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6R71E Johnson - Delayed throttle up

J

jaytdot

New member
Hi,

I have a 1971 6hp Johnson that's been in the family since new. It's in great shape (always stored indoors) and I've just recently picked it up to start using it again. I'm going through all the regular maintenance activities on it but there's two issues I haven't encountered on other motors I've worked on (meaning 3 others!)

It starts no problem, but then two things are happening.
1. I'm getting surging at low RPM. I have it idling decently low but it momentarily increases RPM every once in a while.
2. The second issue is that when I increase the throttle it sometimes does not throttle up right away then just quickly revs up to high RPMs. Sometimes I have to back off the throttle and try to throttle up again until it decides to work. When running WOT it sounds great and steady.

So generally I'm getting inconsistent throttle control. Surging at low RPM, and delayed response throttling up.

I've cleaned the carb twice and replaced the needle valve washers. The spark plugs are new. I'm waiting on a new fuel pump to rule that out. I'm also using a new fuel tank and hose.

I'm wondering if this has anything to do with the timing (no experience in this) or if its most likely still a fuel/air mixture issue.

Appreciate any feedback so I can keep ticking things off the list of possible issues.

Thanks
 
If it has never had new coils installed , it is overdue.----Install new impeller.----Check thermostat , I often find them stuck open.-----Check end of low speed mixture needle, as in does it come to a point.----I would never buy a new fuel pump.----A simple diaphragm replacement is all that is needed 99 out of 100 times.----Yes a new diaphragm is available all day long !
 
Do you know someone with a compression gauge? Low compression might have something to do with it. Also note that the head gasket on these motors can fail.
 
racerone said:
If it has never had new coils installed , it is overdue.----Install new impeller.----Check thermostat , I often find them stuck open.-----Check end of low speed mixture needle, as in does it come to a point.----I would never buy a new fuel pump.----A simple diaphragm replacement is all that is needed 99 out of 100 times.----Yes a new diaphragm is available all day long !
Click to expand...
Thanks for the info. Got the flywheel off and sure enough the casing of the coils is cracked, time for them to be replaced. I can also visually see that the points aren't set the same, so I'll adjust those while I'm in there and then run some tests with a multimeter.
 
The factory gasket was just plain material.----The replacement gasket has metal rings.------Much improved.----If original you should replace it with a SIERRA version.----I order them 4 at a time.------Cylinder head will be warped and needs to be refinished with emery paper on glass.
 
Yes, I recommend wet or dry paper and use it with water. I've had great results with 120 to 180 grit, then finish with 240 to 320. I use an old door window glass from 67 to 72 Chev truck, flat and durable. Head bolt holes should be blown out and if they are showing oxidation or more solid debris, run a tap in and out with lite oil. Clean bolts with wire wheel and treat with a small amount of anti seize....you don't want any more than is going to smear into gasket area when you torque them down. New bolts, when the motor was assembled, had a zinc coating to discourage any oxidation, but when the bolts are removed....especially after all these decades....the zinc is gone when you clean the threaded holes and the bolts themselves. So when most mechanics reinstall the head with the original bolts, they overlook this and install the cleaned bolts dry. This will make it very difficult to ever remove these bolts again.
When setting coils, have the front face at the inner edge of tapered bevel at the top of the mounting posts. You don't want them to rub the flywheel at all. If you install new points, be sure to put a tiny amount of high quality grease, I use Amsoil, on the pivot post then don't let that little clip get away from you. For cam lube, either a drop of oil on the cam wick, or a tiny bit of that Amsoil red grease on the cam, so equal amounts will be distributed on leading edge of the points' cam follower. If all goes well, you won't have to bother with it for another couple decades.
 
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PROBLEM SOLVED.

In the end it turned out to be the coils. The interesting part is that I tested the coils with a multimeter and based on a video I watched the readings were all accurate. I only found one post somewhere that mentioned the readings may be irrelevant once under load. That seemed to be the case in this instance.

Anyway, she runs beautifully now.

Thanks again for the help.
 
Yes, it does happen where multimeter will show adequate values, but coils will arc internally, or somehow get to ground. It's not entirely uncommon.
 
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