Anybody remember carburetors?

70 Blazer, 350, 300hp crate motor, have replaced fuel pump, installed hei ignition, 4bbl Rochester carb has been rebuilt.
I've got an occasional "loading up" at lower rpm's, 2000 or below. Engine
will die at idle. This has been occurring before and after a new engine and later elect. ign. Anyone know what might cause this Rochester 4bbl to do this? OR, could it be a non vented gas cap causing a pressure build-up to blow through the fp and past the main jets? I frequently have a pressure build up when I remove the cap to refuel (which is not too often with a 37gal tank). LD
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Regarding " From: snipped-for-privacy@earthlink.net (LD) 70 Blazer, 350, 300hp crate motor, have replaced fuel pump, installed hei ignition, 4bbl Rochester carb has been rebuilt. I've got an occasional "loading up" at lower rpm's, 2000 or below. Engine will die at idle. This has been occurring before and after a new engine and later elect. ign. Anyone know what might cause this Rochester 4bbl to do this? OR, could it be a non vented gas cap causing a pressure build-up to blow through the fp and past the main jets? I frequently have a pressure build up when I remove the cap to refuel (which is not too often with a 37gal tank). LD" ---------------------------------------------------------------- LD,I had this problem with the 4mv quadrajet and I believe I had to replace the float with the new style one.Also added a large fuel filter in line before the regular one cause a tank that old probably has loads of crap,(mine did)Somehow that crud was just big enough to unseat the float valve and let the floatbowl level get too high ,and sometimes I actually had fuel coming out the vent.This was a few years ago so it's kinda foggy but I think if you got a modern float(they're like a solid block of plastic )and add a fuel filter you might see a difference,cause if sometimes it runs fine and suddenly it's all rich to the point of dying,it would seem like that would be the problem. I kinda doubt that tank pressure would do this since the fuel-pump supplies fuel at something like 5-9 lbs,and to have more than that in your tank doesn't seem too likely to me.Plus the float-valve would not necessarily let in more gas anyway,up to a point.Doe4s this make sense?It's late!
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I installed this tank just a few years ago (original was only 21 or so gal, couldn't go anywhere without stopping for gas). I'll look at the float but I think they replaced it when rebuilt. Once, when it died, on the side of the road I took it apart, bent the float down about 1/16" wondering if that was the problem. My thought on a filter is that the more gas it wants (high speed) the worse it would be. LD
(LD)

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Check the float level and also the needle/seat. When you remove the center section look under the mainwell jets. There should be a seal block in the carb base. When the mid section and the base are together this base should seal the bottom of the mainwells. I am assuming this is a quadrajet btw. Let us know how you do. Larry

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See reply to B. O. on the float. Not sure what you mean for the "mainwell" jets. It's been so long that I had this apart, I don't remember anything under the main carb body. The top comes off exposing the floats and removing that, with the needles you see the main jets. I remember leaning then out .002" some years back. I also remember, (in reply above) when I adj the float level (after rebuild) I saw they put in viton tip needles. This block is under the main carb body or "mid section"?? Can you describe the shape and material of this block? Thanks to both, LD

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It's a foam block and it seals the bottom of the main well. It's about 1x1.25" and about .375" thick. If it's not there the plugs under the main jets can leak and cause the problem you have. I fixed more of them than I can count. Larry

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They also sell replacement plugs for the main wells. Pull the old staked in plugs out. The new ones have an o-ring around them to seal the fuel off forever.
Brian

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It appears to be fixed. After I had to have it carried back to my house one morning, I replaced the gas cap with one that allows venting. I bought a rebuild kit but only pulled the top, replaced the inlet needle and seat, accelerator pump, filter, and the float.
What I found--
There were a lot of small particles of trash in the bottom of the bowl; rust? sand? broken pieces of the rubber gasket that used to be on one end of the sintered bronze filter? Also, the filter, with a broken and deteriorated rubber gasket was not filtering, and the vition tip on the inlet needle was grooved. I don't know which or what combination of bad things caused the problem but.........
My theory is:
The former gas cap, non vented, allowed pressure to build up in the tank several (5-10)psi beyond the (10-12?) supplied by the fuel pump. With the amount of trash and with the groove in the inlet needle I'd say it is a fact that it was not stopping the fuel flow (which appeared to be flowing out the top of the carb, even with the engine off, shortly after it flooded and died, which is why I think the pressure build up in the tank was a factor). The float may have been OK, I don't know. I wish I'd taken the time to weigh the old and the new on a re-loading powder scale, accurate to .1 grains, (which is 1/4375 of an ounce).
One other thing (and this is embarrassing). When I started to work on it, I also noticed that the primary wire to the coil (on the hei I installed recently) used a 1/4" female spade connector to a male on the firewall and had become disconnected. This, as we all know, contributes to "lack of spark"!

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