I've always been told that 10 was normal for a 350, 12 meant you are most likely one tooth off but everything is still ok, so 16 seems quite advanced for a 305.

THe sticker on one of my radiator covers for an original 305 says 5 degrees initial for a manual, 8 for an auto.

 

You gotta remember though...he is running no vac advance. Depending on how the vac advance is hooked up...it can add a generous amount of timing at idle. Without it, I can see why it handles more. Plus, has it got a cam in there? The larger cam will like more timing as well.

I have to ask though....why no vac advance? Did you mean you dont run one at all.....or were you just stating that when you unhook the vac advance, you have 16 degrees initial. If your not using one, definitely hook one up to a full manifold vac source.

As far as the timing curve...factory settings are just guidelines really. If you have the know how and the means to experiment, by all means.....do. Play around to find out just how much total it likes and at what rpm. Than, check into how much initial it can handle. Chances are once you figure these two values out, you will have to adjust the curve so that you get just the right amount of intial and total. For example, you got 36 total right now. Say it likes 36 total the best. Say it also likes 20 initial after experimenting. Well, if you bump initial up 4 degrees from 16 to 20, total goes up from 36 to 40. And of course, since the motor dont like 40 in this example, you will have to curve it so that it only advances to 36 total with 20 initial. Generally, its good to try bringing your total timing in between 2500-3000rpm. thats an experimental thing as well.

After doing your experimenting...hook up an adjustable vac advance(Crane sells a cheap unit)....and hook it up to a full manifold source and play with it til you get it dialed in well. It should idle better and cruise better with a vac advance. Proper timing tuning may or may not cure your stumble. The stumble could be carb related, so it might take further digging to totally fix the problem.

 

Thanks for the replies. The timing was set with the vacuum advance disconnected. I run the vacuum advance on the street. The vac can provides ~ 10* timing. As far as I know, the engine has a stock cam.

I replaced an old mechanical advance Mallory dual point with the current vacuum advance distributor. It definitely runs smoother with the vacuum advance, and I figure I'm in the ball park as to where the timing should be. I wasn't sure if 305s in general liked less timing than 350s, possibly due to the small bore size. I guess I'll try bumping the timing up and see how the car responds. If it pings, I'll go the other way and see if there is an improvement.

The hesitation could be carb related, and I plan to work on that after I get the timing dialed in. The current Q-jet will eventually be replaced by an AFB carb to allow an air cleaner to be run. Unfortunately the Performer/Q-jet combo is too tall to allow an aircleaner to fit under the stock hood.

 

My 305 runs very well with 22 initial and 36 max all in by 3000rpm. I am running a manifold vacuum source for the advance. That's with 8.5:1CR and a XE256 cam. So cylinder pressures should be a little lower then a stock motor.

Steve

 

Wanarace, thanks for the information. I'm currently running on 87 octane and want to be able to continue to do so. I believe the vacuum advance is currently hooked to a ported vacuum source. I'll have to try manifold vacuum and see how that affects driveability.

 

ITs not guaranteed that manifold will do better....but it seems to in lots of situation. You end up with more timing at idle where you can use it...plus, at a light throttle cruise, manifold vac will be high and the manifold vac source will add a fair amount of additional timing. This is good cause the leaner mix at a light throttle cruise will like the additional timing. And then, when you roll into it a little(just for light acceleration...not full throttle), manifold vac drops and so will the timing added by the manifold vac source. This is good as well because when you add more pedal..you enrich the mixture and the enriched mixture doesnt need as much timing....and of course, when its set up on manifold vac...the additional timing you dont need will start to go away at this point.

Its worth a try cause you may get better results. Once again, you seem to be doing well with your timing settings. reguardless of what the factory says..it can usually be improved upon so if you make some changes and get better results with a "non factory" timing curve...that dont mean that somethings wrong, it just means that you made it better. Especially in the years of your motor, everything was tuned sub par to help with emmissions.

 

So one clarification to what Greg wrote...

Just to make it clear: ported and manifold are one and the same except at idle.

You may however note a difference between a vacuum port on the manifold and another vacuum port into the carb throat. The true manifold vacuum may run 1-2" higher than the carb throat vacuum port.