I have a stock 350 chevy with edelbrock carb w/electric choke. I've had the carb for about 15+ years. For awhile now, it's been loading up,running rich,won't lean out. I finally rebuilt the carb,new needle and seat checked float levels,metering rods, etc. Still ran rich.Idle screws wouldn't make it stumble when turned down every time. Even though the fuel pump is a stock mechanical type, I installed a fuel pressure regulator and set it at 5 psi. Still no difference. A few times I turned the idle mixture screws in until they bottomed out trying to get it to "stumble" while running.Is it possible I could have flattened out the bottom of the screws and they're not able to lean things out? Should I get a new carb where I've had this one so long? Thanks for any help.
I had similar issues last year with one I have. I think part of our problem is the E-10 that we have here. You might have that now too. I think the density is different than regular gas was. I'm thinking that ethanol is less dense than gas, so mixing that in decreases the density of the fuel. That means to me that the float doesn't ride as high in the lighter fluid. That means for the needle to shut off the fuel, the fuel level is higher. So what I did was lower the float. Whatever the manual said on float height, I added 3/16 to it to shut the needle off sooner. It's a lot better now but sometimes the engine will still stumble if I stop real quick. I could probably go a little further, maybe add 1/4 in to the spec. While you got the top off, make sure the metering rods look straight, if they got bent while you were installing the top, they might be hanging up. Frank
I had similar probs, float setting was the thing. Seems to be a weak link on these otherwise nice carbs.
I have an Eddy 600 that runs OK but I find fuel collecting in the well areas where the counterweights on the secondary shaft swing. I think its the gasket under the top.
It's the crappy gas that is causing the problem . With all the cars today having fuel injection there doesn't seen to have any problems so far . I read someplace Barry Grant had the same problem with some of his carbs last year where the needles weren't seating correctly . Something about the rubber ? Maybe that is the problem I am having with my lawn mower & snow blower not running correctly !
Check you fule pump pressure output. I've heard that if your fuel pump is putting out more than 8psi ( I think it was 8) that it will run rich. Todd
When you say idle screws, do you mean the air fuel mixture screws? Idle screws just set the RPM. If when you turn in the air fuel mixture screws and don't get any change even when turned all the way in, then your throttle plates are not seating properly and leaking or the throttle shafts are leaking. If you have the carb off and close the throttle plates all the way (hold it up to a light) you should not see any light or space between the butterflys and the housing.
A couple of things. One, you may have deep seated the needle and deformed both needle and seat which ruins the idea of 1.5 turns out. You really have no idea where you are on needle setting. Another possibility is that the needle never reaches the seat. Usually the result of an improperly swapped spring, needle, or both. If you can't close it off, you can't find that zero reference. I have swapped needles before to salvage a carb and seen different tapers on the needles. You have to take that into account when tuning. Just like fuel needles on bike carbs, a narrower taper will flow more with less lift out of the seat. All these considerations apply to fuel enrichment needles, too.
As a rule, the AFB types are sensitive to float level. Any excess fuel overflows into the carb venturi, richening the mix. Continue this over time with poor fuel quality (is there anything else?) and it can cause erosion of the carb wall that will result in even normal fuel levels overflowing. I once had a Holley 2 bbl on an old Plymouth Valiant that would stall every time I turned a corner one way, but not the other. It would hard flood the motor so it would take a half hour to restart. It was a hole eroded in the float bowl wall that dumped right into the venturi. I'm telling you all this because casting erosion is a big concern on older carbs, regardless of condition. Age, electrolitic corrosion, fuel quality, enviroment can all take a toll on the metals and alter the needle seats, air jets, sealing surfaces, etc. Check everything when you rebuild a carb. New seals and rubber parts are not enough sometimes.
Float level is key as well as your timing. If the timing is off the fuel doesn't combust correctly and your carb floods out
This last post has really got me thinking.....I've had an Edelbrock/AFB 4-sucker for a good while. Ran great for a good while, but started stumbling when going into tight corners and sudden stops(and I know the timing is "spot on"). Pulled it all apart, cleaned everything....new floats(set to edelbrock's specifications), re-jetted and such(a friend works at a carb shop and dyno-tuned it). Runs great at start-up...but after it runs for a while, it starts pushing fuel "over the top" into the venturii.......might try setting the floats a little lower.
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