15hp Johnson stalls when increasing throttle

Hi Gents,
Some advise please.


Johnson 15hp Belgium 1992




Recently out on the water - motor cold, motor starts second pull, need to play with choke until warm & pickup speed - then runs fine.
After running for a while, slow down to idle it will stall.
Then need to use choke to start even though motor is warm.


Back in the tank now.
Starts and idle - bit roughly on no throttle,
if I throttle up, it will raise for couple of seconds then splutter & stall.
Either throttle back or choke at this time stops from stalling, I can get it to rev higher if I keep the choke on half.
Is it temperamental and taking a while to warm up?

Ive tried adjusting the lean/rich knob, but doesnt seem to have any affect, started with 1.5 turns from closed.
Same with the idle adjust on tiller (This thing is stupid - seems to turn without end in one direction)
Fuel bulb is full, a pump doesnt have any affect


Put into gear, it will splutter & stall unless I use half choke.



I dont think its fuel supply
Possibly Carb needs clean?
Need new plugs?


BTW
Fuel tank - my tank does not have the breather knob on cap.
I usually open the cap to let the pressure out once before going out.
The cap needs to be on tight during operation to keep the fuel pressure good - right?


Thanks in advance

Cheers.

(Belgium model has nearly no water out the telltale - water comes out exhaust and small hole bottom of leg)

Possibly the slow speed adjustable needle valve requires adjusting, as follows... OR... the high speed jet within the carburetor is slightly clogged, fouled, gummed... clean that with a piece of single strand wire.

Engine running in neutral.

Gently seat the needle valve, then back out 1-1/2 turn.

In increments of 1/8 turn, turn the needle valve clockwise, wait for the engine's response, then turn again..... As you turn the needle valve in, the rpms will increase... lower the rpm as needed to a idle setting.

Continuing the clockwise turning of the needle valve until the engine either starts to die out or spits back, then back up the needle valve approximately 1/4 turn.

Somewhere within that 1/4 turn, you'll find the smoothest setting.
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Hey Al,
Thanks for the advice, Im not sure if i have achieved that.

In the drum at home.
I cant get the motor to idle alone, I've got to constantly play with the choke & throttle to keep it running.
If I turn off the choke, within 5 secs the motor will die out.
If I back off the throttle, It will also die out.
I can get a happy medium on half choke and Max neutral throttle.

I've adjusted the slow speed needle, but with it needing choke & throttle, bit difficult to tell.
Also adjusted the slow speed stop, on end of tiller, could not tell if it was making any difference.


When Im on the water, I manage to get it up & running with choke, then running for time on high throttle without choke, but when I slow to idle speed it will stall.

Any advise appreciated, thanks.

Looks like time for a thorough carb cleaning and float setting also you want to make sure when you are running it in a tank that the cowling is off and you have a fan blowing across the motor supplying fresh air.........if there is not a nice breeze to clear the exhaust away. Otherwise what will happen is that the motor will intake heavier amounts of monoxide and that will mess up your ability to adjust the mixture properly. It needs oxygen in order for proper combustion and adjustment.

Check thermostat.-----Do a compression test.------You have replaced the water pump impeller every 3 / 4 years on this motor ?

Great advice timguy.

Hi Gents,

I dont have a compression tool, so took my motor to a mechanic.

Told him the motor was only idling while I adjusted choke , that it would run if i could get upto speed, but stall when on low throttle.

He tells me he adjusted the carb needle, and checked the compression - said it was alright (Should have got the measurement).
But the original problem was still there, said he noticed the motor would run a short time after starting, then seem not to be getting enough fuel.
Then said he would need to take off the head and investigate further, that finding the problem may cost more that the motor is worth.

I picked up the motor & he charged me $50.

Im thinking i should get another opinion.

Cheers.

Just picked up a 1992 15 HP here.-----Marked as having poor compression and weak spark.------Easy fix and have any and all parts to fix it on hand.------So post your compression numbers.-----Does spark jump a gap of 3/8" ( 1cm ) or more, yes or no ?-----Have you checked the thermostat ?-----Checked the flywheel key ?----Replaced the thermostat ?----Test run with another tank and hose.-------Or bring it over , I can fix it !------Trouble shooting has to be done by you.

Did the carb ever get cleaned? Your shop is typical, adjust the low speed needle, do a compression test....bingo....50 bucks for 5 minutes work! What ARE the compression numbers?