slogger Posted October 4, 2016 Report Share Posted October 4, 2016 Hi all, I have recently had a TY Mono fully rebuilt (engine) but whilst it runs "ok", comparing it to a friends on Sunday who has recently bought one the engine goes appear more flat. Now that I know the engine itself is 100%, I want to explore the front exhaust (the rear has been replaced with a new box) and also the carb, so questions: 1) I have a brand new Mikuni VM26. Has anyone tried one of these and do they have a starting point for jetting (slide, needle etc) 2) Are replacement front exhausts available or is it a "cut it open and weld it up" affair? thanks, any advice appreciated.... Quote Link to comment Share on other sites More sharing options...
baldilocks Posted October 4, 2016 Report Share Posted October 4, 2016 The TY was modified by lots of people back in the day who opened up ports, skimmed cylinder heads and cylinder bases, bored them out to 262 etc etc so you may be comparing apples and pears. Check your bike has the correct piston. Someone did try to sell me a 262 piston and they genuinely didn't realise the gudgeon pin to piston crown distance was different and would therefore lower compression. Fitting a better carb is still a good idea Quote Link to comment Share on other sites More sharing options...
taylo63 Posted October 4, 2016 Report Share Posted October 4, 2016 Hi Slogger I too have an 85 TY mono that had a few running problems. all of which were resolved by :- 1. Replacing the very worn original carb with a Mikuni Vm26 2. Cutting open and cleaning the middle exhaust box... below is a paragraph from my own post in this forum in regard to the middle box. Starting with the backbox ( cos I knew I could get an aftermarket replacement)Using a standard hacksaw I carefully cut off the lip that runs around it...As you do so you can see the two halves of the exhaust, and once you have removed the lip all the way round the backbox simply comes apart and in my case revealed 30 odd years of black oily carbon sludge! In fact It was so bad I 'm surprised it was running at all...and I ended up chucking it away and getting a Sammy Miller replacement. Using the experience gained cutting the back box open, I used the same method to cut open the middle box and this too was completely cacked in black oily sludge..Inside the exhaust there is fibre packing too, so trying to decoke with caustic is NEVER going to work. It took me several hours to clean the crap out and one by one unblock the perforated holes in the baffle with a drill bit. Once it was completely clean I repacked with fresh packing and took it to my local welder who welded it back up for me... The bike now sounds crisper and runs so much better, I also replaced the standard Tekei carb with a Mikuni VM 26 from a Beta Rev3 and now it runs how it should....So in summary if you want to decoke your exhaust the bestway to do it IMO is to cut it open, you'll be surprised just how badly blocked they become... Hope this helps... Quote Link to comment Share on other sites More sharing options...
alta Posted October 4, 2016 Report Share Posted October 4, 2016 Just did my middle box at the weekend. 28 years of gunge, some of which had hardened like glass. Judging by the state of the insides it would almost certainly be worth doing on any old mono Yam. Yet to try it though, just got barrel back from Nigel Birkett after porting, so need to refit that first. Quote Link to comment Share on other sites More sharing options...
twinshocktosser Posted October 4, 2016 Report Share Posted October 4, 2016 Sorry to hijack the thread, but alta what type of price does birkett charge for porting? Thanks Quote Link to comment Share on other sites More sharing options...
alta Posted October 4, 2016 Report Share Posted October 4, 2016 £100 + vat and postage, which I thought was pretty good considering you're paying for not only the physical work but the knowledge of what to do. He went into a fair bit of detail over the phone regarding other improvement mods. Wouldn't give all his secrets away though which is why I got him to do the porting. This is my third mono - recently bought from ebay but the previous two had the benefit of tuning. The first was in 1985, an "S" version that Simon Wigg used in order to keep fit when he was riding Long Track and speedway. Julian had tweaked it and it went well. We never had the motor apart so I don't know what the extent of the porting was. The second was a new Pinky which we took out to 264 or thereabouts with a std IT 250 piston. The inlet tract was shortened and the reeds were altered and the porting was copied from a Shirty barrel but we didn't lighten the flywheel. Too much for me nowadays tho!!! 2 Quote Link to comment Share on other sites More sharing options...
twinshocktosser Posted October 4, 2016 Report Share Posted October 4, 2016 Thanks for that info alta Quote Link to comment Share on other sites More sharing options...
slogger Posted October 6, 2016 Author Report Share Posted October 6, 2016 All, Many thanks for the feedback. The exhaust work definately seems a solid starter. Taylo63, when you have 5 mins is their any chance of whipping your carb off and giving me the full jetting, slide and needle information? thanks again Rob Quote Link to comment Share on other sites More sharing options...
alta Posted October 6, 2016 Report Share Posted October 6, 2016 It's a shame I won't be able to give a definitive answer as to what difference the exhaust re-pack makes - two changes at once, what with the barrel also. Being a test engineer, I should know better! Repacking the middle box on my Bultaco 199 made a sizeable difference and it was nowhere near as choked as the Yam, so I'm hoping for similar. I aim to ride a few trials to see how it pans out before taking a bit off the ignition flywheel. a spare one would be handy though - just in case....... Quote Link to comment Share on other sites More sharing options...
alta Posted October 8, 2016 Report Share Posted October 8, 2016 Bike back together this afternoon {half hour practising in the garden - understanding neighbours!)and it's transformed. Suspect the barrel made the biggest difference but exhaust note is now mellow, motor is so much more responsive off the bottom end and is stronger at top. While the barrel was away I lowered the footrests as low as is practical and this has been a positive step also. Didn't move back, just down. I'd appreciate any info on fork mods and feedback on Hagon or Ohlins shocks. Has anyone replaced the standard rear shock spring with an Ohlins? If so, which one? Cheers. Quote Link to comment Share on other sites More sharing options...
searay175 Posted November 3, 2016 Report Share Posted November 3, 2016 Had a spare exhaust that was in rough shape. I had burned the sludge out last year when doing another one. I opened it up today just to look. The pics show that the packing was pushed to the back but the perforated holes are clean. Quote Link to comment Share on other sites More sharing options...
barfy Posted November 12, 2016 Report Share Posted November 12, 2016 I wonder if anyone has ever thought of replacing the packing from the centre box with baffles so that you could use caustic soda in the future? Quote Link to comment Share on other sites More sharing options...
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