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scubaru

Rejetting for a bike that used to run race fuel

7 posts in this topic

hi all, first of all thanks to those members who helped me narrow my problem down to a jetting issue. Had a mishap while testing the bike the other day and am now stuck in bed with a broken collar bone and bruised/torn rib cartilages : :excuseme: : . My issue with the bike is you can't rev the bike at any position of the throttle in neutral at a constant speed without it popping and there is a fair bit of decel popping when engine braking. Other than that it starts great and pulls extremely hard Thu the gears without any hesitation at all. Did a search on jet sizes but was starting to get confused with some of the opinions so will ask for some advice with the bikes specific details.First of all the bike is an x supermotard bike so it was probably jetted for race fuel and now I am/will be using 98 Ron unleaded. It has a GYTR titanium exhaust , head and cam mods and was dynoed by previous owner at 58 hp at wheels. Whilst I had the carby apart for cleaning I checked the jetting sizes - Starter jet -72

Pilot jet- 42

Main jet-180

Needle- 3rd slot from top

When changing the spark plug it looked to be running lean and the altitude the bike is being ridden at is approximately 300m/400m (900ft/1200ft) .I have tried adjusting the air/fuel screw out to about 4 turns out with only very minor success. Any ideas on jetting sizes would be appreciated or should I just ignore the popping altogether as it pulls extremely hard as it is. cheers and thanks

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A "little" popping is fine, a relatively constant popping when decelerating, is not..and shows a lean condition. I wish I could help you further, but with the bike being set-up for SuperMotard, I would be guessing as far as jetting goes.

I would definately post this in the "Jetting" section, and ask for TT member "burned" to help you.

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Thanks flintlock28, I will copy and paste it in the Jetting forum. Was just there reading some old posts actually. Seems the pilot jet may be a tad small, but will post it there and hopefully burned might see it and respond. Thanks

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You need to jet the bike back to the stock settings - see you manual

then tweek as needed - :excuseme:

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I would have guessed the main to be around a 170 for sea level and 168 up to about 3000'. Race gas will definitely need a bigger main due to being oxygenated. Otherwise the starter and pilot sound about right as does the needle setting.

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I was always told to lean your motor for race fuel. ohhh so many opinions!!! I run much leaner jets on my snowmobile than I would if I ran pump gas but that is a 15:1 two stroke running full 114 race fuel.

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thanks for the advice, love this forum. Forgot to mention that the carby has been machined a couple of mm bigger. Burned seems to think that the main jet seems about right so I will just play with the pilot (a 45 or 48) and try lifting the needle up 1 notch. cheers

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