We took my 400 out by the bonneville salt flats to get it topped out. It topped at 58 mph(about 55 at the top of fourth gear). I run a wb pipe with rev box and no airbox cover. DOES ANYONE KNOW WHY IT BOGS IN FIFTH GEAR? (loss of power)

 

Have you adjusted the throttle? Have you jetted it for your mods & altitude? It's jetted lean before changing anything, if you add a pipe and perform airbox mods, it will make things worse.

My stock bike doesn't have a hint of bog in 5th, will pull to the rev-limiter, in fact, with just a little encouragement, will pull 5th gear wheelies.

 

I had it rejetted once but the shop I went to wasn't a dealer and could only up the main and not the pilot due to stock parts. so it still has its 38 in it. They adjusted the needle and now it backfires on deceleration or downhill. It rocks in first and second.

 

Your quad seems to be leaning out. There are other causes of backfires like exhaust system leaks and stale gas. Take your quad to someone who really understsnds tuning.

 

has nothing to do with the pilot, if its running good in fourth but boggs in fifth, your main mite be too fat...remove the air cleaner alltogether and test it again to see if that cures the problem and you'll know how to rejet.

 

I believe barring a other problems, a backfire on deceleration condition is caused by a mixture that is rich. All the old 350X's did this from the factory... Maybe they raised the needle too much. Lack of power can be caused by an overly rich or overly lean condition. This is difficult to diagnose over the internet.

Read the plug... Go out and do a hard acceleration run, preferably make it bog in 5th, pull in the clutch and shut off the ignition. Remove the spark plug. Note the color. Get back with us.....

With that information, you can take it to someone who knows what they are doing (not necessarily the dealer) and talk intelligently with them about what the bike is doing, and what needs to be done....

 

The backfire on deceleration is caused from a lean condition in your idle circuit (pilot). You need to adjust it to make your idle mixture (fuel/air) richer by turning the screw out in 1/2 turn increments (max 4 complete turns out) If at 4 turns out it still does it then move up to the #40 jet. The mixture screw is located in front of the float bowl. Look in the tech connection on the main page and select advanced search, you will find all your answers there - I did.

 

OK... Here's the deal. I did a little research to confirm my findings on backfiring and mixture. I will post a link below to a nice explanation I have found. This goes along with what I have noticed over the years and especially since tuning in my fuel injection system on my Vette from scratch (where I can tune on the fly and see results quickly and easily).

Basically, as far as mixture goes, a lean condition will cause backfire on acceleration (this is very bad and should be corrected immediately). A rich condition will cause backfire on deceleration (will not really cause much harm).

http://x42.deja.com/getdoc.xp?AN=359...91335&hitnum=4

 

I live in SLC also and have run on the salt flats
also. My 426ex pulled better in fourth gear and would hit the CT revlimiter but in fifth gear the resistance of the salt is a little much to overcome. I was running a 16 tooth front sprocket W/22 in tall tires and and was keeping up with traffic on I 80 in fifth gear (75+) but it reached a spot and would not accelerate any farther. On the pavement this problem was gone. My neighbors 426ex also had the same problem. The salt has alot of resistance. as far as your backfire problem try going up 1 pilot jet size dont overdo it because 400ex carbs like to flood out when cold up here. Contact of me if you need some tech help.

http://www.trxoutlawz.com/


99 400ex, Bored to 426 with 11-1 Weisco piston. WebCam 450-451, ported, polished, Keihn 39mm FCR,
DMC exhaust, K&N, Modified Airbox.
Beats ds650's up sandmountain!!!!!!!!!!!!!