I recently had an MSD 8572 Tach drive vacuum advance distributor with the ignition kit installed on my '70 350/350.

The car idles well, runs ok at higher RPMs, but stutters and backfires with aggressive accelleration at low RPMs (mostly i notice this is 1st gear). It sounds like the backfire is through the carb.

The carberutor is a recently rebuilt original Quadrajet.

I wasn't comfortable with installing the distributor along with the ignition kit, so I had this work done at my local mechanic. He doesn't tune performance systems, so I don't know if he set this non-factory correctly.

Any suggestions from someone who is running a similar system? Initial timing, advance timing, advance spring adjustments?

 

Where is the vacuum hose attached to, the manifold or ported (base of carb)?

 

Run a 8572 out of the box with a 6AL box on my 70 L-46. No TCS. Just run from the carb(7040207 right?), to the distributor. Timing at 12 degrees BTDC. Runs perfectly.

 

I have the same distributor. It works great with the MSD Blaster coil and 6A multispark HEI box. There is a very good C3 sticky here on timing you should read as well as others about setting up your carb. If you go to the MSD web site there is also the owner's manual and good info on timing. Mine is set at 13* initial, 20* mechanical with 10* vacuum advance. You can go higher initial and mechanical up to 36* and "all in" up to 52* if you get no pre-ignition or pinging.

One thing is for sure if you have an MSD multispark HEI set up. You can't use solid core spark plug wires. You must use the heil wound or spiral wound super conductor wire.

Here is the timing sticky

http://forums.corvetteforum.com/c3-t...long-post.html

 

One thing to remember, Unless the harmonic balance is new, there is a good chance that the outer ring that has the notch in it for timing has rotated from the correct position it should be located. I have more times than not, in my shop, found this problem to be true. I use a vacuum gauge to set the timing on a warmed engine. The gauge will tell you what is best for the engine. Then I will check it with my advance timing light and see where it is set and note these issues to my customer. If the spitting back up through the carb is new , no problem, its a timing issue. If was doing it before than there is a good chance that one of your exhaust lobes is worn off the camshaft. I do not know the history of your engine so I am just letting you know what else it can be if this problem of spitting back was going on for some time. You have purchased a serious ignition system that is much better than stock. If you have access to a chassis dyno and have the $$$ and time you can change spark plug gap and other settings and actually see the improvments in real time. There is alot of improvement to the factory set-up that can let you squeeze the max out of what you have now."DUB"

 

Off topic I know, but may help Dennis (or me). Is the spring on the choke/fast idle assembly in the correct place? I think it's supposed to go to the diaphram

 

Nope goes right there. I asked about this as well awhile back. Posted this pic. Trying to find the info. Think it was over at the NCRS board

 

Grandmaster has a point about the harmonic balancer. You can check it by placing your #1 piston in exactly top dead center with a piston stop tool or dial indicator and see if the mark on the balancer is at 0* on the timing tab.

 

did you make any adjustments to the advance springs or bushings? or did you use it straight out of the box?

 

Nope just plug and play