50 hp Mercury Thunderbolt that won't start

[Scottina]

I have a 70ish 50 hp thunderbolt that I bought recently. I can't seem to get it to crank. I started and ran fine when I bought it. The only way I have managed to get it to crank is to spray starting fluid into the carb. It has spark and seem to be getting fuel. The motor does not have an electric start. You have to pull the cord. Does anybody out there have any suggestions. I am very frustrated.
:facepalm:

 

[hotrod53]

Re: 50 hp Mercury Thunderbolt that won't start

If I had to guess, I would say that your carb float needles are stuck in the up (closed) position. This happened to me multiple times with my '77 500 Thunderbolt. The Ethanol on the fuel swells the rubber tips on the needles if you don't run the carb bowls low after running the motor. This can happen in the matter of just a few days of sitting.

Unfortunately there is no way to unstick the lower carb needle without removing it and the top one is easier once removed as well. If like mine, you will have to pluck the needles out with needle nose pliers .... they're that stuck! I suggest that you remove your carbs and check your needles. Thereafter, everytime you run your motor, pull the fuel line when you're done and run some fuel out of the carbs. No need to run them dry, just enough to run them less than full and it will drop the needles down off of the seats. Replacement needles do not have the rubber and will not stick, enzyme treatment in your fuel is supposed to keep this from happening too.

If you remove the carbs be careful with the plastic carb sync piece between the carbs, it can be brittle yet it is still available. The choke linkage is a little tricky too, yet it is pretty sturdy.

Hope this helps!