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Old 01-23-2013, 09:26 AM   #1595
Gnarly Adventurer
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Joined: Jun 2006
Location: Boone, IA
Oddometer: 334
The general consensus on the Yahoo W650 group is that the main jet is already too RICH. I believe stock is about 118 and the ideal for stock air box and exhaust was found to be 112 by several who have dyno run and checked AFR with a sniffer. The overly rich main makes up for the non-ideal needles.

The needles are not tapered enough, this is an emissions thing. It allows really lean running in the operation range where the emissions are evaluated (low to mid throttle), then the overly RICH main jets help protect the engine at high load/rpm. Ideally, you should buy a jet kit with needles that have a more aggressive taper so that a 112 main can be ran, this will give a more consistent AFR throughout the operating range. The Factory Pro jet kits have the necessary needles.

The idle jets seemed like there was no consensus. Either run the stock and back the idle screws out to 3.5-4 turns (or there abouts) or go one size bigger and turn the screws in. I read opinions that going to the 38 idle jets caused increased consumption, and it was better to keep the stock 35's with backed out screws. If you don't care about increased consumption, go with the 38's to get a quick warm up.

This is all information I am regurgitating and paraphrasing from the Yahoo W650 group. I can't link the exact posts, but if you join and do a message search for "Jet Kit" or "Factory Pro" I think you will find the information.
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