sh59 Posted October 21, 2017 Report Share Posted October 21, 2017 Hi Guys I was on here recently with a query regarding ty forks and you were so helpful I am back now with another query. I have stripped down the cylinder on my recently bought TY175 and found the piston head stamped with 68. I am assuming this means it has been rebored to 68mm. If so what other alterations should I be looking for or carrying out to go with the rebore. ie; should the jets be bigger and if so what size and any other alterations? Quote Link to comment Share on other sites More sharing options...
shakennstirred Posted October 22, 2017 Report Share Posted October 22, 2017 You shouldn't need to alter the carb for a rebore unless you're doing a big bore 200-220cc upgrade. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted October 22, 2017 Report Share Posted October 22, 2017 Mine went from 67mm to 72.5mm bore and from memory the only thing I needed to change was to go a half-size richer on the pilot jet (25 to 27.5) Quote Link to comment Share on other sites More sharing options...
sh59 Posted October 22, 2017 Author Report Share Posted October 22, 2017 Thanks guy's I will leave well enough alone then. There is a short flat spot at the begining of a rev and thought it might be related. Quote Link to comment Share on other sites More sharing options...
scifi Posted November 16, 2017 Report Share Posted November 16, 2017 'At the beginning of the revs' would be in the range where the slide cut-away plays an important part. You could try sticking your thumb in the inlet, just before the slide, and seeing if the additional choke-restriction helps remove the flat spot. We had a Honda that hesitated at this throttle opening, and as we couldn't get a slide with less cut-away, we ground 1mm off the engine side of the slide, to lower the cut-away down a bit... it cured the problem, but you do that type of mod at your own peril..! . Quote Link to comment Share on other sites More sharing options...
feetupfun Posted November 17, 2017 Report Share Posted November 17, 2017 On 10/23/2017 at 7:31 AM, sh59 said: Thanks guy's I will leave well enough alone then. There is a short flat spot at the begining of a rev and thought it might be related. How the air screw is set makes a big difference to the off-idle response Quote Link to comment Share on other sites More sharing options...
scifi Posted November 18, 2017 Report Share Posted November 18, 2017 Yes the air screw does make a difference, the books say set for a peak of the revs, but setting a bit further rich may give a better response to a blip of the throttle. Chain-saw manuals always say to set the fast running jet for maximum revs then richen to reduce the revs by about 1000rpm, to ensure the best mixture when under load. . 1 Quote Link to comment Share on other sites More sharing options...
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