1972 Johnson 6hp only runs with cover off?

raaaidvw

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May 9, 2012
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I just picked up this motor and had to fix the recoil. Got that done so got some fresh fuel and fired it up. It ran ok but under wot i gear it would rev but not full. It would rev right up sporadically though. Out of gear it will rev up no problem but hard to idle. There's no adjustments on the carb i can see. If i put the cover on the engine it sounds like it choking itself out and it smokes itself till it dies. I'm thinking the car is the culprit and possible the float sticking or not fully closings. Any thoughts. I had an evinrude 4.5 that would just purr on idle and rev right up when needed. Hoping I can get this to do the same.
 

F_R

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If you are running it in a barrel, that is your problem concerning the cover. As you suggested, it is inhaling it's own exhaust, coming up around the bottom of the covers where the air comes in.
 

raaaidvw

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I am running it in a barrel. makes sense now. i checked the cover and its solid fiberglass with no openings. my Honda had a bit of an opening in the back .i looked underneath and theres not much room either for fresh air. how did these things run from the factory like this? i took the flywheel off and checked the points and they were tighter than specs of .020. i opened them up to .020 but now it seems to stumble a lot. also the coils themselves are pretty rough looking. the coating aroundthem is severely dry rotted and it looks like some white powder almost corrosion like on them. i hauled the carb off and cleaned it out and it was spotless inside. still has cork float but its sealing up good when i force very low pressure to it upside down and while i clock it it opens up. any thoughts or should i start by getting this thing out of the barrel first? run it in a lower barrel im guessing should work? thanks again
 

F_R

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Those coils are toast. So now or soon, you will be replacing them. Believe it or not, those motors do get plenty of air from below the lower cowling. But you can't have it sitting in a cloud of smoke. Barrel testing is ok to see if it runs, but to do anything meaningful, you need to do it where it was designed to run...on a boat, on the lake. Yeah, I know, depending on your location, that may not be practical at this time of year.
 

nwcove

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May 16, 2011
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I just picked up this motor and had to fix the recoil. Got that done so got some fresh fuel and fired it up. It ran ok but under wot i gear it would rev but not full. It would rev right up sporadically though. Out of gear it will rev up no problem but hard to idle. There's no adjustments on the carb i can see. If i put the cover on the engine it sounds like it choking itself out and it smokes itself till it dies. I'm thinking the car is the culprit and possible the float sticking or not fully closings. Any thoughts. I had an evinrude 4.5 that would just purr on idle and rev right up when needed. Hoping I can get this to do the same.

I am running it in a barrel. makes sense now. i checked the cover and its solid fiberglass with no openings. my Honda had a bit of an opening in the back .i looked underneath and theres not much room either for fresh air. how did these things run from the factory like this? i took the flywheel off and checked the points and they were tighter than specs of .020. i opened them up to .020 but now it seems to stumble a lot. also the coils themselves are pretty rough looking. the coating aroundthem is severely dry rotted and it looks like some white powder almost corrosion like on them. i hauled the carb off and cleaned it out and it was spotless inside. still has cork float but its sealing up good when i force very low pressure to it upside down and while i clock it it opens up. any thoughts or should i start by getting this thing out of the barrel first? run it in a lower barrel im guessing should work? thanks again

can you post pics of this carb/motor? it just doesnt add up that there is no adjustment on the carb of a motor with points and cracked coils ?
 

boobie

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Nov 5, 2009
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Post a model #. The 1972 carb had a slow speed adjustment on it.
 

raaaidvw

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May 9, 2012
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there is the one lean/rich adjustment by the choke but no others that I see on the carb. model number is 6R72D. also did a compression test with wide open throttle and closed throttle and both plugs out(not sure if it matters but the results were the same regardless.) and they were 92 on the upper and 94 on the lower cylinders. j61.jpg j62.jpg j63.jpg j64.jpg j65.jpg
 

nwcove

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the lean rich is your slow speed adjustment.....your coils are shot....what were the compression numbers?
 

raaaidvw

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May 9, 2012
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the numbers are above the pics on the left, I guess they got spaced. they were 92 and 94 psi
 

raaaidvw

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May 9, 2012
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as for the adjustment I just assumed there would be more adjustments for idle but I guess since theres no kill switch you can lug it down to nothing. is there any specific way to install the low speed idle adjuster after it was removed. I turned it in until it lightly bottomed then put the jamb nut on snug then put the knob at the max rich setting. hopefully that makes sense.
 

racerone

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Dec 28, 2013
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Just finished assembling 5 of these 6-hp motors.-----4 of them came to me with new coils and one needs a set of coils.-----Very common problem is those cracked coils.-----Install a new set and your motor will likely run as a new motor.
 

raaaidvw

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May 9, 2012
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what would make the motor run better if I replace the coils? do they gain/loss resistance ? I thought a coil will just quit all together,no intermittent symptoms. ive never run into problems with coils so I have limited knowledge of them.
 

raaaidvw

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May 9, 2012
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what do you guys think about compression? those numbers good? ive got a sled and they are 135psi so not sure if 90 is good or bad
 

robert graham

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Apr 16, 2009
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Maybe run the motor in your tank while blowing a fan on it to provide fresh air/disperse exhaust fume?.....
 

geoffwga1

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Aug 8, 2010
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394
The # are fine for that motor providing they are accurate.Your low speed needle should be turned in til lightly seated and then opened up 1 1/2 turns.
See the top secret files for the whole procedure.
 

raaaidvw

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May 9, 2012
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ok thanks for all the help. im going to get a different set up to run it and change out the coils aswell and report back
 

racerone

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Dec 28, 2013
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I suggest you remove the magneto plate to install the new coils.----Wires must be fully pushed into the coils before installing the coils.----Carefully note the position of the coils as they are now.---Coils must be positioned accurately to get the right airgap with the magnets....Inspect bottom of the old coils to see if spark was jumping to ground from a burned through hole.
 

F_R

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Jul 7, 2006
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28,195
Compression is fine. But the coils are even worse than you indicated. That motor will never run right till you replace them. As somebody said, it will make a "new" motor out of it.

I'm not sure what you said about how you did the slow speed adjustment. But the needle should be open somewhere around 1, 1/2 turns for a beginning point. Then adjust for best idle from there....on a boat, on the lake.
 
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