Need help to set idle

[david.skinner]

Thank you all.

I've just spent 1/2 day rebuilding the carb with extreme care and checking all the passages are clear etc. Assembled it with gasket sealant as well this time but no change in engine behaviour. I tried the brake clean squirt thingy and initially thought that I was onto it as the engine would burst into life and the vacuum would rise significantly but it turned out that it was sucking the vaporised cleaner in the air intake and it liked it. Didn't matter where I sprayed I got the same result and as soon as the electric fan turned on it stopped having an effect because the vapour got blown away.

It seems to run better at higher revs and (say >1500) and when up there I am seeing 18" of vacuum. As I let the revs reduce gradually I am also hearing the odd miss and this seems to become more noticeable as the revs reduce. I am going to change the distributor as I have a spare one next just to eliminate that and then I will pull the plugs and check them as well and then change the coil to try and eliminate the ignition system as a potential source of trouble. I don't think it will make any difference but I'm an engineer by trade and we have to do this stuff to be sure don't we....

Terry - I went over the manifold carefully and there is only the one port at the front. Given I have no knowledge of the background of the engine I can't even say for sure that the manifold is correct for an 81A.

Phil, I put you wrong on the statement that I was getting an ok manifold vacuum previously. I double checked the vacuum gauge and the green starts at 18" so I think that the reading previously would have been around 17" so this low manifold pressure at idle may have been around for some time.

On the compression I have previously tested this and allowing for the fact that there are different compression heads on each side (yeah I know...) I got spot on 80lbs dry on all four of the left and 100lb dry on the right with less than 1lb variation on each side.

Regards all