My new boat has marine machine throttles and they are very loose. I want to add some friction so they do flop to idle if I remove my hands from them. They do not have the set screw inside (like Livorsi).

How can I tight these up?

There are 3 bolts that hold the entire assy together, if you tighten those the levers all get more "squeeze" and thereby tighten the friction. I don't know how to tighten just one at a time or if it is even possible.

I have Latham on mine and they come back to idle if I let them go.

The spring on ours are located at the throttle linkage at the attachement by the blower. If you take the spring out they will not return by themselves anymore.
This is on Merc 600SC's.

Right there.

Yes, but if you remove the spring then what happens if your cable should break or fall off ? The return spring is on the unit for this reason, so if you have a mechanical failure you would not be running with no throttle control. ( kinda like when the throttle bores freeze up on a snowmobile ) I personally preffer the friction method. My 2 cents.

Oh, nice motors by the way !!

Mine have plastic friction buttons on each lever. You could make some buttons that are slightly thicker: I think.
Due

What you are describing is a design flaw that Marine Machine knows about. They changed their design about a year ago. They will not do anything to help you. How do I know? I custom order a brand new set and did not install them right away. When I went to install them, I had the same problem. If you tightened the center screw (big phillips head screw in that acts as the center shaft) You could tighten them but how much differed drastically from one throttle to the other.

I returned mine to MM for and adjustment. They were brand new, never installed. They tightned and returned. "we changed the design to fix that" "You need to buy a new set if you don't like it". wow. Yes they were a year old but still new in the box. All for $1600!

They are improved in a tighter setting but still not equal in resistance to movement.

Next time; Latham

I called MM and they offered to help me. I was told to send them in and they would get it right.
Now exactly what "right" means, I don't know.
They said on the phone they made a mistake with these older throttles.
I'll send them in about 2 weeks and we'll see what they do to them.

I only saw 1 big phillips screw and it was on the port side on the throttles.

?????