Yamaha 30hp Misfiring.

[Craig Butcher]

I have a yamaha 30hp that idles fine, but any increase in revs, causes it to backfire. I tried adjusting the air/fuel screw on the carb, but doesn't seem to change anything.The plugs are new, the carb is clean, the filter is clean, the petrol is new.
Any help would be appreciated.

[AllenF]

Timing check its advancing and retarding correctly

[Jizm]

Originally Posted by AllenF

Timing check its advancing and retarding correctly

Indeed, if you don't have a manual then some one on here will probably be able to oblige with the relevant information.

[Craig Butcher]

I do not have a manual. So how would I go about checking that she is advancing and retarding correctly. She is an older model, 2 cylinders, and single carb.

[Jizm]

Originally Posted by Craig Butcher

I do not have a manual. So how would I go about checking that she is advancing and retarding correctly. She is an older model, 2 cylinders, and single carb.

what year? a pic would help us identify the motor...

[outboardtech]

pull the flywheel off , your woodruff key is probably brocken that connect the flywheel to crankshaft . At idle it will run but increase revs and timing will be out and BACKFIRE SHE WILL . Had LOADS of these buddy . cheers BAZ