Need help with Johnson outboard

[WilsonFamily]

I have a 1977 Johnson 70 ... runs great when I take it out in the winter months when water is cold but as soon as it is warm/ hot water it runs great at low speeds but it won’t open up ... just hogs down like it is missing. Help please replaced so many parts ... don’t know what else to do! Thanks in advance

 

[jakedaawg]

Start with a compression test, post numbers.

open air gap spark test, set to 3/8". Post results.

fuel sample into clear jar, what do you see? Do this even if it's "brand new".

 

[WilsonFamily]

The compression test was all reading 100.

 

[WilsonFamily]

What is the other thing you listed and how do I do that?

 

[WilsonFamily]

This is what all has been replaced on boat
- carburetors rebuilt
- replaced all 3 coil packs
- water pump replaced
- new fuel tanks
- new fuel lines
- new fuel pump
- new spark plugs
- compression test with all 3 cylinders at 100
- spark test all burning good color

If I remember something else that has been done I will add it ... just done so much and the problem still exists.

 

[Tim Frank]

This is what all has been replaced on boat
.......
- spark test all burning good color

.

What does that mean?

Is the motor new to you?
If so, has this problem been there from day 1?

Do you have an OEM manual? They are about $40 and looks like you have already thrown several hundred dollars at it that may or may not have been necessary. The manual is the single best "special tool" you can own for that engine.

 

[jakedaawg]

Spark is tested with a tester, not a plug. We don't care what color the plugs are...we care how far a spark will jump.

 

[racerone]

compression of 100 psi is not encouraging.-----My tester would show 140 on a good one.----High speed jets confirmed clean ?---They are screwed horizontally into the bottom of carburetor bowl.

 

[oldboat1]

Jake is a pro. Your spark tester might look like this:


About $10 at an auto parts store. If water temp. seems to trigger issues, consider replacing the t.stat -- didn't see that listed.

Carb cleaning isn't rocket science, but have to be thorough. To me, that mean complete disassembly, soaking, using soft wire or similar in all openings, followed by carb spray.

 

[WilsonFamily]

No we have had the boat for about 6 years ... it ran great no issues ... put back in water spring of last year and this problem occurred. Runs fine at start and low speeds but didn’t want to open it ... it would bog down like it was missing. Water pump went out and replaced it and the list just started from there of trouble shooting ... yes a lot of money spent or at least for me it is! But last spring it would run fine until I would attempt to accelerate and it just wouldn’t open up, like I said like it was bogged down or missing ... with that being said every now and then it would bog down a while and then surprise me and take off. But this past fall and winter when the water temperature was colder .... it went back to running like a top. No issues whatsoever... I was amazed! Then took the family out on it a couple weekends ago and it’s doing it again. The only differences is the water temperature at the lake. No I don’t have the OEM manual but will definitely get one.

 

[WilsonFamily]

I am trying to find out why or what would make it run good when the water temperature at the lake is cold and then do what it is doing when the water temperature goes up

 

[racerone]

In order to find out what is going on it is best to answer questions and do some trouble shooting.

 

[Rustywrench]

Might look to see if timer base is advancing. They can get sticky on older motors. May need some fresh grease/oil?

 

[F_R]

You say the water pump went out? Might be ingesting water from heat-damaged gaskets. How about piston damage?

 

[Tim Frank]

Where are you geographically? i.e. what swing in water temps are we talking?

Given the obvious correlation between air temps and water temps, are you sure that the common denominator is not AIR temp?

In my experience most problems in here are straightforward and diagnosed and solved well by normal troubleshooting.
An external temp cause is pretty unusual and more likely just exacerbating a pretty routine issue.

IMO an improved performance in colder conditions is possibly an electrical issue.

That said.... 1) can you confirm that spark jumps a 3/8" gap? "there is a good spark"...."spark looks good"....etc. are not the same.
2) what plugs are you running?

3) when you cleaned carbs did you remove the high speed jets and verify that they are clean to full size? They can get a varnish build up that constricts them. If you have a number size drill set you can check once you look up the spec for the HS jet diameter. I guess in theory when gas is colder it is denser....and when it is warmer it can be more prone to vapor-lock and odd issues but in practice I have not seen it.
I did once have the same bogging issue with a 3-cyl 3-carb 55HP which is similar o your 70. There was a fly in the HS jet path....no idea how it got there.....a bit obscure but a simple cause and repair.

 

[WilsonFamily]

I will give all these things listed a check and give you all updates. I really appreciate the help and comments .. I do notice that in the warmer months the bulb on fuel pump isn’t always staying primed and sometimes there isn’t even gas in the clear filter to see. Also the only thing I did to the motor before this occurred was ... it’s an old motor and my wife wanted it painted ... so I painted it ... would there by any weird chance painting the motor messed something up?

 

[racerone]

Inspection, testing and trouble shooting is the path forward.

 

[Tim Frank]

I. I do notice that in the warmer months the bulb on fuel pump isn’t always staying primed and sometimes there isn’t even gas in the clear filter to see. Also the only thing I did to the motor before this occurred was ...

I suspect (the pros may correct me) that is an in-line add-on filter installed by the previous owner.
Have you ever changed it? They do not last forever.

 

[Dmpaul89]

Could be water in the gas. When temps rise condensation happens. Test spark, test fuel, run it and pull the plugs to see if any are different in color or wetness.

just because carbs were gone through doesnt mean they are good to go either. They often need torn back apart even after a "rebuild".


does choking the motor while driving improve the running briefly?

 

[WilsonFamily]

Yes I have changed the in line add on filter. No choking while running doesn’t help.