77 115hp starting/running problems

[tower1]

Hi all

I am hopping someone here can point me in the right direction.

A friend of mine got a "new" boat this year it has a 1977 115hp Johnson motor.

The problem/s

The motor is hard to start we have to spay premix into the carbs to start it.

Once it is running it runs good until you idle for 2-3mins then when you try to go it will stall, you have to "play" with the gas until it clears out then it runs good again.

So far I have rebuilt the fuel pump and the carbs replaced the fuel lines. I have tried to "tweak" the floats started parallel with the carb body, then tried bent back a little (richer) no change.

Any ideas?

Thanks

 

[ezeke]

Re: 77 115hp starting/running problems

Cold starting problem on this series is usually caused by the lack of synch between the two carbs choke plates, which must be 100%, fully, no joke, closed to start. The reason that you have to keep using the spray bottle is that the choke is not closed on one or both carbs.

The only way to verify is to look down the throats while someone hits the switch.

You can adjust the relative position by moving the solenoid body further away. You use the linkage adjustment to synch.

 

[tower1]

Re: 77 115hp starting/running problems

Choke plates are both closed, have closed them manually and using the electric.

 

[Joe Reeves]

Re: 77 115hp starting/running problems

As "ezeke" above states, the choke butterfly operation is a must.

The most common cause of the problem you're encountering is fouled carburetors, usually due to sitting for a operiod of time. The cure is to remove, clean thoroughly, and rebuild them with complete carburetor kits.

Be sure to manually clean the fixed high speed jets which are located in the center bottom portion of the float chambers in back of those 7/16" hex head screws. You can clean them where they are with a piece of single strand wire.

(Carburetor Float Setting)
(J. Reeves)

With the carburetor body held upside down, the float being viewed from the side, adjust the float so that the free end of the float (the end opposite the hinge pin) is ever so slightly higher (just ever so slightly off level) than the other end. And when viewed from the end, make sure it is not cocked.

 

[ezeke]

Re: 77 115hp starting/running problems

A 1/16" gap is not fully closed.

The operation of the motor is fairly simple, the movement of the pistons pulls the air and fuel through the reeds. The choke blocks the air.

If the choke is fully closed, the floats bowls are full, and the carbs are clean, the pistons pull adequate fuel and you don't need a spray bottle.

 

[tower1]

Re: 77 115hp starting/running problems

I rebuilt the carbs with new kits, I pulled the jets, soaked them in carb cleaner and blew air though them. I can pull them again and check (I am getting good at it LOL).

The floats started slightly higher, when I rebuilt them I made them level as it said to do in the rebuild kit now they are slightly lower. It has made no change in the way the motor is running.

To me it seems that the motor is to lean.

 

[tashasdaddy]

Re: 77 115hp starting/running problems

did you use new floats, old one get to where they don't float. cold start procedure should be , connect fuel line, pump bulb until hard, idle lever all the way up, if no idle lever , shold be button in center of the shift handle push in on button and advance lever forward. push choke button or key in and hold, turn key and start, if does not start pump bulb again, and try to restart,

 

[tower1]

Re: 77 115hp starting/running problems

Just remembered did not pull the jets soaked the float base and blew air though as I could not get the jet out and was afraid to snap it.

I am not a complete newbie as I have been working on jet skis for years (don't hate me LOL)

This carbis very simple and I replace every thing but the jets and the float itself (new ones did not come in the kits) could the floats be bad? They are solid black not air filled.

 

[tower1]

Re: 77 115hp starting/running problems

I guess I will try new floats any other thoughts?

 

[dsinger]

Re: 77 115hp starting/running problems

What kinda compression you have.

 

[dsinger]

Re: 77 115hp starting/running problems

Is there a lot of slack in the throttle body. It is common of that motor to get a lot of slack and you timing base will not go back to the start postion. It sometimes helps to take it apart and clean relub and put a little more tension of the spring that advances the timing base. Don t let that spring in the middle of the body hit you in the face it will sure pop out if you don t watch it.