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Discussion Starter #1
I just bought an 03 400ex and it doesn't want to start i have to pull it behind my truck for 5 minutes to make it run. when it finally starts up the exhaust pipes start glowing. it has a slight backfire out of the carb too. what could be causing this.

it has a curtis sparks exhaust and 165 jet. I have no idea if thats the right jetting for this bike. Its how I bought it. and it was sitting for a while so the carb might be a little clogged I really have no idea. Any help is greatly appreciated.
 

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I am not sure about the jetting you need. It sounds as if you are running lean. Clean the carb! Somebody will come along and may be able to give you some more ideas. Check your valves as well!!
 

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Discussion Starter #4
if I take the carb off to clean it i will change the jet and i'm curious what the proper jet would be for this setup. personally I thought 165 would have been too big
 

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I would try cleaning the carb and air filter and check the exhaust to make sure it dosnt have any blockage. Give the carb a good cleaning. remove all parts making sure all the jets are clear of any blockage. If you go back to stock jets you will need to put the factory exhaust back on and air filter.
 

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no u dont want to go back to stock jetting u alwas want to rejet when u get a pipe
 

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Clean the carb, change your gas, and clean your air filter. don't start changing jets yet.
 

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Agreed if anything you may be too lean to much air not enough fuel will cause you head pipe to get really hot... after you get everything clean in the carb run it if it still acts up
try this... This is directly from DynoJEt:
1. Remove the airbox lid.
2. Remove top carb plate. Remove the slide lift arm screw and the two
needle plate screws. Flip the linkage forward and remove the slide
(Fig. A).
3. Install Dynojet needle on groove# 3 for applications below 5000 feet,
groove #2 for above 5000 feet, using all stock spacers. Install the Dynojet
washer above the E-clip.
4. Remove stock main jet. Replace with the Dynojet Main Jet Adapter
(DJA001). Screw the Dynojet main jet provided into the Main Jet Adapter.
If you are running the stock exhaust use the DJ165 below 3000 feet,
DJ160 from 3000 to 6000 feet and DJ155 above 6000 feet. If you are
running an aftermarket exhaust, use the DJ170 below 3000 feet, DJ165
from 3000 to 6000 feet and DJ160 above 6000 feet. Be sure that the jet
you are changing is the main jet.
5.Locate the Fuel Mixture Screw (Fig.B). For 2005 models ONLY use the
tool provided (DT008) to adjust the mixture screw. For 1999-2004
models, use a flat blade screwdriver. Turn the mixture screw clockwise
until it seats, then turn out 3.5 turns below 5000 feet or 3 above 5000 feet.

Good luck
 

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just bought a 02 400ex same problem was poping through carb header glowing it was running lean i turned fuel screw out fixed it running good now
 
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