Hello all
I recently bought a Innovate wide band A/F meter and have found it to be an excellent tuning tool. I have also found it to be a very good diagnostic tool. While tuning my ZZ430 (350) engine with a stock GM HEI (the one that came on the crate motor, supposed to be somewhat of a performance distributor) I found that my data line on the chart when you play back the data on the meter, shows a relatively smooth line. The O2 sensor is very sensitive and shows the slightest deviation in mixture. When I replaced the engine (Warranty) the new engine came with a MSD Billet HEI. I thought BONUS!!! Well sort of! Anyway I found that the engine does not run nearly as smooth at idle. While idleing I can feel the misfires (urethane motor mounts) and when I do a tuning run with the A/F meter recording the data, the line is a little less smooth and there are several lean spikes in the data line proving the misfires are there. The misfires are intermittent and occur only while cruising. Has anyone had any experience with the MSD HEI (other than plunking it in a motor and driving) Is there a way to fine tune it? I always thought a hotter more accurate spark would make a performance engine run smoother. Anybody have any ideas?
Thanks
Jim

I have heard that distributors with light fast advance springs will tend to not idle as well because the light springs will try and let the thing advance some at idle. I'd check for that problem.
2nd, if its gettin a better spark, and if you have a demon carb, the idle / transition circuit may be too lean, and could be causing a sputter while cruisin.

Jim, is that with ported vacuum for the canister?

Try limiting vac advance until 10"hg

On the timing, how about 12 intial and 38 total all in at 2500?

[ 10-21-2004, 11:46 AM: Message edited by: ZZ430DropTop67RS ]

Sounds like you changed the whole engine so don't limit your analysis to just the distributor. You might have a vacuum leak somewhere.

If the distributor were mis-firing (the cylinder did not fire) wouldn't that show rich on the A/F meter because the fuel never burned?

Thanks for the reply guys
Greg O A misfire shows lean because there is a lot more air in the cylinder than fuel. It shows a lean spike big time. I've checked for vacuum leaks too.
67RS
I'm running ported vacuum. My setup doesn't like manifold vac at all. I get this big flat spot off idle. It really performs well with ported.

The setup now is 32* full advance all in at 3000RPM and a base of about 13* and I'm running a 10* vac can ported. I'm using a Holley 750 Vac secondary carb with #70 jets up front and #74's in the rear. Cruise mix is about 13.8 to 14.2 AFR. (a little rich) Idle is about 14.2 to 15.0 AFR (a little hard to read because of the misfires.) This misfire problem isn't really that bad. It's anoying more than anything and the other engine didn't do this with the stock GM dist. Not all engine are the same so I may try a stock GM distributor to see if it makes a difference.
Don,
I may try a little more advance but doesn't yours ping with 36*? I have a friend with a ZZ430 like mine and it doesn't like more than 34 max.
Thanks
Jim

Jim, mine responds to more advance, but of course I'm at 6000 ft, so I might just be wasting your time smile.gif

With the GMPP distributor that came with mine, I drove it at 36* total for a while, then went with the MSD HEI and found I could get away with 38. I even tried it as high as 40 :eek: , didn't "hear" any detonation, but thought I'd better go back to 38 which it likes alot.

Carb is the 3310 with 4150 conversion, jetted 68-72 with a 5.5 PV.

I'm only at 600 ft. here. I'm gonna have to wait until next year to get to the track to do any more WOT tunning but I think I will try to find a distributor machine over the winter to make sure the MSD is working properly.
Don, have you had your car down a quarter mile? If so, how did you do?
Thanks
Jim

[ 10-22-2004, 07:47 AM: Message edited by: GMJim ]