running problem

[frankscr]

i have a 1973 johnson 85hp runs good for a while then all the sundden it wants to bog and wont go any (slows down to almost a idle )faster. does this only sometimes i had the carb rebuilt new coils plugs new gas tank lines i dont no what elas to do any help thanks

 

[CharlieB]

Re: running problem

3 possibilities that you have to check for when the condition occurs

1 engine temp, is the water pump flowing enough to keep the engine from overheating. Can you hold you hand on the cyll block for a couple - three seconds without burning/pulling away. Does it run better after cooling off for a period of time?

2 fuel tank vent restricted, is the primer bulb soften or suck down flattened? Mud daubers have been know to build nests in vents restricting air flow and restricting fuel flow when fuel use causes a vacuum to build in the tank.

3 electrical ignition component may be overheating and failing to provide hot enough spark, immediately perform a spark test, looking to find a hot blue 'snap' across a 1/4 inch gap, any less and the engine will not deliver full throttle power. Retest stone cold, if a difference between hot and cold then repost and further testing will be advised to determine which component may be at fault.

 

[frankscr]

Re: running problem

yes to number one not overheating and the vent ball is new so is the tank ect. i think its the powerpack but i was told that cant be it

 

[jeff_smith_0423]

Re: running problem

yes to number one not overheating and the vent ball is new so is the tank ect. i think its the powerpack but i was told that cant be it

I would run all of the standard ignition tests. I would think that if it was the powerpack it would quit or perhaps not fire on one or two cylinders, but anything is possible. I'd be looking at the stator and coils.