59 johnson wont go faster than 10 mph!!!

[no clue]

I recently got involved in restoring an old 15'cobia.it has a '59 50 hp v4 on it.it runs like a scalded dog out of the water-hooked up to water of course.when it gets to the lake it just doesnt want to go.i thought that a 50 hp would've made this boat fly.it has a michigan brass?? prop.i have no idea what the pitch or anything else for that matter.the only numbers i can find on the prop is 104.it says cut and cutter.is this the correct prop for this setup?or is this the decarb solution.i have cleaned the carbs(2).i have no idea where the high speed jets are so i dont know if they need to be cleaned.and last but definitely not least only 50 psi at all 4 cylinders.plz help!

 

[roscoe]

Re: 59 johnson wont go faster than 10 mph!!!

If the compression is as low as 50, it is amazing it runs at all. <br /><br />How does it run? rough? smooth? Does it acheive high rpms, or only about 1/3 throttle? Does the fuel bulb pump up and stay firm? Does the engine run faster if you pump the bulb while running it?<br /><br />If the engine is revving into the higher rpm range, then I would have the prop checked to see if the hub is "spun."<br /><br />You can check it yourself by removing the prop. Then scribe a small line inside the prop. It must start on the inner (hub) portion, and extend to the outer (housing) portion of the prop. Put the prop back on and go run it, hard accelleration a few times if possible. Then remove the prop and see if the lines are still lined up. If they are mis-aligned, then the prop is spun. It can be fixed at a dealer or prop repair shop.

 

[no clue]

Re: 59 johnson wont go faster than 10 mph!!!

thanks for the response.unfortunately i have no tach.but out of the water it gets good rpm (by ear).in the water it only gets half of that.the prop has sheared a few shear pins.a friend said this was because i shifted from foward to reverse to fast.the last time i replaced the shear pin with a#8 hardened bolt thru the prop and shaft.it didnt shear the bolt when i tested it the other day but also didnt get but 1/3 throttle even with it wide open.<br /><br />model #v4sl-11 b<br />serial#1971542

 

[no clue]

Re: 59 johnson wont go faster than 10 mph!!!

as far as fuel,i put a new 6 gal tank,lines fittings and bulb on it.tes the bulb stays semi hard.if you pump it it really doesnt make any difference

 

[iRich]

Re: 59 johnson wont go faster than 10 mph!!!

Hi no clue, Try checking the compression again and squirt a little oil in each cylinder to see if it goes up. If it does then that would indicate rings. Also about the prop shear pis shearing off, they are supposed to shear off to prevent engine/ lower unit damage. I wouldn't replace with a bolt. How fast is your idle set at? It sounds like it is to high and that is probably causing the pins to shear. <br /> You could also check for a spun prop. Search the forum for more info on this. <br /> I'd get that bolt out of your prop before using it again.<br /><br />Rich

 

[no clue]

Re: 59 johnson wont go faster than 10 mph!!!

ok i checked the board on the spun prop idea.my problem is when out of the water rpm are great.in the water only about a third of the rpms.this motor sat for quite a few years.i had to put a lower unit from a '63 75hp superseahorse on it.my new question is how far below the bottom of the boat should the prop be.this lower unit is longer than the original by 4 inches i think.would that make any difference.i still am lost on the shear pin though.why am i going thru so many?

 

[no clue]

Re: 59 johnson wont go faster than 10 mph!!!

ok___new problem.as it turns out it has nothing to do with the prop.id still like to know how low the prop is supposed to be.i ran the engine and started pulling plug wires and lo and behold no difference when i pulled the left side wires.plz help!!!!!