1975 Johnson 50 HP Runs bad

[Rilloo]

Hello, i have a johnson 50-1975, 4.5meters long boat, not so big. It has been under water and was without ignition, had everything apart and blown clean and warmed it all up, suddenly, I got the spark on both plugs Compression is 10.2KG on both cylinders. (145 psi) It runs poorly at idle precisely you manage to get up the RPM with the hand throttle if you sit for a while. manages to run away if I get max rpm och the lever, then i throw in gear, then it runs smooth and stable, but really tired. was 18 knots at full throttle. This engine with this little boat should do at least 30, I think. Then I removed the cover in front of the carburetors, splashing out more gasoline from the lower carburetor, but still comes from the top, but less. Should it be like this? Then pulled out the upper plug cap. The engine changed a little bit in the run but not much at all. continues to run, I pull out the lower spark plug cap and the engine dies. Have had loose carburetors 4 times and double-checked and cleaned everywhere, had loose reed valves checked cleaned, are now completely without ideas about what it can be. New spark plugs, I have, of course, tried two new rounds .. Almost feels that the engine is running like on 1? cylinder because it barely changed when I pulled out of the cap. Looked after and i do have spark. Any idea what the problem is??On the film is the hand-lever is in full throttle, you can get it to rev up more if you go down and up on the lever. I tried today to spray starting-gas in the upper carburator, but then the engine almost dies. so i think the engine gets enough fuel? I also trying to press the bulb for the fuel but nothing changes. https://youtu.be/kh0ba-NRpQo

 

[Rilloo]

Did run it 5 minutes up and down in RPM and looked at the spark plugs, black.. one is little bit more wet then the other...

I think it gets to much fuel??what should i check next?

 

[fireman57]

If you have fuel splashing out of a carb then you have a float that is stuck or not working properly all the time. Make sure that when you put them on the are level when turned upside down.

 

[fireman57]

You say that you have cleaned the carbs but did you take the small silver welch plugs out and make sure the small passages under them were open? You cannot use the same welch plugs but they are available to buy separately from the kit. At least they used to be. Also you need to make sure your spark jumps 7/16 of an inch. It must be bright blue and you will hear a snap. If it is yellow then the spark is too weak to work when in gear. When adjusting your throttle you will see two little lines that line up with a roller cam. Make sure these line up as that is where your engine start position is. This also helps with your timing. ONe more thing to look at, pull the flywheel and make sure your flywheel key isn't sheared. If it is do not use a replacement from the hardware store as they are not the exact size or hardness. Get one from a dealer or online. Can I ask where you are from as we get folks from all over the world here

 

[Rilloo]

I bought carburator repairkits, changed floats and adjusted , Now the squirting is the same on both carburators, but the engine is running the same..

I took the boat from the lake to the garage and also bought a new powerpack because i thought maybe the spark is weak.. No difference either.


Then i tried to rev it in the garage, its sounds excately like it gets to much fuel, it "rrrrr" on full throttle, like it gets to much. The lowspeed is okey, it answers pretty good on the throttle on low rpm


Today i took of the carburators again and checked the welch plugs you was telling me, because i didnt change them, they folllowed in the rep.kit.

Was very clean in there so i put new ones back.

Then i realised that 1 carburator is making around 1 mm more throttle, one of the damper was not closing totally,

i adjusted so now they are the same, but still have not tested, can that little problem make such big problem that it doesnt run well?

anyway i will try the engine tomorrow again, i let you know.!



I am from sweden

 

[Rilloo]

A new clip i filmed today.. hard to hear the sound but on full throttle it "4strokes", you know "rrrr".. it doesnt rev out completely clean..


any ideas? it feels like to much fuel but how can that be true? i checked my high speed jet"orifice plug", and it was 58 in size, anyone know if that is the original jet? or if it is changed to a bigger one..

 

[gm280]

Unless you fixed anything since posting the spark plug pictures, you have a weak spark condition. Both of those plugs are wet and sooty. I realize you remove the spark plug boot and it changes some, but I still think suspect coils. I would also recheck both the floats AND the needles and seats to verify they are closing off properly when the fuel bowls are filled. JMHO

 

[fireman57]

You never have reported on doing the spark test. It has to jump 7/16" of an inch and bright blue. Spark and fuel problems will have the same symptoms. Do a spark test

 

[David Young]

Not much happened when you pulled the wire off the bottom plug. Your running on one cylinder.

 

[Rilloo]

i bought 1 new ignition coil just to try, i changed it to bottom and up cylinder, no difference in the running of the motor..




I also tried it in the water, then it was going to 1-2cylinders for 30 seconds, then it remain on 2 i think, but really weak power also now maximum 19 knots..

When i release the throttle and want to go again i have to throttle it to high rpm on the carburators then fast put the gear in and go..






I made a movie now that you can see it jumps pretty far, does this look ok?

 

[gm280]

Well it does look like there is good spark. Is that engine just turning over via the starter or what? Sounds like it was running. :noidea:

 

[Rilloo]

yes only via the starter

 

[gm280]

So you have good spark and compression and fuel, so it should be running like a top. If it gets too much fuel, then you still have a fuel delivery issue. Re-reading the initial post, I have to say it really points to low compression. but you stated you had 145 psi. That isn't low on any level. So if your carb float level is set correctly and not allowing fuel to flow uncontrollably into the engine instead of metering via the typical jets, then it has to be a compression issue. :noidea: