1974 Johnson 25 hp backfire issue and other

[Dalejam]

Hello all,
I have a 1974 Johnson 25 hp motor pull start, Model number 25R76E
It is a long shaft. first thing i did was pull the spark plugs and sprayed oil in cylinders. check for spark fixed the points, re gapped them, ran some 800 sandpaer through them till i got a good streak on paper. took carb apart, the low idle speed was clogged, i took it all apat and cleaned it with carb cleaner, did not put it into the ultrasonic cleaner yet, choke was sticky, but i got it to function some, will need more attention. took plugs out did compression test both cylinders got 140.
Took the line off the fuel pump pumped the bulb a few times till i thought the fuel that was in the lines was gone. it pushed out fuel so it was not cologged. put it back together, will change the fuel lines later. put the choke on gave it a pull nothing first pull, on the 3rd pull it popped loud, so i switched the wires going to the coils. tried it again. it ran for a 4-5 seconds then backfired, so it runs yea....... any idea what would cause the back fire. if people say carb i knew i should have ultrasonic cleaned it.
thank you all

Dale

yes i am the same person who posted about the evinrude 25 1974... are these the same motors, they look identitical ??????

 

[Crosbyman]

most folks do not have ultrasonic cleaners or know about them so don't get hung up on this.

back fire is propably bad ignition work so focus on all electrical issues.
coils, wires, timing etc... the usual stuff.

 

[lindy46]

Is it an actual backfire or more of a cough or hiccup? If so, could be just lean sneeze. Open up the slow speed needle a little.

 

[Dalejam]

most folks do not have ultrasonic cleaners or know about them so don't get hung up on this.

back fire is propably bad ignition work so focus on all electrical issues.
coils, wires, timing etc... the usual stuff.

i think i am going to replace both coils, they are original too. so to start off fresh. also may replace the driver coil. will keep updated after parts come in
thank you all
Dale

 

[Dalejam]

Is it an actual backfire or more of a cough or hiccup? If so, could be just lean sneeze. Open up the slow speed needle a little.

Backfire, get a pop out of it. could it possibly be the one coil is going bad and not firing all the time, then when it does fire all the atomised gas in the chamber goes off all at one time >>>????? just thinking outload.
thank you
Dale

 

[Crosbyman]

Unlikely because the unburnt fuel -oil does not store inside the cyl it gets pushed out the exhaust on the subsequent upstroke and load of fresh fuel oil mix..... at worst ... residual fuel oil in the outgoing down draft of exhaust may be ignited suddenly.

Backfire is a result not a cause ... find the cause first !

if coils are not damaged they could have been replaced years ago are probably fine. find the cause before spending $$$$ do some testing
clean up all connections ... all electrical issues

 

[racerone]

Some folks use the " it must be the coils " approach.-----Most start with the ---" it must be the carburetor " approach.----Simple trouble shooting finds the issues.

 

[Dalejam]

Unlikely because the unburnt fuel -oil does not store inside the cyl it gets pushed out the exhaust on the subsequent upstroke and load of fresh fuel oil mix..... at worst ... residual fuel oil in the outgoing down draft of exhaust may be ignited suddenly.

Backfire is a result not a cause ... find the cause first !

if coils are not damaged they could have been replaced years ago are probably fine. find the cause before spending $$$$ do some testing
clean up all connections ... all electrical issues

that is going to be me approch when i get home. i will go over all the wireing to see if possible a short somehwere ? then double check all connections and look at carb again. i got time. i have another 25 by Evinrude and a 8.5 by johnson. i want to take 2 of my kids out striper fishing. i go all the time on my Kayak. but i want to spend time with my Boys...
thank you
Dale

 

[Dalejam]

Some folks use the " it must be the coils " approach.-----Most start with the ---" it must be the carburetor " approach.----Simple trouble shooting finds the issues.

So I got home gave it a few pullsand it ran nicely then died. So have it more throttle pulled again it ran the stopped . Checked points again they were spot on . Checked for gas . Then spark? No spark?????? So I put my spark checker in and I could see the coil was shorting to the block. Both coils went bad shorting out of side. Must of been like that for a while. I cleaned the motor with degreaser so I probably gave it a place to short out now that the grease mess is gone.
So I orderd two more coils . Will write again after I get the new coils in.

Thank you Dale

 

[CaptnKingfisher]

What did you mean by this?

Checked points again they were spot on .

I understood the rest, glad you observed some arcing to ground and hopefully the new coils fix the issue. Just trying to understand what "points" you checked on your outboard and how ya checked em

Thanks

 

[racerone]

A 1974 model 25 HP has 2 sets of breaker points ( mechanical switches ) under the flywheel.-----They are set to open to about 0.020" maximum gap.

 

[CaptnKingfisher]

A 1974 model 25 HP has 2 sets of breaker points ( mechanical switches ) under the flywheel.-----They are set to open to about 0.020" maximum gap.

Thanks, learning something everyday on here

 

[racerone]

Kingfisher-----visit----leroysramblings-----There you can spend a few hrs and learn all about older ignition systems.----How they work and how to repair them.

 

[Dalejam]

What did you mean by this?


I understood the rest, glad you observed some arcing to ground and hopefully the new coils fix the issue. Just trying to understand what "points" you checked on your outboard and how ya checked em

Thanks

I put the nut back on the motor, rotated to the SET MARK, checked the points on the one side, the. The other side same thing .
If it wasn’t for help telling me to recheck everything I would have been chasing this for a while. Time and double checking

What did you mean by this?


I understood the rest, glad you observed some arcing to ground and hopefully the new coils fix the issue. Just trying to understand what "points" you checked on your outboard and how ya checked em

Thanks

so when you put the nut back on the crank shaft and spin the motor by hand, on the top of the crank is lettering one says (TOP) the other says (SET) you want the the part of the point to line up with the word SET. losen up the screw that holds the points down , then use the adjustment screw to set the gap. when it is set properly lock it back down. the point is now set. mind you there is all types of points, they may not look like these, but the idea is there. hope this helps
Dale

 

[racerone]

You do not loosen the screw that holds the points down.----On that Johnson the cam screw adjusts the points with that screw tight.----Learnt that over 50 years ago.---Fact is still true today

 

[Dalejam]

You do not loosen the screw that holds the points down.----On that Johnson the cam screw adjusts the points with that screw tight.----Learnt that over 50 years ago.---Fact is still true today

I am not saying you are incorrect, but i have one screw that holds the points down to the plate, the other screw is for adjusting the placement of the points. so if this is wrong i am open to learning......
thanks Dale
the small Arrow is holding the points to the plate
the bigger Arrow is how you adjust the contacting of the points when it is on the SET on the Crank. is this not correct ?

 

[racerone]

The screw with the small arrow is tightened when I install a set of breaker points.-----Then the cam screw ( big arrow ) is used to set the points.----Started doing it this way at a dealer over 50 years ago.-----That is how I would do it tomorrow !!

 

[Dalejam]

The screw with the small arrow is tightened when I install a set of breaker points.-----Then the cam screw ( big arrow ) is used to set the points.----Started doing it this way at a dealer over 50 years ago.-----That is how I would do it tomorrow !!

then if i take them apart again i will do it that way, so do you know much about idle issues. i cant get the Evinrude 25 to idle at low speed, so my thought is take the carb apart and clean it again and put in a fuel filter ? your thoughts.
thank you
Dale

 

[racerone]

I could rebuild your entire motor without glancing at a manual and I have many years of simple trouble shooting experience as well..----There could be lots of issues causing poor idle.----Worn out pistons / rings, weak spark, poor crankcase sealing, carburetor flooding, issues with low speed mixture needle , fuel pump leaking., blown head gasket , thermostat missing or stuck open, reed valves stuck open ( sea gull feather ) perhaps.---Broken carbon seal on bottom of crankshaft.---Up to you to do the inspections.

 

[Crosbyman]

dalejam you should catch up on Leroy's articles ....most of what you need to know is there

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