75_yellow

So after the cam swap my car has been running pretty bad. Well I added new plugs and wires. Readjusted the vavles. Bought a new secondary diaphram and lighter spring. Today I installed lighter dist. springs and throw a timing light on it. I set it to 8 degree with the vaccum disconnected ran fine. Put the vaccum advance back up. The car dies, wont idle and is back fireing like its 180 out, no matter how much I adjust the carb and idle screw and the timing. I cant get it to run. So I decide just to get it home im going to do lock out time on it with the vaccum disconnected and set to about 28 degrees and it has never idled better smooth easy to tune and feels pretty good driving it. What would cause this to light of a spring?

Artsvette73

Double check the firing order. Don't ask why I know.

75_yellow

Will do ive checked it twice but i wont hurt to do it again

80Vette80

Have you checked the cap and rotor button?

corvette_maniac

Overcammed? What are the specs on the cam and what kind of compression do you have? Also do you have a stock q-jet?

75_yellow

i think your right about it being over cammed here are the specs
Intake Duration at 050 inch Lift: 244
Exhaust Duration at 050 inch Lift: 254
Duration at 050 inch Lift: 244 int./254 exh.
Advertised Intake Duration: 302
Advertised Exhaust Duration: 312
Advertised Duration: 302 int./312 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.510 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.533 in.
Its factory comp. Was planning on a little turbo set up after delployment. I rebuilt a holley 750 vacuum secondary for it
BTW what i a cap and rotor button?

corvette_maniac

That's a huge cam for the L48 / 8.2:1 CR 350CID. I had a cam that size in a Pontiac 400 with similar compression and it surged at part throttle and was rough idling.

So your engine runs better when you have the vacuum advance disconnected. Are running ported or manifold vacuum to the can? Also when you disconnect the vacuum line are you plugging it or creating a vacuum leak?

You can run a cam like that...it's kind of a pain around town but will be great on the highway and rpms above 2500. It will require some tuning for sure.

75_yellow

The car has ported heads and im running it off the manifold.
i am pluging it when i disconnect it

corvette_maniac

Since you say it is fine at 8 degrees at idle, maybe you should connect ported vacuum to the vacuum advance.

When you mentioned the 28*, is that the total timing?

75_yellow

yes it is total timing
what do you mean ported vacuum? thats not vacuum that comes for the intake?

SanDiegoPaul

Intake vacuum is manifold vacuum. Ported means it's above the throttle plates and only gets vacuum above idle.

corvette_maniac

What SanDiegoPaul said.....

From the info that I've gathered, and this is just typical tuning here.....set your total timing (initial + mechanical) to 36. Rev to around 3K to set it. Then see where your initial timing falls. Sounds to me like your gonna be around 18 (since you said you were at 28 total when the initial was at 8). The mechanical is giving you 20. Now.....once you are done with that .....rev it up and find out at what rpm you just get to 36. I like my total timing all in at around 2500.

It's a good starting point for you. If you get hot start problems and spark knock at WOT or part throttle - we can go from there.

Oh ....and try the ported vacuum. You are definitely not going to want to use the manifold vacuum to the vacuum advance if your initial is at 18.

Good luck.