1977 johnson 6hp throttle cam question

[danielvanalphen]

I own a 1966 johnson 6hp and it runs great. Can get it to idle at around 500 rpm in gear (that is a by ear number) and this year of engine has a very gradual throttle cam. The cam is a constant increase of throttle. I've picked up a 1977 version of the same engine and this year engine has a completely different throttle cam. The cam barely even touches the roller that opens the throttle plate, until the very last part of the cam in which it is a very sharp increase. Im wondering what's the point of this type of cam over a gradual one, when the 3/4 of the cam that doesn't even open the throttle is useless

 

[Crosbyman]

the cam is adjustable loosen the bolts under the mag plate. the other bolt is a pivot bolt. just tighten it after you do the one on the right side .

set tiller to START and cam should just touch the cam follower and line up with the mark on the cam

throttle plate should begin to open as you move the tiller handle towards FAST

make certain the cam party # is correct ..the one on the left does semm odd shaped

 

[hardwater fisherman]

My 4 hp motors are the same. When they changed for CDI ignition they changed the throttle cam shape. And carbs and the cam followers also changed over time.

 

[danielvanalphen]

the cam is adjustable loosen the bolts under the mag plate. the other bolt is a pivot bolt. just tighten it after you do the one on the right side .

set tiller to START and cam should just touch the cam follower and line up with the mark on the cam

throttle plate should begin to open as you move the tiller handle towards FAST

make certain the cam party # is correct ..the one on the left does semm odd shaped

In the picture the tiller is at start and it just touches the cam at the marks. But because of the Shape it doesn't open for a while until it hits the sharp increase. Im just trying to understand why they've done this to be honest

 

[jimmbo]

With these engines almost All of the Spark Advance occurs before the carbs open. Seems to work well. Also, Idle Speed is a result of retarding/advancing the spark, not changes to the Carb Throttle Shaft