T500 vs 500GT timing (powerdynamo)

[samandkimberly]

Anyone have thoughts as to why the spec GT500 timing is 2.9mm BTDC, while the T500 is 3.4mm? That's a big difference, way more than one would use to compensate for the hotter/cooler spark of the two ignitions. Maybe the GT timing refers to the marks on the flywheel, rather than the actual timing?

I ask because I'm installing a Powerdynamo ignition (my second, 1st worked great) and they suggest setting it to 2.9 for the points bike, and 3.4 for the PEI ones. While this is true according to the specs I've read, one of those really cant be right...can they?

I'm almost certainly just going to go with 3.4mm but I thought I'd see if there was some wisdom to the retarded GT timing I'm not considering.
Thx,

Sam

[Zunspec4]

Hi Sam,

A possible reason for the less advanced timing for the GT500 is petrol. Modern unleaded burns faster than the previous lead laced petrol, the GT500 arrived when unleaded was becoming the prevelent blend (although leaded was still avaiable) so maybe Suzuki tweaked the ignition timing to suit. When I run my race engine on premium unleaded I use 2.9mm BTDC as a fairly safe setting to avoid excess running temperature and possible detonation. I would recommend starting out with a conservative BTDC ignition setting and work from there, ideally on a dyno so you can see the effect of timing changes.

Cheers Geoff

[Craig380]

This is common across many of Suzuki's 2-stroke twins and triples - the early models have ignition timing specs which are quite a bit more advanced than later bikes.

An example is the GT380 triple: the timing spec for the J/K bikes is 2.88mm BTDC, for the M model 2.25mm BTDC, and for the final A/B bikes, it's 2.05mm. Yet there is no difference in porting, cylinder head chamber design, piston crown height, etc across the various models.

More timing advance can make the bike feel sharper at part throttle and at mid-range rpm (around 4 - 5,000) but at the expense of a bit of top-end power ... not to mention the risk of holing a piston.

My 10 cents is, go for the less advanced spec. On an otherwise bog standard engine, I really don't think you'll notice any difference as they are so mildly tuned anyway, and you've got a bigger margin of safety.

[samandkimberly]

Thanks, that makes sense. I've always had a tiny bit of ping right at midrange when the bike is hot, so sticking with the more conservative settings does seem to be smarter than going for max advance. I don't really have a power issue, even with a sidecar; I'm competing in rallies with pre-67 250cc bikes, so I have one of the fastest vehicles out there.

It started and ran like a clock first kick tonight, set at 2.9mm.

Best,

Sam

[argo1974]

This is not a Suzuki specific thing.
You will find altered ignition timing on almost any 2 strokes with factory conversion from ignition points to electronic ignition.