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Q: Does anyone remember the pilot jet size that some people change to for better low end riding? .4275 maybe???????
Change the stock Mikuni MK 37.5 pilot jets to MK 42.5's. - Daveg90
IS that one pilot jet per carb? Excuse my ignorance, please. Asked my mechanic about that while he has it down adjusting valves and some other stuff. Said cost would be around $125.00. Does that sound right??
This is from the Vmax site but the carbs are the same except for the jet, needle sizes:
Yup, there is one pilot jet for each carb...I have a set of sizers and reamers from my VW tunning days which is a lot cheaper when you are playing around with jet sizes
http://vmaxoutlaw.com/tech/images/vmaxcarb.jpg
Lots of good info here on the vmax site too:
http://vmaxoutlaw.com/tech/
Ken
Hope you don't mind me jumping in here, but we recently redid the carbs on my V-max (I assume the Venture is very similar) and got some clarification from one of my friends that is a technical expert on the Max...keep in mind this is for an adjustment to Colorado altitude:
What we're going to do is replace the main jets in your float bowls with a 145 Mikuni jet. The stock jetting is a 152.5 which is a bit rich at sea level for a stock bike and WAY rich for a bike at 5000+ feet altitude. This will make the bike run more crisp along with giving it a better top end and better fuel mileage. Shane, you know what I mean by top end after seeing how easily I take my bike to 140+. It never pulled like that when I had the stock jetting in it. There is actually a calculation for determining jetting at altitude. Anyway, that's the story behind the main jet selection. The mains always have to be selected first. Without a good main jet selected, all the other 'circuits' of the carb will never be right. Now the 'pilot fuel jet' is the one that is size 42.5 Stock on a 49 state bike is 37.5 I don't know what a California bike has but I'll bet it's leaner if anything. With the 42.5 you won't have to have the idle mixture screws out so far and you'll also have a better crossover from idle to midrange. All in all, this means no more popping out the carb throats when you gas it from idle. The 'pilot air jet' is part of the same circuit that the we use the 'pilot fuel jet' in. Fuel jets let fuel in and air jets let air in to make a mixture that is fed down the carb throat at idle and slightly above. The 'pilot air jet' and the 'pilot fuel jet' both work together to give a proper mixture at idle and also up through midrange when using small throttle openings. In other words when you are cruising with the throttle held open just a bit. Like when you're going 30, 40, 50, or 60 MPH. It's this jetting arrangement that is too lean from the factory. This helps the factory get past missions testing. It's also the reason that the main is too big. They try and use a larger, too large in fact for best power, main jet to help compensate for a very lean idle mixture. As you can see from the popping that every stock jetted Vmax is plagued with, it's not a very good compromise. This is what we're attempting to fix. Now, this air jet I just mentioned is the same size (not the hole, but the physical size and the threads) as the main jet. That's why I told you guys to get 95 main jets. But Yamaha probably doesn't have a listing for a main of that size. Soooo, what you do is just order a 95 'pilot air jet,' because that is what it really is. You'll see when you get it that it's the EXACT same as your new main jets, just a number 95 and not a 145. The other 'pilot air jet' is called PAJ2,,, meaning 'pilot air jet number 2. It has an effect through the midrange before the jet needle takes over. This also is the same size as a main jet and that's also why I told you to get a 160 main jet. We just won't be using it in the main jet location. In this case, the stock jet (PAJ2) is a 170 and we are going to a 160. When fuel jets get larger, it means you're going richer. When air jets get larger, it means you're going leaner. Because fuel jets let in raw gas and air jets let in air. Basically, more fuel= richer,,, more air= leaner. What we really are dealing with is:
4 main jets in the size of '145' (3G2-14231-29-00)
4 pilot fuel jets in the size of '42.5' (4G0-14142-42-A0)
4 pilot air jets number 1 (PAJ1) in the size of '95' (3G2-14231-19-00)
4 pilot air jets number 2 (PAJ2) in the size of '160'" (3G2-14231-32-
00)
In addition you may also need the jet block gaskets (3JB-14199-00-00) depending on the age of your bike and the condition of your current gaskets.
Shane
Just did mine and it makes a big difference! I bought my pilots at www.sudco.com and they cost under $6 per. Very easy to do if you have any mechanical experience and an adventurous spirit!
I also went to 150 main jets in the rear carbs and 152.5's in the front.
The main difference I found is I don't have the cold-bloodedness, the throttle response is better between 2000 - 4000, and more power at speed (ecspecially while towing a trailer and 2 - up).
Last update: 11:17 PM Tuesday, October 5, 2004
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