1971 Johnson 9.5

[grassman]

I have a 1971 Johnson 9.5 HP. Motor starts easy and runs well at idle and high speed in gear and neutral without the cover on it. When the cover is on, it will run fine at idle, in and out of gear, but when it is in gear and i throttle up, it bogs down and flattens out. Can anybody give me an idea?

 

[Tim Frank]

Re: 1971 Johnson 9.5

http://forums.iboats.com/showthread.php?t=281283

Might be an exhaust leak

 

[Xcusme]

Re: 1971 Johnson 9.5

From the symptoms, it sounds like you have an exhaust leak into the cowling choking the carb.

 

[grassman]

Re: 1971 Johnson 9.5

I read the link Tim sent. Sounds like I am in the same situation. I have rebuilt the carb and installed a new fuel pump. I did a compression check and have 75 pounds in each cylinder. Is that too low?

where would I start looking for the exhaust leak?

 

[ezeke]

Re: 1971 Johnson 9.5

Check the rubber exhaust relief hose #43 at the back of the engine. Then check the large rubber exhaust housing seal that keeps the inner exhaust and outer midsection cover sealed off. It is shown as #87 on the Exhaust Housing diagram: http://epc.brp.com/default.aspx?brands=ej&lang=e

There are several smaller seals, but they would not usually cause the engine to stall under way unless they are missing or badly deteriorated.

 

[F_R]

Re: 1971 Johnson 9.5

First question has to be where are you running it? If in a barrel, forget it. They won't run in a barrel with the cover on.

If on a boat, there are several possible exhaust leak sources. The rubber flap between the housings is usually blamed, but rarely the real fault. That will affect idle at the dock when smoke is bubbling up around the leg. But as soon as you put it in forward gear, the exhaust is buried in the prop wash, way behind the motor.

OK, the real faults:

1. The pleated exhaust relief hose.
2. Somebody had the lower unit off and didn't put the seal back on top of the water pump.
3. The boot seal around the shift rod and water tube, up inside the exhaust housing.
4. A hole corroded through the bottom of the exhaust cover on the side of the powerhead.

#2 and 3 are most common. And the parts are obsolete, you find them where you find them.

 

[grassman]

Re: 1971 Johnson 9.5

Yes, I am running this in a tank. I am going to try and get it out on the boat this weekend.

Does anyone see an issue with the compression only being 75 pounds?

 

[F_R]

Re: 1971 Johnson 9.5

Not as long as it is starting and idleing ok. You might want to run some carbon cleaner through it to free up any ring stickiness.

 

[grassman]

Re: 1971 Johnson 9.5

I was able to get the boat in on Saturday. It ran well. seemed to idle and run better in the water, rather than in the tank. We ran it about an hour and all seemed fine. Thanks for everyone's advice