Johnson 25 hp will not start

[clarifydeveloper]

I have a 1977 Johnson 25 hp longshaft with power pack not points. I have owned the motor for the last 15 years and replaced the power pack a few years back. I have new plugs of the proper time and gap installed. My coils look fine and I get a nice blue spark at the plug on both cylinders.

I was at the river last week and had run the motor off and on for a few hours fishing. I was heading back to the launch and the motor suddenly died (as if it ran out of fuel). I pumped the ball on the line, still firm, and tried to restart - no luck.

I have it on the trailer in the tank at home now and have checked the fuel filter, plenty of fuel getting there when I pump the ball. I drained the carb bowl and pumped again, plenty of fuel in carb. When I remove the plugs there is fuel on them.

I have been able to get the motor to backfire a couple times today - backfire under water through exhaust, not sneeze through carb.

I don't think I have a fuel problem, and it doesn't appear to be a spark problem, but maybe a "timing issue", like spark at wrong time in the piston cycle but I don't know how to check.

Any other suggestions would be greatly appreciated. Please help, need to fish not work on motor

Thanks

 

[tashasdaddy]

Re: Johnson 25 hp will not start

it sounds like you sheared the woodruff key between the flywheel and crankshaft. this throws it out of time. the backfire is a main clue. you need to pull the flywheel.

PULLING FLYWHEEL

you need a harmonic balancer puller, you need 3 - #8 harden bolts, that fit the 3 holes in your flywheel. standard hardware store bolts will strip out, causing more problems. loosen the flywheel nut, leaving it on so it protects the thread. thread the bolts in 7/16 of an inch. then tighten the puller, adjust so it has a straight pull. now tighten the puller, rap the center bolt with a hammer, then tighten some more. you may have to let it sit over nite, and repeat in the morning. this is a compression fitting, it will eventually POP!!. do not loose the woodruff key that goes in the groove of the flywheel and the crank shaft. then installing the flywheel, it has to be totally clean, no oil, woodruff key in place. then torque the nut to the specifications for your particular motor. if you do not do this, the woodruff key with shear, and you will be repeating these steps.

 

[samo_ott]

Re: Johnson 25 hp will not start

Shearing the key is my guess also. Seams to be no other obvious reason.

And welcome to the iboats forum )

 

[clarifydeveloper]

Re: Johnson 25 hp will not start

Thanks guys, how do you loosen the nut on the flywheel? Seems there must be some way to lock the flywheel in place but its not obvious to me. It doesn't seem like I should wedge something in the teeth as it my break something.

Thanks again.

 

[tashasdaddy]

Re: Johnson 25 hp will not start

on a 25 i usually use a big screw driver, and the teeth, not the right way. a strap wrench around the flywheel is the correct way.

 

[14ftgrumman]

Re: Johnson 25 hp will not start

Make sure that you use a torque wrench to tighten it with.

Don't ask how I know this.

 

[samo_ott]

Re: Johnson 25 hp will not start

I use a big screwdriver also... Tightening it up with the torque wrench is a lot harder than loosening it... especially when you do the 40 hp's and it's supposed to be 105 ft lbs! My wife is not keen on helping me then! But I still use a big screwdriver...

I've also heard of folks pulling a plug and stuffing nylon rope in the hole and the using it to hold the piston in position when torquing it but I really don't like the idea of this as it puts a lot of stress on the crank, con rod & piston... I like the big screwdriver... Never busted a flywheel tooth yet!