400ex issue pls help

[Sparrow89]

ok so recently had a new bore done on my 400ex and i put in a bigger carb. now the only thing is once i get it under load for a minute or so it bogs out and dies even if i pull in the clutch and rev it a bit. but i give it 30 seconds it starts right back up no problem just to repeat the process but its only if i put in under load it idles just fine...jets maybe? if so any ideas what jets i should be running. info as in whats done to it is as follows...
-no airbox lid with K&N filter
-White Brothers E series slip on exhaust
-bored over .05
-39mm Carb

 

[Wifesblaster]

I do not know a lot about 4 strokes. My suggestion would be to put your original carb back on it and see if the problem still exists.

 

[Awk08]

i would say no need for a bigger carb without a bbk or at least head porting/larger valves, cam and full pipe.

your very mild mods could have easily been fed with a main jet jump of a few sizes max.

 

[Devilman910]

Could the piston be installed backward?

 

[Larry's Shee]

Did you do any jetting on this carb? Did you set float height? Does it act like it's flooding out or running out of gas. Describe the conditions it's under as to loading?

Could the piston be installed backward?

Good try. Although I'm sure the piston has markings f<>r, it would make no where near the difference it would on a 2smoke. No windows or ring keeper pins.

 

[E00400X]

Sounds like its running out of fuel....check your float height, and check the fuel line to be sure its not kinked or restricted.

Also, the stock carb is fine for most applications with a simple rejet......you may want to put that back on and jet it up a bit to see how it performs

just to clarify, you say you had a new bore, is it just a cleanup bore, or is it like a 440 kit?

 

[Sparrow89]

i tried jetting up the old carb turned out i was paying close attention and the butterfly wasnt in the stock carb who ever had it before me removed it and the parts to fix arent available....so i just went with a bigger carb i know not nreally needed but comeon im a guy yall know what i mean lol jk...its like its running out of fuel and as for load nothn straining just anywhere between 2 to 5th gear if i dont go WOT it does it but if i stay in first never happens and if i leave first if i stay 3/4 to full throttle it doesnt happen...the bore was just a clean up bore just a .05 over

 

[Sparrow89]

oh and the carb is a Keihin FCR 39mm

 

[Kgibson]

the slide has a plate, make sure the plate is not upside down and that the rubber seal is good. What year carb and has it had the ap mod done to it ? Did u test the valves for leaks before u installed the head?

 

[Sparrow89]

brand new carb valves are good according to the honda shop here