I've been out road testing my new 355 and it stumbles at 2 - 2.5k rpm. Gradual acceleration is OK, but mashing causes spits and pops. I set my timing at 9* but do not know what my total mechanical is. Only have a strobe light. I'm using a Petronix that has the springs in it for 23* at 5k RPM. That only gives me a total of 32*, and not until 5k.
From what I have read in posts, most of you say to have around 34* - 38* by 3 - 3.5k RPM.
Should I install the "lighter" springs (23* @ 3k RPM) and set my initial up to 12* ??
I'd like some comments or suggestions before I try it tomorrow. Thanks guys!

Just a thought but do you have the vacuum advance hooked up? That would give you additional timing at part throttle.

Yes, I have the vacuum hooked up. According to the Petronix chart that came with my distributor I should be getting 9* additional @ 1k RPM with the springs that are on now. Does that mean that at 1k with vacuum, I would be at 18* ? If so, then I guess at 3k I would be at 37*.
If this sounds O.K., then maybe I have a fuel problem??

I thought the idea was to have total advance read without the vacuum hooked up??

[This message has been edited by jeff81 (edited March 16, 2005).]

Since you say that you do not have a dial-back timing light, I'd suggest getting timing tape for your balancer. That's what i did before I went to a Streetdampr with timing marks. That way it will be easier to check your timing.

Also, from what I've seen, some people include vacuum advance in total timing, others don't! It's confusing!

The springs should only control cetrifugal advance, not vacuum. That would be by the can. I don't have a Pertronix but it should be similar to Accel replacement HEI that I have.

I also gathered that you should have total advence in by 3k, 34*-36*, not including vacuum.

Sounds like you have an accel pump problem not an advance problem.

what carb? Its not getting gas fast enogh or its getting too much air to fast

I'm using a rebuilt Q-Jet, 750cfm. I adjusted the secondary top flapper tension. They were totally loose. Also installed the lighter springs in my dist. These springs are supposed to have 23* mechanical kicked in by 3k rpm. I'll set the initial timing to 12* in the a.m. and see how she does.
I may still have a carb problem, but at least I'll have the timing alot closer to where it should be.

Remember now that you have the lighter springs in your dizzy the mechanical advance will be kicking in at about 700rpm and topping out at about 3000rpm. What I'm saying is, if your idle is like 900rpm you will have a degree or two of mechanical also so you may be fooled into thinking you just set the initial at 12, but it is really 10 or 11. I drop my idle as low as I can about 500rpm, to make I'm getting a true initial reading.

Get a dial back, or digital timing light, its a great tool to have. It makes mapping out and setting your initial, mechanical, and vaccuum advance alot easier. A good starting point for a mild 350 is 11 initial, 35 total(at 3000) and about 50 with vac. advance (11+23+15 = 50) at cruise at 3000rpm.

The next step is getting that Q-jet tuned for best performance too, then maybe some final tweaks with timing and again final tweaks with the carb. We can help you set up that Q-jet pretty close just by your engine specs, because I'm sure someone here has a setup close to yours.

Thanks for the advise acg73Z/28. I was going to check it out this a.m., when I accidently fried my fuse link wires to the starter. I grounded out the timing light lead on the back of the alternator. Ooops. Anyway, it was probably a good thing, because I found that the metal tube (sheath) was too close to the headers, and was starting to melt the wires anyway. Soooo, I spent this evening installing new fusable links, wires, and rerouting the leads from the harness to the starter.
I'll re-check my timing in the a.m. and post the results. Thanks again! http://www.nastyz28.com/ubb/smile.gif

Well, all I can say is RRRRROOOOMMMMPPAAAA!!
I adjusted the secondary flappers, put in lighter springs to give me 35-36* @ 3k rpm, set the initial timing @ 12*, and she runs GREAT! Thanks to all for your suggestions, comments, etc. Between an old post by 78LT and Marv's post the other day, I determined that my engine was getting too much air too fast due to the flapper adjustment being too loose.
That was probably most of the problem, but I'm sure happy with the quicker throttle response using those lighter springs.
Next week I'll have a dial timing light and be able to check out for real where I'm at on the timing. She should be awful close. Thanks again. http://www.nastyz28.com/ubb/smile.gif http://www.nastyz28.com/ubb/smile.gif http://www.nastyz28.com/ubb/smile.gif