August 30, 20178 yr 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, 20178 yr by pbear62
August 30, 20178 yr 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...
August 31, 20178 yr John Cane @ Ty Trials has the airbox lids, jets and jetting recommendations. All on his website.
August 31, 20178 yr Author Thanks for the info guys - will have a look on TY Trials & then possibly get some number drills too. Andy Edited August 31, 20178 yr by pbear62
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