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 xr 400 jetting
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lawverdict

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3 Posts

Topic started on 02/02/2006 at 1:03:10 PM  Member Profile  Reply with Quote
My 98 xr 400 with modified airbox, uni filter, 97 spark arrestor (no baffle),65/165 jets, honda racing needle, ran poorly and was a constant hard start-hot or cold.
Recently, I took the carb apart, removed the 65 slow jet and drilled it out with a 1/16 drill (I used to use wire size bits on my Holley jets when I was broke.) Expected a hard start, but started first kick. This was the first time the bike ever started on first kick!
The bike ran incredibly even when cold. No bog, hesitation or popping. Instantaneous throttle response right up to mid range, then seemed to lean out. When rapidly opening the throttle from idle, the tailpipe did emit a puff of black smoke, and when I pulled the plug it was black, indicating a full rich condition; however, when riding the bike, the throttle response was incredible-easy third gear wheelies on the street, which I couldn't do before.
Purchased a size 70 slow jet which provides good throttle response, no black puff of smoke, but produces a slight miss when the throttle is rapidly opened. Produced 3rd gear wheelies. Will try a size 75.

GlennF
Newbury, OH

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USA
502 Posts

Posted on 02/02/2006 at 1:34:11 PM  Member Profile  Visit GlennF's Homepage  Reply with Quote
That is a rich jetting combo. #60 & #160 or #62 & #62 would be optimum with your mods. Too rich jetting is better than too lean. I would try the above mentioned jets and play with idle speed and fuel screw for starting ease.

05 XT225 - Dunlop 606 front, Kenda 760 rear, Promoto Billet rack, fuel screw 3 turns out, 130 main, 42.5 pilot, Z1 exhaust mod, 1/2 snorkel, UNI filter, Bill's footpegs.

ThumperTDC
Thumpalicious

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USA
6553 Posts

Posted on 02/03/2006 at 08:14:03 AM  Member Profile  Visit ThumperTDC's Homepage  Send ThumperTDC an AOL message  Reply with Quote
I ride at about sea level to 3500 feet. When I had my stock carb on I was runing 58 and 155 for my jetting with tons of engine mods. It was dialed in perfect, started first or second kick, no hesitation.

To me those jets seem way too rich.

2005 KTM 525MXC - The new canvas
1998 Honda XR450 - The master piece

In loving memory of my son Nicolas "Cole" Allen Carter 10/5/05

lawverdict

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3 Posts

Posted on 02/03/2006 at 1:41:54 PM  Member Profile  Reply with Quote
I agree that on paper the jetting appears way too rich, but I have tried the 65/165 combo and the spark plug indicated a lean condition. I am going to perform several tests with new spark plugs to determine whether the new jetting is too rich.
I ride sea level to 6000' in southern california, sometimes higher in the sierras.

lawverdict

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Posted on 02/13/2006 at 11:17:45 AM  Member Profile  Reply with Quote
On Saturday I rode approximately 4 hours with the 70 slow jet, 165 main jet. Altitude ranged from 4000 through 6500 feet, some fire roads and a lot of rocky, sandy and hardpack climbing (1st and 2nd gear.) At low rpm the bike pulled unbelieveably-compared to my previous jetting. A friend was following all day and he did not see any black smoke. I put in a new plug before riding, so I will pull the plug and provide a further report.
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