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  1. #1

    Hesitation on acceleration

    Hi
    I am the lucky owner of an AK built fantastically by A N Other in 2007 and bought by me in January this year. All is good except for a momentary hesitation from the engine as I go back on the throttle if accelerating reasonably hard and changing up from 2nd to 3rd so mid range revs. After the 1 second pause power comes back on fine and she revs sweetly all the way up.

    I am wondering about replacing the plugs (NGK CPR6ES)?
    HT leads were replaced when I bought the car in Jan
    Not sure if this sounds like carburation or electrical/ignition?

    Spec is as follows (from total head turners advert);
    383ci 6300cc Chevrolet stroker, Aluminium performance heads, Edelbrock performance carburettor and inlet manifold, HEI Distributor

    All suggestions and advice very welcome as a relative newcomer

    Mark

  2. #2
    Join Date
    Oct 2018
    Location
    Shipston-On-Stour
    Posts
    33
    I don't know anything about Edelbrock carbs but if it was a Holley I would start by upping the accelerator nozzles (usually up 3 sizes). Looks like you can do similar with Edelbrocks https://www.summitracing.com/int/par...1475/overview/
    Dax with 1964 Dual Quad 427 and Toploader box

  3. #3
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    787
    Hi

    I would look at fueling issue. Holleys have a power valve and if not correctly adjusted gives the same symptoms your experiencing. What Edelbrock carb do you have? Also vacuum advance. Check pipe from dis to carb

    Look at time 3.50 on the youtube might give you some idea. https://www.youtube.com/watch?v=OeD1UCnDHF8

  4. #4
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    780
    Although lack of fuel is generally the culprit (starting with the accelerator pump tune), I had the same situation which turned out to be something else. In my case it was ignition timing.

    I had started with 12 degBTDC and had that same momentary bog. I kept increasing the initial timing (and for each adjustment, cut back the mechanical advance so I would end up with the same max. advance of 38 degBTDC).

    The engine idle would rise with every increase in base timing, so it had to be re-adjusted down each time. It was interesting to note the heat from the headers kept dropping off each time I increased the idle timing (hence I wonder if this could be the reason for burning paint from the side pipe exit holes that some of you are experiencing).

    The bog kept getting less and less and was finally imperceptible around 18 degBTDC. I finally settled on 20 degBTDC although it seemed fine if a set it a little higher.

    In the end, I would up with a static adjustment (essentially the same as cranking) of 15 degBTD, and idle (about 800 rpm) at 20 degBTDC and a final advance of 38 degBTDC.

    Now the important part: I do not run a vacuum advance. If I did, I could probably set the idle timing to that 12 degBTDC I started with (vacuum disconnected) and then would have a nice high advance at idle with the vacuum connected back up (assuming manifold vacuum) or it could run hot with ported vacuum, but off idle, the advance would quickly come up.

    Now under full acceleration, the vacuum advance drops to zero, however when accelerating in lower gears, it's not likely the pedal will be to the floor for fear of the rear tires breaking loose, so the vacuum advance will keep the timing up a bit... probably in the range I run without vacuum advance.

    So... I tried all the different accelerator pump cams with no improvement. It was the timing I needed to adjust. No doubt due to using a non-vacuum advance distributor and having an engine modified from stock.

    It was either in the FE Engine forum, or the US Cobra forum where I noticed a few people had also set their timing the same, so that made me feel more comfortable with what I had done.

    Now I used a non-vacuum distributor because it came with a lot of used FE parts I bought (basically was thrown in, so in other words "free") plus knowing the timing wouldn't be stock, and that hearing the engine ping was going to be difficult, I felt that adding one more thing to adjust that wou ld affect the timing was going to be a problem. Since I seemed to have to increase my advance to simulate the part throttle advance that vacuum would give me, it tells me that vacuum advance should help with part throttle driveability. Maybe some day I'll try that.

    As a final note, please don't go setting your engine based on my numbers. I'm merely relating my experience so that if carb tuning can't get rid of the bog, an increase in base timing (with an adjustment so there's no increase in max timing) might help. In all likelihood, a carb adjustment will be your cure. It just wasn't for me.
    Last edited by Eggbert; 11-08-19 at 09:56 AM.
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  5. #5
    Join Date
    Jan 2017
    Location
    Mansfield, Notts
    Posts
    90
    I have a similar issues with my SBF EFi 302 when I get down to around 1/4 of fuel. I have a fuel surge issue. I'm told that the tank is baffled but clearly not well enough. For now I'll live with it till I can get round to instaling some sort of swirl chamber arrangement.
    Pete

    Legendary 427 one off Cobra rep
    SBF 302 Efi, T56, Ford Running gear and LSD.

  6. #6
    Join Date
    Nov 2016
    Location
    Stevenage
    Age
    47
    Posts
    232
    Also i guess rolling road person would be the ultimate with edlebrock parts to hand

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