Tourney3p0

Hey guys,

I have a question about a 74 thats had a ZZ4 installed in it. It's not my car so I can't answer specifics off the top of my head, but the guy who owns it doesn't have access to a computer.

Anyway, he changed it over from points and ever since then he's been having problems with the timing. When he "gets on it" the vacuum advance seems to be advancing it way too much and causing a ping issue with 93 octane gas. Right now he has the vacuum disconnected, so he's getting no advance and it's not really running as well as it could.

What would be the best way to take care of something like this?

e3pres

Try total timing it first. Set it to 36 degrees at ~3000 RPM and re connect the vacuum advance and see if that fixes it. Without knowing what kind of curve kit the distributor has in it, that's about all the advice I can give. Since you live in Clinton, send him over to Dragon's Breath Performance. Bob Moss specializes in Corvettes. His forum handle is "Violater". He will be of much more help than me. Good luck. :cheers:

Tourney3p0

I appreciate the response.

I wasn't familiar with Dragon's Breath Performance, but anyone around here who specializes in Corvettes is someone I need to familiarize myself with.

Thanks again.

Tourney3p0

Actually, I know Bob. I had forgotten his last name was Moss, and I thought he lived in Shreveport.

I'll have to give him a shout anyway, even though he probably won't remember me.

Thanks once again.

e3pres

Bob just recently moved to Knoxville and started the shop. It is VERY nice to have a Corvette specialist so close to home.

theandies

Is he using manifold vacuum or ported vacuum for the vacuum advance? If he is using ported vacuum then the only time the vacuum advance comes into play is a cruise/part throttle operation. At WOT/Idle there will be no vacuum advance. Do as suggested above and setup the mechanical advance to 36 degrees "all in" by 2500 to 3000 RPM's. Take it for a test run and check for ping, if it still pings retard the advance it 1 to 2 degree increments until the ping goes away. My advance is set for 34 degrees, anything more and I get a slight ping. My ZZ4 runs great. What distributor does he have? I am running a full MSD setup with a tach drive distributor.

Steve81

I had the same problem with the ZZ4. Way too much timing with the vac adv. and was pinging at part throttle (i am assuming you mean hard part throttle ping, not Wide Open Throttle), even with the inital timing set at 8, still had a ping. Try the Crane Adj. Advance Kit with Limiter Plate. The limiter plate will give you +2 intial and -2 vac. adv. for each notch on the dist. This will allow him to bump up the intial timing and limit the vac advance and eliminate the ping. Worked for me. If you do a web search for Crane Adjustable Advance, you can download/check out the instructions/directions.

Todd Mabry

:iagree: I'm with Steve. Get an adjustable vac advance kit. I had to tweek my ZZ4 quit a bit to get the ping out. Also, as mentioned before, check to see if he is using manifold or ported vacuum. The folks that put my engine in used the ported and never could get it to run right. I finally found this and it made a bit difference.