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Thread: flat spot

Discuss the Austin Healey Sprite and the MG Midget. Two different but similar cars sometimes referred to collectively as the Spridget.

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    flat spot

    I have a 66 Sprite with a rebuilt 1275, new distributor and Petronix. My problem is that exactly at 2500 rpm's I have a misfire and rough running, above that point it smooths out and below it's also OK. I've checked the carbs over and over again but they are the only "old" part on the car so I suspect them. I've checked the float levels too but I suspect that they could be the problem. Recently retarded the timing with no effect.
    Any ideas before I tear into the carbs again.

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    Re: flat spot

    Quote Originally Posted by radibob View Post
    I have a 66 Sprite with a rebuilt 1275, new distributor and Petronix. My problem is that exactly at 2500 rpm's I have a misfire and rough running, above that point it smooths out and below it's also OK. I've checked the carbs over and over again but they are the only "old" part on the car so I suspect them. I've checked the float levels too but I suspect that they could be the problem. Recently retarded the timing with no effect.
    Any ideas before I tear into the carbs again.
    So I was just reading some of the other forums and I have been using MMO in my dashpots and there is a bit of a stumble occasionally on acceleration, so I am thinking I need to use a heavier oil in the dashpots???

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    Jedi Knight AN5Sprite's Avatar
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    Re: flat spot

    Change the dashpot oil, check the dashpot springs too. Should be A. the same and B. not all stretched out. I've seen mismatched and worn needles too. Check those.
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    Steve C & the Tunebug

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    Re: flat spot

    Yes, heavier oil in the pots will help with the stumbling on acceleration. It server the same purpose as the accelerator pump in more typical carbs, enriching the mixture for acceleration. But it will not affect steady speed running at any rpm. Also, there has long been a wise old saying, "90% of all carb problems turn out to be electrical." That said though, I don't have a suggestion yet.
    Was Man nicht im Kopf hat muss Man in den Beinen haben
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    Re: flat spot

    I don't either but do not think fuel. do you have another electrical system besides the new one?? is the distributor indeed new or rebuilt, who did the rebuild? I would suggest that the distributor needs to go on a sun machine.
    Jack Laird
    Retired USAF

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    Fourteen shows, Eleven firsts and counting we hope.

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    fixitright
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    Re: flat spot

    Have you checked your automatic advance mechanism, I dont know if you hace a vaccum controlled advance or just straght manual weight controlled advance mechanism. Also see if you have a broken or missing return spring. Check to see if the distributor rotor will move on its shaft. This is the most neglected part of any lubrication procedure. Most distriburors have a felt pad as a way to retain oil for the shaft under the rotor and should be oiled lightly during each routine oil change.

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    Re: flat spot

    The distributor is new from Northwest Auto Parts (not sure of exact name) I checked the advance (Vacuum)and it looked like it was working. I will check Distributor again for cracks, arcs and advance though. Thanks for the great ideas. I am on my way to Advance Auto for 20 W oil for the dashpots...

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    Great Pumpkin jlaird's Avatar
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    Re: flat spot

    Shucks, anything will work in the dash pots all else being ok. Sewing machine oil, etc, I use what I run in the engine.30W. Know that I have never had an engine tuned to the point that dash pot oil did or could make a difference.

    Call Jeff Schlemmer at Advanced distributors, 612 804 5543. He is the expert on all distributor things and has the right equipment to check them out and is a nice guy. www.advanceddistributors.com tell him hi for me.

    He rebuilt Miss Agathas 50 year old unit that was really bad and made it like new. Runs like new as well.
    Jack Laird
    Retired USAF

    Miss Agatha. On the road again and smiling at her new Calif. home.
    Fourteen shows, Eleven firsts and counting we hope.

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    Re: flat spot

    So you guys will love this. Before going to get the oil I pulled the Distributor cap. I was using for the first time my Costco LED light and it is REALLY bright. I noticed on the inside of the cap sort of a spray of brass particles after each contact. The rotor looks Ok but has been obviously scoring the Distributor contacts and creating a dust of brass particles on the under side of the cap which you can't see in day light. The rotor is a proper orange one with the riveted contact but the cap is black with a rounded top. Not sure of its origin but It looks like a new cap and rotor is in order.
    Not sure if this is THE problem but with new dashpot oil and a new cap and rotor things would have to be better.

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    Great Pumpkin jlaird's Avatar
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    Re: flat spot

    So, throw in your spare, you do have one right? Hows that work?

    Or does that mean that your new distributor has a bad or worn shaft bearing?

    The good race ready rotors do not have a rivet to get loose if that is the problem, could be.
    Jack Laird
    Retired USAF

    Miss Agatha. On the road again and smiling at her new Calif. home.
    Fourteen shows, Eleven firsts and counting we hope.

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    Re: flat spot

    Quote Originally Posted by jlaird View Post
    So, throw in your spare, you do have one right? Hows that work?

    Or does that mean that your new distributor has a bad or worn shaft bearing?

    The good race ready rotors do not have a rivet to get loose if that is the problem, could be.
    Lookin for my spare cap right now. Yeah I know, it should be in the car...

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    Re: flat spot

    And Jeff has the correct Red not orage rotor that you need.
    Jim Gruber - Apollo Beach, FL
    Bugsy I - '68 Sprite w BE Bonnet - Gone but not forgotten
    Bugsy IV - '60 Bugeye - 1,275+.040 and a 5-Speed - CA Car - 2nd Owner from new - 10/12 Painting done, reassembly, cutting, and buffing in progress.

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    Re: flat spot

    Sure is quite on this thread, supose we touched a nerve or..........
    Jack Laird
    Retired USAF

    Miss Agatha. On the road again and smiling at her new Calif. home.
    Fourteen shows, Eleven firsts and counting we hope.

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    Re: flat spot

    Also, there are two lengths of rotor, a short one for the two earlier style caps, and, a longer one for the later cap.

    I had a customer with a Spitfire that did exactly that at mild throttle openings, stumbled slightly about 2500 rpm, but, was fine above or bellow that, and, under hard throttle. It had the short rotor with the later cap which requires the longer rotor.

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