77 Johnson 35 HP what should vacuum read at carburator? At my witts end!!

[flintcreek]

77 Model Johnson 35 Hp runs for 10 seconds or so then goes dead, choke it and it will start back up, at my witts end. I have cleaned carb, replaced fuel lines, gas tank, intake and bypass gaskets, fuel pump. So I am just about at my witts end...so I have made a test plate with a connection for a vacuum gauge to fit on the intake. It looks like the vacuum goes up to 15 lbs. is this good? Not sure how to tell when I am reading which cylinder also. I gues sit is reading both. We were spinning this over by hand with a rope wrapped around the flywheel.

Thanks,
Flintcreek

 

[Joe Reeves]

Re: 77 Johnson 35 HP what should vacuum read at carburator? At my witts end!!

The engine starts when you choke it indicates that the vacuum is fine. Don't be concerned about that area.

Back to the carburetor..... if you did not manually clean the brass high speed jet that is located in the bottom center portion of the float chamber with a piece of single strand steel wire, do so. Solvent just doen't do a good job of cleaning the gunk out of that item.

 

[flintcreek]

Re: 77 Johnson 35 HP what should vacuum read at carburator? At my witts end!!

Joe, thanks for the reply. I was thinking that if it was starting it had enough vacuum. But like I said I am at my witts end. I did take the high speed jet out and it looks clean. However I will look at it again tomorrow and see what I can do. I have the carb laying on my work bench in the garage right now so it won't take but a couple of minutes to run a wire through it. My brother is also going to bring his boat and good running 78 Johnson by tomorrow after work and let me try his carb on my motor. I will post tomorrow night and update.

Thanks,
Flintcreek

 

[Big flop]

Re: 77 Johnson 35 HP what should vacuum read at carburator? At my witts end!!

While carb is off soak idle circuit with power tuner.
Keep shooting tuner in it loosen any varnish or
crud it can & blow out good.
Did you install a new kit & adjust mixture screw.

 

[flintcreek]

Re: 77 Johnson 35 HP what should vacuum read at carburator? At my witts end!!

It has a new OMC carb kit and I have went through the carb along with one of the local boat mechanics here locally. I did not put in a new adjust mixture screw, but he said it looked good and it looked good to me...nice point, no signs of wear. I will try to update again tonight after working on it this afternoon with my brothers help.

Flintcreek

 

[boobie]

Re: 77 Johnson 35 HP what should vacuum read at carburator? At my witts end!!

Pretty hard to measure vacuum on a 2 stroke as you have two different pulses. On a 4 stroke it's different.

 

[flintcreek]

Re: 77 Johnson 35 HP what should vacuum read at carburator? At my witts end!!

Ok finally figured it out, I fished the bearing needle valve out of the low speed needle hole and put the needle back in and it ran just fine.
My brother came by yesterday and brought his boat and 35 hp and we put his carb on my motor and it ran fine. Then we went through my carb again, and this was the only thing I could think of that was in the low speed circuit...it showed in the instructions for the OMC rebuild kit, but seems like my carb does not need it. A big thanks to everyone.

Flintcreek