1970 4w7oE johnson problems starting/propelling

[redrum12]

HI, I'm a newb. I just purchased a jonboat with a 4hp johnson. When I bought it the owner started it for me and everything. when I took it on the water I got it started but I didn't sound right. I couldn't seem to get the right adjustment on the jets. However when I initially got it running, the boat wasn't moving. I turned it off. After that I couldn't get it started again until a couple hours later. Again the same results and have been unable start it since.

I've done some research on your forum and I have noticed that there is excess gas coming from the carb when I try to start. Should there be gas dripping from the carb when you try to start it?

Please help me diagnose. Thanks

 

[Rick.]

Re: 1970 4w7oE johnson problems starting/propelling

No there should not be gas leaking. Order a carb. kit for it and then pull the carb. and clean it perfectly clean and put the new kit in it. But seeing as it it new to you I would first check the compression on the cylinders before you order any parts. If you have good compression the motor is certainly worth fixing. They are great little motors, nice and light, and go for ever on a gallon of gas. Best of luck. Rick.

 

[redrum12]

Re: 1970 4w7oE johnson problems starting/propelling

No there should not be gas leaking. Order a carb. kit for it and then pull the carb. and clean it perfectly clean and put the new kit in it. But seeing as it it new to you I would first check the compression on the cylinders before you order any parts. If you have good compression the motor is certainly worth fixing. They are great little motors, nice and light, and go for ever on a gallon of gas. Best of luck. Rick.

Thanks. How would I check the compression? Would I use the compression tools that are used on cars?

Also should I be worried that the motor wasn't moving the boat even though the propeller was running?

 

[BigB9000]

Re: 1970 4w7oE johnson problems starting/propelling

Check it!:

http://bigb9k.com/brp/compression/

 

[redrum12]

Re: 1970 4w7oE johnson problems starting/propelling

Check it!:

http://bigb9k.com/brp/compression/

Awesome, it's a similar procedure to cars. Thanks. Why haven't they stickied or archived this.

 

[BigB9000]

Re: 1970 4w7oE johnson problems starting/propelling

Cuz I made it all of 20 minutes ago

 

[redrum12]

Re: 1970 4w7oE johnson problems starting/propelling

You wouldnt happen to remember what size adapter you used would you?

 

[BigB9000]

Re: 1970 4w7oE johnson problems starting/propelling

No adapter used, just the built in fitting.

It came with adapters, but I lost them years ago.

 

[F_R]

Re: 1970 4w7oE johnson problems starting/propelling

Boat not moving: Check for a broken shear pin (remove propeller and look).

EDIT: If there is no problem with the propeller or shear pin, that leaves the possibility of the splines rusted out of crankshaft. Bad. Very bad.

 

[redrum12]

Re: 1970 4w7oE johnson problems starting/propelling

Boat not moving: Check for a broken shear pin (remove propeller and look).

EDIT: If there is no problem with the propeller or shear pin, that leaves the possibility of the splines rusted out of crankshaft. Bad. Very bad.

What are splines?

I checked the shear pin, its really rusted but not broken. I also checked the compression with a compression tester that I rented.

At first I noticed that the compression gradually increased. I checked each cylinder twice.
The second time around I started losing compression until I got no compression left

I also bought a carb rebuilt kit for the carb. Gas still comes from under the choke plate. I checked the carb before installing. I tipped it upside down and tried to blow air in with a tube. No air came out.