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Johnson 150 Starts but immediately stalls out

L

loopyboat

Member
1992 Johnson 150hp (tj15oglenc) is starting up and firing but then just shuts down right after startup. When I push the key for the primer solenoid in and the motor picks up RPM and runs. The carbs have all been cleaned, because I had a lean condition and I replaced the rubber seals covering part of the idle circuit. I verfied the high speed and low speed passages were clear. The only thing I did notice was that on 3 of the 6 cylinders the float bowl is leaking a small amount from the rubber seal, can this cause the problem I'm having?

If the high speed jets were clogged again, would my motor still idle or does the high speed jet feed the low speed circuit?
 
I retired in 1991 but can give you a bit of advice here.

The fuel must flow thru the high speed jets before it can gain access to any other fuel passageway.

If the high speed jets were slightly clogged, enough fuel could still flow thru them to allow the engine to idle BUT as soon as you advanced the throttle, the engine would fall on its face and die out.

Your engine has the FAST START feature which electronically advances the spark for a fast idle when starting but to my line of thought, that does not constitute advancing the throttle (butterflies) of the carburetor.

The fact that pushing the key in (activating the fuel primer solenoid) results in a increase of rpms and allows the engine to continue to run indicates a carburetor problem (fuel bypassing the carburetors).

Re-work the carburetors again and be sure to manually clean the high speed jets that are located horizontally in the bottom center portion of the float chambers with a piece of single strand steel wire as solvents just doesn't do a proper job of cleaning those items.

Rubber Seals/Idle Circuit? Are you speaking of the seal assembly that goes between the carburetors and the intake manifold?
 
Thanks for the info Joe. I am referring to the rubber seals that go over the idle circuit on the sides of the carburetors which are item number 31 in my drawings. I was getting a slight lean pop and I thought air was entering through here. Upon reassembly of the carbs, now it wont hold an idle and dies out. My float bowls are leaking, could this be a reason for my problem? Ive ordered replacement bowls and gaskets anyway because they are warped.

The carbs were cleaned well, but I will take your suggestion and look more closely at the high speed jets again.
 
After re-cleaning the carbs I still cannot get this to run. It's starting up off the fuel primer, but after that runs out the idle gets slower and slower until it dies. This happens in about 5 seconds time. Could my idle be set too low or something? I'm almost positive the carbs are clean and not obstructed by anything.
 
On a flushette, the idle rpm should be: 20" shaft = 1000 rpm... 25" shaft = 1200 rpm. In the water, the exhaust back pressure would drop the rpms down to normal. Memory fails me here but I believe that would be 650 rpm in forward gear.

The warped float bowl thing.... it's strange that I have never encountered that problem back when I was working on those things. The plastic carburetors came into existence back in 1985 and I didn't retire until 1991. Now I hear about the warped float bowls almost weekly. Whether that is adding to your problem or not, I don't know, but it is a problem that needs to be corrected.
 
Having retired in 1991, I don't know if the design has changed or not, but normally it is just a matter of adjusting the adjustable trunion on the throttle cable at the cable clamp area.

Hopefully some of the other members that are more knowledgeable of that model will jump in here with added information.
 
I'm thoroughly stumped on this one. I've checked that the high speed passage is clear, the tubes leading up to the low speed circuit is clear and the carbs are full of gas so I don't see a reason why it wouldn't stay running.

If I had a bad fuel pump, it would at least idle for a short time and then die out once the bowls became empty at higher speeds.

When the motor stalls, it slowly looses RPMs until it finally dies out, sounds like fuel starvation. The starboard side cylinders are significantly hotter than the portside bank, they are running lean.
 
Do you have spark that will jump a gap of 7/16" on all 6 cylinders ?--And have you checked the shift interrupt switch ??
 
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Hi.

My motor is quite a bit older than yours, but i have experienced a weak and failing fuel pump that caused what you are describing. I partially agree with your comments on fuel pump above, but at lower speed there is also a lower pulse from the motor meaning that a problem with the pump may be "amplified" when at a low idle.

Can you keep the motor running by pumping the fuel bulb between the tank and motor? (Thereby acting as a manual fuel pump) my motor will idle close to 5 minutes on the fuel jump pumped from the fuel bulb and then slowly die out.
 
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racerone said:
Do you have spark that will jump a gap of 7/16" on all 6 cylinders ?--And have you checked the shift interrupt switch ??
Click to expand...

Yes I've used a spark tester to verify I'm getting good spark. What is the shift interrupt switch? I never disconnected anything, only removed the carburetors. Everything was working fine before I took them off.
 
Keithm18 said:
Hi.

Can you keep the motor running by pumping the fuel bulb between the tank and motor? (Thereby acting as a manual fuel pump) my motor will idle close to 5 minutes on the fuel jump pumped from the fuel bulb and then slowly die out.
Click to expand...

Thanks for the info Keith. When I pump the bulb it the RPM's do not pick up, only when I use the primer solenoid. The pump gets hard, but once the motor runs and cuts out, it is soft and I need to pump it once more for it to get hard again.
 
Many folks mistakenly believe that the bulb should stay hard.-------The bulb does NOT stay hard when a motor is running !---Nor does it need to be.
 
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