Hi all, recently I came across a 1984 Yamaha SRX250 51Y at a good price. It still ran and started with a bit of coaxing and was in overall fair condition for its age. Had good chain and sprockets and tyres, although both are oversize, the back one actually rubbed a hole in the guard witch I have since repaired. I pulled it apart and repainted the frame and motor and tidied up a few broken and cracked bits and put it back together again and took it for a ride. It was hard to start and had trouble idling. When I pulled the carb apart it did not seem to be excessively dirty but I did find the air bypass screw was out over 9 turns, a tad too far. I also note it does not start with the choke at all so some further investigation (and cleaning) required there. The motor ran ok but a tad noisy and seemed to go quite well but a compression check revealed only 95lbs, and after squirting oil down the plug hole, only went up to 100lbs, so some problems there. I have not yet decided the direction or function of this beastie but at the moment it is staying stock, a blight with some dints and scars. This was my first sighting of Rex. (Yes, I name all my bikes )
I think part of your low comp etc it may be caused by tight valve clearance's like @Andych mentioned in your other post And the intake manifold's might be leaking causing a lean mixture, that's why your mixture screw's are turned out so many turn's. The frame look's good what colour is it ?
Just read the rest of your post, sorry New intake manifolds and new o rings and made sure face of intake clean and flat, it did have dodgy intake manifolds when I got it so yes, that probably explains the number of turns out, but all fixed now. Will soon have the answer when I pull it apart. The frame is just silver out of a can. I just wanted to tidy it up until I decide what to do with it. Will see where this journey leads us
Got a chance to open it up today, news not great, looks like its been seized before, also looks like it has a second oversize piston in it already and some scores in the bore, so looks like I will be looking for a 1mm over piston for it cam chain tensioner looks good, chain but is a bit sad. On a good note, big end seems to be fine
I do happen to have a Standard size Barrel and a first oversize piston and rings... Barrel comes with original piston and in good condition... Megazip etc dont show any Oversize pistons for the SRX but..... there are listings for the XT250 (1986) which is basically the same engine only no electric starter. Part numbers are 30X-11638-01-00 4th oversize Piston (1mm) 30X-11610-40-00 Ring set to suit Pricing runs out at around $160 US plus another $20US for freight. You might get luck and find a set as NOS with a Yamaha dealer but I wouldnt hold my breath. For Gasket sets you can source from 1984 (Japan only), 1985, 1986, 1987 XT250. Just make sure it is the Twin cam model. You would also need the Stator cover gasket (different due to the Starter motor) which is available on eBay https://www.ebay.com.au/itm/Yamaha-...m2371ecf4ec:g:MS8AAOSwXeJXelTP&frcectupt=true