Solex P40-II Carb Won’t Go to Full Throttle?

[Steve Watson]

Cleaned up a pair of solid shaft Solex P40-II carburetors I have. I noticed that the throttle plates of left side carb only go to about 90% of full vertical while the throttle plates in the right side carb go to 100% full vertical. This is with the carburetors not installed on an engine. Just working them on the bench. There must be a way to adjust the left one to get to full throttle, but I’m not seeing it. If it’s something simple/obvious I’m going to feel pretty dumb.

[David Jones]

Are they split shaft or solid shaft. If split shaft you may be missing the buffer stop which means they cannot be adjusted until you install a new one and the chances are you need to replace the other one as well. If solid shaft you will have to twist the shaft.
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[Steve Watson]

Solid shaft. What do you mean exactly by twist the shaft? Both of the plates are opening and closing in perfect sync with each other. They just don't go to full vertical. Like something is blocking/stopping the shaft from rotating the extra 10 degrees.

[David Jones]

Sorry Steve, should have read your post a little better. Are the throttle butterflies in the right way round or is the shaft in back to front? Sounds like something is assembled backwards. Carefully compare the good one with the bad one.

[Phil Planck]

Also, check that accel pump rod is sliding freely and that its spring is not jammed up.

[Bill Lawless]

I just this second finished cleaning up a pair..

[Dick Weiss]

Steve,

Fully back off the idle stop screw(s) to check if the butterfly plates will fully close; If the plates won't allow it, they may have been removed out of centralization to the throats and you can slightly loosen the screws to adjust them. Also, check the edges of the plate
relationship to the 1st by-pass hole in each throat--this will equalize the idle and possibly some hesitation from idle-to-acceleration.

Finally, make sure you adjust the throttle linkages--starting w/the 50mm measurement of the pivot arm-to-the-fan-housing's face
shown in the shop manual, and the last thing--check if there's a slight slack in the overall linkage so the carbs will return to the idle stop screw(s) and not holding open the carbs around 1300/2000; Pop off the ball sockets from the carb arms, raise the sockets--should be about 1/16" when the engine is warm/hot. Cause? The engine and transmission "grows up", but all the linkages don't!

Dick