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Old 10-14-2012, 01:59 AM   #7
ejute OP
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Joined: Jul 2010
Location: Canberra Sunny OZ
Oddometer: 13
Originally Posted by 983Bob View Post
Hi Obi. I have vm 36 s on my 76 900 which is stock except for the carbs. The main jet works out to 210,[I wouldn't go higher than 220] 2.5 slide, Q-0 needle jet stock needle in the middle position and 22.5 idle jets with the mixture screws at about 1.25 out. This motor is very similar to yours and starts and idles as well as the Bings with gas mileage being about 2-3 % less. My Rs 77 which is done to the hilt with Tm38s much head work and Staintune 40mm mufflers uses 220 mains 6fj40 needles and 17.5 idle jets. It seems that unless you have a full race motor with lots of cam and a racing exhaust, you don't want to go too rich. I took the 36s off my racer and for the street, dropped several sizes on mains needle jets and idle jets to the specs above. It sounds like you are fairly close with what you have, so if the problem can't be solved with jetting, check to make sure that your air tube to carb adaptors aren't causing a shrouding problem somewhere. You can check this by going for a short ride without the tubes or air filter hooked up and see if that improves things. Also bear in mind that slide carbs won't respond to large throttle openings at low revs as well as the bings. When I nail it, I like at least 4-4500 on the clock.
Hope this helps
Bob thanks for the reply,
I think your R90 would have smaller valves than my 82 R100 which has the “large valve heads” so I’m to believe, the spigots on my heads are approx.52mm. This may? account for some differences between the jetting.
I did run the carbs without any air filtration fitted and it made no perceptible difference.
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