Johnson 4HP with 50psi compression but runs pretty well.

[777funk]

I just found a 69 Johnson 4HP that looks a lot like an old lightwin. It starts first pull when warmed up and seems to idle and run fairly well. But it reads 50psi compression on both cylinders. I'm not positive my gauge is giving the full value but it's reading 50 on both cylinders (consistent). I checked the gauge on a chainsaw and it gave 110 psi. So it will go higher. It seems like WOT is a little jumpy but I'm not sure it's not because the load is going crazy in the can (water splashing out).

The lower plug showed some rust at the end of the plug threads near the electrode. I pulled the head gasket and it looks intact. I can still see some cross hatching on cylinders and there's no scoring.

Also, I can see that some of the reed valves are slightly open at rest. It can mis a little at medium speeds. I put a timing light on each plug and I think it's spark.

I'm curious if 50psi on both cylinders is ok.

 

[Crosbyman]

give it a good decarb with seafoam or similar products

if it works dont fix it

 

[gm280]

Obviously it is a pull start. And with that stated, it really depends some times how fast you pull the rope. A slow pull start can read a little lower then a speed spin over. So if you like it and you think it runs good, happy boating... :thumb:

 

[777funk]

I pull pretty fast. But the other thing to consider I guess is that it has the different than usual vertical pull rope coil and small gear rather than the horizontal coil and bendix. This may or may not make it faster or slower gearing... not sure here.