1989 Johnson 25 hp Converted to 30/35. Help needed!

[sr522re]

Hi, thanks for reading my post. So I have a 1989 Johnson 25 hp outboard that runs great in stock form. I recently changed out the carb and intake manifold from that of a 30/35 hp motor of a similar year. I've read multiple posts about others doing this with great success so I wanted to try it myself. Now that everything has been changed over, the motor runs, but produces a lean "sneeze" at idle and low rpm speeds. If I cover the carb inlet about half way the sneeze goes away which confirms the lean condition. However, If I adjust the idle/air screw and try to richen the mixture the motor stalls out. I am currently running a #39 orifice at the extreme top of the carburetor and the high speed jet located at the bottom is a #65D. I water tested the boat yesterday and it seems to run fine at full throttle however there is zero performance gain from this new carb and intake. My 16ft side console Tracker would do 23-25 mph in stock form with 25hp and yesterday it topped out at 23 mph. Others that have done this modification have claimed a noticeable increase in speed and performance. What am I missing here? Does anyone have any suggestions for me to try? The only thing I have not changed over yet is the cam which is attached to the magneto armature plate. The parts list shows the cam for a 30 hp motor is the same as the 25 hp so I did not change that out. However the 35 hp motor does show a different cam, but I don't understand how this relates to the lean condition at idle or the lack of top end performance. Can anyone offer me some suggestion? Any advice or input is greatly appreciated.

Motor is a TJ25ELCEB
New carb is a 432705

Thank you!

Chris

 

[flyingscott]

Which one did you get the parts from a 30 or a 35.
You also need the cam if it was a 35
There may also be a timing change involved in that.
There may also be a jet change you will need to do some research.

 

[sr522re]

Which one did you get the parts from a 30 or a 35.
You also need the cam if it was a 35
There may also be a timing change involved in that.
There may also be a jet change you will need to do some research.

The updated carb and intake manifold are shared by both the 30 and 35 hp motors for that year. Jetting is also the same for both motors. Essentially my motor should be the same as a 30 with the upgrades, but if I add the cam I suppose that would make it the same as the 35. The 30 hp cam is the same as the 25 hp motor. Ive done lots of research. Haven't seen anyone with similar issues with this mod. Thanks

 

[flyingscott]

What do you mean you are running a 39 orifice but the mix is adjustable. What model did you get the carb off of.

 

[jasper60103]

Regarding performance, I assume you didn't capture the RPMs? 25 HP is rated at 5000 RPM ​30 HP is rated at 5500 RPM

 

[sr522re]

Regarding performance, I assume you didn't capture the RPMs? 25 HP is rated at 5000 RPM ​30 HP is rated at 5500 RPM

You are correct Jasper. When water testing it, it ran around 5200. But with added HP wouldn't I be worried about over revving and potentially need a larger prop? I can't imagine more power requiring a smaller prop. Is there another way to achieve the 5500 rpm's without a prop change?

Thanks for the input!

 

[ondarvr]

Make sure the butterfly in the carb is opening all the way.

​The cam won't change the WOT timing or carb settings, but it will change the profile of both while getting to that point.

I assume you cleaned the new carb.

​If the buttery doesn't close completely it may cause a lean sneeze, and you won't be able to adjust it correctly.

​Timing may be different on the higher HP models.

 

[sr522re]

What do you mean you are running a 39 orifice but the mix is adjustable. What model did you get the carb off of.

Scott, the carb has a high speed jet located at the bottom of the carb. There is also an air jet located at the top of the carb, accessible from the outside front. And yes, there is also a mixture screw on the side of the carb used for adjusting for lean or rich conditions. Not sure what the carb came off of but it's the correct one for my application. The parts list lists 2 different carbs for my motor. The same 2 carbs are also listed for the 30 and the 35 HP motors of the same years. I own both of them now. The 30/35 carb has a larger opening for air to flow through as well as it came with larger orifices (jets).
Hope this helps.

Thanks for the input.

 

[flyingscott]

Put up a pic of the carb. Usually when the orifice at the top of the carb is a fixed jet there is not a mixture screw also

 

[racerone]

No, no----These carburetors have both !

 

[sr522re]

No, no----These carburetors have both !

You are correct raceone. This carb has both. I have tried 10 times to upload a photo but it keeps telling me that my photo either exceeds the 2 mb size limit or the dimensional limits of the photo. I even lowered the quality of my camera settings to the minimum and its still to big. I will keep trying. I listed the motor year and model # in the original post. Check out the parts finder and select the model number to see the carb illustrations if it will help. Thanks all for the input!

 

[sr522re]

No Title

See attached photo...

 

[flyingscott]

Is the carb completely clean all passages and small orifices. Also are you sure there are no air leaks from installing the parts. If you are positive the carb is clean and no air leaks. You may try a smaller orifice like a 37 or 36 these will richen up the idle.

 

[jimmbo]

Is the exhaust manifold and exhaust tuner the same between the two engines? If the everything is truly identical between the different hp ratings after the parts swapping, no rejetting should be required. Jetting is based on the air flow of a carb. A bigger carb generally requires bigger jets. However air bleeds and other things will affect a fuel delivery curve

 

[sr522re]

Quick update:

So I adjusted the throttle cable out more and moved the throttle stop idle screw inwards allowing the motor to rev a little higher. Then I was able to richen the carb at idle with the idle mixture screw which brought the revs back down. The sneeze seemed to go away at idle which I think is good. However, now when I rev the engine a little higher the sneeze comes back. Please see the youtube link if you want to see what I am talking about.

https://youtu.be/NuVtRQwVLKI

Two things that now have me a little confused is, when watching the video, the motor runs clean at idle, no smoke, but when I rev it just a little bit and the sneeze begins to occur the motor starts to smoke along with the sneezing. And one last piece to the puzzle which may or may not be related, I am losing my fuel prime if I let the motor sit for more than a few minutes. I have to pump the primer ball a few times before the motor will start again after I let it sit. Perhaps there is an air leak in the fuel line which is allowing me to lose prime as well as allowing for the lean condition?

Thoughts? Any input is always appreciated.

Thank you!

 

[flyingscott]

That doesn't sound right. Are you sure both cylinders are firing? Do a spark test. Was there a timing change involved for the conversion. Was it done?

 

[sr522re]

That doesn't sound right. Are you sure both cylinders are firing? Do a spark test. Was there a timing change involved for the conversion. Was it done?

Yes, both cylinders are firing, but the bottom cylinder is running a little richer than the top. Probably from priming the carb too much. From the primer solenoid there is a smaller fuel line that send fuel directly into the lower intake manifold. This is likely why the bottom cylinder is running richer during idle. The plug for that cylinder is has more carbon build up on it than the top spark plug. I am beginning to suspect an air leak in one of the fuel lines as you have earlier suggested. Or perhaps the fuel lines are not large enough to handle the larger consumption from this new carb. I will play with the fuel lines next. And yes, additional timing is required and I have made that change using Joe Reeves WOT procedure. Timing is currently set at 34 degrees. Thanks for the input!

 

[ondarvr]

Fuel line size has nothing to do with it. Unless the primer is leaking, it won't make the lower cylinder run richer, a leaking fuel pump may though.

 

[racerone]

Make no assumptions here.------The carboned bottom plug should concern you.----What are the results of a compression test.----Post the actual numbers.-----Does spark jump a gap of 7/16" on both leads ?------Thermostat installed and working properly ?

 

[sr522re]

Make no assumptions here.------The carboned bottom plug should concern you.----What are the results of a compression test.----Post the actual numbers.-----Does spark jump a gap of 7/16" on both leads ?------Thermostat installed and working properly ?

I'm not too concerned about the plug as after I water tested the boat last weekend I pulled the plugs and they both looked great. This motor has a failed primer solenoid and forces me to turn the little red knob on the top of it in order bypass it while squeezing the prime ball. When I do this, it forces fuel not only into the carb bowl but also directly into the intake manifold through a separate fuel line forcing additional fuel closest to the bottom cylinder. I am guessing that the idling in my driveway with the extra fuel in the bottom cylinder may be the cause of the carbon build up on the lower plug. But I could be wrong. I can and will check compression soon. Thanks for the input!