76 Johnson 15 HP

[kryp2nite26]

Compression is around 100 psi pulling the rope. Haven't checked reed valves, fuel pump seems fine. It runs great, just doesn't seem to want to rev to Max rpm. Also noticed sometimes after running wide open, when I come down to a slow troll it has sort of a hiccup for a couple seconds and then goes away.

 

[saltchuckmatt]

Compression is around 100 psi pulling the rope. Haven't checked reed valves, fuel pump seems fine. It runs great, just doesn't seem to want to rev to Max rpm. Also noticed sometimes after running wide open, when I come down to a slow troll it has sort of a hiccup for a couple seconds and then goes away.

You've got a zebra somewhere.

 

[kryp2nite26]

I'm thinking at this point it has to be a carb issue. There isn't anything else it can be IMO. When I got the motor, I tore the carb down and cleaned all jets, reset the float, and cleaned out the low speed idle jet passageways. I did not remove all the plugs in the carb because it seemed to have been recently rebuilt. As much time and money I have trying to get this thing running like it did 2 years after I was born, I could have bought anither one.. Lol. It's becoming an obsession at this point. I'm that kinda guy.

 

[saltchuckmatt]

I'm thinking at this point it has to be a carb issue. There isn't anything else it can be IMO. When I got the motor, I tore the carb down and cleaned all jets, reset the float, and cleaned out the low speed idle jet passageways. I did not remove all the plugs in the carb because it seemed to have been recently rebuilt. As much time and money I have trying to get this thing running like it did 2 years after I was born, I could have bought anither one.. Lol. It's becoming an obsession at this point. I'm that kinda guy.

The obsession is common with everyone here! Human nature really.

When you get the carb apart post pictures of inside, maybe it's missing something.

When you ran it on the lake today you should have shot a little bit of 2 stroke fuel in it at WOT just to see what happens.

Back to the drawing board as they say.

 

[909]

Rebuild your carb. Just because it looks clean and shiny doesn't mean it is.

 

[Crosbyman]

magneto cam arm and carb adjusted (synch'd)
do you see the throttle and throttle pale reaching their maximum range ?any exhaust obstructions ?
does it pick up speed if you shoot some fuel mix in the carb ?

 

[flyingscott]

Is the arm and cam in good shape on the carb not broken.

 

[kryp2nite26]

magneto cam arm and carb adjusted (synch'd)
do you see the throttle and throttle pale reaching their maximum range ?any exhaust obstructions ?
does it pick up speed if you shoot some fuel mix in the carb ?

I have synced the roller to the throttle plate, yes it seems to be opening all the way.

 

[racerone]

Pull plug wire off #1 , will motor start and run ?-----Now try with #2 wire pulled off , will it start and run on #2 cylinder ?

 

[kryp2nite26]

Pull plug wire off #1 , will motor start and run ?-----Now try with #2 wire pulled off , will it start and run on #2 cylinder ?

I have verified that I have spark on both cylinders, but I will try this when I get it off the boat and back into the tank.

 

[OptsyEagle]

Not sure how you are determining spark but that model of motor is notorious for fouling spark plugs. Should use NGK plugs, B6HS are the best. B7HS will work. Don't use that motor for trolling or you will be replacing your spark plugs every 3 or 4 hours.

 

[kryp2nite26]

Holding spark plugs close to ground on block while pulling rope both plugs fire hard and loud. I am using NGK plugs.

 

[Crosbyman]

if electricals are ok , compression is OK carb is clean then fuel combustion is inadequate either from poor delivery from the carb (TBD) or inability to pull the fuel from the carb due to vacum loss in the crankcase (seals) .

can you at least feel a good pull of air on the carb face ?

 

[racerone]

In good condition they will troll for hrs.----Fouling plugs is a bit of a myth.

 

[kryp2nite26]

if electricals are ok , compression is OK carb is clean then fuel combustion is inadequate either from poor delivery from the carb (TBD) or inability to pull the fuel from the carb due to vacum loss in the crankcase (seals) .

can you at least feel a good pull of air on the carb face ?

Upper crank seal was leaking, I replaced it when I did the ignition. I guess it could be the bottom one too?

 

[racerone]

Guessing does not work very well.----Some simple trouble shooting gets results every time.-----Will it start on #1 alone ?-----Will it start on #2 alone , yes or no ?

 

[kryp2nite26]

Guessing does not work very well.----Some simple trouble shooting gets results every time.-----Will it start on #1 alone ?-----Will it start on #2 alone , yes or no ?

Just check right now, yes, starts fine with either plug wire removed.

 

[racerone]

Have you inspected / replaced the fuel pump diaphragm ?-----What # is on the high speed jet ?-----Is the exhaust path clear all the way to the prop ?-----Compression test values should be posted.

 

[kryp2nite26]

Have you inspected / replaced the fuel pump diaphragm ?-----What # is on the high speed jet ?-----Is the exhaust path clear all the way to the prop ?-----Compression test values should be posted.

I've inspected the fuel pump diaphragm. I don't remember the high speed jet size but I will when I tear it down again. No idea about the exhaust path. I did post compression values. Both right at 100 psi pulling the rope. What is involved in checking the exhaust path? Just lower unit removal?

 

[kryp2nite26]

Don't know if this helps, but before the ignition replacement and with the upper seal leaking, I was getting 8 to 9 mph with me and my wife in the boat. But yesterday with just me in the boat and new ignition and new upper seal, I was only getting 7.. So it's literally slower than before.