Suspecting an exhaust restriction might be responsible for some mysterious intermittent running problems, and not finding intake manifold pressure readings (which are supposed to be diagnostic for this) very interpretable, I decided to try direct measurement.

Not having a sensor port (or a catalytic converter) to work with, I made myself a spacer where the front and back exhaust sections join, with a wee T- pipe to take a pressure gauge. Results didn't suggest much restriction, but just in case, I back flushed the disconnected rear section of pipe with a garden hose.

I got some soot and a bit of beercan lid (thicker than the rest of the can and thus less likely to melt), derived from my internal "flame spray" treatment of the exhaust with aluminium and portland cement. This lid could have been an occaisional restriction, but the problem persisted after its removal, and was probably a vacuum leak, since it went away after painting the carb and intake manifold with multiple coats of sunflower oil.

If I had a restricted catalytic converter or DPF I'd probably try back flushing it. The way they are built probably indicates flushing both ways.

Edited by edlithgow on 07/08/2024 at 09:13

Hi, thanks for your reply. Today i removed the lambda sensor and the cur run better then ever even when fully warmed up it got to 7k rpm in a split second. This weekend i will try disassembling the exhaust starting from the rear and trying in between. Hopefully i get lucky and its just the back box.