Re: 1970 johnson 6hp seahorse
old ground, maybe -- may have resolved the issue. In case not, though, I think I would spend some time with the idle adjustment. You said you turn the needle but there is no effect on operation. It may be that you are not turning the needle. If the knob is spinning on the needle stem, you need to tighten it. You may want to remove the knob altogether and turn the needle either by hand, or with a pliers if it's too tight in the packing. It's brass, so be careful. Turning it clockwise with the motor running at idle should increase rpms (leans mix). Adjustment is sensitive (which is why your statement of no effect is curious), so turn it clockwise about 1/8 turn at a time, waiting for the motor to catch up. If the motor coughs or stalls, it's too lean and you need to turn the needle counter clockwise slightly. But the needle adjustment will definitely have an effect if things are operating properly. As the rpms increase, throttle the engine down, and keep up the process until the motor can be throttled down to a very low idle without stalling. Next, put the motor in gear and throttle it up. Throttle-up should not cause the motor to stall. If it stalls, the idle adjustment needs to be a little richer. If the motor is operating properly, you should be able to throttle it up to the rpms you are after with the motor in gear. As you probably know, the throttle is prevented from operating fully when the motor is in neutral. You should be doing this with the motor in a test tank of some kind, and should take care not to over rev.
Another option is to fully seat the needle, then reopen about a turn counterclockwise, start the motor and begin the carb adjustment from that point.
