GT750 firing order???

[v4shopper@gmail.com]

1975 GT750 less than 20k miles, really clean. I don't know any history on this bike. While trying to set up points first thing I noticed was the wheel behind points doesn't match the cylinders at TDC. Point at 4 o'clock is the center cyl. Noon is the right. 8 o'clock is the left. If I change plug wires around to match the points the bike fires and runs. How and why? Timing wheel has a notch to only fit one way. Am I missing something?

[Craig380]

If you're looking at the points plate, the engine spins anticlockwise as you look at it when running. The firing order is Left - Centre - Right.

The pointer doesn't actually show TDC or accurate ignition timing, it's just an assembly guide when putting the side cover and points plate on. However, the markings do approximate (and I mean approximate) to the firing points for each cylinder.

They're usually OK for initial start up but you really should use a dial gauge and set up the timing for each cylinder statically for accuracy. That way, you can also see if the markings are accurate. Sometimes they are, sometimes not.

[old racer]

I thoght it was left right and centre.

[Coyote]

The points cam (and timing marker) is driven by a single pin on the starter clutch. The starter clutch is keyed. If that key shears, the timing plate and cam can be way off. It has happened on here before. You need to remove the left side engine cover to get at it. The starter clutch is a tight fit, but Suzuki provided some tapped holes for a puller. It's my bet the key is sheared on the starter clutch.
And yes,, The timing marks occur before top dead center. In your case. left and right are 3.62mm (.142) BTDC. The center cylinder times at 3.42mm (.134) BTDC. look in the sticky "General specs and info".
Pictured below is the starter clutch and the points cam drive. You can see the key way in the top photo. Numbers 1 & 2 have to do with the water pump drive

[v4shopper@gmail.com]

Good call on the key. It's toast. I have it timed great in all the wrong spots and runs great. I will put new key in tomorrow and time it again.

[Coyote]

ACE hardware usually has an assortment of metric woodruff keys

[v4shopper@gmail.com]

Got woodruff key at tractor supply, retimed, and still runs good. Now it runs with the plug wires in the right order.

[rngdng]

Got woodruff key at tractor supply, retimed, and still runs good. Now it runs with the plug wires in the right order.

That's a good thing.


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