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Technical Nightmare carburetor tuning...

Discussion in 'The Hokey Ass Message Board' started by crazycasey, Sep 3, 2015.

  1. OK! I'll change the story in the first post so you don't have to read all the way through the thread. I WAS having a hell of a time getting a '53 flathead running right, now it's running "pretty good", but naturally, I want it to run better.

    The car starts, idles, accelerates, and doesn't run hot, or anything like that, it's just not very quick, and I'm thinking the Load-o-matic is my issue. Question; do all Holley 94 carburetors for Load-o-matic applications have a spark control valve (looks like a power valve) on the outside of the carburetor base. I ask, because the Edelbrock 94 on my flathead (I know...) seems to be a dead ringer copy of a Holley 94 "8BA", and all the 8BA's I've ever had DID NOT have a spark control valve. The Venturi vacuum source is present, and that "T's" into a manifold vacuum port down below the throttle blades, just no spark control valve. Will this type of setup provide the correct signal for a '53 Load-o-matic?

    I ask because I'm only seeing about 10° total advance with my timing light, holding the engine at about 4,000 rpm, no load. I'm not sure what it's doing with load, but I'd imagine I might have less advance, right? Aren't you supposed to have about 24° total with a Load-I-magic!?! Before I start trouble shooting the vacuum canister, I need to know that it's getting the right signal.


    I need to go back to shop class...evidently.

    I just bought a little A project with an 8BA flathead and a brand new (like last week new) single Edelbrock 94 carb. The motor ran and the car drove ok, but was down on power, leaking fuel through the accelerator pump, and fouling plugs.

    After pulling out a float that was riddled with cracks and full of gas, and replacing it with another I had in my tool box, the fuel leak has stopped, but the engine doesn't want to run. I set the float height at 1-11/32", which is standard for an early style 94 (of which the Edelbrock seems to be copied), and now I can't get the motor to run without the idle speed screw cranked so far open that the idle circuit is bypassed completely. If I cup my hand over the air horn, the idle speed increases, and I can close the butterflies a little, but still can't get them closed enough to run on the idle circuit. If I close the choke "almost" all the way, the engine races. I pulled the carb apart, cleaned all the orifices, changed all the gaskets, and put it back together, with NO change. What am I missing?
    Last edited: Sep 20, 2015
  2. Sounds like you got a piece of crap in there somewhere. Your float lever shouldn't be so important @ idle if it has fuel in the float bowl it should idle.

    I am not getting it, granted I am not really keen on edelbrock pieces but still a new like last week new carb with cracks in the float? Is someone pushin' you leg or mine?
  3. Yeah I'm with beaner getting legs pulled or something is missing in the technical explanation.

    If I squint and leave out the convoluted details, I sorta see a big vacuum leak
    stimpy and falcongeorge like this.
  4. No, like I said, I even pulled it apart. It's definitely brand new. And it's clean inside. I probed all the idle passages with a piece of welding wire. Blew air through them, and made sure it came out the other side, etc...they're clear. And I've never seen a float so cracked, it was cracked on ever line from where it was shaped, before they brazed the two halves together. I mean, that's like ZERO quality control!

  5. No leg pulling, and I thought vacuum leak too, but there doesn't seem to be. I'm sorry that the details are "convoluted". I was hoping they might help somebody stumble upon what I've missed.
  6. stubbsrodandcustom
    Joined: Dec 28, 2010
    Posts: 1,409

    from Spring tx

    sounds like a blockage or restriction in idle circuit.
    I know some early carbs wont idle worth a damn if the float level is wrong... But this one is new.
    Pull the mixture needle out.. Maybe put a vacuum gauge on it also.
  7. belair
    Joined: Jul 10, 2006
    Posts: 8,717


    change the plugs?
  8. What should I see for vacuum for a stock 8BA that's probably on the "tired" side?

    Right now, the mixture screws only seem to effect things if they're all the way closed. The guy I bought the car from had them each about 3 turns out. Without convoluting things further, that tells me that there was something else wrong. I am sort of aligned with the other two guys that said the float level isn't that important, because the car ran better with a float that was full of gas...
  9. Not yet...I know, I know. I cleaned and gapped them. I was hoping to get the carb a little bit closer before I threw new plugs in it.
  10. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 3,401

    from illinois

    A month or so ago it took me 3 tries to get what must have been trash out of an idle/transition circuit.....I've been working on this stuff for 50+ years , we all miss things...
    302GMC likes this.
  11. Touché. And it was late, and I was getting angry. I will go buy some plugs and then double check the idle circuit orifices. Thanks Dave.
    volvobrynk likes this.
  12. When you close off air flow by hand or butterfly and the engine rpm goes up, that's your text book vacuum leak.
    stimpy, falcongeorge and wraymen like this.
  13. I think the older I get the more I miss. That's what the rest of you guys are for.

    I got a trick Holley on the shelf now that someone sugared the gas in a car that I owned. I had the carb together and apart 3 times before I decided to just let soak for a week. Everything was fine except the secondary circuit. It would pull fine at WOT if there was no load but it would not pull an old sick woman off a bed pan in a car and could not get up to speed to use the high speed jets. Finally after a long soak and a good blowing I made it work. Some times it is just a pita when you are trying to sort one out.

    With the Q/C that carb must have had ( judging by the float) there could be anything in the world wrong with it. Or maybe you got a burnt valve.
  14. Gene Boul
    Joined: Feb 9, 2006
    Posts: 805

    Gene Boul

    I would send carb back...if they can send it out with a cracked float, which is now full of fuel, there could be more things wrong that aren't easily scienced out. Regardless you shouldn't be doing their QC. Demand a carb that can be bolted on and started up without being disassembled!
    clem likes this.
  15. check the power valve, the new fuels with alcohol are chewing the old rubber up.
  16. stubbsrodandcustom
    Joined: Dec 28, 2010
    Posts: 1,409

    from Spring tx

    Here I was thinking I was the only one with this issue!
  17. Jimmy2car
    Joined: Nov 26, 2003
    Posts: 1,707

    from No. Cal

    If it were me, Crazy, I'd take apart again. Get a small roll of fine copper wire available at any hardware store. With the carb disassembled, run that fine wire thru EVERY hole/passage you see.
    If it's a new "94" type carb, it won't take you long to go thru it. If that doesn't fix it, then I'd suspect something more internal that you can't get to.
  18. saltflats
    Joined: Aug 14, 2007
    Posts: 10,856

    from Missouri

    Maybe the intake is leaking into the lifter valley.
    You have not said what timing and dwell are set at.
  19. also check the carb base gasket.
  20. Saxon
    Joined: Aug 9, 2008
    Posts: 2,157

    from MN

    Adding some thoughts. Are you using a stock distributor. Is the vacuum advance hooked up to the carb? Should have about 18lbs of vacuum. You can also spray some wd40 near or around the carb base and throttle shaft when running and if it speeds up, there is your leak.

    Sounds like it's clogged up though.
  21. Maybe. I should have prefaced that this is my first flathead. I did a cranking compression check, throttle open, 5 revolutions, highest reading was reached in 3 to 4. I've got 100 psi across 2-4 and 6-8, but 1 and 5 only made it up to 70 psi. I know that's less than ideal, but I figured maybe it was "good enough" to get this old girl running. There is some popping through the exhaust as I give the engine some gas, which would also potentially point to a valve sealing issue, right? But could also be from being so overly rich. Should I quit messing with the carb and do a leak down check, or should I just go right to pulling the heads and maybe try to lap the valves? A rebuild is not in the budget for this vehicle.
  22. Saxon
    Joined: Aug 9, 2008
    Posts: 2,157

    from MN

    Backfires can as you said, be from to much unspent fuel in the exhaust that ignites. Although that's not great on the 1-5 it might improve (carbon build up) with some driving. If you have a burnt valve (a great suggestion btw) it would have little to no compression in that cylinder/s.

    I'd get it running then test again. It should run decently even with the variation of compression.
  23. That's what I was hoping, and why I was proceeding with the attempted tune up.
  24. stubbsrodandcustom
    Joined: Dec 28, 2010
    Posts: 1,409

    from Spring tx

    with those numbers about 15 in should be about in the ball park of vacuum I would think.
  25. oj
    Joined: Jul 27, 2008
    Posts: 6,257


    I'd skip ahead and do a leak down on it, do the known good cylinders first so you can get the testing proceedure down. They can give you false readings if you let the piston go to the bottom, the exhaust valve will open giving you the false reading you expect to see. Know what I mean?
    The float level has to be right for the idle circuit to work right.
  26. Do these carbs have any sort of an idle air bleed circuit that passes thru the bowl and into the airhorn? Possibly a break in the gasket that seals the airhorn to the bowl, or some warpage of the airhorn? I'm just grabbing at straws here... :confused:
  27. Asphalt Demon
    Joined: Jan 19, 2014
    Posts: 307

    Asphalt Demon
    from Australia

    I hope you have had good luck, just noticed your first post and may just be a typing era, but shouldn't the float level be 1 and 1/32 not 11/32 . massive difference,that would explain it Johnny
  28. I read this over real slow..
    Car ran - albeit not well with a sunk float and slobbering gas.
    Question ? Where was it getting enough air to establish air/fuel mixture.
    Correct the gas leak from float and now it won't run.
    Question ? Is it still getting the same amount of air ? How is it going to establish air fuel ratio without fuel in excess.
    Cranking up idle speed screw gets it running but poorly
    Question? Off the transfer slots it's drawing more fuel, actually fuel in excess once again.
    Covering the carb with your hand speeds engine up.
    Question? How is Limiting the airflow thru the carb correcting the excess fuel ratio again?
    Where is the air coming from if your hand closes the flow?

    Closing the choke butterfly with throttle screw cranked in and the engine races.
    Question? How does a even further air flow limit thru the carb correct the air fuel mixture so that the rpms pick up. Where is all this air coming from?

    Purely rhetorical questions to get you thinking in the right direction.
    I'd say there's a big vacuum leak.
    69fury likes this.
  29. flathead4d
    Joined: Oct 24, 2005
    Posts: 888


    What am I missing here? The carb is supposed to be new and the float is screwed up? Send it back. Get a different carb and see it that helps. You didn't say whether you had the vacuum line from the dizzy to the carb hooked up. That's a special vacuum port on the carb. Not manifold vacuum. You might have blown the power valve in the carb. Their very sensitive to backfires. Start with a different carb that's right for the 8-BA and go from there.
    Saxon and tb33anda3rd like this.
  30. Pretty sure it's 1-11/32"...

    I get what you're saying, and I'm far from a carb whiz, but I sprayed carb cleaner around the carb, base, intake manifold, etc, and then tried a propane bottle too...the idle never changed. My only thought with the cupped hand business was that maybe somehow restricting the air entering the venturi was ALSO reducing fuel being drawn into the engine, if fuel was finding it's way in metered or unmetered, in I mistaken that vacuum draws in the idle fuel and the Venturi effect draws in main circuit fuel. A cupped hand partial blocking the air horn would kill the Venturi effect, thus limiting air, but also "maybe" limiting an overly rich situation? In fact, the more I think about it, the cupped hand doesn't really restrict flow at all, it merely restricts the velocity of the flow, so with the cupped hand the engine could be getting just as much air, but not pulling any through the main jets, and/or a leak...unless I am all wet (pun intended)!?! I think I need to check the power valves, see if they're leaking. I had a leaky power valve on a dual 94 setup do something similar, as I recall...

    Yes, only I bought the car with the screwed up "new" carb already installed. Previous owner sold it cheap because he was tired of fussing with it, me thinks. He spent $450~ on this hunk of junk. I think maybe I should find a 94 core and rebuild it...start fresh. As for the vacuum, he had it hooked up to manifold. I need to remedy that. Would that cause these issues though?
    Last edited: Sep 3, 2015

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