Power loss in 1977 Johnson 6HP (1/2 power possibly)

[jimwalt]

I have a 1977 Johnson 6HP on a 12' boat that I purchased in May. I had an extremely reputable motor servicing company in my city look at it when I got it. They are well loved all over the state of Michigan and I even personally know the owner. He ran my motor though ALL the tests and said that it was in absolute mint condition. He even showed me how it's mint compared to others around the same age that he has.

I've used it with my little boy a lot over the summer (at least 1 to 2 times every week). In our last two outings it "feels like" I'm only getting 1/2 to 3/4 the speed that I had got over the rest of the summer. It runs great and starts on the first pull every time.

I'm wondering if it's because it's colder outside (in lower Michigan) than what it was in June/July/August. I haven't changed the "Rich/Lean" setting because I was told by my friend (the motor repair owner) I only need to worry about that during starting when the weather gets really cold like in October.

I've watched the "pee-hole" and the water comes out of it nice and fast just as it has since I purchased it. I use ONLY Johnson oil at the right mix along with Sta-Bil in every tank.

Is it POSSIBLE that the speed could be not as fast as it was?

This started last Saturday when we went full open (top speed while getting from one lake to another), we were at full throttle for about 15 minutes, then slowed down for about 5 minutes when going though a no-wake zone, then full throttle for about 10 more minutes. Hopefully that's okay and doesn't mess something up inside?

I don't see anything around the propeller. I haven't hooked any of "our" fishing line around the propeller. I've hit weeds in the past but have figured out how to fix that by slowing down to a stop, putting it in reverse for a bit, and then going forward to get them out.

So is it possible to have something happen that makes the Johnson go only about 1/2 to 3/4 the normal speed? If so, what's the fix?

Thank you.

 

[oldboat1]

couple of possibilities, of a number -- mix needle can rattle loose with running. There's a gland nut to be snugged up (not so tight you can't adjust the needle if needed). But that's the idle air mix.

You could have a coil going out. If the shop didn't pull the flywheel, a cracked coil might have been missed (coverings crack with age).

A plug wire might be loose at the plug (one cylinder dropping out).

 

[jimmbo]

Sounds like loss of a cylinder.
Hmm I wonder what year your motor is? Johnson didn't market an 8hp in 1977. They started marketing one in 1984. I checked back to 1958, there were no 8hp between 58 and 84

 

[jimwalt]

No Title

couple of possibilities, of a number -- mix needle can rattle loose with running. There's a gland nut to be snugged up (not so tight you can't adjust the needle if needed). But that's the idle air mix.

You could have a coil going out. If the shop didn't pull the flywheel, a cracked coil might have been missed (coverings crack with age).

A plug wire might be loose at the plug (one cylinder dropping out).

Thank you. So how to I check each of these things. I'm new to boat motors. This is my first.

1. Where is that mix needle located?

3. Plug wire.. I looked at the plugs when I first got it, pulled them out and replace. The motor shop said they looked great. I can check to make sure the boot is tight on the plug, but they sure where hard to pull off, so I suspect they aren't lose (on the boot to plug end).

2. Fly wheel..... that might be over my head. I believe I know what that wheel is the big round silver/gray part.... but I sure wouldn't try to take that off myself.

 

[jimwalt]

Better Pics

 

[jimwalt]

Sounds like loss of a cylinder.
Hmm I wonder what year your motor is? Johnson didn't market an 8hp in 1977. They started marketing one in 1984. I checked back to 1958, there were no 8hp between 58 and 84

My mistake............ 6 HP (6R77M) Sorry.

 

[jimwalt]

Loss of a cylinder???? Is that expensive?

 

[oldboat1]

Mix needle is the brass rod shown in your pic (top of the carb). The nut shown at the carb is the one I'm referring to. See if it's tight (i.e., snug). If it's loose, post back -- have to readjust the setting, which is easily done.

If the plug wire boot was tight on the plug, OK there. It's possible the metal connector inside the boot is not contacting the metal core in the wire, but you might not want to disassemble that yet -- might twist the wire a little at the boot, on the chance that a loose connection might be fixed that way (if so, will want to reassemble).

The flywheel is on top in your pic. Some ignition parts are underneath, but "dropping a cylinder" is likely due to the CDI unit on the back of the motor (guessing).

[ed. coils on your '77 are on the outside (correcting my earlier post), and DIY replacement pretty easy. For testing, need a multimeter if you are up to that.]

 

[jimwalt]

Maybe I should have said............... When I FIRST start out it seems like it's at normal speed, but after about 75 to 100 yards it seems that I'm not going as fast. It doesn't just "drop out" in speed, it just seems to gradually not go as fast as from when it first starts.

 

[jimmbo]

BOAT, is the Acronym for 'Break Out Another Thousand'

I meant the cylinder wasn't firing, as mentioned by Oldboat, it is likely an ignition problem.

Have you tried running it and unhooking one of the plug wire? If the engine doesn't run different, it might not be firing that plug. If the engine dies, the remaining plug probably is not firing. Then test for spark.
Fouled plugs, bad coil, power pack, wires could cause a no spark conditon
Yes the big grey thing that spins is the flywheel. Not to difficult to remove, but it does require some attention when reinstalling.(cleanliness and proper torque)
Have you done a compression check?

Edit: Is the vent on the fuel tank open?

 

[jimwalt]

Mix needle is the brass rod shown in your pic (top of the carb). The nut shown at the carb is the one I'm referring to. See if it's tight (i.e., snug). If it's loose, post back -- have to readjust the setting, which is easily done.

If the plug wire boot was tight on the plug, OK there. It's possible the metal connector inside the boot is not contacting the metal core in the wire, but you might not want to disassemble that yet -- might twist the wire a little at the boot, on the chance that a loose connection might be fixed that way (if so, will want to reassemble).

The flywheel is on top in your pic. Some ignition parts are underneath, but "dropping a cylinder" is likely due to the CDI unit on the back of the motor (guessing).

Okay. thank you very much. I'm going outside now and looking.

 

[jimwalt]

My fuel tank doesn't have a vent.

 

[oldboat1]

and....check the tank vent like jimmbo mentions. Look for the simple stuff first. Use a 50:1 mix with 2-cycle oil -- about 3 oz per gallon of gas (a little less). When the motor acts up/slows up, pump the primer bulb once or twice and see if that makes a difference -- may indicate the fuel pump needs service. The tank should be somewhere in the stern of the boat. It's a small pump.

[edit. You're too quick for me. Try loosening the cap a little while running, just to make sure it's venting.]

 

[jimwalt]

My fuel tank doesn't have a vent.

 

[jimwalt]

I bet you guys just figured it out.

Went outside with flash light. The nut is tight on the rod that adjusts Rich/Lean.

Spark plug boots are nice and tight on plug

Gas cap............... I almost couldn't open it with my hand it has suctioned itself on so tight. Finally got it to break lose and I heard a long ssssssssss as the air entered. Bet you $100 bucks it was having a hard time getting fuel.

Think that's it????

 

[jimmbo]

Your tank is most likely the kind that vents when the hose is connected.
Did you notice if the primer bulb had collapsed when the motor was running out of steam?

Edit:
Maybe the cap on the tank is the wrong one
I know you guys in the States have a whole bunch of weird EPA rules when it comes to gas tanks
Do you have another tank you could try

 

[jimwalt]

Yes I'm using a 50:1 mix with 2-cycle oil. I purchased a bottle to pour the oil in that shows by the gallon of gas how much oil. I do that EXACTLY as it says.
The Primer Bulb is brand new as well as the fuel line (the seller told me that, and my friend said it looked brand new too).

Were is the fuel pump?? In the Johnson or in the tank?

"The tank should be somewhere in the stern of the boat" What's that mean? I have the tank near the front seat with the lines going to the Johnson.

 

[jimwalt]

Your tank is most likely the kind that vents when the hose is connected.
Did you notice if the primer bulb had collapsed when the motor was running out of steam?

Edit:
Maybe the cap on the tank is the wrong one
I know you guys in the States have a whole bunch of weird EPA rules when it comes to gas tanks
Do you have another tank you could try

Good point. On Saturday when I had the problem the primer bulb had collapsed when the motor was running out of steam. YES!

I suspect the cap on the tank is right. I got the boat from an older guy that I bet was the original owner. The boat was in his garage and his garage was like none you have every seen. There was a very old car in perfect condition and you could EAT off the garage floor! So this guy took care of his stuff. I can't believe he had the wrong cap, and my friend that owns the boat servicing business had my tank and fuel lines/primer and I'm sure would have noticed if something wasn't right.

Unfortunately this is my only tank. So I don't have another to try.

 

[jimmbo]

OMC tanks vented when the hose was connected. I can't tell the make of your tank, nor can I see the fitting where the hose connects, A pic of the tank fitting without the hose attached would be nice. I guess the tank's cap could have pressure differential valve that is supposed to let air in as fuel drawn out, but seals to keep vapours in.
Your tank is fine where it is, it will help hold the bow down. If the primer bulb collapsed, it shows your fuel pump is actually working pretty good.

 

[jimwalt]

Will these pics help?