open at idle. Does it close at WOT?
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Old 10-27-2008, 07:10 PM   #17
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Re: runs great, at first

The truck should have originally had a vented cap, like you said. If you put on a new, not vented cap, the truck will run fine until the tank starts sucking in on itself, then it will cut off and die. Put the old cap back on, or run it without a cap on, just to elimate that as a problem.
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1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc
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2001 Jeep Wrangler Sport 4.0L 5spd
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Old 10-27-2008, 07:14 PM   #18
1970heavychevy
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Re: runs great, at first

I put a new vented cap on. The old one was vented also just a brittle gasket. What do you know about wiring the choke open like (2bits) said?
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Old 10-27-2008, 07:20 PM   #19
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Re: runs great, at first

Quote:
Originally Posted by 1970heavychevy View Post
I put a new vented cap on. The old one was vented also just a brittle gasket. What do you know about wiring the choke open like (2bits) said?
Sorry, I misunderstood. There have been quite a few people who post symtoms like yours and it turns out it was their gas cap!

Sorry, I'm not much help with carbs, mine's electric (the choke.)
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Old 10-27-2008, 07:41 PM   #20
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Re: runs great, at first

Thanks anyways
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Old 10-27-2008, 07:48 PM   #21
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Post Re: runs great, at first

What brand of module did you get? If it's just the generic parts store no name brand I would bet that it's your problem, if it's a accel, msd, or OEM it should be good to go but the cheap ones dont last very long at all. I put a summit brand dist in my truck and It acted just like what yours but It tested fine at the store until I tapped on it, I put the dirty old GM one back in and it's still working fine
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Old 10-27-2008, 07:52 PM   #22
1970heavychevy
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Re: runs great, at first

It runs great for about 5-10 minutes out of the gate. Wouldn't the module cause it to run bad from the start?
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Old 10-27-2008, 08:05 PM   #23
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Re: runs great, at first

no it heats up as the truck is running and then it takes a crap did you use the thermal paste? brand of module?
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Old 10-27-2008, 08:08 PM   #24
1970heavychevy
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Re: runs great, at first

I did use dialectic grease. But I was having this problem before and after buying the new module. What are the odds of both being crap.
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Old 10-27-2008, 09:48 PM   #25
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Re: runs great, at first

I would say check for vacuum leaks. It sounds to me like the truck runs fine until the choke opens up. Once the choke is open the truck is running so lean it won't hardly run. That.s where I would start.
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