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Technical Nightmare carburetor tuning...

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

  1. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    They don't have vacuum. Heres 3 of them I'm doing right now, they work perfect and I know carbs. If there was anything wrong from Edelbrock I would have posted the problem.
     

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  2. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    My experience is the HAMB don't like the simple answers....;) so it cant be a vacuum leak. I'd get a new carb. Yea, that must be it! If you get real lucky, hell, maybe you'll inadvertently fix the vacuum leak when you change carbs! Worth a shot...:rolleyes::D
     
    31Vicky with a hemi likes this.
  3. When an engine speeds up- everything is right.
    When an engine speeds up with the choke closed it develops a massive low pressure area under the flap. Everything at a higher pressure will try to enter the low pressure area including fuel even though the Bernoulli principal is stifled and the Venturi doesn't get the proper signal.

    You'll not correct an over rich situation by covering the carb with your hand or closing the choke. That is exactly how you create a rich situation.
     
    falcongeorge likes this.
  4. seb fontana
    Joined: Sep 1, 2005
    Posts: 8,444

    seb fontana
    Member
    from ct

    Dist vacuum advance plumed to intake will make for full advance at idle and as you try to drive the car the vacuum drops which will [you guessed it] retard the timing and give grief..Dist should be plumed to carb dist vacuum port...Set timing with engine idling and as you apply throttle the vacuum will advance, really makes a big difference.....You can see the above with a timing light..Oh and the vacuum advance diaphram unit is exactly the same as used on a 65' comet 200 six..As previously said if engine runs with mixture screws in then there is a power valve/gasket as gas getting into the clearence well which "sees" [ported to] manifold vac gives a direct by pass of mixture screws..Reading in the green bible for a stock carb [49-51] the float height is 1.322-1.355...I assume thats bottom of float to gasket surface with needle seated..
     
    Saxon likes this.
  5. Ok. That makes sense, and I was definitely thinking about the principles the wrong way. If there's a vacuum leak, it must be coming from inside the lifter valley...otherwise passing the propane bottle around the carb and intake would have affected something, right? Thanks for trying to point me in the right direction.
     
  6. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    Diagnosing vacuum leaks is easy. Its the finding part that can sometimes be a real bitch...
     
  7. I noticed that base gasket was mentioned a few times, but if the intake gasket is old and crusty you can be looking for an air leak there too. What ever happened to starting with the basics which are cheap and easy? Also I'd have a vacuum gauge on the intake and a remote tach while tuning the carb after it's guaranteed to be air tight around the intake passages and carb base. The power valves in the carb rely on a correct vacuum signal to be present or they open early and just dump fuel. Throwing new carbs at something that has evidence leading to an air leak is not going to help anything. Also those load a matic distributors are fussy as hell and work best paired with a real 94, not a copy since the special port in the 94's control the ignition curve through out the entire operating range of the engine, no centrifugal advance at all, so they will be thrown out of synch with a vacuum leak.
     
  8. Saxon
    Joined: Aug 9, 2008
    Posts: 2,157

    Saxon
    Member
    from MN

    My 2 cents... This is a single carb setup.

    Borrow a known carb from a friend.

    Throw away the original dizzy and get one with a mech advance. Or hook up your vac advance. Or get a mech advance dizzy (said that twice for a reason). See gmcbubba

    Set timing with a light. Bump should be around 2* btdc and 28* atdc is all in. Which without any advance you won't get there.

    Then you'll at least know what going on.

    Adjusting valves (maybe the front set are out of spec) and lapping valves won't hurt a thing :)
     
    Last edited: Sep 4, 2015
  9. Ok. Thanks for the input. I don't know if you saw where I said the base gasket was fresh, along with all the other gaskets in the carb, and I've passed the propane bottle all around the edges of the intake manifold and I've noticed no change in idle. It could be a vacuum leak coming from the valley, but since that's impossible to diagnose, I find myself trying to hold on to some other cause of the running issues.

    Is the idle speed increase with a cupped hand partially covering the air horn a 100% guaranteed sign of a vacuum leak, or could there be another reason the reduced air flow is having this effect? To be more clear, as you lower your cupped hand over the air horn, the idle smooths slightly, then as you continue to cover more of the air horn the idle speed increases EVER SO slightly (maybe 100-200rpm just guessing), and then as you keep going the motor starts to sputter and die almost as quickly. Closing the choke makes the motor race, but that's because the throttle blades are already so far open just to make the engine run, and the choke opens them even further.

    I DID find that the vacuum advance is hooked up to a port underneath the carburetor, and not the carb's timed vacuum port. The Edelbrock carb DOES have a timed vacuum port a la Holley 8BA. I will get the proper fitting tomorrow and switch the vacuum advance. Having full advance at idle "could" explain why the motor won't idle down, right? I'm assuming my distributor is the stock load-o-matic, as it's definitely vacuum advance only.

    I get what you're saying about doing the easy stuff first. I haven't spent a dime on this car over the purchase price, YET. The PO was the one throwing cash at it and getting frustrated, and I was hoping to step in and be a little smarter and make a couple bucks, but so far I guess I'm not as smart as I thought I was. My conundrum is that if I'm going to pull the intake and buy new gaskets, I'd just as soon swap the manifold too, but I sure would like to know that this motor will run halfway decent before I spend any money.

    Thanks again for the advice.
     
  10. It could be a vacuum leak coming from the valley, but since that's impossible to diagnose, I find myself trying to hold on to some other cause of the running issues.


    If there's an oil filler you can test it right there. Best to do it with a vac gauge and rubber plug. But only if you seal all opening to crank case but one. The crank case pressure should flutter. Blow by will raise crank case pressure, a leak in the intake will cause a vacuum in the crank case that gradually increases. Simply taping a bag on the filler tube will show you within seconds of running. If the bag sucks in there's your leak.

    Satisfying the "wanna know it runs first" need without spending money or time isn't something I've been able to do.
     
    Last edited: Sep 3, 2015
  11. I was going to ask if a vacuum leak in the lifter valley would offset crankcase pressure enough to create suction at the tube. I'll give that a try...

    Hey, I really appreciate all the help and advice. Thank you very much.
     
  12. I suppose you could open a propane cylinder at the oil filler tube as well and see if the idle speed picks up.

    What does the engine have in the way of crankcase venting? Just a road draft tube or has it been upgraded to a PCV system that might have a leak somewhere?
     
    Last edited: Sep 4, 2015
  13. You could do the propane trick.
    however that's filling a closed container with explosive gas with no way to control anything else. Not something I'd tell anyone to do.

    All your your trying to do is diagnose a intake manifold vacuum leak. Lets say you've wisely used the process of elimination and shown that the likely hood of something else being the cause is less than 20%. That means there's a 80% chance your correct. Is it worth pulling the intake on 80% chance? Well lets see,,, what's it going to cost you if you're wrong? A set of gaskets and a couple hours time maybe. How old are those intake gaskets any way? 40, 50,
    60 years or maybe more. They certainly don't owe anybody anything so eliminating another possible cause is still not a unfruitful.
     
  14. Yep. You're right, of course. :( I needed to think that thru a bit more before posting this suggestion. :oops: DON'T TRY THIS AT HOME, or anywhere else for that matter.
     
  15. No harm no foul. It's early fellas. I haven't had my coffee yet either...
     
  16. Moral of the story. I'm not a complete idiot, though I do sometimes forget some things...trying to cut "this" corner always bites you in the end.
     
  17. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    Did you hook up a vacuum gage to see how much vacuum you do have?
     
  18. Not yet. I only had about 10 minutes of daylight left when I got home last night, just enough to look at what type of distributor I have and where the vacuum advance was connected. Hopefully I'll have a couple hours of daylight today, and a whole weekends worth after that. And believe it or not, the local O'reilly supposedly has a FelPro intake gasket in stock! Hallelujah! Think I'll start with fresh gaskets, new plugs, and the distributor hooked up right. Time it, put a vac gauge on it, and go from there.
     
  19. Saxon
    Joined: Aug 9, 2008
    Posts: 2,157

    Saxon
    Member
    from MN

    Put a straight edge or lay your intake on a very flat surface (glass if possible) to see if the intake is warped. Cast iron intakes (which you most likely have) rarely do. Old aluminum ones are susceptible to warpage. Just something to check while your there.

    Might as well check the valve lash too since you'll have the intake off.
     
    Last edited: Sep 4, 2015
    crazycasey likes this.
  20. Yeah, good call.
     
  21. flathead4d
    Joined: Oct 24, 2005
    Posts: 898

    flathead4d
    Member

    Manifold vacuum will definitely screw up your stock distributors advance. Check the module on the dizzy for a leaking diaphragm.
     
  22. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    Maybe they put an intake for the 59A, I believe there is a mismatch problem that is solvable,
     
  23. Float level adjustment; Hold the top plate upside down, measure from the air horn to the bottom of the float 1- 11/32".
    Vacuum leak: check the Power Valve AND its gasket.. Also check the base to bowl gasket as I have seen them shift and cause a leak.
     
  24. This could probably be it's own post. I pulled the top of the carburetor body off of the base on the car just after running the engine. There was NO gasoline in the power valve well in the base, but the power valve gasket did look wet. I've run into a leaky power valve before, and I always seem to have a tough time getting the power valve gasket to seal up, so I'm sensitive to it, but like I said, no gas in the well, and since the gasket is essentially sitting in gasoline, I guess I could see it being wet. What do you guys think?
     
  25. flathead4d
    Joined: Oct 24, 2005
    Posts: 898

    flathead4d
    Member

    It's my understanding that there are two different power valve gaskets and the new kits don't have the correct one. So, they leak. Go to the fordbarn.com for the latest info and post your question there.
     
  26. 2X ^, The outside of the gasket should not be wet...is it a red gasket? They a two parts that are glued together and will leak with alky mixed fuels. I use the nylon gaskets only....
     
  27. 20 some years ago went thru some nightmare heating issues with a bbc with a brand new set of Edelbrock alum heads , their qc dept claimed that it could not be the heads because of the way they test them. Make a long story short the right head had more than one water passage blocked it took cutting head apart to get them to own up to it. They made good on it than . Having had this experience I would not trust that carb at all .
     
  28. Larry W
    Joined: Oct 12, 2009
    Posts: 742

    Larry W
    Member
    from kansas

    Seems to be some issues with the "new" crab. I would find a "old" 94 , and there are plenty of them out there, and make a swap. Just a thought. then I would look for a better distributor. But that's another day..
     
  29. Saxon
    Joined: Aug 9, 2008
    Posts: 2,157

    Saxon
    Member
    from MN

    Any updates
     
  30. Sorry Saxon, I didn't see your post. It turned out to be a leaky power-valve gasket. It was the two part gasket, and sure enough, it came apart perfectly on the glue line.

    Once I got that right the car fired up and idled without popping, the mixture seems right on the money after adjusting the screws, which now actually do their job. Followed that up with a switch to ported vacuum on the load-o-matic distributor, reset the timing, and now she runs like a sewing machine. I've got to swap out a leaky radiator; then I can put some miles on the old girl, and see if 1 and 5 regain some of that lost compression.

    Thanks everybody for all the help!
     

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