1986 Johnson 70 HP Cylinder 1 Bog Down

[Seadoomanls]

Ok so everybody on here is usually pretty descriptive of their problem, so I am going to include as much information as possible.

To begin:
I just purchased this motor, and it is very clean.

The Problem:
The boat starts turnkey and idles well. However, when you try to plane out, it just bogs down when given any gas. I narrowed the problem specifically down to cylinder 1. I disconnected the linkage. I started the motor on ONLY cylinder 1, tried to rev it, but nothing but a bog down. Did same test on cylinder 2 and 3 (independently) and they both revved perfect!
I have dissassembled and cleaned all the carbs. Also, i switched carb 1 and 3 to see if it made a difference, but same problem. I am getting spark at ALL 3 cylinders. I have switched all the plugs around, and same bog down. I have even tried switching the coils around. Still, cylinder 1 bogs down.

PLEASE HELP!



Compression Check (Cylinder 1- 145, Cylinder 2- 140, Cylinder 3- 135)
Fuel pump is fine.
Spark plugs are new.
Fuel line is fine.

 

[poor man]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

have you checked the compression on the cylenders? i would do that and see what you have.

also just because a spark plug looks good and sparks "out" of the engine DONT mean it wont fail under presure. i had one do that and it drove me crazy, plugs are cheap replace all at once...

 

[Seadoomanls]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

From my first post:


"Compression Check (Cylinder 1- 145, Cylinder 2- 140, Cylinder 3- 135)"

"Spark plugs are new."

Thanks for your response though.

I know all the beginner steps (carb cleaning, fuel lines, spark, coil, starting, linkage, all that stuff) im looking for an intermediate to expert to help me here and give me some kind of new idea that a beginner-novice wouldn't normally know.

 

[Boss Hawg]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

I had about the same problem on my '87 70VRO
Seems you've dun everything i did to correct the problem except de-carb the motor
Might want to give that a try

 

[Seadoomanls]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

De-carb the motor? I am not sure I know what that is.

When you de-carbed your motor, did it solve the problem. I want to have this fixed and done by May 2nd for my birthday party on my lake! If it comes down to it, I have to hire a mechanic.

 

[Boss Hawg]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

De-carb the motor? I am not sure I know what that is.

When you de-carbed your motor, did it solve the problem. I want to have this fixed and done by May 2nd for my birthday party on my lake! If it comes down to it, I have to hire a mechanic.

Tash explains much better than me-http://forums.iboats.com/showthread.php?t=302825

I de-carbed + what we've discused & my motor ran great
Just can't say what particual thing "did it" but all i'm sure had a positive effect
Good luck--

 

[tx1961whaler]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

Hmmmmm...
Good spark, switched coils and problem still there. Switched plugs, and problem still there.
Switched carbs, and problem still there.
Compression good.

The only thing I can guess at is the spark plug wire to that cylinder is shorting or arcing. You can sometimes pick that up by using an inductive timing light, or by running it after dark and looking for the light show.

 

[jonesg]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

The only thing you didn't switch is pistons and reed valve.
I'd seafoam it.

 

[Seadoomanls]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

Yeah I am going to have to sea foam it. What exactly happens with this de-carb process? I mean what is it doing for me? Is this cleaning out carbon build up or something? Just wondering.

 

[tx1961whaler]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

De-carboning will burn out excess carbon deposits from your engine. I don't think that's the problem here.
Since I'm not looking at the motor here, or have the manual, which cylinder does the fuel pump's pulse line go to on that motor?

 

[Seadoomanls]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

I am not sure what you are referring to as far as the fuel pump's pulse line? From the fuel pump, one single tube gets split into three equal size tubes that go to cylinder 1, 2 and 3.

I may have a carb problem here, two dirty carbs. Now my cylinder 3 is doing a less severe version of what cylinder 1 is doing.

How would i know if my reed valves were bad?

 

[tx1961whaler]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

The fuel pump runs off of a vacuum pulse from one of the cylinders. Sometimes a leaky fuel pump diaphragm will cause that cylinder to flood.
The pulse line for the VRO is #13 on the diagram.
The only way I've ever inspected reed valves is to completely take off the intake.

 

[k4ubr]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

make shure your timing base is moveing freely with the throttle cable. sometimes it can stick or that little plastic pice will brake. doing a propper sink and link could help.

 

[nanastew76]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

I would check the power pack line to that coil.

 

[Seadoomanls]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

Thanks for all of the responses! Here is where it gets fun again! Ok, so I cleaned and soaked all three carbs for 24 hrs. Now, cylinder 1 and 2 will independently rev. Cylinder 3 is now bogging down. Do I have a bad carb? It looks to be ok. Also, I can get cylinder 3 to rev by revving either cylinder 1 or 2 a little first. (So, i disconnect to linkage, open cylinder 2 about 1/6 the way, then I can freely rev cylinder 3.)

I am also thinking maybe this fuel pump is no good. Is it the cylinder or the carb that creates the vaccuum?

Also, I should tell you guys that the boat does get up on plane now and runs really decent. The motor however is giving these little half second jolts that show me i am running on only 2 cylinders. You can feel that the engine wants to go a little bit faster.

 

[jonesg]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

Put some premixed fuel in a spray bottle and spray it into #3 as you put the coals to it , see if it helps as the carb is bypassed.
Also try pumping the bulb to test the fuel pump.

I suspect you need proper rebuild kits for the carbs, maybe change filters and lines too.

 

[Seadoomanls]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

The carbs got the proper rebuild kits. I have a brand new fuel line from the gas tank up to the engine. The only thing that I haven't changed would be the fuel line set up under the cowl.

I have primed the bulb while running. No change in performance.

A motorcycle mechanic told me I could try to set the linkage so that cylinder 1 and 2 kick in before cylinder 3 does. The problem is, this causes my idle to be too high.

What is a link and sync, and how do I perform one.

 

[billy4hp]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

The carbs got the proper rebuild kits. I have a brand new fuel line from the gas tank up to the engine. The only thing that I haven't changed would be the fuel line set up under the cowl.

I have primed the bulb while running. No change in performance.

A motorcycle mechanic told me I could try to set the linkage so that cylinder 1 and 2 kick in before cylinder 3 does. The problem is, this causes my idle to be too high.

What is a link and sync, and how do I perform one.

Not to beat the proverbial dead horse, but you would save yourself a lot of grief by purchasing an OEM service manual, there are several flow charts for drivability issues... If your going this far into your engine you should absolutely have one and skip a SELOC or Clymers manual completely...

That being said did you ensure your fuel pump is not leaking fuel through the pulse line? On my 1978 70hp Johnson the fuel pump pulse line is fed off of cylinder #3 on the port side of the engine...

Good luck,

Billy

 

[tx1961whaler]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

That being said did you ensure your fuel pump is not leaking fuel through the pulse line? On my 1978 70hp Johnson the fuel pump pulse line is fed off of cylinder #3 on the port side of the engine...

That's why I asked earlier about the pulse line location. Never got an answer.

 

[Seadoomanls]

Re: 1986 Johnson 70 HP Cylinder 1 Bog Down

If the pulse line is the one leaking, would that cause one of the cylinder to not want to rev independently...like I said I was having this problem with cylinder 1, which has now transfered to cylinder 3.