Re: Throttle control has a huge deadspot???
Regarding this and your later post: I have never worked on a 5 cylinder 150 but I am certain that control linkages are set up the same as the three and four cylinder engines. SO, with the engine off:
You can control somewhat the amount of free play in the throttle if you have a spring loaded quick-connect on the throttle cable at the engine end. The purpose of this free play is to allow the engine to shift into gear BEFORE the throttle starts to advance, so you must have some. Again, if you have a spring loaded quick connect at the engine end, and it is pulled all the way out (1/2 inch) in neutral, if you loosen the locknut and screw the connect off the threads about 1/8 inch more, it will now reduce the amount of travel in the cable before it starts to actuate the throttle cam. Normal spring loading is 1/4 to 3/8 inch pulled out. If you have the brass quick connect that is not spring loaded, there is not much you can do.
Now regarding your butterflies not opening fully: The throttle cam will either have one or two scribed lines on it. These lines are meant to be where the roller on the bottom carb contacts the cam when setting and synchronizing linkage. (at the single line, or between the two lines) They are initial reference points. Note that after setting the idle speed, these marks may no longer be at the point of contact, but they will be close.
If the link bar between the tower and cam is too short, the mark(s) will be above the roller and you will not get full opening of the butterflies.
The adjustment is: Using the (two plastic) ball ended bar, set the line or lines so that they are in contact with the roller. If the roller does not already contact the cam, there is part of your problem. Note that the roller is on an eccentric cam screw. If you loosen the nut, you can turn the screw so the roller just touches the cam. Then tighten the nut. Now push the throttle all the way forward. The roller should ride up the cam and the finger on the end of the cam should push down the roller for the last bit of travel. Adjust the length of the connecting bar with the two plastic ball ends so the butterflies are substantially horizontal when control is at full throttle. Note that full throttle is not adjustable. There is a plastic button on the linkage tower which bears against the block and stops travel.
Now, with the engine in full throttle position check the see that all three carbs are open substantially equally--it is not possible to get them exact. If they are not close to equal, disconnect the ball end from the linkage tower and move the cam out of the way. now loosen the tie bar between all three carbs and let them all close all the way. Tighten the tie bar. All three carbs should now open substantially equally. Re-attach the ball end and you are ready to fire up the engine and set idle speed using the screw and locknut on the linkage tower.
PLEASE NOTE: Most people are sure that that last 1/4 opening of the butterflies gives them a lot more speed. Not So! Because timing is fully advanced at about 3/4 throttle opening, the engine runs most efficiently at this setting and actually produces the bulk of its rated horsepower here. When you get on the loud pedal, full throttle gives a lot more noise, uses a lot more fuel, and only gives (depending upon application) a couple of MPH more. So when you get your butterflies set, don't expect 20 MPH more.
Remember: Doubling speed requires 4 times the horsepower. So: it would take approximately twice the horsepower to go from 40 to 60 MPH and that is just not available with the last 1/4 opening of the throttle butterflies.
