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

[jimwalt]

No Title

 

[jimwalt]

Tank is a "System Matched Parts & Accessories - Dura-Tank. 6 gallon.

 

[jimmbo]

The vent and fuel valves in the tank are opened when this pin(white arrow) is pushed in by the hose connector. You probably need a new fitting, or new tank

 

[Joe Reeves]

Yeah... Mint condition is an understatement... new, just out of the box is more like it.

Fuel pump is the little square thing on the starboard (right) side with two fuel lines attached.

When in doubt about the air vent... loosen the fuel cap.

If the rpms of the engine increase... BUT... the boat slows down, suspect a slipping hub within the propeller. - The propeller is a three piece unit... a brass hub, the aluminum propeller, and a vulcanized rubber between the two (like a motor mount). The bass hub is attached to the propshaft via a drive pin. If the vulcanized rubber fails, the brass hub slips within the propeller resulting in a lack of power.

(Spark plugs removed for the following tests)

Check the compression... what is the compression psi of each cylinder? Note that compression coincides with the speed of which the engine is cranked over so crank it as fast as possible.

Spark... The spark should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! Does it?

Spark plugs should be Champion QL77JC4 plugs gaped at either .030 (long life) or .040 (strong spark)

Let us know what you find.

 

[F_R]

That does not look like a 1977 original equipment fuel tank. It might have an automatic vent that only admits air when the hose is attached---I don't know. Anyhow, the simple test is to loosen the cap when it is acting up.

I don't think it is a mixture adjustment problem. That is for slow idle mixture adjustment and has little or no effect on full throttle operation.

But you may very well have a fuel delivery problem. Any air leaks anywhere between the fuel pump and the level of gasoline in the tank can cause what you are describing. So can a failing fuel pump. And of course, an unvented tank. Have you tried squeezing the hose bulb while the problem is happening?

Can we assume the motor is not overheating? That is a serious issue if it is.

 

[jimmbo]

When asked, he said the bulb had collapsed when the problem had occurred, that the cap was very hard to remove, and he could hear the air hissing as he pried the cap off

 

[Tim Frank]

Hard to tell from the picture, but if that is a pre-assembled fuel line from the tank, I do not see the bulb near the tank.
The bulb is directional.....there should be an arrow on it which shows fuel flow direction. Most lines that I am familiar with have the bulb close to the tank.
If he bulb is near the motor, for "convenience", you may have it backwards.

 

[oldboat1]

Think I would check the arrow on the bulb (arrow in direction of motor), then loosen the tank cap and try it. If still a problem, would move the tank back to the stern by the motor, and shorten the fuel line. Good idea to distribute the weight of the tank to the bow, but might be too long a reach for the little fuel pump.

 

[jimwalt]

Okay I was out today and i think i figured out the problem, now i just need you guys to tell me how yo fix it.

I started the motor at the dock. First pull with choak all the way out, second pull with it all the way in, and it started just like i do everytime when its cold. I put the throttle on high speed and i take off. About 20 yards later it slows down....... so i thought about fiddling with the choak. I pull it about 3/4 out and the engine about dies. I slowly push it in until its about 1/3 out and im at full power. I push it all the way in and I'm going slow again. So i pull it out about 1/3 and it works at full speed.

Prior to last week i always had the choak all the way in and i had full speed. Now it reqires it to be out about 1/3. Why????

Im in Michigan. The weather is still in the 70's just as it has been all summer. Only thing different is maybe the water temps have gone down by 5 degrees or so.

So whats yo with my choak and how can i fix it? Thank you.

 

[Joe Reeves]

The brass high speed jet located horizontally in the bottom center portion of the float chamber, way in back of the drain screw, is slightly clogged. Clean it carefully with a piece of single strand steel wire.

 

[jimwalt]

The brass high speed jet located horizontally in the bottom center portion of the float chamber, way in back of the drain screw, is slightly clogged. Clean it carefully with a piece of single strand steel wire.

Sounds easy, but i need pictures. Im clueless. Thank you.

 

[oldboat1]

You would remove bolt #29 at the bottom of the carb to access the jet behind it: http://www.iboats.com/Carburetor/dm/cart_id.726481664--session_id.156428424--view_id.1532321 . To begin with, try some carb spray, using the plastic nozzle. I wouldn't take the jet (#27) out -- brass (easily damaged).

Doesn't take much to cause blockages. Good idea to routinely disconnect the fuel hose after use, and run fuel out. It's not perfect, but helps some to keep the system clean. Old fuel turns to varnish, and clogs up small passages.

It's not hard to clean and rebuild that carb, when it comes to that. To do it, the carb is removed and largely disassembled -- some soaking and poking, finishing with some carb spray in every small opening you can find (good to discover how the spray moves through the carb too). Everybody has a favored technique for cleaning.

 

[jimwalt]

You would remove bolt #29 at the bottom of the carb to access the jet behind it: http://www.iboats.com/Carburetor/dm/...iew_id.1532321 . To begin with, try some carb spray, using the plastic nozzle. I wouldn't take the jet (#27) out -- brass (easily damaged).

Doesn't take much to cause blockages. Good idea to routinely disconnect the fuel hose after use, and run fuel out. It's not perfect, but helps some to keep the system clean. Old fuel turns to varnish, and clogs up small passages.

It's not hard to clean and rebuild that carb, when it comes to that. To do it, the carb is removed and largely disassembled -- some soaking and poking, finishing with some carb spray in every small opening you can find (good to discover how the spray moves through the carb too). Everybody has a favored technique for cleaning.

Thank you very much, but HOW IN THE WORLD do I get to that screw????? It's buried down inside the motor housing. Also instead of steel wire, how about compressed air? I might be able to get air down there (if I can get the screw out).

When you (oldboat) say carb cleaner, are you saying put that in the hole of bolt #25, or into the hole (possibly the carb) above the bolt that opens/closes as you push/pull the choke????

Thank you again.

 

[oldboat1]

The carb comes off the motor -- would service it on your workbench. However, you should be able to remove the hex bolt with a box wrench, taking care not to drop it in the pan. (A magnet is a useful tool to have available.)

The brass plate that opens and closes is the choke plate, located in the throat of the carb. You can spray carb cleaner in both places, using the plastic wand that comes with a can of carb cleaner. Assuming you are not quite up to removing the carb, you might try the spray and see if it makes a difference.

 

[Crosbyman]

try 1/4 inch drive ratchet with a universal joint and proper socket or try with a flexible shaft to bend in at the bottom

 

[jimwalt]

The carb comes off the motor -- would service it on your workbench. However, you should be able to remove the hex bolt with a box wrench, taking care not to drop it in the pan. (A magnet is a useful tool to have available.)

The brass plate that opens and closes is the choke plate, located in the throat of the carb. You can spray carb cleaner in both places, using the plastic wand that comes with a can of carb cleaner. Assuming you are not quite up to removing the carb, you might try the spray and see if it makes a difference.

So I took the boat to the lake, fired it up and took off. I barely got going (not even 10 yards) before it slowed down. I played with the choke to help it speed up a bit, but couldn't get full speed. I took off the cover and sprayed a quick burst of carb cleaner. That stalled the engine. I started it back up and tried playing with the choke a bit to get it just to the right spot, but only got about 3/4 the regular speed. Shot it again with carb cleaner as it was going but didn't notice any difference.

Got home in the driveway and removed that bolt. Carefully pushed a very fine piece of wire in the hole (wire like a twist-tie in thickness). It went in about 1/2 inch maybe. Replaced the bolt, put engine in a bucket of water and started it up. Kicked the throttle up a bit while in neutral. It goes, but the only way I will really know if I did any good with removing the bolt and putting the wire inside is by taking it back out to the lake. Might try that tomorrow after work.

I'm not comfortable trying to remove any parts in the engine. Took some stuff apart as a kid and ended up with trash. I'm really not mechanically gifted.... Unless there is a very detailed YouTube video where I can see every step of the way (visually). I guess I have repaired small things on my car in the past with the help of YouTube.

Any other suggestions? I hate to take it in to the shop and spend $100 to get it unplugged if that's what's wrong like one of the posts said.

Thank you.

 

[Crosbyman]

next time it bogs try hand pumping

it goes you may have ​ a bad fuel pump

 

[jimwalt]

next time it bogs try hand pumping

it goes you may have ​ a bad fuel pump

Primer bulb in the fuel line between the tank and the Johnson? Is that the "fuel pump"? If so, my primer bulb is new (as is the 2 fuel lines). Or is there a "fuel pump" inside the Johnson?

Thank you for your comment!!!!

 

[oldboat1]

^^agree with Crosbyman.

Maybe you already solved the problem working on the high speed jet. If not, a middle ground in rebuilding the carb is to work on it yourself first, then pay the shop if you can't get it to work. They are pretty simple to work on (I say that as a non-mechanic). Look at a selection of uTubes, and have a parts diagram in front of you when working on it -- and ask questions here. Basic procedure is to buy a carb kit for your motor, remove the carb and disassemble most of it. Then soak the top and bottom in carb cleaner, use thin wire in all the openings and finish by blowing them out with carb spray. Needle adjustment is easy.

But see if its running better first. Sometimes they heal themselves with running. Make sure it's operating in the right range (120 to 140F or thereabouts around the top of the head, avoiding the hotter areas around the plugs). You can hold your hand or fingers on it for a few seconds at that temp. 160F is too hot (and will want to burn your hand). Your motor has a thermostat at the top (that triangular cap) -- if stuck open will cause the motor to run too cold (safer than overheating, but won't run well if it doesn't get up to temp.) The little tell-tale tells you the water pump is working (unless the tell tale is clogged) but doesn't tell you whether the engine temp is correct.

The fuel pump can also be rebuilt with a kit -- I usually replace the small ones, just because I don't like to work on them (tiny parts, big fingers). The fuel pump is the little square device in your pic in #5.

 

[jimwalt]

I had the cover off where the thermostat lives and I pulled it out one time. Would it help to spray (or soak) it in carb cleaner?