Club 80-90 Forums

hi ye ive recently had my 2l Aircooled engine out and replaced some valves and seats, its gone back in and its very week on sucking on one bank, now i have near perfic compression. it does suck and run perfic when cold but when it warms up after only two mins it runs rough again , i have messed about with the adjustment on the valves but it still rouns rough and doesnt suck propperly could we have sloppy hydraulic tappets??

Welcome to the club!

cheers i think ive covered everything ive got all vaccume hose's connected servo..just cant get to grips with the lack of suck. its had new rings carb dont leak

How are you measuring "the suck"?? and what figures are you getting?

BOXY wrote:How are you measuring "the suck"?? and what figures are you getting?

hes either got a calibrated crypton sucking gauge or a lady friend thats into vans

mm

nice one, first it was through the carb (top( then i tookout the spark plugs and found no suck or hardly any suck from there no gauge needed although i have a compression gauge which i dismantled to get true straight down chamber

You don't measure "suck" unless the engine is running. You measure it at the mouth of the carbs with a vacuum gauge when you want to balance the carbs.

On the compression stroke the gauge will read a positive pressure definately no "suck"
On the power stroke (going down) the pressure will drop but it won't suck. It won't suck because all that's happening is the air in the cylinder is decompressing after being squeezed, it's returning to it's start volume.
On the exhaust stroke you won't get any "suck" or pressure because the exhaust valve is open and the air is being pushed out of the cylinder.
On the inlet stroke it will "suck" through the carb via the inlet valve. You won't get any "suck" at the spark plug because is will "suck" from the path of least resistance (the carb).

If you've got a compression gauge that's all you need to check the piston rings and valves are doing their job. If the compression is good the suction will be good as well, unless a valve spring in snapped and the valve is being pulled open on the power stroke.