Own a YZ400/26 READ!

Two monthes ago I bought a 1998 yz400f as a woods bike. It had all the conventional problems, Hard start, sputter down low, pop on decel, hanging idle, no idle sometimes, etc... but it ran like a MF while it was running. I knew before I bought the bike that it would need freshining.

At first i thought, in my ignorance, that i could replace the fuel related parts in the carb. $100.00 later with quite a bit of reading i realized that this would not be the case.

Sooo first i started with the carb. the old slant FCR's just plain suck as off-road applications. After intense research i found that the latest model YZF style FCR is the optimal carb for the 400. The TPS IS PLUG AND PLAY! I cross referenced the voltage specs on the old to the new and they all match up in the opperating range. (new style has a small discrepancy as the max output is like +1 to the old style)

The exact carb i ordered was a 2007 yz450F takeoff. It came with a boyeson QS2 accelerator pump cover and I added a #48 pilot jet. I Left the stock main, leak, and starter though i have a kit to mess around.

Incredible was all i could think after the install. It ran, idled, responded to the fuel and idle screw, etc. Still I was not satisfied. The freshening, as i had come to call it, was not even close to complete. I knew that buying a 13 year old 4 stroke motocross bike could lead to heartbreak. A complete rebuild was in order.

I went to various sources from TT, Ebay, and the Stealership herself and this is what i came up with! All prices are shipped to my door.

Parts List.

2007 Yz450F Carb (w/ SL fuel screw.)...........$285.00 Ebay

Wiesco Piston #4649mo9200.........................$38.00 Ebay

Flywheel puller............................................$13.25 TT

Tapered feeler guages...................................$9.45 TT

Pilot Jet #48................................................$3.59 TT

Balancer Straight Key.....................................$4.43 TT

Timing chain................................................$45.00 TT

Brush research Flex Hone (95mm)....................$65.00 Brush research.

ASV clutch lever/perch w/ Hotstart.................$33.95 Ebay

Motion Pro clutch cable.................................$11.75 Ebay

Moose Gasket kit #808675 (full kit).................$30.00 Ebay

OEM Head Gasket........................................$35.00 Ebay

FMF Powerbomb 426 takeoff..........................$67.00 Ebay

4 shims (all 5 adj. one reused)........................$5.00 local shop.

add another $100.00 for various bolts, Amsoil, Assembly lube, etc. (certainly missing something)

All of it took me one days worth of worktime. It sat overnite only waiting on oil really the next morning. After all was said and done she started over 3rd kick (with oil poured into the sparkplug hole lol). I rode her hard for2 hours and she totally seated everything. After breakin i gave her new oil and filter, she runs soooooo smooth and quiet, without any hesitations or inconsistencies and kicks over first time everytime, though she did after the new carb.

This writeup is for anyone struggling with 400 or 426 problems. I paid 900 for the bike, and now i own a machine that ANYONE, from someone that owns the newest YZ or the most beat bike around would be envious to ride. All I know that is when I go ride with my friends it isn't me that is staying with the truck because their bike isn't running well lol.

Got any pics?

Nice writup and work. Good to hear it is everything u wanted now. I have a 08 kx250f and a 01 426f. Love both bikes. Two different animals!


2011-04-08140437.jpg DR250.

2011-05-12211827.jpg missing jug.

2011-05-12211851.jpg Old stock cast piston. not too bad of shape.

2011-04-21105449.jpg beautiful. All the more so for $38.00

2011-05-12211923.jpg A work of fuel delivering art.

2011-05-12211910.jpg head removed.

I didn't take any pics after the rebuild. too busy riding lol.

Thanks for the tip about the carb. Just installed a 09 450 carb on my 99 400 today. Didnt do any rejetting tho, started on 2nd jump, it can idle, no popping, no glowing exhaust, and the throttle is way more controlable.

The inlet rubber needed 2 min of work with a razorblade, else its plug n' play =) In total i ordered clutch perch, throttle and carb, payed around 200$ in total, all in perfect condition!

FINALLY a answer what works as me and my mate bought a 99 400 about amonth ago with every problem you have above so just printing this out now to show him tomorrow then we are going to go on the hunt as we were about to order a carb rebuilt kit I'd say the onlt other thing to do which we are going to do anyways is put the 450 decompression cam in like

anyways top work


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