Throttle Cam

[99yam40]

maybe I am looking at it wrong, but it looks like once the roller gets past the 90 the throttle would open back up some

[mitch184]

I disconnected the other carbs and the middle still won't open all the way. If you look at the WOT picture, it seems like once the roller gets past the 90° bend in the cam that the cam just needs more height. I have a tiller on this motor and 3/4 throttle is where the roller hits the 90° bend in the cam.

I didn't have the tach hooked up when I did it, but there is some RPM's left when I manually push the butterflies open that last 1/8". Since that cam is not available to buy anymore, I thought about just ramping it up with epoxy or JB weld.

[99yam40]

maybe I am looking at it wrong, but it looks like once the roller gets past the 90 the throttle would open back up some

I meant to say close up not open

have you looked at the plates to see which way they head after the rollor goes past the 90?

[mitch184]

As sharp as that 90 corner is the butterflies basically open as far as they're going to right after turning it. If you rotate it all the way to that small raise area it will open them all the way. But there is not enough throw in the linkages to actually make that happen. Plus if you did you'd have a dead zone for a lot of throttle movement.

the plates... assuming you mean throttle blades.. can't go past horizontal since the hard stop is there. I want to say I checked that the stop wasn't being hit prior to WOT but I'll have to double check. But I'm 99% sure they dont

[zenoahphobic]

It's been many years since I owned a similar 90, but I do remember that cam on yours looks different than mine that I think was black plastic.

I also remember they were annoyingly fiddly to adjust.

What I can see it just needs adjustment, maybe you need to go behind the throttle lever at your helm. Your lever may go past its max to actually start to reduce the throttle. Go look and see.

If all else fails I would then suspect it is a derated engine (they made 80hp). And you may get a replacement (black), and if not have one made from flat alloy sheet.

I hope this is useful.

[mitch184]

That would be weird if it is a detuned cam but it kinda looks like it.

It seems that part is no longer available to buy. Maybe I'll have to modify this one.

[99yam40]

As sharp as that 90 corner is the butterflies basically open as far as they're going to right after turning it. If you rotate it all the way to that small raise area it will open them all the way. But there is not enough throw in the linkages to actually make that happen. Plus if you did you'd have a dead zone for a lot of throttle movement.

the plates... assuming you mean throttle blades.. can't go past horizontal since the hard stop is there. I want to say I checked that the stop wasn't being hit prior to WOT but I'll have to double check. But I'm 99% sure they dont

I was just wondering if the throttle plates closed off some once the roller made it past the 90, and
is the second pic showing where all of that linkage ends up with the controls at WOT

[99yam40]

That would be weird if it is a detuned cam but it kinda looks like it.

It seems that part is no longer available to buy. Maybe I'll have to modify this one.

where did you find the part number for that cam?
I have not been able to find the parts breakdown that shows it

[mitch184]

Yes. The 2nd picture is WOT with my current throttle linkages.

The part number for the accelerator cam was listed in a previous email. Its #30 on the controls schematic I believe it was.

[99yam40]

Well it looks like that cam fits 75,80 and 90 motors and a bunch of years
https://www.boats.net/product/yamaha...b9f47a19aa9835


Might want to find someone with one around you so you can compare to see if their carbs work different than yours

[zenoahphobic]

As sharp as that 90 corner is the butterflies basically open as far as they're going to right after turning it. If you rotate it all the way to that small raise area it will open them all the way. But there is not enough throw in the linkages to actually make that happen. Plus if you did you'd have a dead zone for a lot of throttle movement.

the plates... assuming you mean throttle blades.. can't go past horizontal since the hard stop is there. I want to say I checked that the stop wasn't being hit prior to WOT but I'll have to double check. But I'm 99% sure they dont

I have just reread this you say "if you rotate it all the way to that small raise(d) area it will open them all the way".... so why do you think you need a new cam? It is doing it's job, your problem is back from the push cable attachment! We don't see much more in your first picture.

You mentioned it is a tiller throttle control, I've not had a lot of experience with these except remembering the cables get knocked about from the up and down movement. Trace that cable all the way and adjust it. This maybe a push setup, in which case all slop takes up length under compression until perhaps you run out of adjustment.

[mitch184]

I am maxing out the scissor arms or whatever they're called already. As in the arm that the throttle cable coming from the tiller pushes. It's all the way maxed out.

So any adjustment... to me... has to be made from the pickup timing arm to the cam. But there's nothing

[panasonic]

Couple of questions:
Are you the original owner?
Do you have the service manual?

I would start all over and set the engine up right from beginning as if you had taken it completely apart. Procedures in SM.

Maybe this is what you are doing already... but I don't see reference to it.

[mitch184]

Motor is new to me but freshly rebuilt. No service manual yet. I have re assembled and adjusted the throttle linkage from carb to tiller handle multiple times.

I'm nearly positive the cam is just slightly off. Im going to continue trying to find a new one but it has proven to be a very difficult task