96 Yamaha 2stroke C40 Idles to High

[Ormonddude]

I Purchased a Boat not registered in 3years with the 96-C40 on it I did a compression test and was pleasantly surprised at 150psi both cylinders I rebuilt the carbs and fuel pump and changed all the fuel lines and first click it fired right up I was running 25:1 oil/fuel in case there was any rust on the crank or cylinders- OK so I ordered a cheapo tach as the Idle sounded High its a watch battery Job ya wrap a wire around the #1 plug lead and it feels the pulse- Anyway after adjusting the fuel mix to 100:1 and adjusting the fresh carbs I cant get the idle under 2000 rpm its Bizarre because the RPM's start to go up before the throttle push rods are even activated the timing Linkage seems to be off a few degrees but I am not sure how to adjust it and Manipulating the Push rods or tuning the carbs does NOTHING except make it stall when the engine has a bad mix anyway is it Possible to adjust the firing time? its as if its firing the plugs way to close to TDC at Idle? Again the Idle Screw is all the way up and The Throttle linkage is not even activated. Why would it Idle so High? other than this it sounds beautiful spins like a top!

 

[99yam40]

Re: 96 Yamaha 2stroke C40 Idles to High

use a timing light and see what the timing is at
and look in your service manual to see what specs are at idle and fully advanced.
The Yamaha service manual will have the procedures and specs

My guess is the tach is not correct reading or the timing is too far advanced

 

[Ormonddude]

Re: 96 Yamaha 2stroke C40 Idles to High

And that is the Problem there is no instructions on adjusting Timing in the owners manual - and I don't have a repair manual any Clue's would be Helpful, Thanks

 

[robert graham]

Re: 96 Yamaha 2stroke C40 Idles to High

Are your carb butterflies really closed with the motor idling at 2000 RPM's?

 

[Ormonddude]

Re: 96 Yamaha 2stroke C40 Idles to High

Yes they are and I guess that would suggest a manifold leak but it looks fine I am really perplexed.

 

[99yam40]

Re: 96 Yamaha 2stroke C40 Idles to High

what is the reason you refuse to check to see what the timing is and tell us what you get?

 

[Ormonddude]

Re: 96 Yamaha 2stroke C40 Idles to High

Well Mostly because its a 2 stroke the timing is set by the flywheel, Now on the starboard side there is some ignition timing Linkage for the throttle top end advance and it is off by like 5-10 degrees can someone please tell me how to Manipulate it the Pop rods don't seem to have the correction needed -Unless maybe the key on the flywheel is sheared and let it rotate out of synch (I Will Check a few things and get back to the Board) -Like I plan pulling the manual choke and see if it stalls to check for leaks and removing the pull starter to see if the timing is correct on the flywheel key there- anyway I let you all know what I find.

 

[99yam40]

Re: 96 Yamaha 2stroke C40 Idles to High

On my 1999 C40 TLRX the timing is controlled by CDI
It starts at 7BTDC once warmed up it drops back to 7 ATDC.
WOT it is at 12 BTDC (I believe without looking at manual)
and you can check timing with a timing light just like on a auto

But if TDC on # 1 cylinder does not match up to TDC timing marks on flywheel you have a problem that needs attention