1976 Johnson 25hp UPDATED REPAIRED 7/13/2010

I had some trouble with my motor Sunday Morning. It started up and idled great but it wouldnt plane the boat out, even with just me in it. It seemed that it lacked power once we were under power moving forward. Could that be an engine problem or just a lack of horse power? I couldnt tell for sure but i couldnt get all the rpms out of it once in gear. I could manually push the gas and rev it up real loud in nuetral but not while in gear. We were going maybe 10 mph with no planing. Any ideas?

Sounds like it's running on just one cylinder.

I agree on the one cylinder.Make sure it has spark on both cylinders.Little more info on your motor would help also.Mostly the
year.May have points that need adjusting.

crazymanme2 said:

I agree on the one cylinder.Make sure it has spark on both cylinders.Little more info on your motor would help also.Mostly the
year.May have points that need adjusting.

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Its a 76 Johnson. I'll check the plugs first I guess. How can u tell if it needs new ones?

How do you set the points?

They're under the flywheel.(.020) is what you gap them at.

crazymanme2 said:

They're under the flywheel.(.020) is what you gap them at.

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Do you think thats what the problem is?

Pull both of your plugs out & make sure they're grounded to the motor & pull over to see if both have spark & go from there.You can not see if a plug is bad usually.If you don't know when the last time they where replaced I would change them before pulling the flywheel.

This is the new motor?

Dont mean to ask a dumb question, but you sure you have a short shaft motor on a short transom? The cavitation plate should be close to level with the bottom of the boat, if its much lower that extra drag will really slow you down.

WTL said:

This is the new motor?

Dont mean to ask a dumb question, but you sure you have a short shaft motor on a short transom? The cavitation plate should be close to level with the bottom of the boat, if its much lower that extra drag will really slow you down.

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Im sure.

Try checking to see if you are running on one cylinder. Those motors are tough and will run decent on one cylinder but half the power.

Change your plugs, there cheap enough. (might just be a bad plug hopefully)

Spark plugs- (torque to 17 to 20 foot pounds with a torque wrench)
Spark plugs gapped at 0.030 (use a feeler gauge)

Check to see if you have good spark on both cylinders using a spark plug tester, not just a spark on the end of the plug. Yes grounding the plug against the motor can let you know if there is spark, but it does not let you know the quality of the spark. Low quality spark (on a spark plug tester) could be oxidized or improperly gapped points.

( Please undo both plugs, so you don't accident start the motor) Should have a good strong spark at 1/4 to 5/16 inch on the spark plugs tester. (ground the tester to the motor). If you have a cylinder that has no spark or very weak then your basically running on one cylinder. Father in-laws Evinrude 6hp motor was running ok and idle a little rough but it was running on one cylinder, no spark on top cylinder and was running about half power. Had to change the coil on the motor and now it runs smooth and he is happy again. These motors are tough and will run on one cylinder but poorer than usual.

Another way to tell if you are running on one cylinder is to start up the motor(in the water) and let her warm up for a minute or two. Carefully (don't want to get a little jolt ) unplug the boot to the top plug, if runs rough but maintains some then the bottom plug/connnected cylinder is firing. If it dies then you know that the bottom cylinder is not firing/spark. Replace the top spark plug boot carefully and let a run for a minute or two, then unplug the bottom plug boot, if it dies then you know that you have the top cylinder plug/wire that is not firing/spark. If runs rough but maintains some then the top cylinder is firing.

spark plug tester $7.00

feeler guage $7.00

torque wrench $21.00


**Make sure your vent plug is open plug on your tank open when your running/starting your motor if you have a plastic tank. (You may laugh, but all of us have forgotten to open that vent plug while starting up the motor in the morning for a day of fishing and find a little while later the motor is running like do do, because the air can't entering the tank. The motor's and fuel pump is now trying to suck gas from a tank that has a negative pressure in it. **


cajuncook1

Does the spark tester indicate how to use it? Not a mechanical guy at all.

Troutman3000 said:

Does the spark tester indicate how to use it? Not a mechanical guy at all.

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Yes, the spark tester is pretty simple.




use the clip to the left in the picture and ground it to the motor.

use the part on the right of the picture that looks like the end of a spark plug and connect it to the spark boot as though it were the spark plug itself. Put in a position that you can view the spark when you pull the starter handle or crank the electric starter. Should be a good blue spark at 5/16 to 7/16 of an inch. If it weak looking then the points may need to be cleaned, regapped or replaced.

If there is no spark, then you have to inspect your coils, points,condensor and you wire going to the spark plug. (The points and condenser should be under the flywheel and your coil should be external on that year motor.

Just reviewing this, no insult intended at all, just trying to help you out.
Oh, just for the sake of mentioning it, did you adjust your tilt on your motor? If it is tilted too much in then it causes the boat to plow and the boat will not plane and you will get poor speed and performance. Plowing is when the bow of the boat is somewhat pushing down in the water, so to correct this just the tilt at one hole position at a time to get the best performance and planing.



cajuncook1

Just reviewing this, no insult intended at all, just trying to help you out.
Oh, just for the sake of mentioning it, did you adjust your tilt on your motor? If it is tilted too much in then it causes the boat to plow and the boat will not plane and you will get poor speed and performance. Plowing is when the bow of the boat is somewhat pushing down in the water, so to correct this just the tilt at one hole position at a time to get the best performance and planing.

Yes - i thought of this and tried all three different positions. I also thought it may be the weight factor, but I dropped my passengers off and no luck. It was no where near planing and after having an early eighties rude that plane out pretty easily I just assumed something was wrong.

Really it all makes a lot of sense now, the guy i bought it from on ran it in a bucket with minimal throttle. Everything appeared to be fine, the motor was real clean and still had the original stickers on it. As I was leaving he told me he hadnt changed the spark plugs in a bout 8 months or so. I think he knew there was a problem with the spark and it wasnt just a plug. Which leads me to think he knew it was fubarred and passed the problem on to me. I dont want to be that guy but if I cant get it fixed reasonably cheap I may have to sell it as well.

As long as the motor has good compression it should only be a few parts to get it going.

lckstckn2smknbrls said:

As long as the motor has good compression it should only be a few parts to get it going.

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The compression is solid. I can barely pull the rope sometimes, so now I just have to pin point my problem.

If your hesitant to tackle this yourself, because you don't feel that you have the right tools or mechanical inclination, then I would suggest asking around for a trustworthy mechanic. Most mechanics charge $85 to $100 hour for labor. (This is in my neck of the woods and maybe different in your area)

You can call around to different referred mechanics and get an estimate of what they will charge.

Chances are you have points that need to be changed/cleaned or a bad coil.

Also your carburetor 's high speed jet maybe dirty and need cleaning.

All this with parts a labor could run about 200 to 300 dollars. (Now you must decide if your willing to spend this amount of money to get your motor running properly) You can sell the motor and try to buy another, but again do you know what you getting?? If you fix this motor then you know what you have!

One last thing for you to look at on your boat, just to make sure it is make sure your prop is not spun. It may not be fully spun and slips under load. (Chances are it is not this but, it cost you nothing to check it out)

look at this link please https://www.tinboats.net/forum/viewtopic.php?f=4&t=13786

Good luck!

cajuncook1

cajuncook1 said:

One last thing for you to look at on your boat, just to make sure it is make sure your prop is not spun. It may not be fully spun and slips under load. (Chances are it is not this but, it cost you nothing to check it out)

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If his hub was spun, he would have no problems getting the rpm's up.

(just thinking out loud)

Quackrstackr said:

cajuncook1 said:

One last thing for you to look at on your boat, just to make sure it is make sure your prop is not spun. It may not be fully spun and slips under load. (Chances are it is not this but, it cost you nothing to check it out)

Click to expand...

If his hub was spun, he would have no problems getting the rpm's up.

(just thinking out loud)

Click to expand...

Oh, must have I missed that part in his description....well then I agree with ya Quackrstackr

Ok Guys I found the culprit I think. Looks like the coil is busted, I spark tested the top cylinder and no spark, spark tested the second, spark.

Then bassboy reminded me that he may have saw something when he was looking at the motor but it just slipped his mind, well I looked and I found this.

Where can i order this part?