69 650 4cyl too lean to idle or too rich for wot

[Cariboo Milkman]

I have been trying to get my engine to run properly and was told by a dealer mechanic to set idle by slowly turning in till falters and then back out 1/2 turn. When I do this it will idle fine but won't rev past about 1/4 speed or so even in neutral. If I crank them in, I can get it to run at high speed eventually and it runs smooth and fast but it won't stay idling without blipping the choke button. Carbs have been cleaned and rebuilt but I did not link and synch. Compression is good. (115-125 across) Any suggestions? My wife says sell it and get something newer but I'm not quite ready to give up on it yet. I think it has potential.
Thanks for any help.

 

[Bosunsmate]

Re: 69 650 4cyl too lean to idle or too rich for wot

I dont know your motor but a lot have a speed limiter in neutral so 1/4 speed would be about what it could be designed to get too, but i suppose you are getting it up to high speed in neutral too when you wrote that.
You could try individually choking the different cylinders at idle to try and track down a specific problem carb. Needles/carb gasket could be the issue

 

[merc850]

Re: 69 650 4cyl too lean to idle or too rich for wot

Are you adjusting the lo speed while in gear in the water?That's the way to do it not in the driveway on flush test -start with the needles 1 1/2 turns out at about 1100 rpms then turn them slowly 'til the motor will idle smoothly and accelerate without stalling.

 

[CharlieB]

Re: 69 650 4cyl too lean to idle or too rich for wot

Idle mixture MUST BE adjusted while on the water and in gear. This provide the correct amount of exhaust back-pressure and load on the motor.

Starting point is 1 1/2 turns out from lightly seated, this should be enough fuel to get started and into gear. From there, adjust each carb until you get the Best idle speed while in gear. Make sure you adjust very slowly and give the motor plenty of time to burn off any excess fuel before making another adjustment.

From best idle, even more idle fuel is needed for crisp acceleration with bogging or getting a lean miss or cough. Back each idle mixture screw out just the width of the screwdriver blade slot. Test acceleration by rapidly opening the throttle ( still in gear, right).

Repeat until perfection.

Note, a heavier loaded boat can require even more idle fuel for acceleration. It is always recommended to have your boat loaded as you normally run it when making all adjustments. The addition of a full cooler can make a difference.

 

[Cariboo Milkman]

Re: 69 650 4cyl too lean to idle or too rich for wot

Thanks for the suggestions. I'll give them a try next weekend when I'm at the lake. Hopefully it'll work and I won't have to make any more excuses to my wife.

 

[Silvertip]

Re: 69 650 4cyl too lean to idle or too rich for wot

Low speed mixture is adjustable -- high speed mixture is via fixed jets so there is no relationship between what happens at high speed and what happens at low speed. The low speed adjustment does affect the transition from idle to high speed.