Logo
FULL SITE MENU

Engine will not stay running

C

Contusioncharger

Member
Hi, if i had hair I'd pull it out right now. i have a 1971 Johnson 125hp. I had to rebuild the engine do to a broken piston ring. I have been trying to get it running all weekend. I have everything set as the manual says, slow speed screw 7/8 of a turn out, timing at 5, throttle closed, line on cam aligned with the center of the carb linkage. The problem i have with it set like that it only run with the key in start, once it starts the start goes down but i have to leave the key in start as soon as i let it go it dies. If i raise the start lever to full it runs on its own, but no less then 3500 rpm. I just tired this. i removed the throttle cable, moved the carb linkage so it stayed close, and used the idle speed screw to move the timing lever. Move it half turn out. i got to about 1 o'clock with the lever and it started right up and idled at 1000.I haven't checked what the timing was at, getting late. My question is why? Could i of installed the distributor wrong, i used the messing with car. It seemed like it only went one way. But i think it maybe be off. Like a tooth off in a car. Thanks, I did try this method which was the same result as before, only running with the key in start.

i do have spark. As I can get it running if the timing is advanced a lot. Only thing I can think of is if I left out the rotor pin and the rotor is off or something. Will look at it tomorrow.
 
Having those slow speed needle valve open to only 7/8 of a turn, I'd be greatly surprised if it ran. See below..........
********************
(Dual Carb V/4 With 4 (2 each carb) Slow Speed Adjustable N/Valves)
(J. Reeves)

The adjustment procedure of the carburetor slow speed needle valves follows. NOTE... if the needle valves turn too freely, replace the nylon bearing retainer (the nylon item at the front of the carb that the needle valve goes through first) with the newer type RED retainer #315232. If your engine has that weird linkage that connects all four of those needle valves, the newer RED retainers will enable you to discard that linkage. The RED retainers make it impossible for the needle valves to vibrate out of adjustment.

(Carburetor Adjustment - 2 Slow Speed Adjustable Needle Valves, each carburetor)

Initial setting is: All (4) Slow speed valves = seat gently, then open 1-1/2 turns.

Facing the carburetors, start with the top left needle valve, then the top right valve, then the bottom let valve, then the bottom right valve. It may be necessary to redo these steps to get the adjustments ideally set

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

Do not attempt to gradually adjust all four of the valves at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.
********************
 
Thanks I will give this a try when i can get a chance. Its start to rain here. The problem is when it does start it will only idle at 3000. When I try to adjust the idle speed it dies. But maybe that was because I have the slow speed valves not set right. I just cant seem to get it to the point where it will idle slow.
 
Last edited:
Yeah.... Even if everything else is like new and set perfectly, if those slow speed needle valves aren't set exactly as mentioned above in the sequence stated, it's likely the engine would run rough. Touchy, touchy!
 
Yea. Everything is new. Besides the distributor and stator. I do have the red nylon retainers. Carb rebuilt, new pistons, rings and so on. Thinking the 7/8 of a turn setting was for fuel in the 70’s. It does say in the manual run on premium leaded fuel only.
 
Messed with it today, I first tried you setting, had the same problem. Sat and thought, it only fired when i held the start key in start. But i did get it to run on its own but would only idle at 3000. I have done the diode from starter side of the relay to the purple wire. So i didn't think anything of it. So i removed that and jumper the purple wire to the battery wire and it fired right up. Could not get it idle below 1000. but ill get that once its in the water. i guess i need a new ignition switch. thanks
 
I didn’t. The switch is messed up inside. I ohm’d it out. I had now power to the purple wire in start position. The diode was the reason is was firing when I held it in start. The switch was causing it to lose power during the transition from start to run. So with out that diode I had no power to the purple wire in start. With the diode I did.
 
Last edited:
I got the boat on the water today. It ran good, with a few concerns. I am not sure if the tach is reading high, at 3/4 throttle it was at 6000. I can not get it to idle blow 100 and the low speed valve dont seem to do to much. There was a little stumble off idle. Its about 4 miles from the boat ramp to my house. At about 1/4 mile from house going 30 at 5000rpm. It stumbled once, I slowed down and sped back up. And it started to sound like it was missing a cylinder. Idled around my place adjusted the idle timing to 5 degrees. Played with the slow speed screws. It sound the same idling but when i increase the throttle in bogs and sounds like its missing. any thoughts.
 
The tachometer must be one that operates off of a 6 pulse charging system.
It will usually have a dial on the back of it which must be set to #6. Is it?
 
Other stuff?... Keep in mind that engine is 48 years old, however.................

The four slow speed needle valves need to be adjusted exactly as stated previously.

The four brass high speed jets must be absolutely clean.

Bogging... dying out when throttle is applied is usually contributed to fouled high speed jets... a sticking timer-base under the flywheel... or... the throttle butterflies opening up too soon.

The throttle butterflies should open and close at the same time... not one closed and one ever so slightly open.

The throttle butterflies should just start to open when the scribe mark of the cam is dead centered with the cam throttle roller... not before or after.
 
Back
Top