'90 4hp. Johnson intake vacuum test

[oldcatamount]

I have a 1990 4hp. Johnson that I can't get to start and I'm thinking the intake vacuum pressure is not strong enough. This motor has 95lb. of compression on both cylinders, the carb is very clean, the fuel pump seems ok, and the ignition is good.To test the vacuum pressure, I removed the carb and stuck a piece of thin masking tape (blue, painters tape) over the intake manifold opening and cranked the motor over while watching the movement of the tape. I could see the tape suck inward (slightly) as I pulled the starter cord. To compare, I have another (good running) 4hp Johnson ('69) and did the same test on that one. The tape seemed to react the same way on both motors. Is there a way to better test the vacuum pressure or, am I wasting my time with all of this?

 

[boobie]

Re: '90 4hp. Johnson intake vacuum test

What happens if you squirt some premix fuel into the throat of the carb and try and start it??

 

[JB]

Re: '90 4hp. Johnson intake vacuum test

Go to the Top Secret file ^^ and do the troubleshooting.

 

[raczekp1]

Re: '90 4hp. Johnson intake vacuum test

my 4.5 start had 60, 65/psi and start and run only with chocke pulled out.
95 is a lot of compresion
spray some premix or wd in carb troath, should start.
slow speed needle 1.5 turn out

 

[oldcatamount]

Re: '90 4hp. Johnson intake vacuum test

I have sprayed pre-mix into the throat of the carb with little result. I say "little" because it still wouldn't start but, it would try. I could hear it fire, and I could feel it firing (slightly), through the starter cord. When I got this motor, it had a broken ring in the top cylinder. I had the cylinders honed, replaced the bruised piston, and put new rings on both pistons. Re-installed, with new seals and gaskets. I'll try spraying the throat again (with a better spray bottle) this time.