Johnson 1972 50hp top end power loss

[rebmo]

I have a 1972 Johnson 50th Anniv Edition on a 14' glass Modified V Lund. It fires up fine, idles well, but does not deliver at top end 23-24 knots tops. The boat and engine have been extremely well maintained and the PO used to pull kids skiing. It has the original prop in great condition, the carbs have been rebuilt with all new gaskets and seats, and idle & high speed circuits clear checked with compressed air. When at top end it does not sound like an outboard at top end, it sounds like it is at half speed? I tried a power prop and it came out of the hole good but even still, did not develop rpms? I have heard good things about these motors, but I wish I could get at least 30knots out of it on this small boat. It has done this for 4 years now with several incremental improvements, fresh plugs, fresh gas always, new fuel pump, fresh fuel lines with stainless clamps, always change lower end lube, clean hull, dry hull (stored out of water over winter).

Any thoughts on what I can check? Anything typical with these motors I can check, timing, anything???

Thanks, REb

 

[HighTrim]

Re: Johnson 1972 50hp top end power loss

rebmo Welcome to the board. I would make sure have good spark on plugs, should jump at least 3/8 of a inch. If no spark from one cylinder or weak then time to pull flywheel and check or replace points and condenser for each cylinder. When it is running bad try pulling plug wire off one at a time to see which cylinder it is. Check compression on both cylinders, Shold be even or within 10 percent and 100psi. If low or uneven then decarb again the engine and see if that helps.When running bad, pump the primer ball and see if makes any difference, also pull the choke our a little or for a short time and note difference.By this time should have a idea where problems lies.

 

[rebmo]

Re: Johnson 1972 50hp top end power loss

Thanks for the welcome HT,

I will try the Decarb process this week while I'm on vacation on a lake. This engine has a power pack, no points or what I would call a condenser and has strong spark on both cylinders with fresh plugs. Thanks for the hints, I already have some Seafoam and a spare gas tank that I will load up with a premix and see if we can generate some smokin. I do like that Seafoam, used it in my old dirtbike and my wifes scooters since they don't run much, and it really smothed out the idle and performance. Never thought of using it to Decarb. I'll post when I get back and can report results of the Decarb and get a chance to do the compression test.

Reb

 

[rebmo]

Re: Johnson 1972 50hp top end power loss

I checked the compression and it's 160 in Cyl 1, 155 in cyl 2. I may be a little off due to the fact that the pressure was dropping slightly (2-3psi) as I ran back to the gauge from the key, but very good even readings. I cranked for 4 seconds on each cylinder on a warmed up engine.

I usally run mid-grade unleaded, I hope this is O'K with this compression. My old Volvo car with fuel injection has compression in the 190# range accross 4 cyls and that needs premium. As said, I will do the decarb process next and report back 6-7 days.

Reb

 

[tashasdaddy]

Re: Johnson 1972 50hp top end power loss

actually thats on the high side. but guages are different. run regular 87 octane. is it possible the boat has some water intrusion into the foam. thus weights more, than before.

 

[rebmo]

Re: Johnson 1972 50hp top end power loss

The boat is stored out of water almost all year with the drain plug out. The hull is in really great condition as it was hardly used when I got it 5 years ago, and up till then it was stored in a garage under a cover. The boat is a Wisconsin freshwater boat. I know even hairline cracks can make a difference but it has always been slow to me even though it starts up, idles and runs fine except for top end performance. It does plane at 23-25 knots, but the rpms (sound) dosen't seem to get beyond what I would consider 1/2 to 2/3 throttle on similar boats.

How could I check the foam in case it is holding any water? It is a double hull boat. Any easy way?

Reb

 

[tashasdaddy]

Re: Johnson 1972 50hp top end power loss

with a drill and hole saw cut a test hole, then take piece of 3/4 or 1 inch pvc pipe, notch some teeth into the end. twist this pipe into the foam, then push the core out is the slightest bit damp there is water there.. if not reseal the hole with 3m 5200 or marine tex. what kind and how big a boat is it on. it also may be propped wrong, now allowing the engine to turn up to the correct rpms.

 

[HighTrim]

Re: Johnson 1972 50hp top end power loss

I dont think you;ll like my answer but I BELIEVE, not positive, you'll have to pull the floor to get a look at the foam. There are many good foam on the markets nowadays that hold very little water if any at all. I still believe there should be a pathway for the water to get to the bilge area just in case, no foam is 100 percent water proof. That way at least when you pull the boat out of the water and pull the drain plug it will have somewhere to go. Might wanna make sure the any holes in the floor from previous owners are sealed up such as for seats and whatever, etc... GL

 

[HighTrim]

Re: Johnson 1972 50hp top end power loss

Tashas Daddy's method is much quicker , id go with that, lol. I just didnt want to be the one to reccomend drilling into your fibreglass, gl

PS Is there adjustments for the height and angle of the trim tilt?May be too low giving you the initial thrust but no top end.

 

[tashasdaddy]

Re: Johnson 1972 50hp top end power loss

HighTrim, i do that all the time. before i ever start on a boat. I drill thru the floor. some time 2-4 holes.

 

[HighTrim]

Re: Johnson 1972 50hp top end power loss

Ty for the tip, im gonna try it.

 

[rebmo]

Re: Johnson 1972 50hp top end power loss

I'm heading to the lake this Saturday for about 5 days. I am going to Decarb and I noticed the motor in the second tilt hole out from the transom seemed to pitch the front down based on the angle at level hull on the trailer. I moved it out to the 3rd hole of 5 and I'll see if that makes a difference. It will be quite here for 5-6 days until I get back. I don't want to start drilling any holes before I go but that may happen when I get back.

Reb

PS I know some folks jumped in at the middle of this thread, please read the intial posts to answer some of the later questions.

 

[mikesea]

Re: Johnson 1972 50hp top end power loss

check on the starboard side under the flywheel and be sure the timing base is connected to the throttle linkage,you might not be getting full timing as the plastic ball and sockets ofter dry and break

 

[crazyinkc]

Re: Johnson 1972 50hp top end power loss

I wonder if his stator is going out? I have a 72 and a 74 50hp Rudes and both of them had the oozing stator problem. Look for a green sap under the flywheel. My 74 would not go over 1/2 power due to the stator laeking. They break down and leak the resin out of the coils on the stator. I rebuilt the carbs, new power pack, bulb, fuel pump, plugs, etc. until I found the problem.

 

[rebmo]

Re: Johnson 1972 50hp top end power loss

Timing base looks O'K. Leaking Stator?? hmm. Since I have owned it I have had what I thought was carb drool and it may well be. But it is sticky and runs down from somewhere under the cylinders onto the the shaft housing. Would a stator leak go on for 4-5 years and ooze all the way down the motor? Or, is it just as others have called it, carb drool from fuel running down out of the carbs after shut-off. It hardly does it any more since I rebuilt the carbs, or, could the stator be done oozing?

Do I have to pull the fly wheel to check the stator or can I check it somehow without a pull? I do have a puller, just want to know what to look for. The shop manual does not go into detail on defective stators.

Reb

 

[tashasdaddy]

Re: Johnson 1972 50hp top end power loss

just look up under the edge of the flywheel you can see the bottoms of the stator coils. doubt it would do it for that long.

 

[rebmo]

Re: Johnson 1972 50hp top end power loss

I didn't realize the stator was so easy to see looking from underneath. I was getting ready with the puller, but I can say it looks super clean with no deterioration of the insulation covers. They are a bright green plastic it appears. Touching them did not reveal any stickyness or deterioration. I would not suspect the stator from a visual inspection standpoint, however, it did sound like a possibility. Half power is about what I feel like I'm getting at top end.

Thanks for all the great leads. I'm not shotgunning, but checking all the suggestions and making sure I have all specs to the book. Any changes I make, I change back if they have no impact, so fear not.

Reb

 

[crazyinkc]

Re: Johnson 1972 50hp top end power loss

Both of mine were oozing. The 74 was the worst. It had oozed all the way down the port side. I suspect it was dropping a cylinder at higher RPM. I thought one of my high speed jets was clogged but they were clean. It looked like the guy I bought the boat from tried to remedy the problem before he gave up and sold it. I bought it off craigslist and it ran fine on muffs when I checked it out. I still got a good deal even with the new parts but it sure was frustrating driving 50 miles to put it in the water each time to find out I did not fix it.

 

[rebmo]

Re: Johnson 1972 50hp top end power loss

OK, here is the status:

I inspected the stator and it appears to be very clean, non-oozing, with no visual defects whatsoever. I took the boat "up north" (northern Wisconsin) and did the de-carb process recommended in the link in this thread. I used 3/4 Gal of gas (regular unleaded 89 octane with up to 10% ethanol), 1 16oz can of Seafoam and 3oz of 2 cyl oil. Can't avoid ethanol gas anymore, even up north. Anyway, started an ran it at very low speed for 15 minutes, shut it off and started after 15 minutes. Tons of thick white smoke when repeating the process the second time. Ended up doing this cycle 6 (yes SIX) times until the thick white smoke subsided. I had to mix another batch of the above to finish the job. Took the boat for a run and it did 28 mph on the speed gauge compared to 23mph last year. great improvement.

I also checked the timing and found it was advancing only 15 degrees at full advance. I adjusted it to 19 degrees which is what the shop manual spec is. This did not increase top speed, but it did seem to give better response over the operating range and more even power throughout. Even on rougher water the speed did not seem to drop more than 1mph at top end or lose much acceleration.

The other thing I tried is tilting the motor back one notch. This helped the boat come out of the hole better and it planed with the bow just slightly up which per the manual is correct. It used to take longer to get to plane and planed more at a level position than with the bow slightly up. No speed increase with the tilt, just better out of the hole.

Anyway, the Decarb process was the big contributor, giving 5mph from last years 23. The timing seemed to help acceleration as well as the tilt adjustment, but neither of those 2 items made any change in top speed. I also probably lost 1-2 mph over last year since the gasoline up there now has 10% ethanol compared to none last year.

Overall I was very happy with the results, and thanks to all that contributed suggestions, this is a really great group with vast knowledge. My goal was to get to 30mph but still this was a great improvement. I was able to pull a tube at 20mph and the kids had a blast (that got them up to about 30mph on crack the whip) Since the boat is a 1972 with a double hull, I am going to inspect the foam yet because I suspect there could be some water trapped in the hull layers within the old foam. After a core sample, I will report back and maybe get some improvement there with new foam. Any suggestions on how to go about that? I can work with fiberglass, just don't know what foam to use.

Reb