Carburator Adjustments- 73 Johnson 9.5

T

Traxion

Petty Officer 2nd Class
Joined
Mar 22, 2004
Messages
101
Guys, I am looking to do some carb adjustments on my 73 Johnson 9.5. I use the motor mainly as a kicker motor for trolling. It seems throughout the RPM range I am rich. I've checked the plugs at WOT and am a bit rich there as well, but not near what I am at lower RPM's. I know these aren't the most efficient motors but I'm getting a lot of oil/gas blow by in my exhaust. I expect some with the motor but right now it seems excessive.

Part of the reason for the rich condtion is my altitude, I'm over 3000'. First item of business, are there main jets available and a chart to adjust to? I think one size leaner would adjust my WOT rich condition. What about at lower speeds? What is possible for adjustment there? I haven't dug into the carb yet, but I know I'm not familiar with the design.

I've done lots of carb adjustments (needle, jet needle, pilot and main jet, etc.) on Mikuni carbs so I'm not totally out to lunch. Just need some direction. Thanks!
 
F

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
Re: Carburator Adjustments- 73 Johnson 9.5

The only low speed adjustment is the knob on the front panel. The high speed is a fixed jet and yes there is a chart showing a whole bunch of different sizes, but being at sea level here, I have not messed with adjusting for altitude.

OK, having said all that, those motors are notorious for leaking exhaust gasses under the hood and making them run rich. Does it run better with the hood off? If it does, that's your problem. Major exhaust leak possibilities are:
Seal on top of the water pump
Bellows seal on the shift rod, up inside the exhaust housing
Bellows hose connecting the powerhead to the blow-hole in the rear
The boot between the exhaust housing and the outer shell
A leak (hole) corroded through the bottom of the exhaust cover on the side of the cylinder block

The boot is most often blamed, but rarely the actual problem--especially at higher speeds, in gear.

The water pump seal and shift rod seal are the most common. A lot of the parts are NLA. Seems like BRP would like to deny the existence of those motors.
 
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