Home › Forum › Ask A Member › 1972 Johnson 2hp – low speed and idle problem
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stan-k.
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July 18, 2015 at 12:11 am #2039
I realize that my motor may not qualify as an antique, but I was hoping that someone on this forum could possibly shed some light on my problem.
I’m restoring a 1972 Johnson 2 HP (M2R72). I’m having problems getting it to run at low speed or idle. The carburetor has been well cleaned (all ports are clear) and the needle valves and seats are all in good condition. The leaf valve on the intake manifold is in good shape. I’ve tested the motor with the high and low speed settings set correctly, but it will only run at high speed. I’ve tried to adjust while running, but no luck.
I didn’t replace the cork float. It appears to be in good condition…could it be the cause of the problem?
I’ve also replaced the two main crankshaft bearing seals.
Could low compression be at fault? It tests at 85 PSI max.
Any suggestions would be greatly appreciated.
July 18, 2015 at 12:19 am #20322Low compression immediately came to my mind, however 85 is good. So that isn’t the problem. I have to think carb adjustment or throttle/spark sync. Are the exhaust relief holes open and not submerged?
BTW, 1972 is a "Classic" and is allowed here.
July 18, 2015 at 1:09 am #20323What EXACTLY is the engine doing at low speed? Your description is a bit vague.
Is it dying out? Will pulling the choke momentarily bring it back ? More information is always helpful here. You did a good job letting us know what all has been done by the way.July 18, 2015 at 1:16 am #20324As I slowly return the throttle back to slow speed or idle the motor starts to sputter and then die out. Pulling the choke didn’t appear to help.
July 18, 2015 at 1:22 am #20325Thanks Frank. Could you explain "throttle/spark sync"?
The exhaust relief holes were above the water line when tested.July 18, 2015 at 2:09 am #20328Where do you currently have your low speed adjustment needle? From a lightly closed position how many turns out is it?
I take it you put a complete kit in the carburetor? What parts did you use around your low speed needle? Describe the part or parts used there if any?July 18, 2015 at 7:31 am #20335quote Stan_K:Thanks Frank. Could you explain “throttle/spark sync”?
The exhaust relief holes were above the water line when tested.Speaking of when the carburetor butterfly starts to open as you advance the spark (throttle lever). It’s been awhile since I’ve looked at a 2 but I suppose there probably is a mark on the cam that opens the butterfly.
July 18, 2015 at 10:34 am #20337To answer Pappy’s question – Low speed adjustment needle is turned out by 1and 1/2 turns. High speed by 1 turn.
No, not a complete carburetor kit, just the following : main float bowl gasket, packing seals for both high and low speed needles, internal rubber seal for standpipe, intake manifold gasket. The carb was cleaned by ultrasonic cleaning and I traced all ports with a fine wire to make sure they weren’t plugged. Both high and low needle valves appear to be in good condition and the inlet needle valve is in good condition and seating well.July 19, 2015 at 1:07 am #20364Without having a carb like yours in front of me is this the one that the idle fuel comes through the main jet into the nozzle well then off at a 90 degree angle to the side of the bowl before going up into the main body?
July 19, 2015 at 11:12 am #20376Here is an exploded view of the carb that may help. http://www.marineengine.com/parts/johns … Carburetor
BTW, I also re-adjusted the float so that it sits level with the bowl when closed, but I haven’t tested it yet to see if it made a difference.
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