1980 Merc 40HP wont start after rebuilding carb

[bennythomson]

I recently rebuilt the fuel pump and carburetor on my 1980 Merc 40 HP. I replaced the diaphragm and gaskets on the pump and cleaned and rebuilt the carb the standard way.

I also installed a new throttle control box. The engine started great and ran well before the rebuild. I just rebuilt it because it had poor throttle response and would sometimes bog down at WOT. I went to start it today (the first time since the rebuild) and it would crank over but wouldn't cough. I suspected spark problems, but i used an inline tester and it was fine. I sprayed some starting fluid in the carb and it started up, revved like crazy and then died out 15 secs later. This is the first time I've ever rebuilt a carb, and although I followed the manual and feel like I did it right, I'm wondering if i screwed something up.

What could be causing it to only start with starting fluid and then die out? I'm just guessing here but I don't think it's getting enough fuel. How do I check that the carb is getting sufficient fuel?


Suspected problems

1. jet or hole is clogged somewhere.
2. hose clamps may not be tight enough
3. idle mixture screw not far out enough
4. something wrong with float/valve


I really appreciate the help!

 

[achris]

It may be the pump. First off, put away the starting fluid unless you want to be rebuilding the engine in the near future. Use just normal 2 stroke fuel if you must.. Squirt some fuel in through the carb (as you did with the starting fluid), then as the engine starts to run, try giving the fuel primer a few squeezes. See if you can keep the engine running by doing that...

Chris....

 

[enginepower]

Did your primer bulb feel like it was pumping for a few squeezes then get hard or was it hard on first squeeze? How old is the fuel? Did you replaced the float needle valve? If so, was it the same length as original? Just some things to check....

 

[WrenchHead]

Don't make the mistake some people make by looking in all directions. 99.9% of the time the problem is the part you worked on. Take the gas line loose from the discharge side of the fuel pump and spin the motor to see if the pump is delivering gas. If it is then it's not the pump and the problem is the carb. You put something together wrong, you left something out, the needle valve is stuck, the carb is loose and sucking air, etc. Could even be airlock in pump or carb.