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Hi all,
Since the day I got my bike 2 and a half years ago I simply had the urge to fiddle with my bike and have tried many &sometimes extremely stupid things like fitting an HPI filter reversed in the filter cap of the airbox to avoid removing/cutting it.Recently I again got the urge to fiddle and this time my target area was the carburettor.I did read a lot about the madness of performance levels achieved on replacing CV carbs with flat-slide and D-slide carbs.Now those carbs cost upwards of 20 grand(including throttle cable,intake flange and jets).Being a student I obviously cannot get my hands on them right now so I did some more research and was overjoyed to find that VM carbs from the older bikes also have a similar flow control mechanism in comparision with the flat-slide and D-slide carbs.So I got myself a similar carb for my RTR180.The RTR 180 has a Mikuni bs-29 carb and the nearest size on the readily available VM carb is of the Bullet standard 500 which has a vm28.Using up savings from two months pocket money I got a new carb for Rs.1500 from a local store and I installed it on my bike directly by filing the stopper on the end of the throttle-cable to a size small enough to pass through the top-cap of the carb.Now obviously the carb was jetted for a 500 and here I was trying to run it on a 180 without re-jetting it.The results were highly amusing with lots of misfires and spluttering.I did end up damaging a new spark plug due to the overly rich mixture.So next thing I did was consult a bulleteer from Indie thumpers who is quite a good tuner and has set-up several bikes for races (Including an apache).He did seem highly amused by my fiddling but was courteous and suggested that I try different set-ups by downsizing the main and pilot-jets.I tried the following jets
Pilot:25,22.5,21,20(Stock jet from the bs29)
Main:125(Stock from BS29).115,110,100,95,90
But all of them ran the bike rich I had also installed the needle in the lowest possible configuration which only gave a minor nudge to the A.F ratio in the right direction.I got impatient and consulted him again.He told me that the smaller diameter of the carb was probably the culprit.I did not want to give up so easily and got the carb overbored by 1mm at a local lathe.Then I installed the carb again.The fuelling was closer to ideal this time(Main jet 125& pilot jet 20) but a new problem has emerged,after the engine has run for some time it begins to auto-accelerate.I suspected a leak in the intake manifold but did not find any upon inspection. I then took off the filter and saw the plunger-cum-throttle piston lift automatically due to the flow of air.I am now considering a stiffer throttle spring but would also like to hear from you all as to what else to try to get the set-up right.
Thanks in advance
Since the day I got my bike 2 and a half years ago I simply had the urge to fiddle with my bike and have tried many &sometimes extremely stupid things like fitting an HPI filter reversed in the filter cap of the airbox to avoid removing/cutting it.Recently I again got the urge to fiddle and this time my target area was the carburettor.I did read a lot about the madness of performance levels achieved on replacing CV carbs with flat-slide and D-slide carbs.Now those carbs cost upwards of 20 grand(including throttle cable,intake flange and jets).Being a student I obviously cannot get my hands on them right now so I did some more research and was overjoyed to find that VM carbs from the older bikes also have a similar flow control mechanism in comparision with the flat-slide and D-slide carbs.So I got myself a similar carb for my RTR180.The RTR 180 has a Mikuni bs-29 carb and the nearest size on the readily available VM carb is of the Bullet standard 500 which has a vm28.Using up savings from two months pocket money I got a new carb for Rs.1500 from a local store and I installed it on my bike directly by filing the stopper on the end of the throttle-cable to a size small enough to pass through the top-cap of the carb.Now obviously the carb was jetted for a 500 and here I was trying to run it on a 180 without re-jetting it.The results were highly amusing with lots of misfires and spluttering.I did end up damaging a new spark plug due to the overly rich mixture.So next thing I did was consult a bulleteer from Indie thumpers who is quite a good tuner and has set-up several bikes for races (Including an apache).He did seem highly amused by my fiddling but was courteous and suggested that I try different set-ups by downsizing the main and pilot-jets.I tried the following jets
Pilot:25,22.5,21,20(Stock jet from the bs29)
Main:125(Stock from BS29).115,110,100,95,90
But all of them ran the bike rich I had also installed the needle in the lowest possible configuration which only gave a minor nudge to the A.F ratio in the right direction.I got impatient and consulted him again.He told me that the smaller diameter of the carb was probably the culprit.I did not want to give up so easily and got the carb overbored by 1mm at a local lathe.Then I installed the carb again.The fuelling was closer to ideal this time(Main jet 125& pilot jet 20) but a new problem has emerged,after the engine has run for some time it begins to auto-accelerate.I suspected a leak in the intake manifold but did not find any upon inspection. I then took off the filter and saw the plunger-cum-throttle piston lift automatically due to the flow of air.I am now considering a stiffer throttle spring but would also like to hear from you all as to what else to try to get the set-up right.
Thanks in advance
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