1972 25hp Johnson -- Up and runnin

[James Akers]

Let me start with the motor’s history…<br />It’s a 1972 Johnson 25 hp<br />When I bought the pontoon that is sets on, the owner showed me a receipt for some work that had been done last fall by a marine mechanic that I am familiar with, and he is reputable.<br />He replaced points, plugs, condenser, and the water pump. He also charged the guy for “checked out coils – OK”<br />I was a little suspicious of the water pump replacement, so when I got the boat to the driveway, I had bad compression on one cylinder and water seeping from the head. <br />So… I pulled the head, cleaned it up, checked for trueness, installed a new head gasket, and fired her up --- perfect compression 132 top and 132 bottom. <br />By the way… the gas was nasty, so I rinsed the tank out with fresh gas, replaced the fuel line and squeeze bulb, and installed an in-line fuel filter.<br />It ran like a dream, so we put her in the water. <br />After a couple of days, it began to miss, spit and sputter, so I took the carburetor off, washed it out with two cans of carb cleaner, blew it out good the air compressor, and put it back on the boat. I found a small bit of something hanging on the low speed jet needle valve when I pulled it out.<br />It has a fixed high speed jet and an adjustable low speed jet.<br />I got it running great as per carb adjustment courtesy of Joe Reeves’ instructions.<br />Now my unsolved mystery begins…<br />Next day, I fired it up and it ran like a dream on the pier. I took off at an amazingly smooth idle, and ran for almost 20 minutes at this idle with no shake, no miss, no sneeze – like a sewin machine. When I increased engine speed to a fast idle, it ran well for about 20 seconds, and then it was (and is) like I lose a cylinder. When I open it up WOT it clears right up. When I slow it back down to a fast idle, it begins to miss again. I can idle it all day long without any mishap, and I can run it WOT without any problems. But anything in between, I loose a cylinder, spits, sputters, then I get it back for a few seconds, only to lose it again. I checked the timing advance, it seems to be working very smoothly. <br />Any ideas?

 

[Bass Runner]

Re: 1972 25hp Johnson -- Up and runnin

Sounds like you might have trash in the high speed jet, or a plug laying down on you. At wot does it seem to be getting full rpm even though it's running smooth?

 

[James Akers]

Re: 1972 25hp Johnson -- Up and runnin

At wide open throttle it appears to be perfect in every way -- plenty of RPM's and very smooth -- doesn't even give me a hint that something's wrong. If you didn't ever hear it at mid throttle, you would think that it couldn't sound any better.

 

[James Akers]

Re: 1972 25hp Johnson -- Up and runnin

Oops... <br />I forgot to mention...<br />I put new spark plugs in it when I cleaned the carburator --- Gaped at .030"

 

[Paul Moir]

Re: 1972 25hp Johnson -- Up and runnin

Did you synchronize your carburator with the spark advance? In other words, perform a link&sync? <br />I'm thinking this because it only matters at part throttle.<br /><br />Another idea: perhaps something is arcing over, or a wire is rubbing against something at part spark advance. You can check at night to see if you see any sparks. This would probably be obvious because it would suddenly drop a cylinder. Try tugging the spark plug leads with an insulated hook too.<br /><br />Another idea: try running it on one cylinder to see if the problem is isolated to one cylinder. Ground out the unused spark plug lead. Then compare it to the other cylinder.

 

[James Akers]

Re: 1972 25hp Johnson -- Up and runnin

Duh... I don't know what link&sync is. Guess I'd better do some research on this process in other postings. Its just beginning to get dark here, so I think I'll try looking for sparks first. Since the boat is on the water at the pier, and its starting to get dark, I'll try that first. If I don't see anything amiss tonight, I'll proceed with one of your other recommendations tomorrow in the daytime. <br />Thanks a bunch.

 

[Paul Moir]

Re: 1972 25hp Johnson -- Up and runnin

Link&sync is explained in a service manual. The exact procedure differs from year to year and from engine to engine. Even if I had a manual that covered your exact engine, it is difficult to explain the process without pictures. <br />If you're handy with a wrench, a manual will save you money. If you don't wish to buy a manual, you can often borrow one from your local library. Otherwise, Iboats offers aftermarket manuals, and you can get technically superior OEM ones:<br />TheOutboardWizard<br />Mastertech<br />Marine Engine<br />Ken Cook <br />Also, check ebay 'Evinrude manual' or 'Johnson manual'. You can often find original OEM ones for a fraction of the price of a reprint. Unfortunetly, I only see '71 service manuals for your HP now.

 

[James Akers]

Re: 1972 25hp Johnson -- Up and runnin

Well, the wind finally died tonight long enough to check for sparks or arcing. No arcing that I could see... I even took the plug wires off of the mounting brackets, and let them hang loose out to the side of the motor, and there's no change. I was reading my old 135 hp Evinrude manual, and it says that unless the timing stuff has been messed with, synchronizing spark advance and carbs will never be necessary... I guess that I'm a little confused...<br />If the motor was running fine -- then started running rough, and the only thing that I did was pull off the carburator, clean it, put it back on, and hook up the carb linkage that has no adjustments on it, how can link&sync be needed?

 

[Paul Moir]

Re: 1972 25hp Johnson -- Up and runnin

Well, like I said, I don't have a manual that covers a '72 engine, but I'll tell you what I'm looking at on a '70 engine. Ignore this if it doesn't make sense:<br /><br />See how the throttle butterfly on the carburator is moved by a linkage between the little roller that follows the cam on the armature plate (beneath the flywheel)? That cam, roller, link, and clamp on the butterfly shaft communicates spark advance to the carburator. The throttle opening must be synchronized properly with the spark advance. Notice how there's two marks on the cam? The throttle butterfly must *just* begin to open when the roller follower is between those two marks. You adjust it by adjusting the clamp on the throttle shaft.<br />Now, since you removed the carburetor, I'll bet you removed the clamp, or the carburetor's position was changed ever so slightly. So it needs to be resynchronized with the timing.<br /><br />Actually, don't ignore it. It explains why you must do a link&sync everytime you pull the carb.<br /><br />I hope this helps!

 

[James Akers]

Re: 1972 25hp Johnson -- Up and runnin

Thanks Paul, It makes sense now... I'm heading down to the dock to take a look, eventhough its midnight. These things have a habit of driving me nuts until I understand them. Will keep you posted.

 

[James Akers]

Re: 1972 25hp Johnson -- Up and runnin

Oh...<br />Started out the door and found out its raining hard...<br />Guess I'll let ya know when I get aroundtoit.<br />James

 

[Paul Moir]

Re: 1972 25hp Johnson -- Up and runnin

Ok, good stuff. It's 2am here, but I just finished putting the lower unit on my brother's outboard. <br /><br />Here's a few pics to keep you from getting wet. You can actually see one of the cam marks to the right of the follower if you look close.

 

[James Akers]

Re: 1972 25hp Johnson -- Up and runnin

Paul...<br />I couldn't stand the wait...<br />Went down and got my fanny wet, but I see exactly what you are talking about.<br />My motor looks almost exactly like the pictures.<br />However, my linkage is adjusted perfectly, so I'm back to square one <br />James

 

[Paul Moir]

Re: 1972 25hp Johnson -- Up and runnin

Ok, good. Now we know it's not probably plug wires or probably not sync. Next test would be to try to isolate the problem to the ignition. First, make sure both sparks can jump a 3/8" gap. Auto tool stores sell inexpensive testers for this if you're interested. But you can rig something up too.<br />If that shows no difference, try running the engine on one cylinder. I'm starting to think about those coils.<br />Sorry to make you get soaked for nothing!

 

[James Akers]

Re: 1972 25hp Johnson -- Up and runnin

Paul,<br />Have to dry off and get to bed... got to work in the morning <br />As soon as I get home, I will proceed and let you know how things go<br />Thanks abunch!<br />James

 

[James Akers]

Re: 1972 25hp Johnson -- Up and runnin

I made my own tester tonight and found out something that sounds like I'm on the right track (with your guidance of course).<br />My top plug fires about 80% of the time at a 3/8" gap.<br />My bottom plug won't fire until I close the gap on the tester to about 1/16".<br /><br />Now...<br />Is this problem the coils, or the condenser, or the points?<br /><br />Also...<br />The picture you sent me was to a motor that was two years newer, and it had the coils mounted to the starboard side of the head.<br />My motor is a 72 model, with (my understanding) no charging capability.<br />My plug wires run side-by-side around the port side of the motor, and connect to the timer base assembly (I think thats the proper term for it)under the flywheel.<br />Are the coils under the flywheel?

 

[G DANE]

Re: 1972 25hp Johnson -- Up and runnin

Thats Classic for these motors. Its probably a bad condenser. Change both plugs and condensers right away , not much - check the armature plate for wiggle/wear. and if there is a problem there - search for wiggle here - Joe Reeves posted an excellent cure which is free.

 

[Paul Moir]

Re: 1972 25hp Johnson -- Up and runnin

That would be the problem then: at part throttle, spark happens nearer TDC. The denser air is, the harder it is to arc across.<br />The easiest thing to do is swap parts from one side of the ignition to the other. Condensors first (easiest), coils and then points. See which causes the weak spark to follow. Points must be gapped to open .020" max.<br />To access the components, you'll need to pull the flywheel. For that, you'll need a puller that acts on the three bolt holes surrounding the hub of the flywheel. A 'harmonic balancer puller' available at auto parts stores works well, and is pretty cheap. Do not use any sort of puller that acts on the rim of the flywheel; it will destroy it.<br />You do not need to torque down the flywheel to test the ignition after each swap as long as you don't run the engine. Just set it on top of the taper and tighten the flywheel nut finger tight.<br /><br />One thing to look for, those ignition coils on your engine are known to crack and arc over. Carefully examine the insulation. Iboats has them for around $15 each. Napa autoparts has them for slightly more. If you find one coil bad, seriously consider replacing both.<br /><br />When you've got it working, you'll need the torque spec for the flywheel nut. If it's not torqued to spec, the flywheel key will shear, and the ignition will fail. I belive it is good policy to loctite (blue) any fastener under the flywheel.

 

[James Akers]

Re: 1972 25hp Johnson -- Up and runnin

Thanks Guys!!<br />I'll light in on her when I get back to it after work. Just a few more questions:<br /><br />(1) I searched for armature plate, wiggle, wear, and all terms, and can't seem to find the post for a free cure by joe reeves. <br /><br />(2) Anybody happen to know the specs on flywheel torque for this motor? Just too anxious to wait for a manual to come snailmail.<br /><br />Just thought I'd get my ducks in a row, before I pull the flywheel.<br /><br />You guys are great!! Wish there was a gremlin for a hug...

 

[phatmanmike]

Re: 1972 25hp Johnson -- Up and runnin

You guys are great!! Wish there was a gremlin for a hug...

dude.. no ..