Register now to get rid of these ads!

Technical Holley 4 BBL problems - Expert help no longer needed

Discussion in 'The Hokey Ass Message Board' started by tubman, Sep 6, 2019.

  1. tubman
    Joined: May 16, 2007
    Posts: 5,912

    tubman
    ALLIANCE MEMBER

    I am having a problem with the Holley 4160 on my C2 Corvette (year withheld because some may consider it O/T). I'm asking here because there is more knowledge here than anyplace else I know of. Anyway, the car had been sitting for about two years waiting to get a set of heads with a new set of valve guide seals installed on the "freshly rebuilt" engine (life had taken a major downturn in the interim, causing the delay). I finally got it back together this spring and it ran terrible (it had been running perfectly before, but was burning a quart of oil every two fill-ups). I took the carburetor apart, replaced the accelerator pump diaphragm, checked the power valve, and cleaned everything up. I put it back together, and it ran much better but would have an occasional stumble when accelerating, and even once in a while just cruising at a steady speed. In an attempt to figure out what was happening, I removed the air cleaner assembly, and the engine ran perfectly with no stumble. I had an almost new K&N air filter on it, so I put it back together with a new conventional filter. I took the car out, and it was considerably better; for the first 10 miles it ran great; then, after a hot start at the post office in town, it stumbled a couple of times more. I can live with it the way it is now, but I know it ain't right. Previously, I had spent considerable time on this carburetor ( used my surface plate to ensure the surfaces were flat, set the float levels; everything I could think of and it ran great before this hiatus.

    The carburetor has #61 jets (new, as the previous ones had been drilled out), a 6.5 power valve, and I am at about 950 ft elevation. I am thinking maybe I should lower the primary float, or maybe replace the power valve with a 7.5, or even jet it down.

    Before I start down one of these roads, does anyone out there have any insight as to what may be going wrong and where I should start?
     
  2. Boneyard51
    Joined: Dec 10, 2017
    Posts: 5,360

    Boneyard51
    Member

    Probably still plugged up somewhere, crap moving around. Might try some Seafoam in it, and the old county’s tune up of revving it upmand closing the choke several times. Ifbthat doesn’t get it it has to come apart again!





    Bones
     
    deathrowdave and loudbang like this.
  3. saltflats
    Joined: Aug 14, 2007
    Posts: 11,072

    saltflats
    Member
    from Missouri

    What is your vacuum readings as you are driving it?
     
    loudbang and Boneyard51 like this.
  4. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,579

    Johnny Gee
    Member
    from Downey, Ca

    How big around is the air cleaner? A buddy had a 327 that the air filter sat on the plug wires.
     
    Lost in the Fifties and loudbang like this.

  5. tom in nh
    Joined: Oct 16, 2011
    Posts: 75

    tom in nh
    Member

    How is your ignition system?
     
  6. birdman1
    Joined: Dec 6, 2012
    Posts: 1,308

    birdman1
    Member

  7. tubman
    Joined: May 16, 2007
    Posts: 5,912

    tubman
    ALLIANCE MEMBER

    Spark plugs are new AC45's (NOT AC45R's or any of that other goofy stuff they offer) when I installed the heads. The vacuum was fine when I checked it before I pulled it apart two years ago; I should check it again. The air cleaner is stock (this is a restored Corvette, you know).

    I think the fact that it doesn't stumble when the air cleaner is removed (I put about 30 miles on it that way) is indicative of what the problem might be.
     
  8. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,579

    Johnny Gee
    Member
    from Downey, Ca

    I gambled on my reply and now I know. What's your address? ;)
     
  9. You have one too many barrels!!

    P7280002.JPG
     
  10. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,579

    Johnny Gee
    Member
    from Downey, Ca

    I your write up you seem to indicate it's just a little fat? I read you cleaned the carb well. How about the air bleed circuitry?
     
  11. birdman1
    Joined: Dec 6, 2012
    Posts: 1,308

    birdman1
    Member

    Okay, let me explain why i said sparkplugs. If this shit gas we get now sets over a few months, many(not all the time) it "goes bad" for want of a better term. what I have found out, the hard way, is that after setting too long, when the engine is started with the bad gas, it forms a very thin film of a varnish type on the tip of the plug. this varnish will fire at times but as the plug heats up, resistance is higher causing a miss-fir or worse. I can verify this because of a 2001 Mustang I bought that sat 2 years. I screwed around replacing coil, plug wires, fuel filter, the list goes on. then a bodyman freind of mine told me he had found the varnish on the plugs, replaced them, and engine runs fine. I even tried cleaning the plugs, but still did not start until I but new plugs in it. free advice, you are getting to the point where this might be the answer. thanks, Henry
     
    loudbang and Desoto291Hemi like this.
  12. tubman
    Joined: May 16, 2007
    Posts: 5,912

    tubman
    ALLIANCE MEMBER

    OK. I have been sitting here for a couple of days, and, though there have been some good suggestions, none of them addressed what I think is my problem. Therefore, I have come up with a plan. First, I am going to drop the floats a "scosch" and see what happens. If that doesn't work, I'll return the float level to factory spec and replace the #61 jets with a set of #59's I have. If that doesn't work, I'll put the #61's back in and change to 7.5 power valve. If none of that works, I'll try a combination of the above. Hopefully, something will work.

    "birdmanl" - While I appreciate your suggestion, the plugs were new and installed when I replaced the the heads. Plus, up here in "lake country", every station has "non-oxygenated (NO alcohol) premium", so I don't think I can blame the gas. (Also, I have run 3 tanks of fresh gas through the car over the last month.)

    I'll keep you posted on how this all turns out. (It may not be until next spring) because I do not spend winters in Minnesota any more.)
     
    Last edited: Sep 10, 2019
  13. Hey Denny,
    You say you replaced the accelerator pump.
    Was there any trash or buildup near the check ball in there?
    I have seen junk get near the ball and keep it from seating well.
    If the ball doesn’t seat,,,,when the diaphragm moves,,the gas just goes back up inside the float bowl. Also,,,,if the hole in the bowl is obstructed somewhat,,,it might not let the gas refill the diaphragm quickly,,,causing a stumble.

    Also,,,I can’t imagine that a high float level would affect the engine by removing the air cleaner? Your floats may be high,,,,but the air cleaner part makes me think this is not your problem. Good luck.

    Tommy
     
  14. tubman
    Joined: May 16, 2007
    Posts: 5,912

    tubman
    ALLIANCE MEMBER

    Tommy,

    It seems to be running rich with the air cleaner, but not without. The only thing I can think of is to lean it down. I cleaned the carburetor and there was no junk in it. (Everything is fresh, with less than 1000 miles since it ran great, and less than 5000 total miles since everything was new.) Also, why would it occasionally stumble when in steady cruise (whrn the accelerator pump is not in play)?

    Denny
     
  15. Hummmm,

    Well,,,I have had K&N filters be bad,,,but you stated that you used a new conventional filter and still basically same problem.
    What kind of pump do you use,,,could it be overloading the seat with too much pressure from time to time,,,do you use a regulator?
    Rich sounds like it could be so many things.
    Almost sounds like a partially blocked circuit?

    I know this sounds silly,,,but could the air cleaner housing be blocking any things on the carb.?

    Tommy
     
    Last edited: Sep 10, 2019
  16. tubman
    Joined: May 16, 2007
    Posts: 5,912

    tubman
    ALLIANCE MEMBER

    Again, this is a completely stock, correctly restored car. mismatched components shouldn't be an issue. When I first did the car, I did have a big issue with driveability. It turned out to be several things; a couple of throttle plates installed upside down, #61 marked jets drilled out to about to #70's, and the float level set low to make up for that. And this on a "professionally rebuilt" carburetor. I corrected all of that, and it ran perfect until I pulled the heads and let it sit for two years.

    Everything should be the same as it was two years ago. I will have to rethink the "crap in the carb" theory. I guess it's time for it to come off and gone through again. If that doesn't work, I guess it's time to jet it down.

    I will emphasize that since I installed a stock air cleaner and got rid of the K&N, this has been just a minor irritation rather than a continuing problem. I'll drive around for a day or two and start thinking, "I guess it's solved" and then the damn thing will have a slight stumble again. GRRRRR.
     
  17. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,579

    Johnny Gee
    Member
    from Downey, Ca

    This or ground lead from points going thru distributor housing is messing up as breaker plate moves?
    [​IMG]
     
    Blues4U and Tickety Boo like this.
  18. tinkirk
    Joined: Jan 16, 2017
    Posts: 111

    tinkirk


    Take the carb back apart and with carb cleaner and air pressure make sure every orifice is clear
    kind of sounds like the accelerator pump cam is not adjusted right or it needs a different accelerator nozzle.
    real hard to tell without being there but that's where I would start, your jets have nothing to do with what you have going on, timing, air, and fuel at the crack of the throttle is what needs attention

    Terry
     
  19. Deuces
    Joined: Nov 3, 2009
    Posts: 21,627

    Deuces
    Member
    from Michigan

    # 61 jets????.... Those seem kinda small.... I'd go 3 steps richer too???? 64s maybe???.....
    Are the heads 2.02"/1.60" valve size or 1.94"/1.50"?????...
     
  20. tubman
    Joined: May 16, 2007
    Posts: 5,912

    tubman
    ALLIANCE MEMBER

    You guys seem to be ignoring a couple of things. 1. Removing the air cleaner completely eliminates the stumble, and the problem is much worse with the K&N than a new conventional unit. and 2. With the air cleaner on, it will occasionally stumble during steady cruise down a level highway; I believe this eliminates the accelerator pump from the equation. It does bring up the possibility of an internal leak, however. I reused the gaskets when I put the carb back together because they were only a couple of years old and had virtually no time on them. I think I will replace them.

    I am kind of embarrassed that I'm not sure about the valve sizes, but I think they are 1.94's. They are the correct 327/350 heads with proper part numbers and are dated correctly (they are original to the car).
     
    Last edited: Sep 11, 2019
  21. jimmy six
    Joined: Mar 21, 2006
    Posts: 10,295

    jimmy six
    ALLIANCE MEMBER

    Does your "smog stuff" enter the air cleaner as it was built? Since you say there is no stumble when it's off it' might be something to look at. Look at air flow under the hood also if it runs fine without the air cleaner. An air cleaner does slightly richen up a carb.

    Shit can the K&N, a waste of money in my opinion. We don't run those POS even on our dirt race cars.

    Good Luck
     
  22. Boneyard51
    Joined: Dec 10, 2017
    Posts: 5,360

    Boneyard51
    Member

    Changing from a K and N filter which has less restriction that most stock air cleaners ( less filteration) to a stock air cleaner is creating more restrictions, thus allowing the atmosphere to push more fuel easier into the venturies. You have found the symptoms, now find the restrictions in the carb. You said it worked fine before, if it doesn’t work now it’s because something is clogged up. That is assuming the float level is right and not sticking and is the right weight and power valve is not blown.
    Carbs setting for a long time usually develop varnish and crap in the little passages in the carb. Find the clog.


    See post #2



    Bones
     
    Deuces, Truck64 and Terrible80 like this.
  23. Tickety Boo
    Joined: Feb 2, 2015
    Posts: 1,441

    Tickety Boo
    Member
    from Wisconsin

    What is the list number on the Holley (located on the choke tower) that will tell us what jets the carb started with, also need vacuum reading at operating temperature (like Salty said) to select the right number power valve :rolleyes:
     
    Deuces likes this.
  24. Mr48chev
    Joined: Dec 28, 2007
    Posts: 30,197

    Mr48chev
    Member

    Terry nailed it. You are pissing in the wind and not expecting to get wet until you pull the carb, take it completely apart clean each and every passage and install a new high quality kit.
    The "it looks clean" doesn't fly as you can't see down into those orifices and tubes where some varnish or crud is blocking proper flow of air or the mix of air and fuel or letting too much fuel flow due to not shutting the flow off in a circuit.
     
  25. tubman
    Joined: May 16, 2007
    Posts: 5,912

    tubman
    ALLIANCE MEMBER

    Well, I have solved the problem. Yesterday, I completed a 50 mile+ run without one "hiccup". The solution? I replaced the stock 3" high air cleaner with one that is 4" high. I spent a lot of time making sure there was enough clearance under the stock hood, but when I was done, everything worked out fine. I don't know why this is, but the engine is not stock (I rebuilt it to be able to run on unleaded premium) and installed a more efficient camshaft to make up for the loss of compression. Perhaps this combination calls for more air than stock.

    You guys who were saying that the carb was still dirty were dead wrong. The carb was new just a few years ago, and I went through it completely 3 years ago when I had the initial problems. I went through it again when I experienced this problem, and believe me, there was NOTHING in it.

    As to K&N filters flowing more than regular FLAPS filters, I don't believe this assumption is correct (maybe that is why they sell the tops with additional filter area). This problem was most pronounced when running a K&N filter. It completely disappeared when I ran the car with no filter. When I installed a "regular", it almost disappeared completely, becoming only a minor annoyance. The 4" high filter solved the problem.

    Since I am not an anal-retentive NCRS "nut", I will continue to run the tall filter and enjoy my car.
     
    egads, loudbang and saltflats like this.
  26. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,579

    Johnny Gee
    Member
    from Downey, Ca

    Ever hear the aviation term "flying dirty"?
     
  27. tubman
    Joined: May 16, 2007
    Posts: 5,912

    tubman
    ALLIANCE MEMBER

    Nope; I'm just a car guy.
     
  28. Alright,,,,,I’m glad you got it Denny.
    Years ago I had a K&N filter do this to me,,,,fought it for months.
    I tried everything and spent a lot of time and money trying to make the( Superior) filter work.
    Finally changed it to a stock type filter ,,,,,no more problems.

    I have also had a filter system years ago that was too small.
    Got lucky with that one,,,,it was the only thing I changed and after I drove the car it wouldn’t rev up past 3000..

    Thanks for posting what the outcome was!

    Tommy
     
    Last edited: Oct 11, 2019
  29. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 9,579

    Johnny Gee
    Member
    from Downey, Ca

    Believe it or not, a carb works like an airfoil/planes wing. Anything that causes air current to be disrupted will affect performance.

    Notice were the interior narrows. You'll see two halves of a wing. Now you know.
    [​IMG]

    One type of dirty. Venturi affect disrupted.
    [​IMG]
     
    ClayMart likes this.
  30. tubman
    Joined: May 16, 2007
    Posts: 5,912

    tubman
    ALLIANCE MEMBER

    Other than a design flaw by the Holley engineers, I don't see how the above applies to my situation.

    My theory is that in trying to make up for the decreased compression in the rebuilt engine, the builder selected a camshaft profile that would allow a bit more airflow into the engine. The air cleaner base has a large "dropdown" to allow for a low hood line on the Corvette, resulting in some restriction in air flow, but not enough to effect the requirements of the stock camshaft. When the aftermarket camshaft was introduced, the airflow capacity of the original filter area became marginal, resulting in the problem.

    Sounds as good as anything.
     
    Last edited: Oct 11, 2019

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.