300EX is running too lean

[LdiBiTi300EX]

Hi guys

My friends bought a 00 300ex. But the engine always backfire. The engine run too lean but this quad is all stock :confused:
We checked the spark plug( DR8ES-L the good one ) and the color was brown ( normal color ) We got confused :rolleyes:
This is imposible to adjust the idle screw always too high or too slow.

We did the basic maintenance

-Clean the air filter
-Change the oil ( For GN4 ) and oil filter
-Clean the spark plug

What kind of carb problem is that ?

98 300EX
______________________

-FMF Full System
-UNi air filter
-RaZr Rear tires

****Only use for riding***

[cals400ex]

i would first make sure you don't have an exhaust leak or a leak from one of the boots holding the carb on. if not, then i would try to turn the fuel skrew on the bottom of the carb out a bit in a 1/4 to 1/2 turn increments.

[liljosht]

my 300 backfires too.but im not 100% shure that i dont have an exhaust leak. im ganna check my plug to see. are you talkin about the screw on the very very bottom that is held by a bracket?

[ReconRider25]

maybe ya got bad gas or a seal is gone. i know on sleds when the crankshaft seal goes that backfire like a mofo and have no power.....just bog and back fire.....

[Towlieee]

Brown plug = perfect mixture..

backfires I dont think would happen from being to lean, to rich is when it would happen if anything..

The idle is gonna be alot lower when its cold, and as it heats up it'l idle higher..

We set my friends idle while it was really hot, u just gotta choke it for a couple minutes when u start it..

My friends backfired like mad when u let off the gas, it was when he first bought it so we thought it was normal, sounded like a gunshot when u let off the gas, found out the exaust had a small leak by the cylinder..