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pmk

Compression Release

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'Increased compression' relative to a previous model year doesn't necessarily equate to generally high compression. Some marginal increase from a previous motor that had 6:1 compression to 6.5:1 (for example)... it's still quite low. Don't let sales brochure marketing drivel confuse things.

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40 minutes ago, nhuskys said:

Tryals Shop just had 4 different SY250 in for pre season maintenance.  Mike was the importer, and there isn't much he doesn't know about them.  I'm sure you have spoken to him.  He said this was about the easiest trials bike to start ever, with its long kick lever.  You might want to look into your motor a bit more if it is hard to kick?

Yes, I have spoken to Mike before.  Actually, this bike I have was imported through his shop.  Just to be clear, the bike and engine are fine, yes it has a long kick start lever and starts easily when cold or hot.  The point I want to emphasize is not that it starts difficultly, but rather there is a lot of compression to kick through, even when moving the kickstart by hand. 

I asked about the bleed hole wondering if anyone had done a mod like this before, simply so if the bike stalled while in a section, it would take less effort to refire the engine.  Currently, it takes a dedicated kick to start and while I have not tried to bump start it, I am not even sure that could be done vs skidding to a stop.

If the later years and non UK models are known to have a lighter flywheel, and some people have mentioned the advanced timing and lighter flywheel can combine to have the engine stall without warning, it is not uncommon to reduce compression slightly with a lighter flywheel.  I need to make a call or ask those that may know more questions.  Actually, it is a fine bike as is for entry level like myself, just wanting to sort out a few quirks it does occasionally, like stalling, but not often.

Edited by pmk

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17 minutes ago, faussy said:

Check this out pmk

https://trials.com.au/forum/viewtopic.php?t=5066

As you probably know the sy motor is largely a tyz, never seen a decomp on a tyz before, but going by the barrel casting it looks like a standard fitting to me, weird. Someone else obviously thought it necessary

Well that is interesting.  And yes, the Scorpa cylinder does have a sealed bolt type plug in the hole the linked TYZ photo has the decompression setup.

Let me see if Paul from the Hell Team in Australia replies to my email.  Possibly that other automatic decompressor from the chain saw would screw into that already existing port, and make this thing even easier to fire up.

Thanks for finding and sharing that link.

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No changes made yet.

Thought this was interesting.  Was asked to inspect cylinders of a friends RD Yamaha.  Cylinders inspected good, but has a drilled hole above the exhaust port.

Photo later after I resize it.

 

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On 3/23/2018 at 10:46 AM, faussy said:

Check this out pmk

https://trials.com.au/forum/viewtopic.php?t=5066

As you probably know the sy motor is largely a tyz, never seen a decomp on a tyz before, but going by the barrel casting it looks like a standard fitting to me, weird. Someone else obviously thought it necessary

I have remained a bit intrigued by the photo of a compression release on the TYZ in the link provided by faussy.

Finally, sorted it out.  There was one TYZ model that did come with a handlebar compression release from new by Yamaha.

That model was a Japan version, the specifics are the 1995 TY250ZS Scottish.

https://www.megazip.net/zapchasti-dlya-motocyklov/yamaha/ty250-3456/ty250-9696/4ml1-768572

This model also seems to be the 4ML series, which if you notice, most TYZ parts are 4GG.  The cylinder on the 1996 TYZ for all countries is the 4ML type with the hex head plug above the reed cage.  All the compression release parts are also 4ML prefix.

The Scorpa SY250R uses this same style cylinder, with the hex head plug, same as the other TYZ models for other countries and the non S model for Japan.

At a guess, the TY250ZS is a Japan only street version of the TYZ.  The TY250ZS, has as original, also was oil injected, had a battery, and coolant tank.  All these parts associated with the street version are also 4ML prefix.

 

Edited by pmk
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