msd ignition/timing/carb

[pcollins1]

i have an 81 chevy 350 with an msd idnition--6al--and billett proof distributor. it has a holley 600cfm. it runs ok at idle, but when it gets warm it starts to hesitate. if you run it over 70 it wont hesitate, but it does bog down when i mash the gas, it back fires occasionaly at low rpm . the timing is set at 15 advance. i guess, im not real familiar with timing. i was told the carb was causing the problem so i replaced it and nothing changed.
thanks for any help

[Pamsdad]

You need to set the timing properly before going further.

There are 4 different types of timing:

1 - Base Timing. This is where the distributor actually sits in the intake manifold, rotated to desired setting and then clamped down.

2 - Mechanical Adavance. The amount (in Crankshaft Degrees) that the distributor advances the timing through Flyweights and Springs.

3 - Vacuum Advance. The amount of advance the vacuum canister advances timing.

4 - Total Advance(Timing). Take your Base timing and add it to your Mechanical Advance.

I don't know if your MSD unit has Vacuum on it or not. You should set the Base timing at or about 15 degrees. Your distributor should have about 20 degrees in the mechanical advance. This would give you a total of 35 degrees. That is a good start.

If you don't know how to check these different timings, have someone help you. It's not hard.

Hook the timing light to the battery and to #1 cylinder. That is the spark plug closest to the front of the car on the driver's side. Shine the light at the balancer and read the timing. This is your Base. Now slowly rev the engine while still shining the light on the balancer until the advance no longer climbs. You might need to rev engine to 3000-3500 before timing stops moving.

I'm assuming you have a dial on the back of your light and you know how to use it.

Once you set the timing look at the carburetor. That's where I think your problem lies anyway.