Squirter/pump cam tuning?

[Right hand drive]

Trial .028” mab and see what it does to the lean spike area then observe affect on WOT.

[GTO Geoff]

Dcmd21,

You must have missed this bold type in last post: idle advance.

Not talking about centri curve in the dist. Two ways of getting more idle advance is to use vac adv hooked to manifold vacuum, or one of the digital ign boxes available. GM used vac adv, to man [ MVA ].

More on MVA benefits, scroll down to post #6:

www.hotrodders.com/forum/vacuum-advance ... 47495.html

[dcmd21]

GTO,

Assumed your post referred to distributor initial advance because vacuum advance (manifold or ported) would be of no use when snapping the blades open and causing vacuum to immediately disappear. Ported was designed to help with part-throttle transition way before MVA became fashionable but would be equally useless when mashing it.

Played around with my MSD distributor to see if my lean miss would disappear with it locked out but it just needed the immediate fuel the green cam provided. Sometimes it's not the ignition but the fuel, and a man needs to test. Assuming the OP is versed with ignition and his description sounded like a pump deal to me. The OP has a bigger cam than me and if a higher idle speed, then #2 on the pump cam may be better than #1. I have lots of vacuum; even with just 22* of initial timing, I can't set the idle lower than about 620. I played around with lots less timing to test but same result (good with green), it just does not like the pink cam. Does like lots of timing, too.

Not all those old GM setups used MVA. I have a 1967 Carter AFB that doesn't even have a port on the carb for MVA, ported only. Thinking the AFB on my old man's 63 SS is the same.

[GTO Geoff]

Carters were used on Chrys cars, which used the useless PVA. So your carb may be off a Chrys car.

GM used MVA up until 1968, a transition year, when we got the useless PVA.

Not all Carters used on GM engines had an individual MVA port. The original Carter AFB on my 66 GTO had a brass T-piece that fitted in the back of the carb. This provided manifold vacuum for power brakes, trans modulator &..........MVA.

MVA never quite disappeared from the scene.... In the 1970s, many companies used a temp switch to switch from useless PVA to MVA. When the engine got too hot, the switch was made from PVA to MVA. The extra idle timing that MVA gave made the engine more efficient & generated more HP; as shown by the idle rpm increase; which turned the water pump & fan faster & the engine cooled down.,

[1109RWHP]

[GTO Geoff]

David Vizard has written 30+ books & many of them reference the importance of idle timing. The above quote comes from his latest Holley book, p. 30.

Huh? How can that be, it is a book about carbs, not ign....

P. 30 is NOT the only place in the book in a carb book that idle timing gets mentioned. Smart people realise how important idling timing it is to overall performance of the engine....

Another quote [ not DV ]: '' Carbed engines with long duration cams will benefit the most from vac adv......you should consider hooking the vac adv to straight manifold vacuum. This is counter to what you may have been taught in high school auto shop, but it is actually a really good idea.'

More on MVA benefits, scroll down to post #6.

www.hotrodders.com/forum/vacuum-advance ... 47495.html

[HarrysTaxi2]

How much MVA do you have when the throttle blades are opened quickly?

[GTO Geoff]

About as much as a piece of string....

[novadude]

[HarrysTaxi2]