This is a last resort post to sort a fuel problem that i have. The car is a 2 litre pinto running 40 dcoe's and no4 is running very weak to the point of a mis-fire at 3800rpm. The car ticks over fine and free revs perfectly, there is no popping, banging, farting or backfiring at all.
When the plugs are removed after 100mile or so no4 plug is as new as though no fuel is entering the cylinder hence the mis fire i presume at 3800rpm.
What would cause this problem inside the carbs, as i have had them apart and cannot see nothing wrong. I have changed the mains and idles to see if a difference is made but nothing.
Any help or other thoughts would be appreciated.
Thanks

sounds like a blocked jet or passage in the carb to me. Might be worth stripping again and soaking everything in carb cleaner to try and clear any old crud out. Also use an aerosol carb cleaner to thoroughly blow out all the drillings and passages in the body of the carb.

Is there an open vacuum pipe on No4 inlet runner?

What do you mean by the runner?
On the manifold?
Thanks for the reply?

Yes, a small bore vacuum pipe in the manifold feeding No4 cyl.

I would swap the carbs just to verify.

If it is blocked its likely its on the main jet circuit considering the rpm the misfire occurs at.Try using an airline with a small nozzle to blow out the passages...watch the eyes fuel stings like a bast**d.

Have a look at the weber pages on TEGLERIZER.COM

Unles it has sucked in one of the "O" rings ; Do a compression test -- sounds very much like a burn't exhaust valve.

I have done a compression test and have 195psi give or take 2psi on all cylinders. So i dont think i have a problem there.
Its the as new spark plug on no4 which leaves me thinking that i have carb trouble.

195psi on a Pinto is pretty good 160 psi is more typical even on newly run in unit.

However it might be worth examining the valve springs on that cylinder.

Yes quite impressed with 195psi, although it is a new build, skimmed head and block etc.
I have checked the valve springs and all seems ok the cam seems nicely run in so it looks like its back to the carbs or possibly ignitiuon? But cant understand why its only on one cylinder??
Thanks for the reply