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Technical flathead idle but hesitate to rev up!

Discussion in 'Traditional Hot Rods' started by rodderbilly, Feb 16, 2014.

  1. Hi all hambersnow i need your help for my problem...i have two 94 and the front is without choke....i open and clean the carbs . ...i registre the carbs with uni-syn and engine idles good...but when i pull on accelerator the engine stall and hesitate to rev up about 2-3 seconds then rev up good....i notate when i open the front carb that has the fuel pump spring a little rusty....this is the cause of my issue?the engine has some backfire, i have 4.5 power valves ,main jets are 51 ..can you help me?was thinking to change the main jet to 47 or 49.......
  2. Check you float levels sounds like it flooding.
  3. Do you have a good, stong accelerator pump stream? Does the exhaust look black or smell rich?
  4. nsh57
    Joined: Mar 14, 2004
    Posts: 263


    Sounds like flooding. Check floats & fuel pressure first. 94's hate too much pressure. 51 jets should be ok to get going, depending on cubes of engine. Which of the 3 holes do you have the throttle pump hooked to? Should start on the lowest one.
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  5. when i open the carbs floats seems to be good ....thinking to open another time and check more accurate that floats,fuel pressure is near 2,5-3 psi.....the throttle pump in the 2 carbs are hooked in the middle....only i remember that i try the spring on front fuel pump with some rust...
  6. yes a lot of smell rich....
  7. Kiwi 4d
    Joined: Sep 16, 2006
    Posts: 2,770

    Kiwi 4d

    Wow cool to see there are flathead rockabilly HAMBERS in Italy. Sounds like a lean out on sudden pedal down. Have you checked the accelerator pump and that the power valves are all good. Is the pump rod connected?
    We hope to be in Italy around April . But will only be tourist stuff in Rome.
    Don't expect there are many rockabilly joints in Rome. Let alone flathead guys.
  8. Hi Kiwi..i see the power valves and they are in nice conditions with no cracks...yes pump rod is connected in all 2 carbs....a thing that i can say is that when i acclerate by hand on the pump levers the squirter on the rear carb sprays less fuel ...i think i have a accelerator pump problem...
  9. When it does catch after that 2-3 second dead spot-
    Watch the exhaust for black smoke and rich smell.

    If yes
    you have black smoke and rich smell
    then the problem is too much fuel when the throttle opens.

    If no black smoke and smell
    Then the problem is not enough fuel when the throttle opens.
    The backfire is also a hint to the lean condition.

    Most of the time a good idle with a Bog on throttle is a lean condition caused by accelerator pump malfunction.
  10. Petejoe
    Joined: Nov 27, 2002
    Posts: 10,510

    from Zoar, Ohio

    Have you rebuilt your carbs yet?? Don't sound like it..
    Read this thread.
    Last edited: Feb 17, 2014
  11. tommy
    Joined: Mar 3, 2001
    Posts: 14,758

    Member Emeritus

    Did you play around with the timing any to see if it improves?
  12. Paul
    Joined: Aug 29, 2002
    Posts: 14,893


    I was thinking check timing too.
    You might also go progressive with the linkage,
    might be too much air/fuel at once for the little motor.
  13. sdluck
    Joined: Sep 19, 2006
    Posts: 2,482


    Block off each carb and test run it. see if it is one of the carbs or something else
  14. yes Pete carbs are rebuild...only i notate that the accelerator pump link has some play in the middle position(2)....the hole on the plate is a little large...i try to remove the dual carb linkage and see what happened playing on each carb....
    Last edited: Feb 17, 2014
    Joined: Jan 14, 2010
    Posts: 332


    X2 on timing. Cured my stumble by increasing the timing.
  16. i have played with the timing time ago and the cars likes increasing the i drive the car with only one carb and the engine rev up well....
  17. Other carb delivers air but not enough fuel.
    Accelerator pump would be a likely suspect.
    61klassic likes this.
  18. ROADSTER1927
    Joined: Feb 14, 2009
    Posts: 2,764


    Did you just disconnect the linkage? You should pull one carb off and block the ports, get that running great the do the same with the other, then put them both on and adjust the linkage to where they are at idle. Gary:)
  19. Yes Gary i just disconnect the linkage, i need to made a plate to block the carb i was checking the carb squirts and i notate that one hole in the front carb squirt was clogged,i removed the squirter and clear all with carb cleaner and air....i replace the squirter and moving the fuel pump level i see that fuel comes out from the 2 squirter holes now....Tomorrow i try first to see if was the squirter that made the problem than i try to block the ports on one carb....
  20. tommy
    Joined: Mar 3, 2001
    Posts: 14,758

    Member Emeritus

    Not a good sign for supposedly rebuilt carbs:D That surely will cause it to bog.
  21. after the drive with one carb (was the rear carb)....i check the front carb how works moving the accel pump lever and i have seen that from one hole of the squirter don't came fuel when i i removed the squirter clean it and now fuel came from the 2 holes.....Tomorrow i see what appened...:cool:
  22. Baumi
    Joined: Jan 28, 2003
    Posts: 2,489


    I think you´ll find the problem around the accelerator pumps, the backfires also indicates a lean condition when you open the throttle..
  23. i think the same.....Tomorrow i see if the engine replies good..if not, i try to block one carb ports..if the engine runs well with one carb i'm thinking to change main jets from 51 to 49 or 47.....
  24. Ah.....thanks all for support and help.. hamber friends!
  25. problem not solved ....wasn't the squirter in the nozzle ...i order the accelerator pump from vintagespeed....
  26. 48-760
    Joined: Dec 15, 2009
    Posts: 138

    from OH

    You want leather accelerator pump and not the plastic. Check out the length of the oval hole in the accelerator pump rod and the total length of the rod. At one time the rod and hole were not of the proper length for many replacement pumps. You may want to check out Daytona carb parts and rebuilding kits.
  27. Yesterday i block-off each carb....the engine is bad to idle i don't have very good i try to put a ballast on the +coil wire...i look for the conditions of the spark plugs ,they have only some hours of work and i try what you see in the picture..the central electrode is in bad i put the old spark plugs...that in reality are not very old....and the engine now reply good....
    upload immagini
    Last edited: Feb 20, 2014
  28. ROADSTER1927
    Joined: Feb 14, 2009
    Posts: 2,764


    Glad you are getting somewhere! Again tune it with on carb blocked until PERFECT, then block that one and tune the other until PERFECT! Then adjust the idle with both until it all works!
  29. hotrodderhaag
    Joined: Jan 22, 2007
    Posts: 2,117


    make sure you dont run champion spark plugs... my flathead was a tuning nightmare till i yanked out the champion and bought motocraft SP473's for in it,
    much better!!
  30. Hi hotrodder....i'm running ngk b-6l plugs....only one time i use the champion h10 but i prefer the ngk....

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