motor just does not run right

[big_fisher]

i have a johnsonmodel FD21R serial J2828246 and it wont run right my dad was a mechanic and rebuilt this engine and now after running great for 15 years wont run right. i can get started easily and then it will go nicely but then it will suddenly shoot out like pu into second gear and then go fine untill i slow down then it will pop back into "first gear" and on and on <br /><br />i forgot when he rebiult it he put 33hp jugs on the motor

 

[Paul Moir]

Re: motor just does not run right

There is no way he fit 3.0625" pistons into a 2.5" FD-21. I can't even fit them to a 2.875" bore. They just don't fit the casting.<br /><br />If it's developing a sudden rush of power, I would check that the ignition system is healthy. You should be able to draw 3/8" long sparks off each cylinder.

 

[big_fisher]

Re: motor just does not run right

how would i go about doing that and the spark plugs are champion J6C

 

[big_fisher]

Re: motor just does not run right

could it be a seal leak

 

[Paul Moir]

Re: motor just does not run right

Simplest method is to bang two nails into a board 3/8" apart, spread them at the top, then connect one with a bit of wire to the engine block (a handy screw or something) and place the plug boot on the other. Pull the cord and observe.<br />They sell little adjustable versions of this at discount tool stores for under $5. Your pick as to which is most convenient. <br /><br />You might try the J4C when you're all done and compare. J6C is good if you're trolling all the time, but J4C is better for WOT & regular use.<br /><br />EDIT: Not if the power is suddenly coming and going. Could conceivably be a cylinder head leak. But we'll start by ruling out one thing at a time until we know for certain what the problem is. Do that spark gap test and we can really rule out the entire ignition system as being the culprit. But check over the spark plug wires for cracks while you're at it.

 

[big_fisher]

Re: motor just does not run right

i did it and there is spark cross it and no cracks either

 

[Paul Moir]

Re: motor just does not run right

Great, you checked both right?<br /><br />Pull the spark plugs out and have a look at the firing ends. Compare the insulation. If they're old they ought to be brown, but the same. We're looking for differences.<br /><br />I'm secretly hoping it's the head gasket since I want to see how they squeezed in those pistons if they did use them.

 

[big_fisher]

Re: motor just does not run right

yes and both are a really dark brown

 

[Paul Moir]

Re: motor just does not run right

Oh, hey, maybe I'm looking at this from the wrong angle. When it winds up does the boat go much faster? Or is it like the propeller is slipping?

 

[big_fisher]

Re: motor just does not run right

i will start at idle then give it more gas then it just shoots out and goes twice as fast then stays the same until i slow down then it pops back down its like it almost boggs down but it doesn't sound like that and it still has the prop that was on it whaen my dad got way back when

 

[Paul Moir]

Re: motor just does not run right

Well, I think we can rule out head gasket or exhaust cover problems then. Try tugging on the spark plug wires with with an insulated hook while it's running just to humor me.<br />Do have a look at the fuel pump though. Pop it off the engine, pump up the primer bulb and see if any fuel is leaking out the back. It's a longshot since the plugs don't seem to indicate.