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Old 08-04-2002, 08:35 PM   #1 (permalink)
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What Size Main Jet?

I have a 02 FatBoy with Vance & Hines Bigshots, Arlen Ness Big Sucker Air Cleaner kit and the Dyno Jet Thunderslide kit. I currently have the 185 main jet in as requested by the Dyno Jet instructions, the plugs have a lean color but it runs good I was wondering what every one else is running for a main jet I am thinking of trying one size richer to get some plug color.
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Old 08-04-2002, 10:54 PM   #2 (permalink)
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If it runs fine don't worry about it. A stock bike, or stage 1 if you want, with the Dynojet needle is likely a bit rich on top with a 185.
With the fuel we have these days reading plugs is next to impossible, by the time they show any color they are too rich. The pipes are likely black inside, no?
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Old 08-05-2002, 07:22 AM   #3 (permalink)
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What Jet Size?

Yes the pipes are black on the inside, I just want to be sure it's running the best it can. The plugs will not color even after 3000 miles? how do you tell if the jetting is correct? just by the way it runs.
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Old 08-05-2002, 10:46 AM   #4 (permalink)
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Pretty much other then experience, a infrared gas analyzer or a sniffer dyno. If the needle clip is in the middle groove you could go down in main jet sizes one at the time until you feel a lean symphtom and then go back one size.
Typically you would end up with a 175 main at sea level, but it can change a bit from bike to bike. You are probably pretty close as it is and these bikes are very tolerant to running rich.
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Old 08-07-2002, 07:44 PM   #5 (permalink)
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hi i have similar setup as you do. i have the thunderslide, k&n s+s style breather kit, and vance and hines bigshots long. i also rejetted to 185 as per the directions. i too thought it looked a little lean with new plugs. so because it aint nothing to change jets i went up to the 195 to see how it ran. i put new plugs in and away i went. it ran good up to 75 then it lost power on top end and popped and farted and wouldnt go any faster. so i pulled the plugs and although the tip looked like it did when i put it in new the top few threads were jet black and sooty along with the face of the plug. so i knew i was rich. i put the 185 back in and it runs like a champ. after running the bike awhile the plugs have taken on a near perfect color. the inside of my pipes are just ever so slightly silty. while we are talkin jettin, when is it ever necessary to change the slow jet? what mods would warrant changin it? would i gain anything by goin bigger on the slow jet? my bike runs great and pulls good all the way to top speed, although with my big ass and windshield and saddlebags on my evolution heritage softail tops out about 90ish. there might be an ever ever so slight hesitation if i let completely off the throttle, then roll it on right at the inital point of givin it gas a little pop if you will. would a .45 slow jet help? sorry so long, any help would be appreciated.
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Old 08-09-2002, 10:24 PM   #6 (permalink)
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To "read" spark plugs, you must look way down on the inside/bottom of the plugs. Thats where you look for the brownish color. The new designed cylinder heads are so efficient that they rarely leave any color at all (clean) on the easily visible part of the plug unless your jetting is way off. On the new motors, if its lean, it will ping. I've found the thunderslide directions to be slightly rich, which is probably a legal safegaurd against engine damage . I also dont like to use the bigger accelerator pump nozzle. The stock squirter is more than adequate on a properly tuned cycle.
As for the low speed jet, I almost always step up one size on them. If your bike "pops" when cold or is cold natured, than you need a bigger low speed. However I have heard something to the affect that the new models (02) are too rich and the dealers have been leaning the low speed out. (EPA reasons?) If you change the pipes or the air cleaner, the bigger jet should dial the bike right in.
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Old 08-10-2002, 07:46 AM   #7 (permalink)
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i changed the low speed jet and the bike runs great now
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Old 08-10-2002, 08:30 AM   #8 (permalink)
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Jet Size

Where do you get the low speed ? is it a Harley part or Dynojet part. When you say low speed that is the same as Slow jet correct? what is the exact size you put in? and is it richer or leaner? I talked to the guys at Dynojet the other day and they said a good running street bike will have white plugs, I came from the 2 stroke world and we jet by plug color, have either of you guys tried any race gas?
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Old 08-10-2002, 08:33 AM   #9 (permalink)
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oops

I forgot one....the accelerator pump nozzle is that the emulsion tube? You guys are probally sorry you answered my post lolol I have a lot of questions
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Old 08-10-2002, 04:10 PM   #10 (permalink)
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the slow jet (low speed) i had to buy at my dealership because it didnt come in my thunderslide kit although dynojet suggested a .45 if need be, depending on how free-flowing you exhaust is. i have the bigshots and they are 2 1/2" so i would say they are free flowing alright! it was under 3 bucks. i went from a .42 stock to a .45 now. they come in sizes .42, .44, .45 and so on. it skips over .43 (according to the dealership books. i suppose my bike runs richer now. it took care of a cold blooded condition i was having and it gave me my low end torque. the bike used to occasionaly spit through the carb and it would bobble if i let the throttle off and then back into. of course i am nitpicking but the bike runs like a champ now. if i remember correctly the emulsion tube is the tube the main jet screws into. i would have to look at my dynojet kit instructions again lol!
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