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1970 Chevrolet C20 Custom Camper Pickup
SBC 350, Quadrajet carburetor

I've been having some issues I believe are float related. Wanted to see if my thinking is correct.

Issue #1 - takes a bit of cranking to get it started after it's been sitting. I do have check valve in the fuel filter. This has been going on for a while now. Fires right up when warm. I've also heard this might be the fuel evaporating off. I typically only drive the truck on weekends.

Issue #2 - The other weekend I was driving the truck. Twice, I was pulling out on a road with a 50mph speed limit and a bit of an incline so I was on the throttle about 25-75% for 20 seconds or so when it started stumbling. I let off for a couple seconds and it recovered. I believe it emptied the bowl. That same day I had it out on the highway and it did fine.

After this I changed the fuel filter. I had also changed out my secondary rods. Took it for a drive and it drove great. Good power, good A/F verified with an A/F gauge hooked to a cheap o2.

Issue #3 - This was last weekend. It was about 90* F (32* C) out. Went WOT from ~30mph and it started to stumble almost as soon as the secondaries opened. Later that day, twice, I was pulling away from a light at about 50-75% throttle and when I crossed the street, it started stumbling. Let off and it recovered after a few seconds. Staying less than ~50% throttle, it drove great.

I am thinking it is a fueling issue, not an ignition issue, since when it happens, the engine stumbles for a few seconds, then recovers. I would think if it was ignition related, I would see the issue more regularly and come/go 'right away' rather than having a couple second delay.

Just for reference: Points ignition, 16* base, 18* mech, 12* vac, all in around 2400.

I am thinking the float might be stuck partially open. I am planning on pulling the air horn off and see what is going on in there, and cleaning it up.

Is there anything I should be on the lookout for that would cause these issues?

rpmerf
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3 Answers3

1

If the float was sticking you would see black smoke when it stumbles and would clear up when its pinned.You're right with the acc. pump, would be a consistent flat-spot, but check for a steady stream anyway.All little things add up, so if points, plugs and ignition leads are not 100%, start there.

boltspinner
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Issue #1

Aren't you supposed to prime the carb by pumping the gas a couple of times before cranking? I think the electrics should be on when doing this. That could at least help.

Issues #2 and #3

They're not called Quadrabogs for nothing. Bogging can be caused by a number of issues. Check that the mobility of the larger flaps and the spring returning them is OK. Also the choke rod and the pump pin mobility.

Could be a number of issues, plenty of info around the web.

lofihelsinki
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-1

Start the truck pour a half cup of Marvel Mystery Oil right down the carburator a little at a time. Do not let the truck stall. It will smoke a good rate. Once that smoke clears a bit take it for a nice ride. Old school mechanics.

Arthur
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