Anyone swapped OMC 15hp plastic top carb for metal one?

I have a 1992 15hp Johnson that has been giving me fits lately due to some carb issues where the low speed mixture isn't dialing in well and the inlet needle seems to be sticking at times. I ordered a carb kit the other day and while waiting put on a freshly cleaned all metal 15hp carb off of my 1982 Evinrude.

Took it out yesterday with my boat loaded out exactly the same as always and with calm conditions and was about 2-3 mph slower than with the factory carb and had slightly less holeshot. I was hoping that the performance would be identical. I know the motors have a couple slight differences but I thought the main stuff was exactly the same... like displacement and intake/exhaust manifolds.

So I'm curious if anyone else has done the swap and if so how was performance different if any? Personally, I'd love to go away from the plastic top but not if it means sacrificing performance.

The plastic top carbs are prone to cracking and warping.This can be fixed by tapping an extra bolt(see Leeroy's ramblings).Also I believe the timing plate cam and follower(throttle) are slightly different between pre/post 87 models.You may have readjust the link and sync if using the older carb to compensate.Check to see if the roller is worn or has a flat spot.

muddywaders said:

The plastic top carbs are prone to cracking and warping.This can be fixed by tapping an extra bolt(see Leeroy's ramblings).Also I believe the timing plate cam and follower(throttle) are slightly different between pre/post 87 models.You may have readjust the link and sync if using the older carb to compensate.Check to see if the roller is worn or has a flat spot.

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Yeah, I don't like the plastic top ones for that very reason. Mine appears to be flat still but to me its just an extra piece that can break on me ($$$) as well as a potential air leak area to cause it to run lean. That's why if they have the same throat diameter and jetting, I'd just assume use an all metal one.

I also did do a link and sync after the swap so it should be timed and is fully opening at WOT and my roller is like new as well.

Pappy said:

Sounds like you installed a 9.9hp carb on the 15hp. When you remove it take a look at the carb venturi size vs. the plastic top version. No, it does not matter what you took it off of.....take a look!
As far as being all the same? Far from the truth. Although this does not apply to all model years basic differences include an exhaust tuner vs. an exhaust pipe, an extra spacer on the reed block to allow the reeds to open a bit farther, and of course the larger venturi carburetor.

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I'm 95% sure I installed the correct carb. I have the installed 15hp carb off of a 1982 model as well as a 9.9hp carb on another 1982 model plus a spare 9.9hp carb from a similar year. So I'm very aware of the differences....that 5% of doubt would be if I messed up while playing musical carbs lol. I'm confident its the correct one if for the only reason that when I put a 9.9hp carb on the 1982 15hp once, the boat was considerably slower.

And my comment on being the same was in reference to an older model 15hp to a new model 15hp like my 1992 (not 9.9hp vs 15hp). I know the ignition system is slightly different, the thermostat was relocated to the top of the head, the carb went to the plastic top, the midsection got that exhaust baffle cover added, and then the cable style throttle was added. The only thing that makes me question if the throat size increased any was that the WOT max for my 1992 is listed as 7000 rpms while for the 1982 it's 6500.

I took the carb off and put it back on the original 15hp it came off of. It indeed was a 15hp as I compared the venturi size to the later model 15hp carb as well as a 9.9 carb. Next time out I will take both 15hp motors and test each out with the same prop and boat load out and see what the performance differences are.