1958 Johnson 5.5hp Not Having Power

[TruckerBoi]

Hi Everyone,
I have a 1958 Johnson 5.5 hp that I pulled out of my shed a year ago. I cleaned the carb and replaced the coils and it ran fine in the barrel. I took it out to the lake and when I try to go full throttle, the motor seems to have no power. With no load, it revs up no problem but with a load, it runs but has low rpms. I adjusted the jets and tried priming it but nothing helped. I opened the gas cap and the motor took off at full throttle but died after about 2 seconds. I can get it to run at half power with a combination of half opening the gas cap and pressurizing the tank but I know it can run better. This is my first pressure fed motor that I've worked on and I hope someone sees this and can help.
TruckerBoi

 

[racerone]

Compression test done ?-----Head gaskets were not the best designed item.----Is the shock absorber / slip clutch in the lower unit binding ?----Gas cap is to be CLOSED on the pressure system.-----So perhaps the float valve is leaking and flooding the motor.

 

[F_R]

Classic story heard many times. Most likely running on only one cylinder. But what racer suggested is valid too.

 

[TruckerBoi]

Compression test done ?-----Head gaskets were not the best designed item.----Is the shock absorber / slip clutch in the lower unit binding ?----Gas cap is to be CLOSED on the pressure system.-----So perhaps the float valve is leaking and flooding the motor.

I will do a compression test soon but I need to find a shallow tip for my compression tester. I don't think the slip clutch is binding as the motor can go full power but I can always go and check to see. I will take apart the float valve and have a look. The float valve being stuck would make a lot of sense

 

[TruckerBoi]

Classic story heard many times. Most likely running on only one cylinder. But what racer suggested is valid too.

I replaced the coils and I checked that the motor is running on both cylinders as they both spark plugs give off spark and both sides of the cylinder head is warm after it has run

 

[Crosbyman]

back to compression testing ...

 

[racerone]

Years ago I was at a shop where the owner said --" it is running on both cylinders because the head is warm "-----It took some effort to explain that I heard it was only running on 1 cylinder.----Testing is the path forward.

 

[oldboat1]

If rpms increase when you release pressure by opening the gas cap, it's because the motor is running lean (gas feed reduced). That's why it finally stalls.

I would do a couple of things. Try resetting the air/fuel mix by adjusting the needles at the front of the carb. Lightly close both (clockwise), then open the lower needle about 3/4, upper needle about 1 to 1 1/2. Start the motor in a test barrel or on the boat (preferable). Adjust the upper needle clockwise until the motor backfires -- lean sneeze. Then open the needle about half a turn. To fine tune the lower (high speed) needle, run at wot or close (in your case, as high as it will go), then adjust needle until rpms increase -- c.clockwise given your issues (richer). Finding a sweet spot is normally pretty easy. Try turning each way until engine loses power, then set the needle midway between those points.

To measure spark, get an open air adjustable tester at an auto parts store (not the inline type). When there, see if you can borrow a compression tester and perform that test.

Use a 24:1 fuel to oil mix in the tank.

 

[rowerowe101]

If rpms increase when you release pressure by opening the gas cap, it's because the motor is running lean (gas feed reduced). That's why it finally stalls.

I would do a couple of things. Try resetting the air/fuel mix by adjusting the needles at the front of the carb. Lightly close both (clockwise), then open the lower needle about 3/4, upper needle about 1 to 1 1/2. Start the motor in a test barrel or on the boat (preferable). Adjust the upper needle clockwise until the motor backfires -- lean sneeze. Then open the needle about half a turn. To fine tune the lower (high speed) needle, run at wot or close (in your case, as high as it will go), then adjust needle until rpms increase -- c.clockwise given your issues (richer). Finding a sweet spot is normally pretty easy. Try turning each way until engine loses power, then set the needle midway between those points.

To measure spark, get an open air adjustable tester at an auto parts store (not the inline type). When there, see if you can borrow a compression tester and perform that test.

Use a 24:1 fuel to oil mix in the tank.

not 50:1 ratio?

 

[TruckerBoi]

If rpms increase when you release pressure by opening the gas cap, it's because the motor is running lean (gas feed reduced). That's why it finally stalls.

I would do a couple of things. Try resetting the air/fuel mix by adjusting the needles at the front of the carb. Lightly close both (clockwise), then open the lower needle about 3/4, upper needle about 1 to 1 1/2. Start the motor in a test barrel or on the boat (preferable). Adjust the upper needle clockwise until the motor backfires -- lean sneeze. Then open the needle about half a turn. To fine tune the lower (high speed) needle, run at wot or close (in your case, as high as it will go), then adjust needle until rpms increase -- c.clockwise given your issues (richer). Finding a sweet spot is normally pretty easy. Try turning each way until engine loses power, then set the needle midway between those points.

To measure spark, get an open air adjustable tester at an auto parts store (not the inline type). When there, see if you can borrow a compression tester and perform that test.

Use a 24:1 fuel to oil mix in the tank.

If rpms increase when you release pressure by opening the gas cap, it's because the motor is running lean (gas feed reduced). That's why it finally stalls.

I would do a couple of things. Try resetting the air/fuel mix by adjusting the needles at the front of the carb. Lightly close both (clockwise), then open the lower needle about 3/4, upper needle about 1 to 1 1/2. Start the motor in a test barrel or on the boat (preferable). Adjust the upper needle clockwise until the motor backfires -- lean sneeze. Then open the needle about half a turn. To fine tune the lower (high speed) needle, run at wot or close (in your case, as high as it will go), then adjust needle until rpms increase -- c.clockwise given your issues (richer). Finding a sweet spot is normally pretty easy. Try turning each way until engine loses power, then set the needle midway between those points.

To measure spark, get an open air adjustable tester at an auto parts store (not the inline type). When there, see if you can borrow a compression tester and perform that test.

Use a 24:1 fuel to oil mix in the tank.

I will try adjusting the carb that way when I get back out on the lake. I can't seem to find a fitting for my compression tester for a shallow spark plug. I was recommended to run 40:1

 

[TruckerBoi]

not 50:1 ratio?

I personally run 40:1 on mine. It can run 50:1 but most people like to run more oil heavy (40:1, 24:1) on theese older motors to reduce wear on the old parts.

 

[TruckerBoi]

Years ago I was at a shop where the owner said --" it is running on both cylinders because the head is warm "-----It took some effort to explain that I heard it was only running on 1 cylinder.----Testing is the path forward.

It runs on both cylinders at idle but I don't know about under a load. I put in new spark plugs and coils. Is there anyway I can tell if it is running on one cylinder. I have noticed that the motor starts to make a clicking/tapping noise when I throttle up.

 

[racerone]

You should be running this motor at 24:1 nothing else !-----Check clearance between flywheel and coils.-----If that is not the issue then those noises might be EXPENSIVE.----Possibly damaged bearings or gears.

 

[rowerowe101]

You've made sure the spark is jumping specified gap for this model engine?
Sounds like it could be a carbuerator defect.. Even if idle/high speed settings are proper there can be leaks in the needle/seat, and float improperly set.. I would pressure check the carbs and make sure float setting is correct. And of course compression check should always be done.

I would verify proper spark first, then go to carbuerator next assuming everything from the tank to carbs have been verified ok.