pmk Posted March 21, 2018 Report Share Posted March 21, 2018 SY250r, has anyone made a compression release to let the engine be started easier. When I say made, some of the vintage open class MX machines came from the factory with a small hole drilled above the exhaust port. This bled off a portion of the compression pressure while kickstarting, but was a non issue while the engine was running. Granted the TY250Z engine used in the Scorpa starts pretty easily, but certainly has a bit of compression to kick through. Quote Link to comment Share on other sites More sharing options...
potto Posted March 21, 2018 Report Share Posted March 21, 2018 On a 2S motor like my Montesa there was a 14mm extra hole in the head ,the lever operated decomp fitted to mine was ok but I'am not sure it was really that much use....some said they don't bother with them @ all,what I did find on Ebay was a chainsaw auto decompressor with an adaptor to fit the 14mm hole,I purchased a Husky 10mm one but have yet to machine an adaptor. These work by lifting a button up on them which exposes a small bleed hole,when the engine fires it automatically closes ,still don't know if the bike would start with one of these ?,my old decomp has to 5mm (approx) bleed holes which I presume are too large causing insufficient compression for the engine to fire. After doing some rather serious damage to my leg after a "kickback" I have a more clever starting procedure which works everytime......self preservation really. Hope the info is some use to you,cheers Quote Link to comment Share on other sites More sharing options...
section swept Posted March 21, 2018 Report Share Posted March 21, 2018 (edited) Decompressor was supposed to make starting easier on 2 stroke, it also helped when going down hill or to slow engine when in the nadgery stuff. Decompressor on 4 stroke certainly was intended to help get big pistons over tdc for starting, but again riders used them to good effect in sections to tame the engine delivery in tight sections and hill ascents. Only other use was if you had a push start then the decompressor came in handy. My Sherpa has one and it does come in handy for tricky bits. Edited March 21, 2018 by section swept Added content Quote Link to comment Share on other sites More sharing options...
pmk Posted March 22, 2018 Author Report Share Posted March 22, 2018 Agree on the manually operated cable actuated compression release, they would work too good for what I am suggesting. My 73 OSSA MAR has the cable operated type in the second spark plug hole. Some bikes though have a bleed hole, and it reduces cranking pressure to get it started. No mechanicl device or anything to operate, simply kick and go. Quote Link to comment Share on other sites More sharing options...
nhuskys Posted March 22, 2018 Report Share Posted March 22, 2018 R&D Husky in Australia, used to do this compression release mod to WR360 head. It was from a 2T lawnmower engine. Quote Link to comment Share on other sites More sharing options...
faussy Posted March 22, 2018 Report Share Posted March 22, 2018 (edited) I would be more worried as to why your sy has too much compression. These bikes are one of the easiest of modern bikes to kick over, mainly because of their short stroke and long kickstart. Has your ignition timing been advanced? Edited March 22, 2018 by faussy 1 Quote Link to comment Share on other sites More sharing options...
pauls320 Posted March 22, 2018 Report Share Posted March 22, 2018 Already an easy to manage machine, are you just trying to set it up for a small kid or your wife or something?..If you really needed to decompress...could probably drill/tap head if coolant passages allow, and fit a Husqvarna chainsaw decompresser fitting... 1 Quote Link to comment Share on other sites More sharing options...
pmk Posted March 22, 2018 Author Report Share Posted March 22, 2018 Actually guys, it does start well. Timing is advanced. Most people consider these a high compression motor, and honestly, it requires a pretty good push of the kickstart to crank the motor through. No plans to add a decompression device. Just wanted to get it to spin slightly easier, so if it were to stall, it could possibly refired before putting a foot down. As is, it would be difficult. As I mentioned, some cylinders have a small bleed hole into the exhaust port. Drops the cranking pressure a bit for easy starting and is a non issue while running. Other times the manufacturers have cut key slots extending the port toward the head. Just another way to lessen cranking effort. Quote Link to comment Share on other sites More sharing options...
faussy Posted March 23, 2018 Report Share Posted March 23, 2018 (edited) 19 hours ago, pmk said: Most people consider these a high compression motor, and honestly, it requires a pretty good push of the kickstart to crank the motor through. I understand your desire to lower it, and im not going to tell you not to. I have a few bikes myself with jake brakes so know what theyre about but IMO the sy is far from a high compression motor, they were a clubmans favourite for years because of it. You could start them in slippers! Edited March 23, 2018 by faussy Quote Link to comment Share on other sites More sharing options...
pmk Posted March 23, 2018 Author Report Share Posted March 23, 2018 11 minutes ago, faussy said: I understand your desire to lower it, and im not going to tell you not to. I have a few bikes myself with jake brakes so know what theyre about but IMO the sy is far from a high compression motor, they were a clubmans favourite for years because of it. You could start them in slippers! Interesting, mine takes a pretty good effort more than slippers would allow. I have read the later year versions did have increased compression. Maybe the USA or should more correctly say, the non UK versions have the higher compression that Scorpa advertised in the later models. I say this because those later models, in the sales brochure also indicated the lighter flywheel. Thanks for the reply. Need to do more homework now regarding how they increased compression. Quote Link to comment Share on other sites More sharing options...
faussy Posted March 23, 2018 Report Share Posted March 23, 2018 (edited) 12 minutes ago, pmk said: Interesting, mine takes a pretty good effort more than slippers would allow. I have read the later year versions did have increased compression. Maybe the USA or should more correctly say, the non UK versions have the higher compression that Scorpa advertised in the later models. I say this because those later models, in the sales brochure also indicated the lighter flywheel. Thanks for the reply. Need to do more homework now regarding how they increased compression. I had a 07, 08 and 09 sy in the Uk, the only modification being to rotate the stator virtually right round to fully advanced. Granted this did make them a bit harder on the kick, but compared to shercos and 300 ggs of the time definitely easier to kick over. Ive heard of some countries having lightened flywheels, so if youve also heard of higher compression ratios, then that would definitely explain it. All mine were uk models, so cant comment. Maybe they just had their heads machined down a little more, couldnbt see them changing much else. A lighter flywheel certainly wouldnt help in kicking over compression PS Its been 9 years since ive kicked one so my memory may be off. But my dad who was 60 at the time could start it easier than any other modern bikes ive owned Edited March 23, 2018 by faussy Quote Link to comment Share on other sites More sharing options...
pmk Posted March 23, 2018 Author Report Share Posted March 23, 2018 20 minutes ago, faussy said: I had a 07, 08 and 09 sy in the Uk, the only modification being to rotate the stator virtually right round to fully advanced. Granted this did make them a bit harder on the kick, but compared to shercos and 300 ggs of the time definitely easier to kick over. Ive heard of some countries having lightened flywheels, so if youve also heard of higher compression ratios, then that would definitely explain it. All mine were uk models, so cant comment. Maybe they just had their heads machined down a little more, couldnbt see them changing much else. A lighter flywheel certainly wouldnt help in kicking over compression PS Its been 9 years since ive kicked one so my memory may be off. But my dad who was 60 at the time could start it easier than any other modern bikes ive owned Firing up the laptop, pretty certain I saved the sales brochure that indicates increased compression, I think. If not it is something that was posted on the vast internet. Quote Link to comment Share on other sites More sharing options...
pmk Posted March 23, 2018 Author Report Share Posted March 23, 2018 The actual brochure I had saved did not want to open easily, but this list is what was changed for the 2006 to 2007 model. I did check the parts books, in 2007 the part number for the head was changed from previous years, while the long ride version retained the previous years same part number. This list was pulled from an internet page stating these were the changes to the long ride, but that seems like the list I had previously mentioned in regards to the SY250 racing. Note the near bottom and it does indicate a change to cylinder head volumes. Possibly, they reduced the compression to work better with the lighter flywheel. I honestly do not know. new handlebars, triple clamps, flywheels, rear fenders, head lights, forks, rear shocks, middle exhaust pipes, silencers, sticker kits, cylinder head volumes, foot rest positions. Quote Link to comment Share on other sites More sharing options...
pmk Posted March 23, 2018 Author Report Share Posted March 23, 2018 new handlebars, triple clamps, flywheels, rear fenders, head lights, forks, rear shocks, middle exhaust pipes, silencers, sticker kits, cylinder head volumes, foot rest positions. Want to add, without much effort, it is apparent there was evolution to these SY250 machines. There were certainly changes in the first years with the forks and triple clamps and possibly frame improvements. The list above for 2007, seems the release of the 2007SY250F four stroke saw some of those items make it onto the two stroke Word was the bars and triple clamps now had multiple mounting options for bar location. Supposedly the 2 stroke got the lighter flywheel countries outside the UK had been getting all along. In 07 the forks swapped from Paioli to Marzocchi. The 2007 SY250R got a straight rate rear spring and I assume valving changes inside the shock. The head was changed and not sure where they repositioned the footpegs, but it says they did. Most other items are paint and graphics changes. Quote Link to comment Share on other sites More sharing options...
nhuskys Posted March 23, 2018 Report Share Posted March 23, 2018 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? Quote Link to comment Share on other sites More sharing options...
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