400ex carb on 300ex

[monster300]

I am thinking about putting a 400ex carb on my 300 but will it fit and how much do they cost? Would it be hard or easy to install?

[mod300ex]

do a search i had a thread up about doing it........im goign to do it and oregonrider36(sp) has one for sale its a great deal i think he sadi 75....its easy to instal from what people said..........tell me how it goes.

[330exracer122]

its real easy buy the 400 carb an slap it on u get a major topend increase an the 300 needs one u can use the stock air boot but its a lil tight but can be done..

[monster300]

thanx for the help guys:)

[danney f]

Originally posted by danney f
Sorry I don't have any pics, but you install it the same way you install the stock carb. At least I did.
If the carb didn't come with the throtle cable allready on it, you will have to use the one off the stock carb. First turn off the gas and remove the gas tank. Make sure that every thing is wiped clean to keep dirt out of the motor and carb. Open the drain on the carb a let all the gas drain out. Remove the black boot from the air box to the carb, next remove the carb from the quad, remove the black cover on the side of the carb. If you will hold the carb and push on the throttle a couple times you can see how the cable operates the slide.
CAUTION When you push on the throttle it will spray gas out the end of the carb that faces the head. Do not do this near any open flame or point it at your face or your friends. Just a little warning. I would cover the end with a shop towel to prevent any problems. I didn't and I caught my cat on fire(Thats another story).
Loosen the cable at the throttle as mush as posible and at the top of the carb, next push up on the lever that the cable is attached to and remove the cable. Once the cable is removed just spin the carb off the cable and install it on the 400's carb in the reverse order.
Now to install the 400ex carb on the quad.
The air boots, both of them, are really tight so take some hair spray and spray the inside of the boots then work them around the carb. I suggest spraying one side at a time otherwise the hair spray will dry before you get them on. With the air boot from the air box removed it gives you plunty of room to work it into place. Once you get the carb in the boot connected to the head, tighten the clamp tight, you can use the same clamp and once hair spray dries it helps to make it air tight. After that, spray the air box boot then work it on to the carb than the air box, you will have to use a larger hose clamp on the carb side. Put the gas tank back on the quad, open the drain on the carb than open the petcock on the tank and let gas flow into a cup for a second. It just makes sure that youv'e got fresh clean gas in the carb and helps flush out any debri that may have gotten in there.
You will most likely need to rejet and as far as that goes, trial and error.
One seggestion is that if you buy a used carb, is to remove the bottom cover and clean out the carb.
I hope I explained it well enough just ask ?'s if not.