Wide band 02 sensor

[northeast400]

I know this subjet has been beat to hell but I just talked to a friend with a 400ex. He was running the usual set up: no lid, pipe, and a few other things, well anyway, he ran this set up for years. He went to a dyno shop and wanted to "tune" the quad. well when he made a run with the O2 sensor it said he was lean up top. It took a 185 main jet (stock type) to stay at about a 12:5 air to fuel ratio.? has anyone else tried this?

[Florida400EX]

:eek2: 185!!!!! sounds WAY to high.. my 400ex with pro circuit full pipe and a twin air filter, and no lid, runs a 158 main and a 58 on the pilot.

[cals400ex]

what did the dyno show between the different main jets?

[quadmx7]

man thats sounds really high. my little cousin with hmf pipe has a 175 and when i had my stock carb on my 426 i was using a 180 so 185 sounds a high for a stock 400ex.

[Juggalo]

check the manifold that connects the carb to the head. a lot of times those will rot away and air will get in between the carb and the motor and lean out the motor.

[northeast400]

with a 40 pilot and 2 turns out, needle in stock position, and a 185. It kept it at 12:5 air to fuel ratio. When a smaller main (160) was installed at 5,000 rpm the motor shot to lean til it hit the rev limiter. The ratio at 6350rpm was at 15:1(lean). When the 185 main jet was put in it seem to go real rich at 4,00rpm but then was fine all the way to rev limiter. Then we switched over to dyno jets. Here is the best part, the 185(stock type) readings matched with the same run as when 180 dyno jets were used.

[cals400ex]

how did the horse power compare between the smaller and larger jets?

[northeast400]

about the same. the funny part is that the lid on or off as long as the jetting was right made about the same power

[cals400ex]

Originally posted by northeast400
about the same. the funny part is that the lid on or off as long as the jetting was right made about the same power


i tell people that but many don't believe me. i can tell that when drag racing. i am just as quick with the lid on as i am with the lid off. well of course, i change jetting in both situations. i notice a little more low end power with the lid off or when coming out of a corner on a track. for drag racing, the removed lid does nothing. this is even the case on our 406 motors.