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shorty87

Fuel Mixture Screw Problem

17 posts in this topic

'05 WR450 All Mods: Can't seem to get fuel screw adjusted properly. I have tried the 42-45, 48 pilot jets. I start out at 1.5 turns. I turn it out more and idle drops. When I turn it in, the idle comes up. When it's turned in all of the way, it still runs. I'm new at this but I thought these were supposed to die when in all the way. I have changed my stock fuel screw to the zip tie and made sure o-ring is in place and no noticable difference. Any help would be appreciated.

Shorty87 :banghead:

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ive had similar problems with my 400, unless its my untrained ear, i can have mine out or all the way in, and cant really 'hear' much difference, runs fine, i wish i could tune it properly

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Did you change the needle yet? The 05 has no adjustment, only one setting. Going to a stock 04 needle which you can adjust will give you more fine tuning. Oh yeah you will have to pull the tank off, but you can twist the carb to get the carb top off to change needles. Jetting this bike is a pain!

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this may not be much of a consolation, but when I turn my mixture screw on an XR 400 it also make little difference

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On my '05 I have had the same issue. For the longest time, I thought the fuel screw was little more than snake oil, as it would do nothing unless I turned it almost all the way out. After doing a lot of carb experimentation, I found that you need to have all the circuits in the proper range, i.e. pilot, main, starter, leak and needle clip. Also, you need to have your idle set properly and the bike needs to be warmed up completely. I have my idle set at 1900 +/- 100, and I need to have been riding hard for a good 20 minutes. I know this sounds extreme, but after that, I can get the fuel screw to behave properly.

The best advice I can give you is to follow Indy450's jetting chart to the letter and make small adjustments from there. At most, you'll change the settings by one level, either larger/smaller or up/down. If the various circuits overlap, you'll continue to have issues with the fuel screw. I think the reason the '05 screw came blocked off was because most people won't take the time to jet the bike to this kind of perfection wherein the fuel screw will be needed to fine tune things. Furthermore, I think the '05, with it's minor retooling, may be less effected by such a small adjustment. It took me about 5 months of tinkering to get to the point where my fuel screw has a noticeable impact on performance, but now that it does, I'm able to adjust to changing temps and elevations throughout the day, keeping the bike running at the highest level possible. This is what I've found works for me, so take it for what it's worth. Best of luck...SC

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if i suspect i am rich on the main, should i adjust the needle first (JD blue) or change the main jet?

ie to become leaner, should i either drop to a 170 from 175, or raise the clip?

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Here you go. I suggest you cut, copy & paste it to a word processing program. I have a copy in plastic I keep with my shop manual...SC

Elevation 0 to 4,000 feet

30 to 45 degrees: 172 main, JD Blue #5, 48 Pilot, 2.0 turns, 75 starter jet, #0 leak jet

45 to 60 degrees: 170 main, JD Blue #4, 48 Pilot, 1.75 turns, 72 starter jet, #0 leak jet

60 to 75 degrees: 168 main, JD Blue #3 or JD Red #5, 48 Pilot, 1.5 turns, 70 starter jet, #40 leak jet

75 to 90 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 68 starter jet, #50 leak jet

90 degrees plus: 160 main, JD Red #4, 45 Pilot, 2.0 turns, 65 starter jet, #60 leak jet

Elevation 4,000 to 8,000 feet:

30 to 45 degrees: 170 main, JD Blue #4, 48 Pilot, 1.75 turns, 72 starter jet, #0 leak jet

45 to 60 degrees: 168 main, JD Blue #3, 48 Pilot, 1.5 turns, 70 starter jet, #40 leak jet

60 to 75 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 68 starter jet, #40 leak jet

75 to 90 degrees: 165 main, JD Red #5, 45 Pilot, 2.0 turns, 65 starter jet, #50 leak jet

90 degrees plus: 160 main, JD Red #4, 45 Pilot, 1.75 turns, 65 starter jet, #60 leak jet

Elevation 8,000 to 11,000 feet: (Note: you will loose a lot of power due to altitude but your bike will idle and not foul plugs!)

45 to 60 degrees: 165 main, JD Red #5, 48 Pilot, 1.25 turns, 70 starter jet, #40 leak jet

60 to 75 degrees: 160 main, JD Red #4 , 45 Pilot, 1.75 turns, 68 starter jet, #50 leak jet

75 to 90 degrees: 158 main, JD Red #3, 45 Pilot, 1.5 turns, 65 starter jet, #60 leak jet

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Am I wrong in thinking that the fuel screw only effects 0-1/8 throttle position? I just did mine in an attempt to stop the crazy backfiring when you let off the gas,, worked great, no more backfiring... If your bike is not running good at mid + throttle the fuel screw will not do anything... Right or wrong?

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this dosnt apply to the older fcr does it?

My question exactly. Do Indy's recommendations apply to the entire line up of WR's (400 thru 450). I notice the JD jet kit is common to the entire line up.

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Hey, thanks for all the information. I have the JD kit. I've been running the blue in the third position. It just doesn't seem to matter what pilots or mains I put in there it just doesn't seem to change much. Thought I'd start over from scratch and use Racing fuel instead of pump gas. It pings with pump gas. All my friends say to stop messing with it and just ride it. I'm new to these FCR carbs but I've been around bikes for a long time so I just haven't had good luck with the jetting on this. But I'll try indys chart and go from there except for the 40 leak jet. I ran it before and it just made the bike bog on low end. Thanks for everything

-shorty87

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Shorty87, make sure you haven't got the idle speed screw wound up and have lifted the slide up too far. For the pilot circuit to work properly you need to have the slide closed almost completely so most of the fuel is comming from the pilot jet, air is from the cutout in the slide and it not relying on the needle jet for fuel. I made that mistake which was also resulting in the idle hanging up high and slowly dropping down. I also agree with Clark4131, you need to ride the bike to get it to the correct temperature for adjusting just right. Once you get it right it should rev up without hesitation when you quickly blip the throttle and drop straight down to idle.

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Do Indy's recommendations apply to the entire line up of WR's (400 thru 450)?

No. Indy's chart only applies to the '03's and up...SC

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Dodjy, I think you're right. I was messing around with it and I noticed my header pipe getting hot right after I started it. I turned the idle down and it went away, like it cooled off. Now it's like it's running too rich. I'm going to check the valves to make sure they're still in tolerance and go through and clean the carb. It seems like the bike is missing.

Thanks,

-shorty87

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