WR400 CARB Swap Options???

i just broke my third "valve float", aka that slide plate in my wr400 carb. I changed it along with a new rubber gasket, installed it correctly as directed here, and the thing still breaks. it just can't handle the freeway vibes/constant abuse from using the bike as a daily commuter/supermoto track bike.

Soooooo, i'm thinking it's time for a new carb. will the drz400 carb swap in? i wouldn't mind having a cv carb because a flat slide can be a bit jerky for street riding, and i'm never going to be a competitive racer anyway so i'm willing to trade horsepower for more reliability/smooth ride. plus everyone that has CA drz's wants flat slides so they sell the stockers for cheap. i don't know if it'll fit though.

any carb swap suggestions would be greatly appreciated. thanks in advance...

I swapped out the carb on my '99 WR400 after the third slide plate cracked with a carb from an '04 WR450. I had to mess with the jetting a little but otherwise it was an easy changeout. The slider design is different so I'm hoping they have solved this design problem issue. I also like the remote hot start.

glad to hear i'm not the only one busting these plates. wr450 carb would be ideal but i'm guessing pretty expesive. since i'm a broke student, would the less desirable drz cv carb from the S model bolt on?

Just this past week, I removed my CV carb off of my DRZ400S and replaced it with a FCR39 carb off of a 1998 YZ400.

These are the fit issues that I ran into this week, and that I know you would have to address. (if you have a 1998-2000)

1) The rubber boot from the engine to the carb will not fit. The CV carb is only 36 mm vs. the FCR carb, which is 39. I have the stock (DRZS) rubber boot, but I do not know if the engine’s intake on a DRZ400S is the same size as the intake on a YZ400. If they were the same size, then you could just use the stock rubber boot off of a DRZ400s.

2) The rubber boot that goes from the air box to the CV carb will not fit. The intake diameter on the CV carb is bigger then the diameter on the FCR39 carb. You might be able to use a stock DRZ400S boot, but I would not know if it would fit with an YZ400 airbox.

3) The bracket on the carburetor that holds the throttle cables will give you some fit issues as well. The distance between where the cables bolt on to the carb to where the cable ends are hooked into the little holes on the throttle wheel is longer on the CV carb vs the FCR carb. (When I did my swap, I had to use a set of cables off of an YZ400.)

As you can tell, I have all of the parts you might need. Carb, boots, cables. I’d be more then willing to help you out. To start off, we would need to know the following:

1) What is the outside diameter of the intake on your engine? Then we could compare it to the inside diameter of the rubber boot.

2) What is the outside diameter of the hole on your airbox?

If you do measure these items, it would be best to do it with a dial caliber vs. a tape measure.

Thanks Tom. first step is to fix my current carb, cuz even if i swap it out i'd still want that one complete to sell it. while in the process of that i'll get those measurements (been meaning to buy a dial caliper anyway) :D i'll be sure to post em here. Thanks for taking the time to give me the lowdown.

other option, from what i hear from the supermotojunkie folks, is that they fixed the slide problem in 2000 with the fcr2 carb. just wish i knew that before braking three plates at $75 each.

I'll post up the inside dimensions of the rubber boots as well. I'll be doing some more carb work later this week. It'll be good info to know to save in the archives.

Whenever you wish to pursue this (if ever), send me a PM.

I swapped out the carb on my '99 WR400 after the third slide plate cracked with a carb from an '04 WR450. I had to mess with the jetting a little but otherwise it was an easy changeout. The slider design is different so I'm hoping they have solved this design problem issue. I also like the remote hot start.

What jetting did you end up using. I have a 99 wr400 with an 04 yz450f carb.

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