90 Johnson SPL - Carb Plates not fully opening

[PWH1]

I have had my new to me boat out twice this year and it has run very well. However, I felt like I was not getting all the 90 horse had to offer in regards to performance. I am getting a WOT of approx 33 MPH with max RPM of around 4600 (moderate load - prop 14x17),

This evening, I pulled the carb cover and pushed the throttle all the forward to what would be WOT. As I look into the carbs, I can see that the butterflys (carb plates) are only opening about 1/4 of the way. I have provided a few pictures of the carb and the plate that engages the carbs to open the butterflys. They are all taken with the throttle in WOT position.

Looking for advice...

Do I need to adjust the throttle cable so that it pushes the carb plates further open? If so, how do I go about doing this? Is this whats refered to as 'link and sync?' (fyi - the cables were recently replaced prior to my purchase of the boat - so they are new)

Lastly, when i removed the carb cover, I found this thumb screw in the bottom of the cover. I cannot find any obvious area where this would have come from and I doubt it came out of the carbs.

Thanks - PWH

 

[emdsapmgr]

Re: 90 Johnson SPL - Carb Plates not fully opening

You could have three issues. The throttle cable may not be properly adjusted on the engine end at the front of the lower cowling. Also, there is a factory adjustment called "sync and link" which correctly aligns the spark advance with the carb opening. A factory service manual will describe this detailed procedure. Also, there is a roller and sleeve on the top carb butterfly shaft which is pushed to activate/move the carb butterflys. 432639 Not unusual for the outer part of that sleeve to deteriorate with age and fall off, affecting the opening of the carb slightly.

 

[PWH1]

Re: 90 Johnson SPL - Carb Plates not fully opening

emdsapmgr - thanks for the response....

The roller sleeve is in good shape. However, after looking at the cables closer, I found that the cable responsible for forward gear was not seated properly within the molded carrier at the base of the engine. I took off the small plate, re-seated the cable, and the butterflys are now opening at about 75% @ WOT vs. the 25% I had prior to re-seating the cable.

As I look at the top of the carbs, the wrist pins are just off center. So, I am not sure that there is a lot being left on the table, but feel some additional adjustment maybe warranted.

I will get a chance to find out how much performance improves over the next week. We are headed out early Saturday AM to spend a week on a lake in Canada enjoying all that family, boating, and the beauty of Canada bring.

PWH

 

[ezeke]

Re: 90 Johnson SPL - Carb Plates not fully opening

The linkage and synchronization procedure requires that after checking the timing you adjust the linkage between the carburetors first so that the throttle plates are perfectly synchronized, then adjust the roller to the throttle cam, and then lastly adjust and replace the cable to the engine linkage without adjusting the engine linkage further.

Because the throttle linkage also controls the timing advance, any tinkering with the system in the wrong order will usually make things worse in the long run.

The final adjustment to the linkage for the idle is made on the water, under load, with the engine warmed up.

The Synchronization and Linkage Adjustment procedure is covered in Section 1 of your factory service manual. http://www.outboardbooks.com/index.cfm?fuseaction=search.main

 

[mikesea]

Re: 90 Johnson SPL - Carb Plates not fully opening

regarding the roller,as PWH said,those rollers had a plastic outer covering that dries out and falls into the pan,It would be yellowish in coloer and I dont see it in the Pic.look into the pan and see if you find any pieces of dried up plastic.I have used 5/16 hose and slid it on the stem after taking remaining roller off ,it works

 

[emdsapmgr]

Re: 90 Johnson SPL - Carb Plates not fully opening

The "cable responsible for forward gear" is the shift cable and it shouldn't have anything to do with the adjustment of the throttle-or did you mean to say the throttle cable?