1975 115hp throttle valves not fully open?

I'm inspecting things under the cowl this weekend and I notice the throttle valves are not fully opening when the throttle is pushed to wide open. I have a manual and everything is set to spec on the carb linkage and cam follower, however, the butterflies are not fully opening at full throttle. I'd say they're about 2/3 open and definitely not flat.

I'm wondering if the cable is stretched or flexed since it is pretty old or what would cause the valves to not fully open anymore? The boat has been in storage for quite a while and the settings on the linkages and everything are still factory settings. The engine is in great condition. I'm afraid to adjust anything because it all looks correct per manaual. Just not opening all the way? I did notice the plastic casing on the end of the throttle cable has a little slop in it, but I think this is normal on other cables I've looked at?

Here's a video of it idling on the muffs yesterday.

http://www.youtube.com/watch?v=1ethbRLfheM (sorry for the ****-eyed video, still getting used to phone)

Any help?

Re: 1975 115hp throttle valves not fully open?

Disconnect the throttle cable from the engine temporarily.

Manually advance the engine's throttle linkage at the point where the throttle cable is normally connected. Observe the throttle butterflies.

If the butterflies are now opened fully, then obviously something is wrong with the throttle control cable, BUT if the posiiton of the butterflies remain the same, I'd suspect that the carburetor throttle cam roller has shed its outer covering if using the new style roller (check it). This new type roller has a small black roller covered by a larger clear cover. The combination of the two results in a normal diameter roller of approximately 3/8". This clear cover is subject to cracking and falling away resulting in a small roller of about 3/16" which obviously results in not opening the butterflies to their proper horizontal position.

If the roller is okay (approx 3/8" in dia), make sure that the scribe mark on the cam is dead center with the roller when the butterflies just start to open, not before or after. Let us know what you find.

Re: 1975 115hp throttle valves not fully open?

I'll check it when I get home today.

Going off memory (sometimes not a good thing), I seem to recall the roller being clear and about 3/8" diameter.

I will check the cable then double check the cam and report back.

Thanks!

Re: 1975 115hp throttle valves not fully open?

Manual advancement of throttle lever yields WOT. Cam roller is good. Problem seems isolated to throttle cable. It seems a bit sticky or something at control box bit when helper manually advances lever at the engine I can feel something moving in the box and the plates stay open. Thinking the cable is a bit gummy and needs replacement, unless something can be adjusted at box end?