Logo
FULL SITE MENU

2006 90 hp Johnson 2 stroke bogging down at full revs

T

toyking68

New member
Hi All,
I have a 2006 Johnson 90 hp 2 stroke J90PLSDM. It has always run like a dream and only has 160 hours on it. Recently since Xmas when i open the throttle to full revs (approx 5200) after about 500 mtr it starts to bog down and then rev back up. If i keep it under 4000 rpm it runs all day just fine. I have had it serviced and a new fuel line put on it but with no avail. I have been told it could be the power pack or the optical pickup sensor. Another mechanic said it could be the fuel pump or the VRO. Not sure what to do now. Seems like i could throw alot of money at it just to get a diagnosis which then could be wrong.

anyone got any thoughts or had the same problem?

Cheers
Scotty
 
If this problem is a slow surge... losing power gradually, then the power increases gradually, that would be due to a fuel problem.. that is a lack of the normal flow of fuel to the carburetors.

This could be caused by a kinked fuel line, crankcase pressure falling due to some engine internal problem that would affect the VRO pump, the VRO pump itself failing, a leak in the pressure line running from the VRO to the crankcase, etc, BUT the most common cause is a sticking Anti Siphon valve, explained as below.

If on the other hand, that surge is a instantaneous immediate jump up and down, that would be an ignition problem and I'll leave those answers to another member as I'm not familiar with the electronic circuitry of that engine.

(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.

NOTE: 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.
 
joereeves said:
If this problem is a slow surge... losing power gradually, then the power increases gradually, that would be due to a fuel problem.. that is a lack of the normal flow of fuel to the carburetors.

This could be caused by a kinked fuel line, crankcase pressure falling due to some engine internal problem that would affect the VRO pump, the VRO pump itself failing, a leak in the pressure line running from the VRO to the crankcase, etc, BUT the most common cause is a sticking Anti Siphon valve, explained as below.

If on the other hand, that surge is a instantaneous immediate jump up and down, that would be an ignition problem and I'll leave those answers to another member as I'm not familiar with the electronic circuitry of that engine.

(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.

NOTE: 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.
Click to expand...

Thanks Jo
I believe it is a fuel problem as well. Forgot to mention that the alarm does not go off when this happens.
I'll have a look at the Fuel Anti Siphon Valve as you say.

Cheers
Scotty
 
toyking68 said:
Thanks Joe, I believe it is a fuel problem as well. Forgot to mention that the alarm does not go off when this happens. I'll have a look at the Fuel Anti Siphon Valve as you say. Cheers, Scotty
Click to expand...

I'm not familiar with the 2006 circuitry but the 90hp models in the past never had the fuel restriction warning anyhow.
 
Hi Scotty,

Check first the connections to the battery. Even if the engine starts just fine, they may be a bit loose. This may cause the malfunction of the electrical system e.g. fuel pump. I had the same problem in my J90PL last summer and I checked practically everything (coils, plugs, power pack, fuel line, orifices...). Tightening the loose battery connection solved the problem.

Cheers Antti



toyking68 said:
Hi All,
I have a 2006 Johnson 90 hp 2 stroke J90PLSDM. It has always run like a dream and only has 160 hours on it. Recently since Xmas when i open the throttle to full revs (approx 5200) after about 500 mtr it starts to bog down and then rev back up. If i keep it under 4000 rpm it runs all day just fine. I have had it serviced and a new fuel line put on it but with no avail. I have been told it could be the power pack or the optical pickup sensor. Another mechanic said it could be the fuel pump or the VRO. Not sure what to do now. Seems like i could throw alot of money at it just to get a diagnosis which then could be wrong.

anyone got any thoughts or had the same problem?

Cheers
Scotty
Click to expand...
 
Back
Top