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Thread: TR4A with TR3 distributor and Vacuum Advance

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    TR4A with TR3 distributor and Vacuum Advance

    OK, long story short I've been chasing a dieseling, poor gas mileage, high idle problem for 2 years now. After having switched out the ZS 175 CDs twice and resetting everything I found out yesterday that my PCV valve was assembled improperly and took 20 seconds to fix that. Suddenly the car will idle at 600 rpm like a champ. I enjoyed the much improved idle and my dieseling problem has been substantially reduced. I have seafoamed the car to help get rid of the heavy carbon deposits and I'm sure that this is a partial cause of the dieseling. Any more thoughts here?

    I took note of my distributor and vacuum advance today and saw that they are both TR3 units, (DM 40480, 4-11-7). My question is how much would changing to the proper 25D4 40795 distributor with 2-6-3 vacuum advance help me, if at all?

    I am running 91 pure gasoline and RL87YC plugs. The carbs are at stock settings .100 jets with 2H needles, no gross jets. I have run 100LL aviation gas in the car and it does not diesel at all. Plug gaps and static timing have been checked. Point gap was checked about a year ago when they were new.

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    Re: TR4A with TR3 distributor and Vacuum Advance

    I recommend that you call Jeff at Advance Distributors and discuss with him. He is very knowledgeable and helpful. His number is 612-804-5543.Regards,Bob

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    Re: TR4A with TR3 distributor and Vacuum Advance

    Quote Originally Posted by carpecursusII View Post
    ...I took note of my distributor and vacuum advance today and saw that they are both TR3 units, (DM 40480, 4-11-7). My question is how much would changing to the proper 25D4 40795 distributor with 2-6-3 vacuum advance help me, if at all?...
    I think it will help but the big change will be in the centrifugal advance which presents a very different curve, particularly when advance is 'all in' at higher RPMS:



    Lest I sound like a dizzy expert -- I am not. But these things are not rocket science. Were it me (and it once was) I would source the correct unit and carry the other as a spare.

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    Re: TR4A with TR3 distributor and Vacuum Advance

    My experience with Dieseling is that it was caused bydeposits on the plugs. Once I had some oil rings not seat and it left oil andcarbon deposits that dieseled quit a bit. Another time the problem was weakspark that left deposits. I switched to metal plug wires and that helped. I would suggest keeping an eye on the plugsand setting the fuel mix a little lean along with the correct dwell and timing.Sometimes these old distributors have a lot of play and timing moves aroundjust driving down the road, so you might consider getting a new one. I noticedthat BPNW had them on sale and I would consider that.

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    Re: TR4A with TR3 distributor and Vacuum Advance

    I always had trouble with run-on on my TR4A with strombergs and the stock dizzy. EFI and Megasquirt cured all that, but also added a high level of tuning with a learning curve.

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