Intermittent power loss (need help troubleshooting please)

[trevarthan]

Hello,

I've got a 1971 c10 lwb with the 4.1L straight six.

Recently it has started losing power after driving for awhile (random intervals - as much as an hour, as little as a few minutes). Sometimes this is a complete stall, but sometimes it's just a lack of power. Sometimes it stutters when it loses power. Sometimes the engine keeps running when it loses power, but it just won't go.

It seems to be more likely to happen when the engine is warm, but I'm not 100% sure it matters. It'll stall at idle sometimes too if you restart it immediately after a stall and let it idle. Restarts are usually difficult after a stall.

We thought it might be a clogged carb fuel filter, so we removed the b-nut and changed the filter:





Unfortunately, it's still doing the same thing. So that's one thing that wasn't the problem.

I've read that this can sometimes be the coil. Here's a picture of my distributor:



I don't think this is the standard distributor that comes with the 4.1L engine. It appears to have an integrated coil.

Is there a good test procedure that will tell me if the coil is the problem? If so, where might I find this distributor part?

Open to any other suggestions too. I'm pretty stumped. Thanks!