Throttle Plate Direction '63 75hp

[yorab]

My throttle butterfly plates are not completely circular-they have a notch cut out of one side that either goes toward the "back" of the carb throat (away from the low-speed needles) or the notch goes toward the "front" of the carb throat. It seems to me that the notch should be in the front so that when fuel comes out of the low-speed holes, it won't pool on top of the butterflies. I have a few pics of the carb before disassembly but I can't quite see the butterfly plates. I have a parts carb with a slightly different butterfly and the notch is aligned with the small low-speed holes in the front of the carb throat.

Now, I am perplexed about this because my parts manual clearly shows that the notches should go toward the back of the throat, away from the low-speed holes. Here's a link to a diagram of a different motor, but the carb is the same as mine:

http://www.crowleymarine.com/johnson-evinrude/parts/39803.cfm

You can see that the notches are toward the back of the throat, just like my parts manual. Anybody know for sure which way they go? I can post pics later if needed. Thanks.

 

[boobie]

Re: Throttle Plate Direction '63 75hp

I can't tell you which way the air holes go cause I don't remember. But, if you look real closely at the end of the plate you will see a bevel. This has to fit perfectly in the carb bore when the plates are in the idle position. If they are turned around you won't get a good seal. Hope this helps.

 

[yorab]

Re: Throttle Plate Direction '63 75hp

Okay boobie, I'll look for that bevel today. Thanks.

 

[yorab]

Re: Throttle Plate Direction '63 75hp

I understand what you mean by a bevel, boobie, but I can't see one on the edge of the plate. The edges seem to be perpendicular to the faces of the plate.

Does anybody have an old two-barrel carb laying around that they could peek inside of to see which way the notches are oriented? Thanks.

 

[F_R]

Re: Throttle Plate Direction '63 75hp

I don't have a carburetor, but is this your throttle plate style? It's sort of hard to remember because I never remove those things. There really isn't any need to.

Make sure the threads are still good in the throttle shaft and DO use Locktite on the screws. You do not want those screws ever coming out because they will get sucked in and destroy the powerhead.

 

[yorab]

Re: Throttle Plate Direction '63 75hp

That's basically it F R. The only small difference is that my plate is fully circular on the back end with that notch on the front end. Are you saying that the notch does belong toward the front of the carb, near the low-speed holes and the core plug or is that diagram just for clarification of my throttle plate style?

I may drill and tap those throttle rod holes to one size larger to be certain that the threads are fresh. I'll then use Loctite. I have a blue and a red threadlocker, and I'll do some research to determine which would be best for this particular application.

 

[yorab]

Re: Throttle Plate Direction '63 75hp

I looked closely at one of my parts carbs and I can see "witness marks" on the carb throat when light is shining in the throat just right. At the proper angle, I can clearly see from accumulated dust and grime that the notch should be located at the front of the carb throat. I originally followed the orientation given in the parts manual but I now know that the manual was wrong. The first pic that I've attached shows the notch oriented incorrectly (toward the back of the throat) and the second pic shows the low-speed fuel holes for my motor. I will need to turn the butterflies around.