SBC timing woes (1 Viewer)

[69LC]

I've been messing around trying to get the timing right on my 350 since I stuffed it into my 40, 10 years ago. I've never been able to get the distributor timing just right. The engine's PO "gave" it to me for $50 when he bought it as a rebuild and couldn't get it right. I'm going to tear down the front of the engine to check if the cam sprockets are timed together properly. I've had two local hot rodders confirm this is probably the best next step. It also has always seemed to fall on its face as I get into higher rpms like when trying to power out of mud or sand. When this happens it often develops a miss and eventually cleans out. It has a twice rebuilt vacuum secondary Q-jet.

Any thoughts?

I may miss the major back fires shooting out the exhaust (5-6ft) as I shift while passing the local golf course, but I want better than 3-4 mpg and a doggy engine. My kids watched a golfer lose his club mid swing and then almost get hit by it as it fell back from orbit.

 

[65swb45]

Thots.

1. Stock engine or performance rebuild?

2. If performance, do you know the compression ratio, or cam lift?

3. What is your vacuum reading at idle, and with how much distributor advance?

4. Without this info, speculating on cam timing is premature.

Best

Mark A.

 

[inkpot]

Howdy! Your talking about two entirely different timing issues. Ignition timing is what you change when you play with the dizzy. Valve timing is what is controlled by the cam. Problem could be the "rebuilder" reused the original used/tired/worn out lifters, or cam, so it might not be a timing issue at all. John

 

[69LC]

1. Stock engine or performance rebuild?

I'm not sure what level of rebuild. I bought it second hand.

2. If performance, do you know the compression ratio, or cam lift?

I only remember being told it was an RV cam.

3. What is your vacuum reading at idle, and with how much distributor advance?

I can't answer either of these. I've always done it by ear.

4. Without this info, speculating on cam timing is premature.

Will pass this on to my engine guru.

Howdy! Your talking about two entirely different timing issues. Ignition timing is what you change when you play with the dizzy. Valve timing is what is controlled by the cam. Problem could be the "rebuilder" reused the original used/tired/worn out lifters, or cam, so it might not be a timing issue at all. John

I understand the different timing issues and that one relies on the other. I got whole 83 1/2-ton truck for $50 when I was young and dumb, pulled the engine, found a used AA style conversion kit and stuffed it into my cruiser. It originally had some truck manifolds too, but I swapped them to cheapie block hugger headers.

Thank you both for your insights. I will pass these thought on to the guy who is supposed to help me check it out. I never learned proper engine tuning.

 

[Gumby]

You need to throw a timing light on it.

Then you can get the engine to the proper base timing.

Then you can see if you are getting proper advance. That engine will have a vacuum advance off of a ported vac port on the carb, meaning it is one that increases vacuum as the engine revs. The other ports on the carb decrease as the engine revs. They are manifold vacuum. You also have mechanical advance. That's the wieghts under the rotor. They should have springs on them that regulate how fast they spin out and advance the timing. Those springs can break and wear. The weights can also stick. They can stand to be lubed once in a while.


You could also have a bad plug or wire that breaks up at high engine loads. You could have a bad lifter or valve spring that doesn't open/close the valve.


You can have a bad cap or rotor or coil that breaks up at high loads too.

And you could have a poorly timed cam, but I kinda doubt it. It wouldn't load up and backfire, especially out of the exhaust. That's an indicator of a miss. A cam out of timing wouldn't breathe. It might lean misfire through the carb, but most likely it just would refuse to go.

 

[pb4ugo]

X2 on what Gumby said, also the dist could be 180* out or not installed correctly, maybe a tooth off.

 

[69LC]

Thanks. I'll look into all of these ideas before opening up the cam chain. At least the cruiser is in the garage on a clean floor. It was in the nasty floored pole barn with birds using it for target practice!