1988 Johnson 4hp - full throttle cut out

[purplegrape]

Hey everyone,

I have a 1988 Johnson 4 hp outboard (2 stroke).

My issue is that on full throttle she will run for about a minute or 2 and then it boggs down and cuts out. If I cut back on the throttle chances are it will keep running. If it does not than I pull the cord and off she goes again.
I have a new water pump, carb seems good cleaned it well a couple times, compression is good, and I'm using 91 octane gas mixing 50:1 however the motor has a sticker calling for 100:1.

The motor never seems to over heat and will run for sometime without issues at a low or mid throttle. Ive had trouble with the idle needle but it seems to be in a good spot. Just can get her to run full,

Any thoughts?

Thanks!

 

[Daviet]

Re: 1988 Johnson 4hp - full throttle cut out

Welcome to the forum.
Mix your gas 50:1, remove the sticker that says 100:1.
When you cleaned your carb, did you remove and clean the orifice in the end of the high speed nozzle. Sounds like you are running out of fuel at high speed and it must go through that orifice.

 

[purplegrape]

Re: 1988 Johnson 4hp - full throttle cut out

Welcome to the forum.
Mix your gas 50:1, remove the sticker that says 100:1.
When you cleaned your carb, did you remove and clean the orifice in the end of the high speed nozzle. Sounds like you are running out of fuel at high speed and it must go through that orifice.

Thanks a lot for the reply Daviet,

I cleaned the carb as well as I could. I basically took everything apart that I could. By the high speed nozzle do you mean the nozzle in the pic? I'm no mechanic I just plug away at this stuff myself.

Also, where should I be setting that Idle screw at or around?

 

[Daviet]

Re: 1988 Johnson 4hp - full throttle cut out

Yes, the orifice (jet) is on the end. It has to be clean and unrestricted.
The static setting should be 1 1/4 turn out from lightly seated, then you will have to fine tune it in the water while under way.

 

[purplegrape]

Re: 1988 Johnson 4hp - full throttle cut out

Thanks again Daviet,

Yes I've unscrewed that jet, taken it out and cleaned it with carb and choke cleaner. It does not seem to be restricted.
Any other ideas?

When I take the fuel line off from where it is zip tied onto the carburetor the gas seems to flow steady from the tank. Is there anything else that you can think of that would be restricting the flow of fuel into the carb?

Thanks again!

 

[Daviet]

Re: 1988 Johnson 4hp - full throttle cut out

Float level set properly?

 

[purplegrape]

Re: 1988 Johnson 4hp - full throttle cut out

Yes I believe so. If I took some pics and posted would you be able to tell?

 

[purplegrape]

Re: 1988 Johnson 4hp - full throttle cut out

Any idea what the float measurement should be?

 

[Daviet]

Re: 1988 Johnson 4hp - full throttle cut out

I don't have a manual for your engine, but on most engines, you set the float parallel to the carb body with the carb upside down.

 

[purplegrape]

Re: 1988 Johnson 4hp - full throttle cut out



Heres a couple pics of my Float, to me it seems as though it needs to be set a little lower?

 

[purplegrape]

Re: 1988 Johnson 4hp - full throttle cut out

Here's another for where I'm thinking the bottom of the float should be aligned?

 

[Daviet]

Re: 1988 Johnson 4hp - full throttle cut out

You are thinking correctly, make it parallel to the carb body.

 

[Tim Frank]

Re: 1988 Johnson 4hp - full throttle cut out

Something else going on there.
The amount of "bend" you will have to put in that float tang is crazy.....I've never seen one that far off.
I'm thinking there is something wrong with the needle seating level....something odd like a previous carb rebuilder putting in an incorrect needle or a rubber seat where one is not required..... or something like that.

This also highlights the value of an OEM manual. I have the 1990 version of the manual, which may or may not be the same as 1988.
The critical float adjustment is done with the carb upright, and the float drop is measured. I am not ablr to copy a pic....maybe someone else can.
The measurement from the carb body to the bottom corner of the float .....is spec'd at 1-1/8" to 1/1/2" .

 

[Tim Frank]

Re: 1988 Johnson 4hp - full throttle cut out

Some other info that would be useful for troubleshooting:
1) Are you the original owner? (i.e. do you know the complete history? Something odd about that carb float.... )
2) If not, how long have you owned it, and this a new problem?

 

[purplegrape]

Re: 1988 Johnson 4hp - full throttle cut out

Hey Tim,


Thanks a lot for the reply!!!

I'm not the original owner and the motor was given to me after it sat for years without use. I took it to the shop and asked them to fix it up for me. They got er up and running greased her up and put a new water pump in. Ive had issues with it running full throttle tho.


Now I did bend the tang to see how it would react. The bend is significant and Ill add a pic. Engine performance improved dramatically however with the bend and the float now sitting level to the carb body as indicated in the picture above. She runs more smoothly and now runs full throttle but again it still cuts out after lets say 3 or 4 mins which is an improvement but not fixed. If I cut back on the throttle I can save it and then go WOT again for sometime. Its still like there's not enough fuel flow or something.

This is a crazy question as I don't know a lot about this stuff, but does it look like that float is upside down??? If I flip it over it sits level with the carb body (without the bend I just put in) however the float sits very high I haven't run it this way because I'm having a hard time believeing the floats upside down.

I can still get the float for this model and I will ill end up ordering one as well as the needle!

 

[bassmanatcs]

Purplegrape, Did you ever fix your problem? I am having the exact same problem and could use some help. Thanks.

 

[Vic.S]

What does it say at the top of the page about replying to or hijacking old or existing threads