New Camshaft - runs rough

[bitt01]

I replaced the cam on my 66 f100 i6 4.9l. The lobes on the old cam were worn and this new cam is an oem replacement.
It starts up no problem but only stays running in a high idle. As soon as the choke is pushed in about 3/4 it stalls.
Can this be an EGR issue? I don’t think it’s vapor lock because I did not have this issue before.
Does the engine need to be tuned to this new cam and how do you do that?

[bitt01]

anyone? Bueller?

[sparky72]

You probably do need to retune if your previous tune was done on a worn out cam. Have you checked your timing and measured your manifold vacuum yet? High idle and stalling when the choke is opened sounds to me like it's running real lean, potentially from a vacuum leak.

[bitt01]

Ok I will check the hose. I also Installed A pertronix ignition system in the oem distributor.
How do you adjust the vacuum?

[bitt01]

I don’t have a timing light. I just tuned by ear by turning the distributor while the car is running

[bitt01]

I think the air fuel mixture at low idle is off. it runs fine when the carb is almost closed but dies when its open.

[sparky72]

Vacuum isn't adjusted directly, but it's affected by a lot of things. I would measure it using a vacuum gauge on a manifold vacuum port. You're looking for a high reading (on a stock engine probably 18 or more inches of mercury at idle) and a steady needle. If you have a vacuum leak you will probably have a low vacuum reading and potentially an erratic one as well.

When the choke is closed it speeds up the air speed through the venturis and draws more fuel into the intake charge, richening the mixture. Likewise when the choke opens the mixture leans. An warmed-up engine that runs okay with the choke closed or nearly closed and dies when the choke opens is a classic indicator of a lean condition at idle. Your idle mixture screws could certainly be off, but the mixture could also be excessively lean from a vacuum leak. Getting a manifold vacuum reading would help diagnose that.

I'm not familiar with the I6 engines, so forgive me if this is a silly question, but what all did you have to remove and reinstall when you changed out the camshaft?

[bitt01]

Thanks, sparky. No apology needed!
I think all signs are pointing to a vacuum issue.
I pulled the cam and replaced it with a an oem cam. Replaced crankshaft and cam gear. Replaced water pump and thermostat. Replaced distributor, cap, wires, coil. Also upgraded to pertronix ignition. I only had this truck for a little over a year so I am new to this as well.

[bitt01]

You get the manifold vacuum read by disconnecting the vacuum hose at the carb and hooking up the gauge there, is that right?

[Ranchero50]

You get the manifold vacuum read by disconnecting the vacuum hose at the carb and hooking up the gauge there, is that right?

Try to find a port on the intake manifold for the gauge. Also pick up a basic timing light and use it to set the bas timing and check the full advance timing if you can. If your truck ran well with the old cam it should run at least as well with the new one. The vacuum signal to the carb will be stronger.