1976 Johnson not enough RPMs. Help on timing advance screw

[Brabbtiger22]

Hehe guys I've owned this boat for years. Posted about a year back on it. 1976 Johnson stinger 75hp motor on a 19ft old glass stream boat. Light weight boat. Carbs clean and rebuilt. New fuel pump (vacuum type). Vented tank. New spark plugs. Compression on all 3 chambers 120psi. Runs smooth at idle. Starts like a normal 2 stroke (choke, then open flaps). My problem is getting more HP out of the motor. I feel like the RPMs (throttle) doesn't go high enough to get it out of the hole quicker. I can't pull any floats. If it's just 2 or less people in the boat it will get out of the hole and eventually take off. Then the RPMs go even higher once it's out of the hole. (Less resistance on the prop I'm guessing). My question is do I need to adjust the advance screw that stops the lever from going further. I can take pics if needed.

 

[flyingscott]

Do not adjust the timing advance screw AT ALL. That motor lightly loaded needs to reach 5800 rpm. What pitch prop are you running? What Rpm are you turning at WOT? Have you done a spark and compression test? Starting a boat out is the hardest thing your motor will do and the 75 is not known for low end torque. They are also better suited for lighter boats.

 

[Brabbtiger22]

Yea this boat is a super light bass boat. Isn't like the new ones you see today. Actually the boat it was on was a heavier bass boat. Pitch wise I'm not sure. It has a hand adjustable for the pitch so I don't have a motorized one. I can tell you this.... It putters when I get over halfway with the gear shifter. As I slowly go forward it putters more and eventually catches and slowlyyyyy gains speed and torque. Then it planes and I can go fast. Sparks are firing and compression is 120-125 on all 3 cylinders. I finally adjusted the idle screw so it idles very nice now. Doesn't cut off. So one thing down. I read one techs statement that I may need to drill the high jet holes a little bit larger . Any take on this? It's definitely fuel to air related..

.. I just got off the lake with it and if I'm trying to get out the hole the water has to be smooth. If I hit a wave it kinda bogs a bit and sounds like the engine puttering and puttering until it gets enough of something

 

[flyingscott]

What is hand adjustable pitch? Pitch is fixed on the prop unless your prop is adjustable. Is the timer base moving smoothly? There are service bulletins for venting the prop on those. Do not drill a high speed jet you if anything the low speed jet will need to be changed. What are the RPMs of the motor at wide open throttle??? THis is important.

 

[racerone]

Pitch of the prop and electric trim / tilt have confused the OP here I believe.

 

[Brabbtiger22]

Yea I was saying the tilt and trim is set. I have different slots I can put a pin in. Right now I have the motor set level with the boat (trim wise). Yes I've taken the wheel off and greased it a year ago. Base moves forward easy, but it's that rubber stopper on the bolt which is about 2 inches out. (Aka spark advance stopper) . It's the oddest thing.
i will mention I bought 2 new coils with new wires. Put them on and whenever I first put the boat in the water this week. It would barely crank and wouldn't go. Stalled immediately in gear. Which made me think omg the carbs need cleaning again so I cleaned them and blew them out with stuff. No gunk at all in them. Passages all clear. Still didn't change anything. All I could think was put the old coils back on and whalahhhh. Boat worked again. I'm pissed about the new coils bc I thought it would fix my problem getting out of the hole , but maybe they told me bad ones or wrong ones. Idk if this helps.
What do you mean by venting the prop??? It's blowing alot of bubbles for sure in the water. Lol. As far as prop goes I have one of those plane fins that help u get out of the hole easier. I'll find out the actual pitch when I can. RPMs were pretty high when it finally gets out of the hole and isn't bogging .

 

[flyingscott]

That stopper is there to set timing once it is set no need to touch it again. If you want better holeshot the motor needs to be trimmed in. Need the rpm, pretty high is not an answer because 5000 could be considered high and it would not be. Did you do a link and sync? Do you have the factory service manual for your motor? Are the carbs opening fully to 90 deg? The timer base stops moving around 3500 rpm and the carbs continue moving after that.

 

[Brabbtiger22]

Very good info. Thank you. It just sounds to me like it's bogging down alot then catches... Then bogs and catch's a little more (gets a little speed)... Does this over and over until it catches like a 2 stroke does ..mixes right and slowly takes off. It's like the boat motor is running on 15 hp not 75 ya know.
carbs are all open 90 degrees. If I close them it wants to die down quick. I don't have a link set with me to test RPMs but I know there is a massive difference in RPMs by probably 3,000 or more from when it's in the hole bogging and trying to get out and when it planes out....slowly taking off.
I do have the big factory manual at home. Not here at the lake (camping trip). Do you guys think maybe one of the coils may not be sparking as strong??? Flooding out?

 

[Brabbtiger22]

Or could timing off be causing the bogging ?

 

[racerone]

Timing does NOT go out of adjustment over the years.----A sheared flywheel key does change timing.------Start motor and run at idle.----Pull one plug wire off at a time and stick it back on .----Does motor act the same on each cylinder ?

 

[Brabbtiger22]

Wouldn't touching the plug shock me while running? Lol and should I start it with only 2 cylinders plugged up?

 

[Brabbtiger22]

These are good points. The engine definitely shakes once I get above half throttle lever. Bumps alot like a bogging sound. Sputters alot. I know that one cylinder acts different than the others. In the past with these original coils I would have the engine idling higher and while smooth I've taken a cloth and put it over each carb opening... Probably going to so this again tomorrow and give u guys an update on what happens.