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scotty810

2012 Sherco ST290 Bog and Smoke

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My 2012 290 starts fine and typically runs just great.  Occasionally, when I have been riding for a little while and then stop for a break, after starting the bike back up, it will be low on power (feels like its bogging) and will smoke pretty heavily out the exhaust.  It's not consistent though.  Sometimes I can ride a few times and not have this problem, but then other times it will happen.  The bogging and the smoking have ALWAYS been linked (never see one without the other).  
 
Any ideas where to start?  I've pulled the carb off and cleaned the jets.  Air filter is clean.  I'm running 80:1 gas using premium octane and Maxima Castor 927 premix.
 
Thanks in advance for any ideas you may have!

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What color is the smoke?gray, blue, black?

gray-coolent burning

blue- oil burning

black- gas burning

does it quickly clear up, or take a while?

does it clear up faster if you rev up the motor?

are the conditions the same when it happens?

been under a heavy load? Engine really hot, fan on? Riding downhill? Cold out, hot? Wet?

have you pulled the spark plug out when it happens and see what it looks like?

some more info would help

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I would agree re the use of castor based oil is for highly stressed race engines but I checked out the info on the net and it seems the manufacturer implies it is good for all engines.

Why take the risk ? Their philosophy is more towards being green and environmentally sound but have they checked out the trials bike application of slow running low stress engines as opposed to chainsaw , Karts and motocross ?

 

 

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I love the smell of castor oil in a 2 stroke engine.  It takes me back to the 1960s.

I wish someone would make an additive to make modern fuel smell like the old stuff, that I could put in my Sherco.

Edited by stpauls

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There is some good information above - see beta-blocker. With regard Maxima 927, I too use Maxima 927 and researched it before decision to use. Yes, there is past history of sticking ring grooves etc etc but reading (yes, from the manufacturer who acknowledges that history) these issues may well be past history. I converted to Maxima 927 18 months ago after a long history of using two well known brands used in trials bikes. Why did I investigate and change - some of it was "advice" given by others that they would never use X brand because someone they knew seized their engine and then for the other brand having pulled apart my motor for another reason (one ball bearing delaminating in a well known and respected bearing manufacturer in an engine lubricated by a well respected transmission oil for trials bikes) I found the piston crown with a hard encrusted black carbon, compression dome similarly encrusted and rings and ring grooves horribly gummed up having used a common respected trials pre-mix oil at 100:1 (as recommended by the factory). After much research and some discussion with others, I converted to Maxima 927.

Find attached images of my piston crown and the compression dome after 18 months of use (~100 hours of riding) since previous tear-down (pics taken through the spark plug and by a USB micro camera pointed up from the exhaust port. To be able to still see the size of the piston (see attached image) and, in other pics I have, to see the manufacturing date etc of the piston and to see the clean compression dome (see attached) gave me confidence to continue. As I had the exhaust off (I needed to get the bash plate off) I also took pics of the rings & grooves through the exhaust and they were also very clean (unfortunately I must have deleted them). I use 80:1 pre-mix, (no more than 5L mixed at a time), the plug is a coffee brown colour and I have spent time on carburation and not over-oiling air-filter and my exhaust header did not appear any blacker or encrusted than I have had in the past. The downside is that I cannot use anyone else's synthetic fuel if I run out - the upside, they cannot borrow mine.

So, while there is a perhaps history for those using castor based oil including gumming up rings and grooves, that may not appear to be the current state of affairs, perhaps things have moved on - after all, I started riding trials when 25:1 or 32:1 was standard and using 50:1 was "way out there" in an aircooled engine. I have obviously moved on.

compression insert_1.jpg

JGas piston crown_70.jpg

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If you have a spark arrestor or screen baffle in the end of your exhaust system, check to see if it is clogged with soot or oil.  That will cause the same sort of symptoms you are describing.   A good cleaning will cure it if clogged.

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 You all are thinking two stroke problems. This whole thing is probably the fuel pump/vacuum lines issue along with vapor lock from a hot motor. Damn Sherco with the remote tank anyways.  I was sure happy the day we sold my boys 2012.

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14 hours ago, oni nou said:

I'll get my coat.............And if that's what the engine internals look like I am off to buy a bottle of Maxima 927 and advise that every one else does aswell.

Maxima recommends 24 to 32:1 mix in 50 to 80cc.... 24 to 40:1 mix in 125 and 250cc machines and 32 to 60:1 in 500cc and over.

I would not run out to buy it just yet! I have tested it in the past and MY findings suggest it creates some hard stick carbon in the exhaust that is some nasty stuff!. And even more difficult to remove!

 

As much as I like the smell, I just cannot use it!

 

 

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As far as the OP goes, I think there is a possibility of a sheared flywheel keyway, but yet a greater possibility of a faulty stator plate with a dodgy trigger sens0or that is screwing up the ignition timing and throwing the system into a retard mode. Accounts for the suddenly boggy operation w/ hot restart. I seem to recall similar past reports, so keep that in mind. Bradford ignitions is a phone call away if needed.

 

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That is a lot of oil to mix in, 24-40:1 for a 250 that was probably set up to run 80:1 modern oil, would you notice the reduction in fuel to air ratio ?

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I'm hoping we get an answer on this, I'm still gunning for a failed crank seal, it'll easily cause intermittent issues.

I've had several sheared woodruff keys with 247 and 349 Mont's, they were totally knacked and wouldn't even start.

If it was the rings then surely it would be smoking all the time ?

Anyone taking bets ! :)

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Thanks for all the ideas guys.  I haven't made any changes yet, but I also haven't been experiencing this issue like I was.

I spoke with Ryan Young Products today and they strongly believe its the premix I'm running.  They recommended trying a full synthetic and seeing if that fixes things.  I'll start there!

I also plan to measure the tranny fluid next time I drain it to see if I'm losing any out the exhaust.

Edited by scotty810

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Without wanting to complicate things or upset anyone, here is a picture of a cylinder head and piston after running Maxil 427 (not even a whole bottle since the last rebuild). This is not from a trials bike, it's actually from my tuned vespa that does get quite hot and gets up to high revs quite a bit (which is why I was using castor oil). The rings stuck in the grooves which robbed the bike of compression, and the cooked on oil was really hard to get off the head. I was running at 2%. 

I'll be running Motul 710 next, which seems like it has as good flash point match for my sort of bike.

Anyway, that's from my experience - perhaps things are different when running in a trials engine.

 

Screen Shot 2017-08-02 at 5.38.57 pm.png

Screen Shot 2017-08-02 at 5.38.37 pm.png

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