I am going to be recurving my Mallory Comp 9000 distributor in the next week or so. This is a mechanical advance distributor. I would like to know at what point after the idle RPM the advance should start to come in. For instance, my idle is currently about 850 and the advance starts at 1100. I think this is too far apart. I can set the advance to start coming in before the idle RPM and limit the max to 36 degrees.



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Kent
67 SS 427

You want to avoid having the engine idling inside the advance curve or the idle will likely become unstable. 1100 is a fine place to start.

-Mark.

Mark,

The reason I am asking is if I advance the initial timing the car runs much better, but is almost impossible to start. I have a serious bog off idle and have tried all different types of pump cams on carb. The bog started when I set my timing to 16 BTDC. I don't know what it was before, but it ran much better but was really hard to start.



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Kent
67 SS 427

Yes it will be hard to start that way. Have you seen my recent posts on setting up ignition/curves? It is rather lengthy and posted within the last couple of days. A manifold vacuum advance would be very helpful here in getting it to start easier and idle better. You can back off the initial and set the vacuum advance for an additional 16 degrees at idle once the engine is running. I don't know if the 9000 series can accept a Vac advance canister or not.

-Mark.

Mark,

From what I can tell the Comp 9000 that I have will not accept a vacuum advance. I am going to call Mallory and ask. When I bought this mechanical distributor, I though that mechanical was better than vacuum. I have read your posts and now I am much more informed. I will keep looking to see if I can find a kit or method to put in a vacuum advance.



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Kent
67 SS 427

Kwissman, what is the rest of your combo like? I ran a Comp 9000 for about 5 years on a pretty built 355 and never had any bogging probs that were NOT carb related (that was 10 - 15 years ago though). I never set or even looked at base timing, I always set it for 36 total and it worked fine.

I agree 100% with Mark on the timing curve - if you start bringing timing in below the idle speed the engine will surge at idle. I've done this when playing with springs on my HEI. The vacuum advance connected to manifold vacuum may be useful with a big cam, but I prefer ported advance with less radical cams.

Whenever I've had a distributor with a curve that came in too late it always caused a flat spot in the midrange, like in the 3000 - 4000 RPM range. I suppose it could happen lower, but that Comp 9000 should come from Mallory with a fairly agressive curve with all the timing in by 3000 RPM if I remember correctly. Could something in the mechanical advance be sticking?

ps. another thought - can you borrow another distributor from someone? That might save you some trouble before you start changing around your adv curve.

[This message has been edited by Eric68 (edited 07-08-2002).]

[This message has been edited by Eric68 (edited 07-08-2002).]

You will NOT be happy with a centrifugal-only distributor in a street-driven car, and you'll go bats trying to tune the car for any kind of driveability and throttle response. If the distributor won't accept a vacuum advance can, I'd get one that does, and put your existing one on eBay with a heading like "Mallory Custom Race Distributor" and you'll sell it in a heartbeat http://www.camaros.net/forum/biggrin.gif

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JohnZ
CRG
'69 Z28 Fathom Green