1966 18HP Fastwin

Hello All, first time poster long time viewer. I have a question I hop the experts in here might be able to answer. I have a 1966 18HP Fastwin. Have done water pump, Thermostat, Fuel pump, and Carb Kit with new float. Here is my problem. The motor starts up but after running for a few seconds it starts to cough (backfire) and I can see some fuel shoot out of the top of the carb from a small opening and the motor shuts off. Do I need to adjust the float? If so. What is the proper way to do that? Or is there something else going on with the carb? Thanks in Advance!

Take carb off and remove float bowl from carb and flip upside down. Top of float should be level with carb body( where the float bowl gasket is)
Turn carb right side up ,attach a piece of hose to gas inlet, blow into the hose- air should flow freely. Continue blowing , now raise float with your finger and when its level with carb body you shouldn`t be able to blow air into it any more, If you can needle and seat are not sealing.

Thanks for the quick reply. The fuel inlet is on the bottom half of carb the float is on top. The only way I can think of testing the seal is by leaving the carb in tact and flipping the entire carb over to see if the needle seats properly. How much play should the float have? How far up and down should the needle move? Thanks again!

Also check out the needle valve, the adjustment at the top of carb. If yours is like my 68 Fastwin that needle my be bad.

Thanks for the great tips. Turns out the high speed orifice was 100% clogged up and the float was not set correctly. Motor runs absolutely perfect now. I got the motor cheap has been fun getting it back in good operating condition!

Glad to hear, they are great old motors when running right.