1971 25hp Johnson Engine Bogging Down

[cartisdm]

Hi everyone! I've mostly lurked over the years but this forum has helped me learn so much about 2-cycle engines.

My outboard was running great but recently left me high and dry about 4 miles away from the dock. Symptoms are similar to a bad fuel pump in that it reaches a max RPM and won't go any higher. I can basically reach a high idle and nothing past that. This fuel pump is only two years old so I'm hesitant to pin point that as the problem. I've taken the fuel pump apart and inspected each layer very carefully and it looks good from what I can tell. The rubber isn't worn or super stretched out, the gaskets are in good shape, etc.

I've replaced the fuel lines and primer bulb and fittings from the tank to motor including the large and small diameter fuel lines on the engine.

The reed values look fantastic and show no signs of wear.

An odd behavior is that I cannot rev to high RPMs while in neutral or forward (engine kinda bogs down/doesn't do anything more with the additional throttle). However, in reverse, the engine will rev super high. I've never thrown the engine into full throttle in reverse in the past but it definitely seems like I get the full response. Even more odd, if I then go to forward, I get spotty behavior with the throttle. It doesn't fix the problem 100% but it does seem to make a difference almost as if it now wants to give me more RPMs with the additional throttle.

Sometimes this engine makes me feel like I'm losing my mind but I always find the issue, fix it, then fall in love with my outboard again. We are currently on bad terms

Before I go replacing another fuel pump, am I crazy? Does this sort of behavior make any logical sense in being something different?

 

[racerone]

Sounds like it is running on one cylinder.-----Test compression.----And answer this question----Does spark jump a gap of 5/16" on both leads , yes or no ?

 

[cartisdm]

Funny, I already had a compression gauge and a spark plug tester in my Amazon cart because I wanted to do my first ignition rebuild. I was going to wait until a rainy day but I guess I should go ahead and complete the order. It might be a while before delivery given the pandemic but I'll test it asap. I've been curious what kind of compression this engine would give me as I never really felt like I got a true 25hp (it would eventually get my boat up to about 21mph though). I have a 14' aluminum v-hull with a wood frame deck inside so it's a tad on the heavier side. I could bring my wife or mom out on the boat but another man was too much to get on plane and cruise.

 

[F_R]

I agree, it almost certainly is running on one cylinder. Forget the gas thing until proven wrong.

 

[cartisdm]

Ok, thanks for the help. In my head I want to do a full rebuild of the ignition (points, coils, wiring, etc.) because it seems that will make my motor start up like butter (right now it starts 100% of the time but not without a little coaxing and fiddling. Tinkering with a motor is the last thing I want to do when I am trying to enjoy fishing). Is that overkill and complicating my life for no reason? Should I only replace what is needed to get a good spark?

 

[Crosbyman]

usual approach is not to fix anything that works… synonyme of " start like butter " is ETEC talk

 

[F_R]

Fortunately, your motor has the famous OMC Universal Magneto, and parts are available all over the world, including here at iboats, and prices are very reasonable.

On the flip side of the coin, while coils are widely available, they are also usually bad on those old motors. If they are cracked or sweaty looking, they are shot and need replacement.

There are lots of how-to videos on you tube. Some are very good, some very bad. I like cajuncook's videos.

 

[Crosbyman]

http://www.ebay.ca/itm/2x-Ignition-...77-582995-A-/184030084254?hash=item2ad90c3c9e

if you are not in a hurry….these have worked fine for me

 

[Tim Frank]

Given your description, drop test and spark tests would be fist step. Does sound lie one cylinder is not working.
Compression after that.
Sounds like you had the carb right off since you say the reeds look fine.

Did you open it up?

 

[oldboat1]

^^Agree. See if the throttle linkages are behaving as they should. With the throttle wide open, engine off, see if the throttle plate turns freely (old grease underneath can be the culprit.)

 

[cartisdm]

Throttle linkages all work as expected and the butterfly values in the carb have full movement. I've always suspected it's running on 2 cylinders since I first got it. Partly because I'm hoping that will give me the power I would expect it to have. I've used this motor a ton over three years and aside from always having something to tinker with, it does always seem to get the job done more or less.

Amazon delivered the spark tester and new fuel pump way ahead of schedule but the compression gauge is still at least a week or two out. I have trouble getting a strong spark to jump 7/16th gap. It can happen but it isn't consistent. I was unable to get the fly wheel off using the "cheat" methods so I'll need to get a hold of a puller. I'll order one today and see if Amazon luckily delivers that fast too.

One thing I did notice about the fuel pump is how "snappy" it is when I blow in it. My current one doesn't leak but it's more of a "loose balloon" feel than the tight snap. Maybe the diaphragm is just worn out. I'll go ahead and swap them out today since I have it.

I'll continue to keep everyone posted

 

[kbait]

If fuel pump diaphragm has a leak, it will allow fuel to pass into the cylinder it gets pulse from, flooding that cylinder.
i made a spark tester and it’s permanently set to 1/4”. If sparks jump consistently at 1/4”, you will have spark at installed plug under compression (assuming good spark plugs).
To quickly check compression..with plugs installed, pull recoil slowly. You should feel two compression pulses with each flywheel revolution. If pulses are strong and feel equal, you should be fine.
Good luck!

 

[cartisdm]

Hi all - I finally got the flywheel off. It was UNBELIEVABLY stuck. Now that it is off, I see damage to the ignition system. One coil has a damaged ground wire which leads me to believe it isn't creating a spark at all (maybe intermittently at best?). The rest of the ignition system looks fine on the surface. Any suggestions on where to start? VintageOutboard.com sells an entire ignition kit for $112. Includes coils, points, condensers, ignition wires, boots and Champion spark plugs. Worth it or should I just clean this thing up and repair the green ground wire and call it a day?

 

[racerone]

The green wire ( not a ground ) is the problem.------Motor was running on 1 cylinder.---The other green wire is also in danger of rubbing on the flywheel.----A novice mistake here I say.-------Route the green wires the proper way.

 

[lindy46]

Coils look good, if you can repair the green wire and clean everything up you should be good to go. Clean points and make sure they're set to .020".

 

[cartisdm]

I'll give it a shot! The flywheel shouldn't give me near the trouble in the future so if I end up needing to dive back into the ignition, at least I'll have the tools and know-how. I'll clean things up, repair the green wire, set the points, and to another spark test.

Results expected this week!

 

[racerone]

Those flywheels are stretched over the crankshaft taper when the nut is properly torqued.-----Flywheel tapers should be CLEAN and DRY when assembled.----And yes they do not fall off and usually pop when the locking tapers let go !