Hi there,

I'm just figuring out my new bike, which I love riding.. But it seems like I might have an ignition issue. Perhaps timing?

When riding fast down connecting trails, the engine seems to pre-ignite and knock. It only seems to happen at high RPM.

My jetting is stock, and so is my timing. Should I be adjusting the timing to a better spec than stock? I'm not running race gas.

Thanks,

Jon

Hi there,

I'm just figuring out my new bike, which I love riding.. But it seems like I might have an ignition issue. Perhaps timing?

When riding fast down connecting trails, the engine seems to pre-ignite and knock. It only seems to happen at high RPM.

My jetting is stock, and so is my timing. Should I be adjusting the timing to a better spec than stock? I'm not running race gas.

Thanks,

Jon

I would try a 50:50 mix of pump gas and race gas. That always took care of the problem for me.

Is it just me, or does it seem silly to have to run race gas in a trials bike?? I mean it doesn't have that high of a compression. It's gotta be the timing, right? So.. Has anyone come up with a spec that the bike still starts fine at?

Thanks,

Jon

Yes it is silly to have to run race gas - if it is jetted properly you will be able to run pump gas.

Is it a genuine LongRide, or a SY250 Racing fitted with a Longride tank/seat combo? If it is the later, you may be running too lean a main jet for Trail riding.

What number main jet is fitted?

Do not go less than 145, though you will probably need a 150 or more depending on Temp.Altitude etc. There are many main jet sizes available for the TK carb.

Edited May 23, 200719 yr by arnoux

I've got a full on Long Ride, from what I can tell the jetting is stock, but I haven't checked the nozzles.

I'm at sea-level to 3000ft primarily. I don't want to run too lean. Right now the bike runs fairly crisply, but the off throttle roll-on condition has me thinking I'm too lean on the pilot/slow speed circuit (Or just the timing is way too close to TDC).

Got any good jetting recommendations?

Jon

"When riding fast down connecting trails, the engine seems to pre-ignite and knock. It only seems to happen at high RPM."

"Right now the bike runs fairly crisply, but the off throttle roll-on condition has me thinking I'm too lean on the pilot/slow speed circuit (Or just the timing is way too close to TDC)".

These two statements seem to contradict each other - is it a High RPM issue (probably main Jet)

or is it the other , or both?

For sustained High speed type trail (not Trials) type riding try a 145 / 150 main at least, and time to the standard Yamaha (Scorpa UK spec) mark (not the more advanced Scorpa Racing timing)

arnoux

Edited May 25, 200719 yr by arnoux

I've run into the symptoms you're describing on my '03 SY, it turns out the plug was half fouled. Replacing the plug may fix it right up.

Arnoux, jetting is related to throttle position, not RPM. It is possible to ride at high RPM with a small throttle opening. That's the scenario I'm describing.

I'll check out the timing one day when I have a chance. Hopefully I'm not taking little pieces of my piston and cylinder away while I delay.

Jon

"When riding fast down connecting trails, the engine seems to pre-ignite and knock. It only seems to happen at high RPM."

"Right now the bike runs fairly crisply, but the off throttle roll-on condition has me thinking I'm too lean on the pilot/slow speed circuit (Or just the timing is way too close to TDC)".

These two statements seem to contradict each other - is it a High RPM issue (probably main Jet)

or is it the other , or both?

For sustained High speed type trail (not Trials) type riding try a 145 / 150 main at least, and time to the standard Yamaha (Scorpa UK spec) mark (not the more advanced Scorpa Racing timing)

arnoux

Had the same issues with my bike. The gas was kind of old so I added half race gas. Also went from a standard plug to a new iridium plug. Worked like a charm.

I just thought I'd add some new info. I really love riding this bike, it's allows me to ride the way I know I can.

Anyways, if Scorpa reads this, pleaes keep the Long Ride available, it's a great trail bike!

Jon