Picked up a timing light, how do I use it?

[MadRat 88]

I have had an issue for the past couple weeks with my 81' not getting any top end. I've been through the carbs, up and down with jet sizes and keep getting the same result. I talked to a couple "old timers" and both told me to hook up a timing light and see where it's at. Well I got the light today, printed off some of the service manual and I'm still confused as to how it all works. Anyone have timing for dummies, or a good link showing what I'm looking for and how to check what's going on with my rig? I'm running a stock electronic ignition.

 

[xjwmx]

It's a strobe light that goes off when the cylinder fires. It will flash on the rotor so that the rotor looks still. Then you can see where the mark on the rotor is relative to where it should be, when the cylinder fires. The stock electronic ignition usually won't go out of time. You can adjust the timing on it easily enough if you want to though.

 

[pyrocentric]

Clamp the red lead to positive on the battery(or a spare car battery if it's easier to get to). Black lead to the negative. This is the power for the timing light.

Clamp the plastic probe around the left spark plug wire(left as you're sitting on the bike).

Take off the little round cover on the left side.

With the bike idling at 1200rpm or so shine the timing light on the rotor. It should blink at the right time and you'll see the little mark on the rotor appear to stay put. Here is how it should look at idle.

When you rev the bike to 3000rpm the mark should move clockwise to the left, like this.

If it doesn't advance like it should the ignition could be shot. I don't know much about the 1980 and up ignitions.

 

[MadRat 88]

Thanks pretty simple. The mark on mine isn't in the middle of the "U" shaped marks, it's directely above the right side of the "U". Do I need to advance it so it's in the middle? Do I only need to check the right side or do both sides run the same, and finally how do I adjust?

 

[gggGary]

It is possible your TCI is showing it's age seems like lack of high RPM is a fairly common theme. It might relate to the diode replacement fix

 

[gggGary]

should be close enough, one coil fires both sides, is it advanced at 3000 RPM?

 

[gggGary]

We could do a swap to a known good one.....

 

[MadRat 88]

Yeah it's advancing when I rev it up, guessing at rpm's since I don't have guages. The left side cylindar has a low pitch boom, boom boom, boom sound to it at idle, not sure what this is a sign of, guess I thought if the timing was off it wouldn't fire correctly on boths sides. I would be up for a swap, just may take a while to get there.

 

[gggGary]

Check your battery voltage you should see about 13.5 volts when the engine is revved up. Have you checked compression, set cam chain and valves?

 

[MadRat 88]

Cam chain and valves are good. Haven't checked compression and battery is new. The motor runs and sounds great, just can't get any top end out of the old girl.
Plugs are gapped at .030 and I keep pulling them out black.

 

[xjwmx]

Note the position at full advance in the pic. There's no official mark for full advance, but people use the left side of the drain hole in the cover. You can advance the timing if you want, but you shouldn't advance it so that it goes past the drain hole at full advance. It's an engine killer. I have mine timed the same place yours is now, to allow me to use 87 gas.

For changing the timing, on your pickup is the top hole a slot or just a hole? If it's a hole you have to turn it into a slot. They came both ways. The thing that looks like a rivet holding it on on some of them is a screw with no slot. Just cut a slot in it and it'll back right out.

 

[gggGary]

OK black plugs is a clue I think. What have you done to the carbs? Are the float levels set correctly, are they rejetted to match correctly your exhaust and intake?

 

[MadRat 88]

Right now I am one size up on the pilot, #45 I believe. Stock air jets are 135 and I have 142.5 mains. I have tried sizes 137.5 up to 150 on the mains with basically the same results. Good on the low to mid and chokes at the top end 3rd through 5th gear. I am using the Mikes XS filters, they are the oval shaped ones, the little cone ones cover the air jets at the back of the carbs. Left side starts to back fire after plugs get hot, left carb holder is shot, currently have it wrapped in elec tape to help seal up the cracks a bit.

 

[gggGary]

Ohm out the coil swap plug leads and caps see if the problem switches sides. Deal with that spigot if it is sucking air a holed piston could be next. Try going back to stock main jets I don't think straight pipes don't draw better than stock mufflers.

 

[MadRat 88]

I already tried switching the caps and nothing changed. If the ignition can't keep up with the motor, and the little black box is notorious for wearing away the top end, I think that may be the first move to make before changing all the jets again. I'll e-mail you and see if we can work something out so I can go that route sooner than later.
Thanks Gary!

 

[kvanderploeg]

Might want to check out this thread:

http://www.xs650.com/forum/showthread.php?t=3289

Kent

 

[MadRat 88]

Excellent thread! Thanks much, I'll let you know what I find!

 

[Dillrepair]

you almost certainly have to get new carb holders/boots/rubber whatever you want to call them. it might not or probly won't fix the whole problem, but it can't be running right with them not sealed properly.

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[pamcopete]

MadRat88,

The dual output coil produces a positive voltage on one plug wire ands a negative on the other. The timing light works best on the negative wire, but there is no quick way to determine which is which, so just try clamping the timing light to the other plug wire or just reverse the clamp.

It's possible that the timing light is triggering on the falling edge of the spark, which is negative going on the positive wire, so it would show up late.

 

[XSLeo]

With one bad carb holder you will be running on just one cylinder. JBM Enterprizes is the folks to get replacements from.
Get Uni-Filters If you have the stock exhaust go back to stock on the jetting and test from there. The carb guide will explain how to clean and tune your carbs.
Leo