23 replies to this topic

[copemech]

This stuff is not rocket science, but it IS somewhat sensitive, so here is a reference pic with notations.

All measures are eye reference only, but you have a nice screw right there with a 4mm hole in the hex for a guideline.

I always set mine back 6mm on a new one(center of screw), but after installing the Boyesens on the '07 it almost seemed TOO soft, so a bit more fine tuning to my liking was due.

Taking it back to about 4mm from std(as in piccie), things started to get pretty aggressive again , not bad, but not quite as smooth as I prefer, so I settled upon the 5mm mark, sweet!

Another note on the Boyesens, it does seem that if you really want the bike to clean out on the top end and rev to the nerve shattering MOON, you must change the main jet, as with the stock jetting I had of 120, they will blubber above about 6000 revs, not an issue for most, but even after dropping to a 116 is is somewhat difficult to get things to totally "clean out" ant rev up to the upper 8-9G limits! Most of us never go there anyway, but!!!!! As the Boyesens use no reed stops, is seem a lot more air and fuel get in at high revs! Bloody scarey it is! Even at reduced timing!

If you strain your eyes, you can tell there is more than one head gasket on the '07! One std, one thin!

Attached Images

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Edited by copemech, 22 April 2007 - 03:46 AM.

[John.B]

Thanks for posting the information and picture regarding the timing, it will come in very useful.


If you are talking about your picture then I think you might of meant to of typed base gaskets.

Quote

If you strain your eyes, you can tell there is more than one head gasket on the '07! One std, one thin !

[JayLael]

Good info for sure Copemech. I went to a vintage trial saturday and had a chance to ride a few other Hodaka trials bikes and my own a fair bit. Making small changes to the timing can cause dramatic differences is the way the engine performs. It's a wonderful tuning asset. So you have an 07 Sherco, with boyesens and it can rev to the nerve shattering moon! Sounds like the kind of bike I would like to ride also. I have advanced the timing on my Sherco as well, but never did figure out the actual measurements, just gave the stator a bit of a twist. Also drilled some air holes in the back fender, and soldered up the main jet and drilled it out a bit smaller to get the sucker where it didn't take 60 seconds on full scream to get up there into the stratosphere. (yes poor people do it this way in my case) A properly tuned Sherco is a pleasure indeed.

Edited by JayLael, 22 April 2007 - 01:20 PM.

[scudo]

Does the 6mm setting make for a smooth but still powerful and lively engine or does it flatten the power right off to the point where it is slow and sluggish?

[copemech]

Still rips!

[KTMSprocket]

Am very much a beginner.

I think the message I am getting from the recent threads/posts on this subject is this (if you are a beginner with a 2.9)::

It is probably best to::

1 fully retard the timing to get used to the bike and and do your basic exersises
2 If you have done 1 above, know that there is unburnt fuel in the pipe therefore likely to cause overheating if you run the bike for long periods (or if you start riding the bike harder).
3 Decrease the amount of ignition retarding as you built your skill or time on the bike
4 Once reasonably competant, fine tune to your liking

Is that a fair observation???

[copemech]

Uhhh, not really!

In what testing I have done, if you retard the timing more than 6-7 mm from standard, the bike just does not run properly.

Once again, you can only tame a 2.9 soo much! It is still a 2.9 and has lots of power!

The list of tricks is long, and depends upon year model!

Slow throttle, cheap

Proper jetting, cheap

Boyesen reeds(some have stated the v-force are smooth off the bottom, not sure) cheap, takes some work.

5mm intake spacer(off '05) cheap

Long header pipe ('05) expensive

Stack base gaskets(3 max) Never done it, but? cheap, but labor intensive

Kiehin carb is smoother(Caby bike) expensive

Buy a 2.5, it is 10% smaller displacement!

Once again, the '07 is smoother off the bottom to begin with, as compared ot an '06, which is softer than a '05, '04, '03

[KTMSprocket]

I just finished the timing mod and ran the bike around the back yard for an hour or so.

From the factory marking, I moved the timing back by 7mm (measured as accurately as i could with Digital caliper). I also happened to move the bars more forward as suggested in another thread.

The change in timing made a big difference. The bike was much more rideable and also with the bars more forward and i felt in more control (quite noticeable).

I noticed now that lifting the front was easier and my arms weren't pulled out of their sockets due to poor riding style and power I couldn't quite handle. I pulled wheelies easier but then noticed that the slow action throttle when fitted will help even more.

Happy bunny now.

(of course it goes without saying that a smaller bike would have been a better first bike - but thats life)

(I will keep an eye on any heating and poor running as I get better and push the bike a bit longer/harder)

Thanks for all your help!!!

[copemech]

Good job, go practice! Have fun!

[mad4it]

The 2.9 sherco is not 290cc it is 270 they
just badge it as that!

[KTMSprocket]

copemech....i just revisted the photo you posted.

In the '03 2.9 I just did the timing on, the factory 'mark' on the plate was lined up against the right side of the aluminium post that the allen screw goes into.
(I am sure that the flywheel had never been off before)

[copemech]

That is what I was trying to represent with the first dot on the right side noted STD, that does not mean Sexually Transmitted Desease! Ha!

[ScottT]

KTMSprocket, on Apr 23 2007, 12:45 AM, said:

2 If you have done 1 above, know that there is unburnt fuel in the pipe therefore likely to cause overheating if you run the bike for long periods (or if you start riding the bike harder).

Sorry I just dont get this at all, how on earth can there be unburnt fuel?

If you retard/advance the ignition all you are actually doing is igniting the fuel at a slightly different time, take the 2.9 for example;

The 2002 fires 3.8mm BTDC
The 2003 fires 3.0mm BTDC
Does one burn more fuel than the other? NO they both burn the same amount only one compresses it a bit more before its ignited.

With a 60mm stroke, moving the timing 3deg will change the firing by 1mm (the piston travels 120mm for each revolution) 360 deg divided by 120mm = 3. So every 3deg the flywheel/crank rotates the piston will move 1mm

The 2000 and 2001 290's both fired 2.7mm BTDC

Fitting a 1mm thick base gasket will have the same effect as altering your timing by 3deg and will also lower your compression as the piston isnt going up as high

[ScottT]

KTMSprocket, on Apr 25 2007, 02:00 AM, said:

copemech....i just revisted the photo you posted.

In the '03 2.9 I just did the timing on, the factory 'mark' on the plate was lined up against the right side of the aluminium post that the allen screw goes into.
(I am sure that the flywheel had never been off before)

Thats exactly the same as my 04 250 was before I changed it, there were no marks on the paint on the flywheel nut to make me think it had been off before.

[ScottT]

Copemech, i've looked at your pics and you seem to be moving the backing plate clockwise (from your pic) if you want to retard the ignition you rotate the backing plate anticlockwise, it would seem your advancing it not retarding it.

See here or here