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2001 Johnson 90 stalling at idle speed ONLY after warm

C

Cucumber

New member
2001 Johnson 90 PLSIG. Same as PLSID. No idea what the G is for.

Motor starts easily and will never stall at idle when cold.

I literally could launch the boat and idle in gear through a no wake zone for 20 miles without stalling.



Example of my problem:

I run 3 miles to the reef.

I turn the motor off while catching bait.

The longer the motor is off, the more likely the following happens(but it always happens to some degree):

Motor becomes more difficult to start(although always starts).

I always have to completely prime the fuel system in this situation. I can feel that there is no fuel(soft bulb) and I have to completely pump fuel from the tank to refill carbs. I can feel all the fuel that I am having to prime.

Once restarted, I usually get smoke(more smoke than a cold start) and have to advance the throttle in neutral until motor seems to have enough fuel.

If I accelerate slowly I stall. Bumping the key will cause the motor to stall immediately.

If i accelerate quickly, I can run all day long. For example, I have never once stalled after a long run back to the ramp. I can wait in neutral for a ramp to open up, or I can idle around in gear indefinitely without stalling. If I turned the engine in the water at the ramp, I would have same problem.


When I run the outboard on the hose, it idles at about 800 RPM after the quickstart feature disengages.


In gear on the water, my idle is between 500 and 600 rpm in gear. This seems low.




Carbs are clean.
Plugs are new.
Compression has remained at 120 on all 4 for 2.5 years(3 tests).
No leaks from carbs(new bowls)
No leaks from vapor separator(new gasket)
Boat get used very frequently(always has fresh treated gas)
VRO is disabled and I premix 50/1
Motor runs flawlessly other than this.



Motor has done this from day 1. There has been a random day or two when this problem didn't occur.



Thanks in advance for any help and suggestions.
 
soft primer bulb Sounds like not enough fuel is going through the system.has to be a possible air leak somewhere in the hoses.Bad check valve in primer bulb.colapsed fuel line somewhere.check fuel pressure with gauge.you have not mentioned anything about the fuel pump!
 
Three different brand new primer bulbs. Nothing changed.

I can run wot forever. I thought this would eliminate the fuel pump as the problem.

How do you check fuel pressure with a gauge?

Thanks.
 
All throttle butterflies should be closed shut at idle..... no offense intended Chrissy.

Cucumber (afraid to ask how you came up with that handle!)...... Anyhow, it sounds like the "Anti Siphon" valve on your built in tank is stuck open, allowing fuel to drain backwards into the tank and air to enter the fuel supply line.

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

There has been cases when the output valve in the fuel primer bulb would come apart, and the inner portion of the valve would actually reverse itself and be drawn back into the primer bulb's output valve body. This in effect would create a shut off valve and result in a fuel restriction. If this is the case, you should be able to feel something laying in the bottom of the primer bulb when held horizontally.

The idle rpm setting.........

On a flushette, set the idle at 1000 rpm for a 20" shaft engine... and... 1200 rpm for a 25" shaft engine. When in the water, the exhaust back pressure will drop the idle to the recommended rpm. (Trust me, this procedure works!)

Let us know how you make out.
 
joereeves said:
All throttle butterflies should be closed shut at idle..... no offense intended Chrissy.

Cucumber (afraid to ask how you came up with that handle!)...... Anyhow, it sounds like the "Anti Siphon" valve on your built in tank is stuck open, allowing fuel to drain backwards into the tank and air to enter the fuel supply line.

(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

There has been cases when the output valve in the fuel primer bulb would come apart, and the inner portion of the valve would actually reverse itself and be drawn back into the primer bulb's output valve body. This in effect would create a shut off valve and result in a fuel restriction. If this is the case, you should be able to feel something laying in the bottom of the primer bulb when held horizontally.

The idle rpm setting.........

On a flushette, set the idle at 1000 rpm for a 20" shaft engine... and... 1200 rpm for a 25" shaft engine. When in the water, the exhaust back pressure will drop the idle to the recommended rpm. (Trust me, this procedure works!)

Let us know how you make out.
Click to expand...

Thanks for taking the time to reply.

However, I never said anything about the warning horn sounding off with a constant beep. The alarm is not sounding.

I have used 3 different new primer bulbs. My current bulb is functioning properly and installed vertically within a foot of the motor.

The problem is only after long runs and turning the engine off. Seems to be heat soak.

My idle is low on the flushette.

Can the idle be adjusted with the detent without the use of an OMC ignition analyzer tool.

If so, how?

Thanks again.
 
Cucumber said:
However, I never said anything about the warning horn sounding off with a constant beep. The alarm is not sounding. I have used 3 different new primer bulbs. My current bulb is functioning properly and installed vertically within a foot of the motor. The problem is only after long runs and turning the engine off. Seems to be heat soak. My idle is low on the flushette. Can the idle be adjusted with the detent without the use of an OMC ignition analyzer tool. If so, how? Thanks again.
Click to expand...

I'm aware that you didn't say anything about the warning horn going off, and am also aware of the primer bulb replacement etc etc. What I had to say in reply post was a copy/paste from my database providing general coverage, in this case.... about the anti siphon valve. I just don't take the time to edit to conform.

I retired in 1991 so your idle adjustment setup is foreign to me if major changes were made... check your manual.
 
joereeves said:
I'm aware that you didn't say anything about the warning horn going off, and am also aware of the primer bulb replacement etc etc. What I had to say in reply post was a copy/paste from my database providing general coverage, in this case.... about the anti siphon valve. I just don't take the time to edit to conform.

I retired in 1991 so your idle adjustment setup is foreign to me if major changes were made... check your manual.
Click to expand...

Thanks.
 
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