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mlcjot

New member, bought an old Sherco

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Hi folks,

Picked up a 2000 Sherco 290 this evening for a very fair price. I have a Husaberg FE550 for green laning and light enduro, but now it's time to actually learn some skills!

The Sherco runs reasonably well but has a couple of things that need addressing. One thing I'm wondering about is the revs hanging when I blip the throttle. There's so much conflicting advice online about this but the general consensus seems to be that it indicates a lean condition. I assume this means a lean air/fuel mixture, rather than a lean oil/petrol mixture? I'm new to 2 strokes :) With a bit of luck this can be addressed with the carb, and doesn't mean I've got leaky crank seals :( I am going to play with the fuel screw and idle screw to see if they make any difference.

Video here: https://photos.app.goo.gl/yPfrfujwktA5LjQY7

Apart from that, I'm pretty happy. The bike is a beater, but that suits me just fine.

Cheers,
Alex

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Welcome and well done.

Crank. seals not a big job anyway. If you say “hanging” - do you mean hesitating?  Rather than jump straight in , and play around with the jets and stuff - assume for now that they are ok. Work your way through the fuelling first. Breather pipe , tank (rust?) , fuel down-pipe, tap , filter , fuel pump and carb-connection. If all those are ok - then move on to the electrical system , and disconnect all the plugs and use contact-cleaner in them. Look for loose wires etc.  Check the spark plug condition. That will certainly show if you are lean.  All that should take you a long way on a “beater”.   You will have looked at the airbox of course , and the filter-condition. At least wash it and re-oil whilst you’re there.     I’m not one for squirting loads of carb-cleaner in airboxes. So the next step would be pulling the carb and cleaning it on your bench - and that’s where I bow out and let someone else advise you. 

Oh , edit - You might simply need some fresh fuel in there.

Edited by Nebulous
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Thanks Nebulous! Are crank seals pressed into the case halves from the inside on these engines, followed by main bearings? Or external?

Hesitating as in it takes 5 seconds for the revs to drop to idle after a blip of the throttle. Were you able to view the video in the link I posted above?

I wasn't planning on changing jets for the time being, more just tweaking the fuel screw and idle. But yes, stripping and cleaning the carb is pretty much the first main port of call, after a go through your list of suggestions. The bike fires up first kick wearing slippers. It's the easiest starting bike I've ever had.

I'll pull the ignition and clutch covers at the weekend and see about replacing the crank seals.

Thanks again! :)

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51 minutes ago, mlcjot said:

Thanks Nebulous! Are crank seals pressed into the case halves from the inside on these engines, followed by main bearings? Or external?

Hesitating as in it takes 5 seconds for the revs to drop to idle after a blip of the throttle. Were you able to view the video in the link I posted above?

I think you’ll find you can change the crank seals both sides , without splitting the two case-halves. Which for you is ideal.

Don’t forget to use some masking-tape around the crank-noses - otherwise if you score it getting the old seal off , it may well damage the new seal on fitting. From what I’ve read , they come out easily . Couple of self-tappers and a good tug.  Flywheel side is the one prone to be dry , and fail first - and that info I got from this site.

Here’s a link to the teardown PDF.    

http://shercousa.com/pdfs/sherco_engine_teardown_and_assembly_manual.pdf

Actually that’s not much help in this case , but there’s good pics of all components towards the bottom of the PDF.   I think you would need an M30x1.5 flywheel-puller for the Sherco , but check that.   Bag that woodruff key so you don’t lose it.

I’m not a member of Google , so couldn’t view your vid.

Edited by Nebulous

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Clean the carb properly and insure proper jet sizes. Should be around 38 pilot and 122 main jet. Find a strand of copper wire to pass through the jets for verification. The fuel screw will be out 3.5 turns or so.  Needle one notch below center.

Crank seals are removed from outside, but do not go there as yet.

Edited by copemech
Na

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Sounds lean. The first thing I would do is turn the mixture screw out a couple of turns and see if it solves the problem. If it's more than 2.5 turns out and you don't see any difference check the jets are the right size as copemech said. The check for air leaks. Start by squirting soapy water around the inlet manifold while it's running.

There are billions of results on the web about steps after that but as you say it runs well so to me it sounds like idle mixture screw.

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Some bikes ( in 1970's grass-track ) were required to have no tick-over at all, so needed the throttle stop screw to be well unscrewed. (I am not too sure of the current ACU regulations.)   So you could try that to see if the engine goes to idle sooner.    For Trials you can set whatever tick-over speed you require, some riders even adjust it for particular sections.

Get to see what is the correct method of setting your tick-over mixture and speed.  It is usual to adjust the mixture screw for a peak in revs, then back off the throttle stop screw to reduce the revs to whatever you require...  I usually err 1/8 turn on the rich side of peak, to avoid a lean cut when accelerating.

.

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Hi folks, thanks so much for your superb advice and suggestions. I stripped the carb just now, the inlet fuel filter had some crap in it but nothing major. All passages were clean and clear. Jets are:

Pilot 37, main 270, drain bolt says 110, and the one with the o-ring says either 60 or 80.

Drained the fuel, it looked clean. Going to refill with fresh. The fuel screw was exactly 2 turns out, I have set it back to that and will experiment with it next time I start her up. I didn't remove the reed block but it feels supple and visual inspection yields no cracks or splits. The tank breather is free and clear but the fuel flows pretty slowly out of the tap. Might just be normal though, it certainly flows fast enough for the bike to run. Would old fuel result in the engine running lean?

I popped the ignition cover to have a quick look, the flywheel is enormous! And a bit rusty. Water has got in there at some point.

On an unrelated note, the clutch drags with the lever held in the first time I put it into gear after starting. The clutch drag goes away almost immediately.

How quickly should the revs return to idle after a blip of the throttle? Straight away? I'll keep you updated. If my efforts with the carb don't work, is the next step to pull the flywheel and replace crank seal?

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48 minutes ago, mlcjot said:

Maybe you can see this video Nebulous? Cheers

Yes , could see that fine.   Surely that’s got to be an air-leak somewhere? You were right to closely inspect the reed-block.  But you will have to be methodical in your search. 

35/36pilot and 118main are the recommended sizes for jetting. With a 18.5 mm float height.  So you are in the right ballpark. Most say around 3 turns out is a rough guide.  Make sure that pilot jet is screwed-in tight.   Yes , don’t be pulling those seals just yet.

Edited by Nebulous

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Pulled the reed block. The bottom pair have quite a bit of light showing through. The top pair are closed. Is this normal? Cheers

IMG_20180622_221115.jpg

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Cold stick of the clutch is pretty normal on many trials bikes. As long as it clears quickly, it's not the biggest deal in the world. Try to free it off by putting it into gear and rocking to and fro before starting. If that doesn't work, put the front wheel against something when you first knock it into gear. Read the "clutch mod" thread in the Beta sub-forum.

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1 hour ago, mlcjot said:

Pulled the reed block. The bottom pair have quite a bit of light showing through. The top pair are closed. Is this normal? Cheers

I wouldn’t have thought so. I thought they snap shut - completely closed? Are the bottom ones worn? Installed correctly?

My next suggestion was going to be to check the reed-block to head gasket anyway.

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4 hours ago, mlcjot said:

Hi folks, thanks so much for your superb advice and suggestions. I stripped the carb just now, the inlet fuel filter had some crap in it but nothing major. All passages were clean and clear. Jets are:

Pilot 37, main 270, drain bolt says 110, and the one with the o-ring says either 60 or 80.

A 37 pilot is fine. the Main is the one you are calling drain bolt. Needs to be 120 ish.

Drained the fuel, it looked clean. Going to refill with fresh. The fuel screw was exactly 2 turns out, I have set it back to that and will experiment with it next time I start her up. I didn't remove the reed block but it feels supple and visual inspection yields no cracks or splits. The tank breather is free and clear but the fuel flows pretty slowly out of the tap. Might just be normal though, it certainly flows fast enough for the bike to run. Would old fuel result in the engine running lean?

Three or more turns out on the fuel screw. That may be your main issue! The heavy flywheel will take a bit longer to wind down but your is a bit floaty and surging.

I popped the ignition cover to have a quick look, the flywheel is enormous! And a bit rusty. Water has got in there at some point.

Drill a 3mm hole in the bottom so water can exit and vent.

On an unrelated note, the clutch drags with the lever held in the first time I put it into gear after starting. The clutch drag goes away almost immediately.

How quickly should the revs return to idle after a blip of the throttle? Straight away? I'll keep you updated. If my efforts with the carb don't work, is the next step to pull the flywheel and replace crank seal?

Not straight away! Put the reeds back init and leave them alone.

 

  • Thanks 1

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trapezeartist: Yep I'm not too concerned about the clutch drag! Totally liveable.

Nebulous: The reeds all look fine. I'm not familiar with 2 strokes really, so am unsure if the reeds should always be slightly open, or if this is a fault.

copemech: I'll revisit the fuel screw when I get back to the bike. Good point about the heavy flywheel, makes sense! Should the reeds always be slightly open? For engine idle speed perhaps?

Thanks!

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