1971 Johnson 9.5 HP

[grassman]

I have a 1971 Johnson 9.5 HP. It has low compression, 75 pounds in each cylinder. I purchased a service manual looking for the specs and it is not in the book. Can anyone tell me what compression the cylinders should have?

 

[Joe Reeves]

Re: 1971 Johnson 9.5 HP

Compression on those small hp models depends on how fast one can pull them through. Check the compression via the manual starter, then check it by wrapping a rope around the flywheel. That usually shows a difference.

If the engine runs as it should, I wouldn't be concerned about the compression as long as the two cylinders read close to each other.

 

[eavega]

Re: 1971 Johnson 9.5 HP

I had a 10 HP that only read 65# on each cylinder, and it ran like a top (my understanding is that 65# is not enough compression for a motor to run). I've always been told that the reading is not as important as the two cylinders being fairly close.

-E

 

[grassman]

Re: 1971 Johnson 9.5 HP

The engine seems to be running as it should although it was running rough and cutting out at slow speed idle. I adusted the slow speed idle knob on the side of the throttle handle and adjusted the lean/rich until she evened out. Like i said, it seems to be running good but I lost some range on the throttle handle between start, shift and slow positions.

 

[Joe Reeves]

Re: 1971 Johnson 9.5 HP

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

Note 1: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.

Note 2: If the engine should be a three (3) cylinder engine with three (3) carburetors, start the adjustment sequence with the center carburetor.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

 

[samo_ott]

Re: 1971 Johnson 9.5 HP

75#'s is a tad low from what I like (80#'s and above) but should be no problem whatsoever. I wouldn't worry about it at all but would try and set the carb up as Joe suggests.

 

[ezeke]

Re: 1971 Johnson 9.5 HP

I have 6 9.5 motors that I keep running for different purposes including kickers with 5" extensions and some for the kids to go clamming. They are easy to start and they can run all day on a small tank. None of mine will read 80 PSI, and they haven't since I've owned them. 65 to 75 psi is about right.

Maybe if you put new Wiseco pistons in them with the tighter rings you could get them higher.

 

[grassman]

Re: 1971 Johnson 9.5 HP

I finally got around to trying to set up the carb like Joe suggested. To keep it running I had to really richen it up. Does a carb disassembly, cleaning and rebuild sound like it will cure my problem? I am think that the float is saturated and or the carb gummed up and slow speed orifice clogged.

Thanks, Don

 

[Xcusme]

Re: 1971 Johnson 9.5 HP

If the float is sinking, you'd see a flooding condition. An OEM rebuild kit should have a newer plastic float included along with all gaskets and seals. Soak carb in spray carb cleaner, followed with compressed air.

 

[rmoore8118]

Re: 1971 Johnson 9.5 HP

75# is fine for this motor. Joe Reeves is correct about the rope on the flywheel. If you'll notice, the "unique" starter system on this motor is geared pretty low, presumably to make pulling the rope easier. As a result you don't get the crank speed you do on some other motor designs. Also, it seems that small HP Johnsons are designed with a lower compression ratio than say Mercs.
I don't know why, it's just something I've noticed.

My 1971 9.5hp has 70 - 75psi while using the starter rope and always has had. Runs great.

 

[Sargent Skiff]

Re: 1971 Johnson 9.5 HP

I finally got around to trying to set up the carb like Joe suggested. To keep it running I had to really richen it up. Does a carb disassembly, cleaning and rebuild sound like it will cure my problem? I am think that the float is saturated and or the carb gummed up and slow speed orifice clogged.

Thanks, Don

Does a carb disassembly, cleaning and rebuild sound like it will cure my problem?

Yep, unless you're sure the carb is spotless, like you yourself have cleaned/rebuilt it lately, with the way gasoline is these days, it's a must.

 

[kbait]

Re: 1971 Johnson 9.5 HP

If available, use non-oxygenated (non ethanol) fuel. Alcohol likes to dry out and flake the inside of fuel lines, and clog up jets. Nasty business.. If you must use the ethanol fuel, replace all fuel lines from tank to carb and you'll be good to go after properly cleaning the carb. Carb removal is easy.. Just put in forward and throttle up(engine off..) to get the stator cam out of the way for the last screw. You'll see what I mean when you go to remove it. Good luck!!

 

[cajuncook1]

Re: 1971 Johnson 9.5 HP

The engine seems to be running as it should although it was running rough and cutting out at slow speed idle. I adusted the slow speed idle knob on the side of the throttle handle and adjusted the lean/rich until she evened out. Like i said, it seems to be running good but I lost some range on the throttle handle between start, shift and slow positions.

Fyi, if you are adjusting the low idle in a barrel or such, your going to drive yourself crazy. Because the low setting of the engine, it intakes some of the exhaust in the barrel and idles rough. Your best option is to take it the lake, pond, or bayou and adjust it under load. If you do a search on this forum you will see a lot of the 9.5 knowledgeable guys recommend this method of fine tuning. It helped me and I loved the little motor. Enjoy your motor! Happy New Year.

You have been given excellent advice from all the above members. I just added my little tid bit just for final idle adjustment. This wonderful forum has helped me out more than I can express!!!

Cajuncook1

 

[lindy46]

Re: 1971 Johnson 9.5 HP

Hey guys - this thread is 1-1/2 years old.

 

[bktheking]

Re: 1971 Johnson 9.5 HP

Hey guys - this thread is 1-1/2 years old.

Ya not sure why people keep replying to old threads, must be boredom over Christmas holidays

 

[tashasdaddy]

Re: 1971 Johnson 9.5 HP

open a new thread if you have a question.