Rebuilt 150 Engine. Good spark and new correctly jetted carb. Starts fine and revs fine on the stand. Pulls away and then appears to run out of petrol then picks for a few seconds. This repeats itself again and again. The carb and primary galleries are clean and double checked. The fuel cap is not blocked, the fuel is new. Have I missed anything please.
If its a new amal carb have you checked the float height?
just a possibilty
cheers
Seems fine Derek. Seems to be a fuel issue under load, but there is loads of power when it does pull. Revs on the stand for ages. However will put the old carb back on and see. Thank you.
I would double check the carb again for blockages. Some of those drillings are very fine and can get blocked easily. However, if it dies when opening the throttle up, you would be picking fuel up from the main jet so double check that area.
Not sure about the 150 electrics - does it have a condenser and points? If so, check the condenser is not breaking down.
Will try another carb, condenser new and points clean. It can pull away nice, sometimes for a good 100 yards then just falters but no misfire, defo' fuel I think. Thanks for replies.
Be sure to look for air leaks on the intake also.
Heard this before, how does an air leak cause the erratic behaviour, when it behaves whilst on the stand and not under load. Thank you.
Your problem doesn't sound like air leaks. Air leaks often occur through over tightening the carb which distorts the flange.
A quick way of checking if no obvious gaps or movement is present between the carb and the head is to tightly wrap some insulating tape around the joint and go for a ride and see if it makes any difference. The tape wont last long as it will get hot but usually lasts long enough to see if it makes a difference.