1990 Johnson 15hp only start with carb disengaged

[OptsyEagle]

When slowing down the motor, I don't know how much the cam moves where the roller comes off the cam but I think there is at least some movement where the roller does not touch the cam when slowing down. That motor should have a idle stop knob on it as well, at the end of the tiller, after the handle grip and just before the red shut off button. You can adjust that and what it does is stops the grip from turning so that you don't accidently remove so much throttle fuel that the motor stalls. When running it gives you the ability to quickly go full out and quickly full back down again and the motor will just take off and slow down, but most importantly, stay running.

To set this, idealy you would start the motor and then reduce the throttle until it comes to its stop. If the motor dies you want to adjust that knob a little more so that it doesn't die. I can't remember which way is which. If the motor stays running when you reduce the idle to where the grip stops, then adjust that knob the other way and you should be able to turn the grip a little more to the slow and observe the motor reducing its idle revs. Find where your motor idles the lowest, but still idles well and does not stall, and that is probably the best setting for that idle stop knob.

If that is done correctly you might find that what is happening is that your roller is now moving a little more away from touching the cam. I don't know for sure but give that a look, since I am not sure how it could not be doing that.

 

[Crosbyman]

no tiller gears... :-( great that solves one problem.

 

[sinkingscones]

When slowing down the motor, I don't know how much the cam moves where the roller comes off the cam but I think there is at least some movement where the roller does not touch the cam when slowing down. That motor should have a idle stop knob on it as well, at the end of the tiller, after the handle grip and just before the red shut off button. You can adjust that and what it does is stops the grip from turning so that you don't accidently remove so much throttle fuel that the motor stalls.

Thank you, every post I'm learning something new. I think I'm about ready to give up though. It's running well enough I think. It doesn't seem to idle before that cam mark and right at the mark im already at 550rpm. I'll take it out on the water and see how it goes and make one last update.

 

[sinkingscones]

Finally an update, this is a long one. I decided to do some deeper reading/research and start from the beginning.
So turns out the carb fuel lines were mostly clogged all the way around the outboard, all 2 feet of it.
Fuel pump was also clogged, not only that, the mechanism in the fuel pump that keeps fuel from draining back would stick open and drain fuel back down every 5 mins.
Apparenty the last owner replaced the float but it rests at a steep angle so it would be getting less fuel. I never noticed much, it would slightly bog at wot and I would max at 11 mph. After everything, no more bogging and max at 20 mph.

Two things left is it can finally start with the choke closed now, but I can still also just start right away with the choke unused so no clue if that's worth chasing.

Last thing is the gas tank fuel line, even after pressure built up, with the bulb at an angle sometimes it would completely drain back while squeezing pressure to the bulb. And at that angle it would never build up pressure again unless I shake the bulb or so. Probably just need to buy another new line.

 

[OptsyEagle]

20 mph is awesome. Good job

If it is hot out you won't need a choke. That said I would be surprised if it is starting, without a choke, on a fairly cold morning. Even so if she is running well I would probably leave it. Starting when it should not is a much better problem to have then not starting when it should.

As for the fuel hose. I have had defective check valves in a fuel hose before. Usually the cheaper aftermarket ones. The annoying problem I had was when it was cool out the fuel line worked fine but when it was hot out for some reason the check valves malfunctioned and the fuel stopped flowing and the only way to get home was to continuously squeeze the primer bulb. That grows old quick. Luckily I had another fuel hose to confirm where the failure was but in the end a different fuel hose fixed the problem for me. If that fuel hose came with that motor that had clogged up fuel lines and filter/pump, etc., then it probably got all clogged up around it's check valves, as well.