225hp yamaha excel 1988, timing is -5 degrees at idle after manuals instuctions

sonic NZ

Cadet
Joined
Dec 26, 2008
Messages
16
after timing my excel via post below from cousinabe my timing light shows -5 degrees at idle and +15 degrees at around 3800 RPM

is this normal??




(original post)

how do i tune my motors spark


this motor doesn't have a distributor all its firing times are done through a computer.

on the side of the throttle there is a stepper motor which twists as you accelerate, this has been moved.)
 

sonic NZ

Cadet
Joined
Dec 26, 2008
Messages
16
Re: 225hp yamaha excel 1988 - throttle position sensor, tuning

Re: 225hp yamaha excel 1988 - throttle position sensor, tuning

thank you so much that's an awesome piece of info.

I did this but with the timing light it showed -5 degrees at idle and + 15 degrees at around 3500 RPM does this seem right?

I thought it was around +7 degrees idle and about +30 degrees at WOT
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: 225hp yamaha excel 1988, timing is -5 degrees at idle after manuals instuctions

spec on that engine is -6 at idle and 22*BTDC at WOT, WOT being 5000-6000 RPM,3800 is only just above half throttle and all tests MUST be done under a load.
either on the lake,with a dynomometer or test wheel YB1626. DO NOT attempt it in nuetral.
that is NOT a stepper motor on the throttle its a Throttle Position Sensor.
basically a poteniometer.
gives the micro processor information as to what is the throttle shutter anle of opening .
if you move it you must use the correct procedure and a digital multimeter to properly reset it to .41 volts.
engine timing on that engine is NOT adjustable and the spec is for reference ONLY.
 

sonic NZ

Cadet
Joined
Dec 26, 2008
Messages
16
Re: 225hp yamaha excel 1988, timing is -5 degrees at idle after manuals instuctions

thanks, I wanted to make sure - it just sounds odd to fire when the piston is on its way down, but if that's the way its meant to be --- so be it

3800 is only the rpm i was willing to apply without load,
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: 225hp yamaha excel 1988, timing is -5 degrees at idle after manuals instuctions

revving a two stroke with no load,not to be blunt, is plain stupid and shows absolutly nothing.
that system uses a crank position sensor to signal RPM and a throttle position sensor to signal throttle opening.
with no load it may only take 30* of throttle angle to make 3800 and the ign timing is going to only give enough for the commanded throttle angle and RPM.
most likly with no load and 4 spark plugs tossed in the creek you could still hit about 3800 running on two plugs.
so quit the revving with no load, its not only meaningless but can lead to bearing damage.
one of the easiest ways to control engine RPM at low speeds with carbs is to alter ign timing,farther you retard it slower it goes.
as on a crbed motor its difficult to alter air or fuel into the intake the simplest way is to retard engine timing electronically.
4 strokes only make a power impulse every OTHER time the piston is at TDC and they also have to drag a valve train with them.
two strokes make power EVERY time the piston comes up.
most 4 strokes you will see idle something close to TDC, most 2 strokes are around 7 ATDC.
best thing I can tell you is carefully follow the YAMAHA service manual and learn what and why each sensor is on that motor and what the A-B connectors do and when would you ever need to touch them.
that was an early venture,crude as it was, into electronicly controlling a carburated engines ign charecteristics to make it more efficient.
 

sonic NZ

Cadet
Joined
Dec 26, 2008
Messages
16
Re: 225hp yamaha excel 1988, timing is -5 degrees at idle after manuals instuctions

also, is there a general screw position for the air fuel mixture. I noticed the port side carbs have 168 size jets and starboard side 160 size jets but all the mixture screws are set one complete turn out. doesn't sound right to me but its not the first time with this motor.
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: 225hp yamaha excel 1988, timing is -5 degrees at idle after manuals instuctions

sonic, so far you have done well. after all adjustments you 1 * different than what the ECU would command on a perfectly machined and set up block.
book says -6* and your so close I wouldnt say no.
pilot air screws have a call out of 1 1/8 your very close.
the main jetting was squirrly and the only way I can do those old 225,Excell and v6special motors is by writeing down the jets as I remove them and then compare my findings to the parts guide and pray.
occasionally the last guy had no clue and randomly stuck them where ever.
so far your looking good I am thinking.
how is it running ?
 

sonic NZ

Cadet
Joined
Dec 26, 2008
Messages
16
Re: 225hp yamaha excel 1988, timing is -5 degrees at idle after manuals instuctions

holly s#@t you wouldn't believe the amount of power being created now, its crazy

so lets look back

1. mixture screws starving carbs of fuel
2. timing 12 degrees out
3. blocked fuel filter
4. gummed plugs

take a look now

http://www.youtube.com/watch?v=W_syQ07k9Fs






thank you so much.
Matt :)
 

cousinabe

Senior Chief Petty Officer
Joined
Nov 13, 2001
Messages
765
Re: 225hp yamaha excel 1988, timing is -5 degrees at idle after manuals instuctions

That's awesome! Looks like she's running great.
Nice video.
Glad you got everything sorted out. I'm sure you learned a lot about your motor and yamahas!!
 
Top