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General Category >> Rubber Side Down! >> Overlap between pilot jets (plus general jetting)
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Message started by Alex Wheatley on 05/02/17 at 06:51:44

Title: Overlap between pilot jets (plus general jetting)
Post by Alex Wheatley on 05/02/17 at 06:51:44

Hi guys,

Turns out - wholly unsurprisingly - that the North Carolina springtime isn't fun for carburetors, given that the temperature will quite happily change by 30-40F day-to-day. What this seems to have meant most obviously so far is that sometimes I want to roll my idle mix out more than three turns to avoid leanness (obviously I don't, I keep it around 2.75, but it wants more), but later in the same day it needs to roll back a little to not be rich.

This is with the stock pilot jet on my 2012, which I assume is a 52.5.

The question, then, is whether a 55 pilot might be more flexible and allow me to get rich enough on colder days (which it will), but without necessarily running crazy rich when it's 95F outside. This really depends on how much overlap the idle mix screw gives you between jet sizes...

So, before I go and spend a bunch of time messing around with it, does anyone have any insight?

More generally, any word from others who live near here and deal with the same schizophrenic spring/summer as to what setups you use would be greatly appreciated.

Title: Re: Overlap between pilot jets (plus general jetti
Post by Dave on 05/02/17 at 07:20:51

I don't know what you setup is (air cleaner, muffler, engine mods) - but you shouldn't have to change you mixture setting from day to day with temperature/humidity changes.....and if opening up the fuel mixture screw beyond 3 turns does nothing....as the tapered part of the needle is out so far at 3 turns that it no longer provide any change in the fuel flow. Your idle fuel screw should only have to be opened 1.5 - 2 turns.....or you either need a larger pilot jet.....or your existing pilot circuit has some debris clogging the small opening in the jet.

What are the symptoms the carb is giving you? Have you done any changes to the carb....like the white spacer mod?

I can ride my bike at 23 degrees.....or 100 degrees in both the Savage and my Ninja 250 and not have to fiddle with the idle mixture screw - you really should be able to set it and forget it.

If you have a stock air filter (either paper or K&N), you shouldn't need to go to a #55 pilot jet.

Title: Re: Overlap between pilot jets (plus general jetti
Post by justin_o_guy2 on 05/02/17 at 07:39:19

Anyone who understands the hows and whys of car b ration well enough to ask that question is able to solve the problem.

Asking questions about which jets to try without details about intake and exhaust makes it tough on the carb guys. They are usually kinda anal about elevation, too. I'd be surprised if Durham is not pretty close to sea level, for jetting purposes. It's Humid, so , were I you, I'd jet for the average temperatures and humidity levels you're gonna get During the time of year you'll be riding. Durham averages humidity above 80, and generally survivable temperatures.

http://www.usclimatedata.com/climate/durham/north-carolina/united-states/usnc0192

https://www.currentresults.com/Weather/North-Carolina/humidity-annual.php

Remember to adjust the idle down to adjust the idle air.

Title: Re: Overlap between pilot jets (plus general jetti
Post by Gary_in_NJ on 05/02/17 at 08:29:30

I'll add my $0.02. I don't spend a lot of time on the Pilot circuit. When the engine provides a steady idle and I have a smooth transition to the needle, I'm done. The pilot circuit is fairly forgiving of usual atmospheric changes. Once the engine warms up or gets to normal operating temp it sorts itself out. I have my idle set at 1,400 rpm - the ambient conditions only dictate how long it will take to settle into it's set idle speed.

Title: Re: Overlap between pilot jets (plus general jetti
Post by Alex Wheatley on 05/03/17 at 06:43:02

Thanks to your comments, I realize I've been silly, of course.

I'd been noticing, as the temperature rose the last few weeks, that the bike had been idling rich, and got less powerful. I'd attributed that to warmer air meaning richer condition, when actually it had been tuned rich all along, but that only becomes apparent when the engine is properly warmed up. My commute is only 2.4 miles, and most of my day-to-day riding is less than 4 miles per trip, so...

Warmer weather = more long rides for fun = more rides where the engine gets properly hot = more often noticing a rich idle.

I guess it can't have warmed up properly last time I spent more than 30 seconds on the circuit. I fiddled with it again right after a long ride, and it was happiest at a little over 2 turns out.

Anyway, thanks for the comments and sorry for what turns out to have been a bit of a time-waster...