pbear62 Posted August 30, 2017 Report Share Posted August 30, 2017 (edited) Hi guys, I'm just getting my TY250S (#53Y model) head machined (faced & squish band modified) & am getting the barrel rebored to suit a new Pinky piston & have been advised that it's going to need a bit of an increase in jet sizes when I get it all back together. The original TK carb (28mm) has a 110 main jet and a 48 pilot jet which is different to anything I've read about (this bike has been in our family since new & has never had jetting changed) The bike still has the original flat airbox lid with the 'snorkel' fitted which I believe will also need modifying so it can breathe better. Has anyone got any suggestions for a starting point with the re-jetting? Yamaha don't have many different jets available & they're expensive too so I don't want to have to buy too many! Alternately, are Mikuni jets the same size & interchangable with TK jets? Or, should I just replace the whole thing with a Mikuni? I can get a new round slide 28mm Mikuni but I've read that people seem to go for a 26mm? If I decide to go for the Mikuni option, what's the deal with the TK carby screw-on cap - it appears to be attached to the throttle cable & not removable? Thanks in advance for any assistance & suggestions, Andy Edited August 30, 2017 by pbear62 Quote Link to comment Share on other sites More sharing options...
jon v8 Posted August 30, 2017 Report Share Posted August 30, 2017 This is going to sound terrible... Back in the day,(1988) I had a well used Ty250R which ran badly and ate spark plugs.I got so fed up with it that one weekend I attacked the main jet with a mig welder nozzle cleaner,which is essentially a tiny round file.It took 2 or 3 attempts but I gradually opened up the jet until the bike ran perfectly. Good motor once you get them to run right,it was because I was servicing loads of V8 Range Rovers that I didn't complain about the cost of spark plugs it was using.Once I got the fuelling right on the main jet,one V8 plug would last for ages... 1 Quote Link to comment Share on other sites More sharing options...
thai-ty Posted August 31, 2017 Report Share Posted August 31, 2017 John Cane @ Ty Trials has the airbox lids, jets and jetting recommendations. All on his website. Quote Link to comment Share on other sites More sharing options...
pbear62 Posted August 31, 2017 Author Report Share Posted August 31, 2017 (edited) Thanks for the info guys - will have a look on TY Trials & then possibly get some number drills too. Andy Edited August 31, 2017 by pbear62 Quote Link to comment Share on other sites More sharing options...
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