jimbo1972

Hey Guys, Im trying to get my ZZ4 fast burn 350 crate motor dialed in. Here is my set up... ZZ4 350, 4spd, 3:73 rear. Holley 650 double pumper. Jets are stock 67/73. Right now I have 35 front and 31 rear squirters Black front pump cam on hole #1 Blue rear pump cam on hole #1. Timing was to zz4 spec (12 idle, 32 at 3000rpms). I am running vac advance and it likes it. The carb pulls 18" vac and idles smooth at 750. Here is my issues...slight bog/hesitation when you floor it from idle (very slight). Slight bog/hesitation when you floor it in 4th gear at around 2000-2500rpms. I am also getting some pinging when accelerating hard. I have tried backing off on the timing but it still pings (will ping with or without vac advance hooked up). Should I go up in jet sizing? Any advice would be great!! Thanks! -Jimbo

scottyp99

28" of vacuum? Could you please correct that? Also, are you sure that the timing is all in at 3500 rpm?

Scott

birdsmith

Which power valve are you using? Whatever your idle vacuum is, it should be a number 1.5 below that, i. e., if you're seeing 8" vacuum at idle a 6.5 valve should work well

jimbo1972

Sorry. Its about 18" of vac. Yes all My timing is in by then. Im running an MSD dizzy. PV is what is came with. Its a 6.5 Thanks for the help! Jimbo

7t9l82

you might go up 2 sizes on your primary jetting. and if its an air gap intake go up on your front squirter. these carbs out of the box are lean. i went up 3 sizes on the primary with a 750 double pumper.

427Hotrod

I'd put more initial in it..more like 18-20* and cut back on mechanical. Use the largest bushing that came with the MSD. Probably have to cut back on vacuum advance with more initial. Flooring it at 2000 rpm in high gear is a tough goal to hit with a 4 speed. An auto would have converter letting engine rev and the thing would downshift to 1st gear probably. I wouldn't keep doing that regardless of the tune with the hypereutectic pistons.

Have you pulled the plugs after a good long pull? Drop a clean plug in one hole and make a hard run...then immediately shut it down and coast to side of the road with no idling. Pull plug and inspect.

JIM

jimbo1972

Great info. Thanks. I did pull a plug after a nice cruise (with min idleing). They are a little white like its slightly lean. Thats why I am thinking up a few sizes primary and secondary. Maybe go 73/78. Im at about 5deg now idle mechanical timing that puts me at about 15-16 vac adv timing at idle. The car really runs pretty good so far. Im impressed w/ the crate motor. Jimbo

427Hotrod

I'm talking about 18-20* without vac advance. You have to remember, when you crack the throttle, vacuum drops and that vacuum advance is going to drop away for a little bit...or a good bit depending on throttle opening. That can make for hesitations etc. I'd want more initial...limit the total to whatever it likes (32*?) and THEN play with vacuum advance to help with light cruise mileage etc.

Do some study on plug reading. You have to look deep down in there at the porcelain to see what it's really got for mixture under full load.

JIM

jimbo1972

Thanks for the help.
I will look at the plugs and play with the timing.
Playing with the shooters and cams today, It running and not bogging on acceleration or off idle. I just want to get rid of the pinging under hard acceleration.
Thanks again!
Jimbo

flyeri

I would worry about the ping before I worried about the hesitation. When I went from a non vac advance Mallory to a vac advance MSD I set up the distributer to closely resemble the curve I had with the Mallory. That did not work at all. With the vac advance and lighter springs I got pinging 4th and 5th in the upper teen rpms with light acceleration. This is the cruise rpm for the car so that would not work. I had to go back to the heavy springs. I now use 11 initial which gives me 26 degrees at idle with manifold vac. Mechanical is 36 but all in about 4500rpm. I plan to experiment with less vac advance and lighter springs but for now it does not hesitate, does not ping and still pulls very strong. It has a much cleaner, smoother idle.

jimbo1972

Good idea. I just ordered a spring kit for the msd. When that comes in, I will start playing with the timing. The car is so much fun to drive, I want to get it dialed in asap!
Thanks again to everyone who is helping out.
Jimbo

427Hotrod

Did you get the bushings also? They should have come with the distributor if you bought it new. You need the bushings to play with the timing curve.

JIM

jimbo1972

Yes the kit I ordered comes with bushings. I could not find my original kit. Prob left it at my buddies shop somewhere.
Thanks again.
Jimbo

diehrd

Increase the front squirter by 2 sizes .

Street Rat

Here is a link to a Holley tuning page. Good information.

http://www.holley.com/data/TechServi...ech%20Info.pdf

jimbo1972

I should have my msd kit soon. Here is my plan. Let me know what you think....
My bogging issue is almost gone from playing with the shooters and pump cams.
I am going to put the largest bushing on the msd dizzy. (The black one will give about 18deg) This will put me at about 14deg inital timing, 32 mechanical advanced (no vac advance).
I will use the heavier springs to have all the timing in at around 4500rpms.
I will watch the plugs and adjust jetting from there.
My goal is to get rid of any pinging. Then I can move on to playing with the vac advance.

7t9l82

Those heads have a modern chamber maybe shoot for 44 degrees all in. You might back off to 12 degrees and check you advance can yours is probably too much now. Once. You get about a 12 degree can tailor your advance around that. I think yo should go up a jet size you can always go back

68/70Vette

Where I live, there is a garage that has been specializing in performance American cars since the late 50's. They have new owners, but the new owners are not that young. The specialize in performance tuning of cars up to the early 70's when there are no smog rules effective. I took my ZZ4 to them after I dropped it in the 68. When I got it back, it was just a fantastically new car...tremendous power for a SB.

Find a performance shop that is knowledgeable with older cars.

jimbo1972

I got the MSD spring/bushing kit today. I installed the stiffest springs and largest bushing.
Originally I was running the +25 deg bushing and springs set to have the advance all in by 3000rpms.
Now my timing is 15deg idle and 32deg mechanical advanced at about 3500 rpms.
The car runs great with or without the vac advanced hooked up now. No pingings on the upper end and the hesitation/bog is almost completely gone. Vac advance is giving me about 10deg more.
I am going to play alittle more with the shooters/cams and also go up alittle with jet size because the plugs are showing a little on the lean side.
Thanks for all the help!
-Jimbo

jimbo1972

Well, I got the car running near perfect. I went up in jet sizes and have eliminated the bogs and the pinging in all gears at all rpms. Plugs look great now.
The only issue I am having now is setting the transition slots. When I set them up (primary set w/ feeler guage at .020 and secondary matching the angle of the primary), my idle is very high (1500rpm).
To get it to idle around 750rpms, I have the secondary screw backed all the way out and the primaries backed way out and not even close to the transition slots.
Car idles perfect, mixture screws perfect (18" vac), doesnt smell at idle and there are no vac leaks.
Any ideas??
Thanks!
Jimbo