Just Fixed One And Then What Happens.....

[neo]

Thanks Stork,

My 250's been behaving itself this week for 98% of the time. But I know I'll find this Lean/Rich problem eventually .....When I do you're all invited to a Trials party!!!

I'm keen to know if the de-coke will have any effect on this.....time will tell over the next few weeks.

Best of balance.

Neo

[jse]

Thanks Stork,

My 250's been behaving itself this week for 98% of the time. But I know I'll find this Lean/Rich problem eventually .....When I do you're all invited to a Trials party!!!

I'm keen to know if the de-coke will have any effect on this.....time will tell over the next few weeks.

Best of balance.

Neo

Neo,

I also use Castrol TTS (at 70:1) and find it keeps the chamber quite clean, so I doubt that premix oil is the cause. Keep us up on what you find out, you have a very interesting problem and I'd sure like to know the final cause.

Cheers.

Jon

[neo]

Hi Jon,

I've been mix it at 80:1 for a year and a half ...But I am not the original owner of this bike so who know what went in before. And the Silencer box has been a heavy weight for as far back as I can remember....it's so much lighter now.

I'll keep you posted ;-)

Best of balance.

Neo

[copemech]

Hi Jon,

I've been mix it at 80:1 for a year and a half ...But I am not the original owner of this bike so who know what went in before. And the Silencer box has been a heavy weight for as far back as I can remember....it's so much lighter now.

I'll keep you posted ;-)

Best of balance.

Neo

It sounds somewhat encouraging that you did that, the methods vary, yet I think you are finding results!

[neo]

Ok...here's the update.

Bike sounds good ....bikes rides goodish, kinda.....but the hunting is still there on occasions....It's very mild now but still enough to feel when moving off. And as before, it seems to happen more when the fuel tank is below half.

There's one other thing I noticed. The bike used to rev up as if the very first part of the throttle (or very first part of the needle) was too rich....that brief flutter/pop has definitely gone now.

For me the next stop is the main bearing seals....I reckon I can get the old ones out without spitting the case ....Might give this a go next week....wish me luck

But if anyone has any more ideas please drop us a post?

Best of balance.

Neo

[clav3]

Hi Neo,

I did alot of testing on the weekend trying to find a solution to what seems to be the same problem.

I have made my 290 run very similar to what it used to by going up one pilot size (42 to 45) and up to the next richest needle (jjj 4th clip to jjh 4th clip).

Main jet is still the same (112).

Its like the motor has decided it just wants more fuel.

Here is the reasoning behind my wild theory of this problem being motor wear and or exhaust clogging.

Both happen gradually in the life of the bike.

I have owned my bike since new and just after run in I fitted Boysens and the Keihin.

At that time the bike ran sweet with a 35, yes thats what I said, a 35 pilot and jjh on 3rd clip.

After about 6 months of head in the clouds bliss, it started hunting at idle.

I always keep my fuel and carb clean. You have to, especially when running a Keihin.

I used to wind up the idle to stop the hunting but in the end this did not work.

I changed back to the standard reeds looking for a solution and realising I would probably have to change the jetting.

A 40 pilot worked at 1/2 turn but I used a 42 at 1 1/4 turns and JJJ needle on 4th clip.

I was sure that the Boysens were the problem. Maybe I was wrong?

Not long after this I twisted the crank and on rebuild naturally replaced rings, bearings and crank seals.

The bikes tuning did not change. So that meant the original seals had nothing to do with the hunting 35 pilot.

And hear we are about 7 months on.

New reeds, spotless carby... all the crap from previous posts!

Now 42 pilot only justworks at less than 1/2 a turn out which is pretty much out of tunning range and JJJ on 4th clip nearly sent me into orbit while blipping across some triples.

But 45 works at 1 1/4 out and JJH on 4th clip seams alot like I remember the old needle setting was.

Now to the Dellorto.

While I was never fond of the standard 3rd clip D 36 needle, this setting is now unusable, alot like, if not worse than the JJJ orbit needlefrom the Keihin. Bottom clip works fine.

The 33 pilot used with this bottom clip needle is still rich enough but is out a full turn ( 2 1/2 to 3 1/2 ) from when the bike was new with the bottom clip needle.

Now all of these points through the life of this bike seem to point towards a slow but sure change in the way the motor runs and uses fuel.

In the next month I,m going to try,in this order,

A new exhaust

A new piston and rings

This motor has done alot of work in 2 years and not just weekends. It's due for a treat and we'll see what comes of it.

I really do feel these changes are not as noticable when using a Dellorto but are still there.

My last resort will be crank seals but maybe that will change if you changing yours works.

Hope you have luck,

Mark.

[copemech]

Clav, have you tried cleaning the muff yet?

Possibly some creedance in that theory of higher than normal back pressure? More partially burnt(lean) mix entering through the exhaust when opened by the piston at low rpm's. Also an increased mid range surge as things come back into pulse range dynamics, and even accentuated by a richer needle.

I still favor the electric heat gun thingie, one that you can set to just blow air after the fire is started!

As pre Neo's statement of weight loss? I have an old dented muffler that is set aside for welding practice, and i weighed it out at 2035 gr., or just over two kilos. It has some buildup in it, seems hard carbon. Just not sure how this might possibly relate, but may give some point of referance as/ if one is signifigantly heavier.

Edited May 19, 2009 by copemech

[neo]

Hi Clav,

Sounds like you're doing a good job mate ...and hope this stays consistent for you.

Ok, my current settings are 120 Main, 45 pilot, JJH mid clip, running original reeds. But I have to say that my problem did not really go gradually. One week it was working great and the next it was hunting when hot. And now days, on a bad day, it hunts when it's warming up too.

It was originally running a 38 but hit 48 on the pilot before I decided I was doing the wrong thing. And I'm now getting the best results with a 45. But I remember trying a 35 for a while (almost 2 years ago) but the bike was too flat for me like that. I've never really played with the main jet....BTW I use BP Ultimate 98...how about you? And why does this problem show more (for me) when I'm below a third of a tank of fuel?

Also, I'm still considering new main seals because I don't like the way the engine runs fluffy (then I have to rev the engine clean) during the first 5 mins after starting. I didn't have to do this 9 months ago.

Another thing...if it was general engine wear of some form then a lot of Sherco's would have this problem by now...not just you and me

What we need is a knight in shining armour ....a Trials engine Sir Lancelot ....a lateral thinker and a solution provider .....Cope, Jon and Wayne, are you ready to take on the challenge?

Best of balance.

Neo

[clav3]

I haven't cleaned the muffler. Did think of trying but mine is also dented and would like a new one anyway. Not much spare time and sick of wasting time on things that aren't working.

My muff was 2020gr on 24/8/08 when I fixed the crank. If I get time tomorrow with all the rain here I will weigh it again and let you know. Iwill definetly be weighing the new one as a reference.

Neo I found while testing the other day If you have a lean needle particularly with pinging and a fast idle setting it will hunt.

Turn the idle down and if the pilot and air are set right it wont hunt.

About the engine wear, alot of people just ride it no matter how it runs, and its amazing how many people have never heard the pinging blasting from their engine that others can hear. Also most still run Dellortos which tend, I feel, to run richer from the pilot to the low mids. I think this is why they dont tend to hunt with (whatever this problem is).

Also, more higher grade riders would use Keihins and I know for a fact that the expert riders in Aus rebuild the engine each year maybe even more.

Don Murry has told me that he attended the SSD a few years ago and the Sherco mid silencers were replaced each day for performance purposes.

I might be totally off base but thankfully we're running out of things to try.

Just thought of another clue for someone with good engine knowledge like Cope.

I used to fix the hunting idle when the bike was about 7 months old by increasing the idle slightly. Even with a lean midrange.

The other day with the hunting 42 pilot I tried a rich JJG needle on 4th clip position to see if increasing the idle would stop the hunting and it did not.

I have also previously tried a number 3 slide with the same results.

[jse]

What we need is a knight in shining armour ....a Trials engine Sir Lancelot ....a lateral thinker and a solution provider .....Cope, Jon and Wayne, are you ready to take on the challenge?

Neo

Yes!, yes we are! I know we can do it! And, as oldest member of the Diagnostic Triumvirate, I'll cheer the other two on and keep track of their lap times!

If I had the engine in my shop, one of the first things I'd do is a leak-down test to determine the soundness of all the sealing devices. One of the common places for a two-stroke, case-reed engine to leak is under the manifold part of the case just above the top of the trans part of the case. I've seen missing gaskets and pinholes in the casting there and it's really hard to see the telltale oil spot that usually shows up with leaks of that type.

What makes me think that a leak is, at least, partially to blame for the problem is the oft mentioned pinging ("pinking" in the UK). Unless there are unusual circumstances, like a clogged radiator for instance, a well-tuned engine, from my experience, should not ping. Pinging is the symptom of a problem with the combustion process and that generally means that some part of the engine/ignition/induction system is not doing the job as designed. Although it may not be fesible depending on what's available where you live, but any good two-stroke mechanic should be able to test the engine for you.

Jon

[stork955]

Gday Neo, don't worry about the hunting while warming up - keep in mind that the engine is probably just off choke but not at operating temperature yet, so don't go looking for a cure for this as you will only upset some other aspect of its running. As for the pinging thing in 2 strokes it can be related to the squish clearance between the piston and the cylinder head. Obviously this is measured with the head off. There is a heap of info on the internet about this topic, google Squish band and this will be rewarded with a plethora of info. Another thing I thought of yesterday, which may have some bearing on your bikes, was a Gas Gas I did some work on for a guy in my local club. He was having some issues with it, primarily poor idle and slow running stuff and we cleaned the exhaust etc, reset his carb to standard and he freshened up the top end with rings. I noticed the base gasket had been displaced from under the pot (probably from new) and was leaking the smallest amount. This was not visible from the outside of course. A leak down test as Jon suggested will reveal this, but not show where it is occurring... Importantly this can happen mostly when sealers or grease are applied to the gasket - a lot of modern gaskets are impregnated with sealer so it is not required, neither is it required on normal paper gaskets. The gasket surface should be perfectly clean and flat, that is the most important thing. Anyway, that might be worth having a look for on your bikes.

Cheers,

Stork.

[copemech]

Well Neo, I do not know about all that, I am sort of a Forrest Gump style fundamentalist! Just try to work through issues in the most fundamental and cost effective manner I can think of.

All that said, I and others in high standing on this side of the pond simply do not like the Kiehin's as they are overly sensitive and have issues!

Up hill, down hill, temp and baro changes, whatever, they work best in one position, and that is WIDE OPEN on a PRO bike! They make a bit more power! And these guys like Smage and such pay the price and adjust accordingly for maximum performance! A trade off. Set'um rich off the bottom, and let 'er rip! Clean them every day if needed!

They do seem to work better in a level position, such as jumping from log to log on the rear wheel!

My ne off the '03 bike forward was issued with the 45/125 set and the JJH needle. Ran ok, barring the downhill issues. Adjust for the day.

Yes, I had my fair share of the pinging issues with the dellorto untill recently, seems ok for the most part now, and yes the motors are still basically tweaked for preformance from the factory is seems. Squish, compression ratio, timing are all somewhat on the edge to begin with. Add this ****ty fuel we get with up to 10 percent alcohol and then?

If we wanted them to run like a Scorpa, they would have built them like a friffin Yamaha motor.

I found the entire issue somewhat beyond the scope of my patientence and checkbook sometime back!

Not necessarily trying to be the killjoy on this issue, and is though a major reason I have been interisted in the "Neo" factor, as he is trying things that I could not find the time or money to do!

We shall see what Clav reports with the exhaust change.

Edited May 20, 2009 by copemech

[clav3]

My muff was 2020gr on 24/8/08 when I fixed the crank. If I get time tomorrow with all the rain here I will weigh it again and let you know. Iwill definetly be weighing the new one as a reference.

Hi all,

Weighed the muffler again today. Came in at 2074 grams. Nine months after the first weigh and 54g heavier

It's been raining alot here and not working much for the last two days so the muff is soaking in fuel tonight ready for a burn tomorrow.

I'm not too worried how it goes. It's dented and have noticed, after filling it with fuel, a 15mm split in the top weld.

I will weigh it, or the pieces after the burn. Dont know what it will mean. Just a reference if it fixes the problem.

I can understand your thin patience Cope, mine vanished two weeks ago.

But thats what this forum is all about. Some poor ******* going through weeks of agony so that another poor ******* dosen't have to.

Edited May 20, 2009 by clav3

[jse]

A leak down test as Jon suggested will reveal this, but not show where it is occurring

Stork,

If done correctly, it would pinpoint the leak, as part of a leak-down test is to spray a soapy solution on the suspected areas to find out just where it's leaking.

Jon

[stork955]

Gday all, I should have said that Jon, I knew that... of course the leakdown test by itself only tells you if there is a leak. Anyway - I was wondering are the Sherco mufflers repackable? (In that they come apart for cleaning and repacking) For the record I have had a few earlier (1999 - 2001) Sherco front and mid pipes in my cold parts cleaner tank for cleaning with no adverse results afterwards and it works well. For you other guys in Aus I use Hunters' Carbo Clean in a 25 litre plastic bucket. Also really good for cleaning your barrells and other engine and carb parts but nothing plastic. If you can get some it might be worth a try to make sure the inside bits of those pipes are really clean. At least then you have a known good point to work from.

Cheers,

Stork