69 Z28 302 is timing 60 dgrees

69z28boy · Dec 26, 2012

Steptoe said:
I suggest u guys back up a heap of pages and read / rethink what u are doing.
33 degs at idle is crazy, just to get a good vaccuum....
When tuning (not dialing in) one adjusted for best vaccuum withing the dialed in tuning specs... NOT dial an engine in to mac vaccuum.
Every engine .. due to stuff like can durations overlap etc have there own 'best vaccuum' charactoristics, and it is NOT, EVER the highest vaccuum u can obtain.
High duration/ overlap, at low rpms the valves are open far longer, far less time to devalope good cyclinder pressure and vaccuum...or put another way, low rpms hopless engine efficiency... of coarse it will have lower vaccuum, and trying to increase and match a more stock cam by wacking idle advance up above 22 degs is false compensating and cabn do long term engine damage ...inaudable detonation at idle is just one, then there is the high NOx emissions, oil contamination and poor lube issues....

i agree with you - but these guys are saying that they can't get their engines to idle without 33 degrees - and when they try setting the timing to "suggested" initial specs - they get very low vaccuum and the engine will barely idle...In which case, i think either something is terribly wrong, or their timing light isn't reading properly.

Cheers

my guess has to do with

Gary L · Dec 27, 2012

alanrw said:
Gary, has your idle issue been resolved, I recall you were having problems with it, in fact, I still have the thread bookmarked.

alan

Mostly. I need to send the carb to Eric. The front metering block was replaced and I have concluded that the idle feed restrictions are too small and need to be opened up. Idle is too lean and I cannot open the mixture screws enough with out removing them.

alanrw · Dec 27, 2012

Hmm, I googled "holley idle circuit tuning" and got a bunch of hits, this one was interesting:

http://www.carcraft.com/techarticles/ccrp_0807_holley_carburetors_basics_guide/viewall.html

Any chance the gasket is partially blocking a passage or trash in the block itself?

alan

fastfreddy · Dec 27, 2012

Thanks for the replies. I forgot to mention that I have headers with 2 1/4 exhaust pipes with electric dumps just in front of the axle. I also mix the 110 fuel with good pump gas.
It really idles very good at 28 initial, but has that stumble with quick throttle opening which it doesn't do with much lower initial. I converted the dist. port to manifold vac. so I can run lower initial and VA at idle then set the total by tweaking the centrifugal. I'll see what happens when I get the new vac can. The old original 400-15 works and holds, but doesn't pull all the way in at 8 in. Does anyone know the vac specs on one of these? Also, does anyone think that advancing the 30-30 cam by 2 degrees (cam) will do anything at all to idle vacuum? I'm also thinking about trying different valve lash settings.

Gary L · Dec 27, 2012

I don't think anything is blocked. The carb was looked at by another "good" shop. I think that by exhaust reversion the fresh mixture is too lean. I can't get a too rich smell at all. By opening the idle feed restrictors the idle screws will have adjustment that they do not have now. Eric will know how to handle it. Other than slowly dying out it runs like an animal. No hesitation or bog at all. The higher initial gets the butterflies closed where they need to be. Holly's also idle off the secondaries too. That is a different story.

If you have never messed with a "stock" 302 you have no clue what an odd bird the 30-30 is. The DCR is around 7.2. Very low.

Good article.

Gary L · Jan 21, 2013

What happened Freddy?

pjam · Mar 10, 2013

Ok, I will also add to the list of folks who get a 30+ timing at idle on their Z. I have checked everything top to bottom, as everyone has suggested, and read multiple threads on this. Nonetheless, the car runs great and starts right up....at 30+ at idle. It doesnt make sense. Im using a craftsman pro light on it and decided to put it on my stock 1988 suburban (79K original miles) and guess what I got at idle....30+ when it should be 4 BTDC. So I got a cheap light at Harbor Freight and the numbers were the same. Any other lights to recommend or thoughts on this?

PJ

69 Z28 302 is timing 60 dgrees

69z28boy

Gary L

alanrw

fastfreddy

Gary L

Gary L

pjam

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