450R carb problem

[sextonjd99]

I installed a 450r carb on my 1999 400ex and I'm having troubles getting it to run right. I've got a full yoshi system and a K&N, 50 pilot, 190 main, 3 clip, 3 turns of air screw.

Ok heres the deal, Easter weekend go riding, 40 degrees or so, ran awesome on the top end but was getting popping and backfiring on decel and was sluggish in low rpms. I pulled the plug and it was white, which i though i means running lean, so i ordered a 52, 55 pilot.

Now last weekend with the same settings as weekend before, it will idle fine but will backfire through the carb if i give it any gas. I checked the plug now and its all black. I did a compression and it read 110psi. I checked the valve clearance. They were off a little but didn't help when changed. I've checked for air leaks with carb cleaner, and didn't find any. I've completely taken carb apart and cleaned and blew out with air.

Anyone have any ideas on what to check next?

[underpowered]

well that jetting sounds real rich for a stock bike.


i would try a 48 pilot, maybe the 50. for teh main, i would try a 175 or so, the 190 is way to big for a stock/ piped bike.

[dariusld]

Did you try messing with the air screw and testing it?

[sextonjd99]

I know the jets are big, but it ran the best with that main and was popping and backfire on decel with the 50. Which means lean, correct?
I've tried all the airscrews setting with the 50 and 52, and all same results. I don't get how it will run decent one weekend and the next it'll barely run at all.

[sextonjd99]

Anyone else have any ideas? I've a 45 and 48 pilot ordered but they won't be in until friday.
If the timing jumped would that cause it to do this?

[sextonjd99]

If my timing has jumped would i still get a good compression test?

[lpmaster]

i would check for intake leaks first.......im running a 48 pilot, 3 turns, 3rd clip, 205 at sea level with a completely worked engine.