Series 3 petrol trouble shooting

I purchased a 1973 Series 3 short wheel base last summer from a gentleman who was tired of putting money into it. It came with a newly rebuilt engine that had spun a bearing shortly after the rebuild. I installed an unknown engine that I got running and drove it all summer but it didn't run great. It was low on power, often died when decelerating, and smoked. After a leak down test determined the valves were bad I swapped in the rebuilt head from the rebuilt engine it came with but I'm still having some of the same issues.

The truck starts right up, but idles poorly, like it's misfiring and puts out a lot of smoke still. I did a compression check. All four cylinders had 150+ psi. I did a leak down test and all were low 25-20%. I checked valve clearances, point gaps, change to brand new spark plugs, reset the static ignition timing again. It's definitely getting spark. About the only thing I can think of is the cam followers being worn, cam lobes damaged or cam shaft timing being off.

Vacuum test shows rapid fluctuation between 7-18 in Hg. Any way to check the cam timing or cam followers without removing the timing cover or head? Any other ideas as to what I could look into?

What sort of smoke, what colour is it? Does it smoke all the time?

With 150 per pot can not see it being a wear issue. What carb? Has ignition coil been swapped.

White smoke, intermittently puffing. Carb is a Zenith replacement but I think I've got is set up well after adjusting the float. Very little difference in running when I adjust the air/fuel mix screw.

I could swap carb with a known runner and swap the coil too.

I should also note that the port for a PCV valve is blocked off at the base of the carb now. It will run better if I connect it to the valve cover breather and air cleaner intake with a 3 way barb but when I do vacuum is low and it fluctuates between 10-15 in Hg and runs lean.

Here's a video of it running with the vacuum gauge.

That sounds awful. What colour are the plugs? Don't worry about the vacuum gauge just yet it will bounce all over if it's not damped

You need to get the idle speed up a bit then check the ignition timing and set the fuel mix

Plugs are wet with petrol. If I raise the idle speed the fuel mix screw doesn't seem to do anything, even 4,5,6 turns out.

I should also note that the port for a PCV valve is blocked off at the base of the carb now. It will run better if I connect it to the valve cover breather and air cleaner intake with a 3 way barb but when I do vacuum is low and it fluctuates between 10-15 in Hg and runs lean.

Here's how it was running with the vacuum vented to the valve cover breather and air cleaner elbow.

Then it's too rich
Increase the revs slightly then turn in the mixture screw until it runs better. The revs should increase. If they increase too much then you might need to turn the revs down a bit too compensate
I don't know anything about zenith copies or if they are any good

I don't think it's carb related. I posted another video just above this with the idle up.

yes, but dont worry about what is happening to the vacuum readings
the throttle is closed and valves are opening and closing all the time
if the compression is good then dont worry about that needle too much

is there much pressure coming from the rocker cover?

It's not forcing oil out. Not sure how I would check that.

i mean, take the rocker cover breather off, is there gasses forced out? there will be a little bit but not much

Nothing irregular coming out of the rocker cover. I advanced the distributor timing quite a bit, and readjusted the carb which resulted in a slight improvement but mostly when it's running fairly rich.

I suspect the cam timing or worn cam followers still. I'm going to check the EP point and the exhaust valve on cylinder 1 to see if it lines up accurately. If not, I guess it's off with the front cover and possibly a new timing chain.

Checked the exhaust point and the cam timing seem to be correct. I'm going to recheck everything tomorrow and see where I end up.

I was able to check everything over today and it turns out it was the carb. I really should have started there I guess. Cheap Zenith reproduction that hadn't given me any trouble for a year finally did. I changed it for a known good one and it fired up, idled well and eventually stopped smoking after it blew out all the petrol and moisture in the exhaust.

If you still have an original Zenith, overhaul kits are available.

I've just been through this last week with my series 3, it was running poorly so I replaced the usual serviceable items and it ran even worse.
At first I overlooked the carb because it looked new, but alarm bells rang because they no longer make them and therefore it was most likely a copy. Anyway, I fitted a Weber and it's now running smoothly. I'm pleased to hear yours is too . If you haven't done already, I'd check the timing as well.