Morris Minor Owners Club

Have converted my car over to the marina engine and running gear have fitted a marina pedal box and I am using the marina brake servo....

Had a bad air leak from the servo so was advised to replace it although the car was drivable only issue was lost power at about 50mph which I put down at least partly to vacuum leak from the servo.

Changed the servo today and now the car is running like hell incredibly lumpy won't idal without throttling it. And as soon as off the throttle cuts out.

Have tried just removing the vacuum pipe and same issue as well as blocking off the pipe completely. Have fiddled with the timing and it won't run at all in any other position.

if anyone has any ideas what might be causing this please let me know have a car show I want to go to and as far as I can tell have now destroyed a usable car...

Have you checked the mixture?
If it was running before with an air leak through the servo then I would have thought the mixture would have been overly rich to compensate. Now you've replaced the servo with one that doesn't leak (also the same as plugging the vacuum pipe) the mixture will be too rich.
Check the plug colour for an indication of mixture.

Make sure the carb piston is not sticking, sometimes oil can get to it and it prevents it from moving freely, causing the problems you describe. Having checked that make sure there are no air leaks and the car should be running like before again.

Does it run OK with servo pipe clamped off ?

Thanks for replying. Car runs the same with the hose clamped. Piston goes up and down fine and dash pot has right oil in it. I pulled the plugs and they are completely black as is the exhaust pipe so obviously very rich. Tried to adjust the mixture but has only made the car worse. Now the car no longer starts on the button to make it fire I have to operate the piston while engine is turning over that allows it to start then I have to operate the throttle to keep it running but runs really awful I'm guessing it's mixture and timing related haven't checked the timing yet but will get to it over the weekend.

Obviously an excess of petrol. Look for flooding float valve, excessive pump pressure ? Or the s the air filter chocked? Try without....