Sync cam throttle on 71 Johnson 25hp

[davidmbv]

Hello, I’ve been trying to adjust the cam roller position in order to line it up to the two marks on the cam of my 1971 25hp Johnson. I read the service manual for my motor and did the recommended steps . I set the throttle to where the roller sits between the two marks on the cam and loosened the linkage screw and held it against the cam to hold the correct position while tightening the linkage screw. I made certain the butterfly was closed at the correct position. However, after making this adjustment, I tested and noticed the linkage and carb begin to move (open) as the roller hits the first line (mark). No matter what I do, the roller wants to engage the cam before at or just before the two marks. Should I try advancing the throttle (open) so the roller is well past the two marks, then hold the roller at this position against the cam and tighten the screw and then check to see if the roller then touches at the correct position? Sorry if I’m not making sense, doing my best to describe what I’m looking at. It’s like the cam is the same shape/length before it hits the two marks so the roller engages early. I hate to loosen the cam and start messing with where it sits.
I’ve got the motor running ok, but at high speeds it occasionally will hesitate like it’s cutting out only momentarily. I’ve rebuilt the carb, new tank, lines, quick connects. Proper adjustment on the carb float cleaned high speed jet.
Could adjusting the low speed needle affect how it runs at WOT?
Could the throttle positioning /cam sync affect the way it runs at WOT? I’m thinking that the cam throttle adjustment only affects when the throttle starts on the steering/tiller handle?
The cam roller moves along the cam ok but just engages a bit early. When I first got the motor, it was adjusted so the roller didn’t hit the cam until well past(advanced) the cam marks and actually near where the two marks on the flywheel are located . It ran great but then I ran into unrelated ignition issues caused by a bad/loose ground on a coil that melted one coil. I have new points, good spark, and good compression. I’m also thinking that the hesitation at WOT could be caused from the long fuel line I’m running . I have the gas tank under the middle bench seat I’m my 13’ Gregor and the fuel line is a bit on the long side. Also, I just put on a new aftermarket (eBay/ not OMC) fuel pump. Has anyone had good success with the aftermarket fuel pumps. It seems to squirt gas ok like 6” stream when cranked over. I hate to drop 90$ on a OMC fuel pump unless absolutely sure it’s needed.
thanks and sorry if I’m not using the correct terms to describe the throttle/cam parts. It’s been a fun project and it’s almost running like a top.
Dave

 

[Crosbyman]

how did you clean te HS jet behind the bottom bolt on the carb

did you run a small mono or very small gauge wire to dig out any built up crud
you should see light clearly if you look into the HS jet
cutting suddenly at WOT may be a fuel restriction issue...if not electrical

the low speed circuit doesn't contribute much fuel at high speed see descrip. on an older style carb much like your today

clearing the center post in the carb is also important (small holes allow air to mix in the fuel and emulsify for easier draw into the crankcase at HS .

 

[F_R]

As for the cam, those are very difficult to get "Just Right" on that model, as you have found out. I say get it as best you can and don't fret over it.

Now, let's talk about that momentary cutting out at high speeds. I seriously doubt the cam has anything to do with that. Can you give us a better description of the cutting out? I'm going to go out into guessing-land and ask if it is a quick bump or shake as if you hit something? Then go on till the next time? If that is a lucky guess, it is the motor jumping out of gear, rotating half a revolution, and slamming back into gear. Way common, and is caused by a worn out clutch dog and maybe forward gear in the lower unit. Good guess????

 

[racerone]

Lots of good fuel pumps are replaced as a wild guess.-----Run with a timing light to see if ignition has a miss.------And I agree a 50 year old motor needs lower unit taken apart for inspection of clutch dog.----No special tools or knowledge needed.

 

[Crosbyman]

deleted

 

[davidmbv]

Thank you all for all the responses. I’ll keep the cam adjustment where it is for now.
I cleaned the highspeed jet really well and held it up to the light and it looks super clean. Especially after break cleaner and compressed air blew through it.
The miss at high speed feels like a quick cutting out/sputter/ then corrects itself . Kind of sputters just for a second or two.
ill look at the service manual and plan to look at the lower end eventually if issues continue.
I was thinking today, I have a stern mounted trolling motor clamped on next to the Johnson motor. I tilted it up to reduce drag but do notice it causes a lot of turbulence from dragging behind the boat at high speeds . Could that turbulence cause any issues with it running? I’ll try to pull the trolling motor off next time I’m on the water and see if that does anything.
thanks again for all the responses.

 

[Crosbyman]

run a good decarb product... not a big expense for a trial

to much turbulence could cause cavitation

 

[davidmbv]

Thanks