1995 70 hp johnson motor i need a little help

[wisemack34]

it's been doing this a little while
sat i went fishing......in the morning it runs great then i stop and trolled for about 5 hrs then started up run great trolled again for about 2 hrs and it wouldn't get over 3400 rmp.......it's like you start it up cold it runs good........but if you start it up when it still hot it won't get over 3400 rpm.....i bring it home till next weekend run great when i put it in the water cold.. troll for a little while start it up and 3400 rpm is it.......

 

[OBJ]

Re: 1995 70 hp johnson motor i need a little help

Very good chance your dropping a cylinder once it gets warmed up to operating temp mack.

Next time it does this.....start pulling plug wires. What your looking for is the wire you pull and it does not make a difference in the way the engine is runing. That's the bad guy.

Sometimes a coil or power pack will break down from the heat of the engine. So it runs good when it's cold and bad when hot.

 

[wisemack34]

Re: 1995 70 hp johnson motor i need a little help

are they a way to test the power packs...or coil.......i have a avg 129 psi on all cylinders......what would make it drop a cylinder when it gets hot?..........

 

[OBJ]

Re: 1995 70 hp johnson motor i need a little help

When things get hot they expand. A coil will expand possibly opening the coil winding. Or maybe a component in the power pack is opening when it gets warm/hot enough.

If you can find the torublesome cylinder (if losing spark to the hole is the case) you can swap the coil on the bad cylinder with the coil on a good cylinder and see if the problem follows the coil. If it doesn't, likely the power pack is the problem.

 

[JB]

Re: 1995 70 hp johnson motor i need a little help

To add to OBJ's good advice: When you have been running the engine it gets up to temperature. When you shut it down the temperature rises because the heat is still there and the cooling isn't.

The most common cause of "it starts and runs great when cold but misbehaves when started hot" is a failure from the post shut-down heat rise.

You can test this with a hair dryer while the engine is on muffs. Heat the ignition components with the hair dryer. That will usually cause a hot failure to occur.