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1971 "Stubby" 9.5hp idle rough

guido2

guido2

Regular Contributor
This little motor was stored for years, best compression I could get was around 55 psi after wetting cyls. with mix. Would low compression cause a rough idle? Motor great otherwise. Thanks, Tim
 
Re: 71 "Stubby" 9.5 idle rough

Bad compression would of course affect the performance of any engine BUT the compression of that engine would be affected by the speed in which it is cranked over. Use a cord wrapped around the flywheel for a higher cranking rpm.

With plugs removed, does the spark jump a 1/4" gap with a strong blue lightning like flame..... a real SNAP?

Rough idle can be caused by pitted points, improperly set points, failing condenser or coil, misadjusted carburetor, etc.

(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.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay store at:

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store

(Point Setting Of Magneto Models)
(J. Reeves)

Set the points as follows. Have the flywheel key aligned with the fiber rubber portion of the ignition points. Adjust the gap so that a .020 gauge will pass thru but a .022 will not. Should there be any question of the points being dirty (touching the contact with your finger would cause them to be dirty), clean them with a small brush and acetone or lacquer thinner.

NOTE: Should the operating cam have a small portion on it with the word "SET" imprinted, align this portion with the fiber rubbing portion instead of the flywheel key.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay store at:


http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store
 
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Re: 71 "Stubby" 9.5 idle rough

Thanks so much, Joe. Your imput is invaluable. Its going to get the flywheel pulled and a tune-up kit installed. Will double check carb as well and do a higher speed compression test. One just never knows enough of the "tricks". Take care, Tim
 
Re: 71 "Stubby" 9.5 idle rough

Hi and thanks again Joe. The best compression I could get was 60 psi with a perfect pull.

Replaced condensers then cleaned and set points as you described. There is no pitting and feeler gauge slides through perfectly.

Ended up with "stellar" spark. So set carb low speed as you described. Ended up at about 1 3/8 turn. Customer took motor and said its "always run like that".

Still it is idling very rough and nothing like other "Stubbies" I've had and worked on.

All I can figure is the low compression. It runs progressively smoother as you bring up the speed and at 1/4th throttle it is quite acceptable.

I'm still not happy.......but the owner will try it for now.
 
Re: 71 "Stubby" 9.5 idle rough

I'm thinking the carb and intake configuration make good vacuum/compression more important at low speed on these "Stubbies". What do you think?
 
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