Install 06 YZ450F Carb on 98 YZ400F

I have read many carb swap threads on here but I'm unclear on the hot start parts that are needed. My 400F has the stock carb, cables, & hotstart setup; I just bought an 06 450F carb off ebay ( It comes with the throttle cables, throttle tube and the hotstart cable but no lever.

What parts do I need to order to get the hotstart system set up on my bike? I have seen some mention a strange hose but I think that is from an aftermarket system. I have also seen some mention a different clutch perch with a lever mount. If someone has part numbers or pictures that would also be of great help.

The other question on this is do I even need the hotstart? I've never used it on mine with the stock config it always started even after being dumped. I only started having issues after the bike sat for an extended period (ankle surgery) and I can't seem to get it cleaned out to run properly so I figured now is the time to change to the 450 carb as the parts to rebuild mine will be almost as much.

Well, I think I cleared up my confusion... I was looking at the 06 parts breakdown and kept seeing what I thought was a compression release on the clutch perch. It just dawned on me that the 06 doesn't have a compression release :banghead: as it is automatic. That will give me two levers by my clutch, is anyone aware of an alternative way of setting this up?

You can buy an aftermarket clutch perch that is for the new four strokes. They have the hot start lever on them. You need the lever to actuate the cable unless you want to have it tucked behind your number plate and pull the cable by hand. But that would be horrible when your on a hill, sweating, legs shaking, or in an endurance race.

The carb is installed and everything is working great. I used a factory style clutch perch for an 06 with the hot start lever and moved my compression release lever to the right side under my throttle; I can pull it with my index finger. The carb did need a new slide seal & accelerator pump diaphragm but is clean & running excellent now. I am very glad I "upgraded" to this carb, the bike starts easy, idle is steady and it has zero hesitation. I think the only change I will make is to find the back of a perch clamp so I can use it and another hot start style lever on the right hand side for the compression release. Then it will be the same on both sides, the compression release will not be in the way as much and I can operate both while holding the clutch or brake levers.

My question is how worth it is it??? Cause I have a 99 and I have throttle issues just right when I pump the throttle to get going which could be a jet issue or something I could fix with the r&d power bowl but through out over all performance is way better than if it was just jetted and tuned right ?

Phantom, sorry I didn't reply sooner but I just saw your post. I think it was well worth it and would do it again. The problem you are talking about when you pump the throttle is the exact issue with the original carb. There has been countless money and time thrown at fixing it, by some really smart people and companies. Almost every common mod you see is related to it and they are not real effective. The reality is the accelerator pump circuit on the original carb is junk and the best way to fix it is to replace it just like Yamaha did on the newer models. They didn't change the jetting, they changed the carb. No more stumble off idle, instant power with a twist of the wrist at any RPM level....It is like a whole new bike!

It's alright I know people get busy and ok thanks man I kinda jumped on it already!! I actually just got an 07 carb yz450f carb with all the cables and everything the other day and the jets are so much different than the stock carb are far as size and I'm intimidated about putting it on just for the fact I feel retarded when it comes to jetting

Check the jetting in the carb you bought.  I suggest you start with this:


Main Jet: 162/165
Pilot Jet: 45
Starter Jet: 72
Leak Jet (located in bottom off the float bowl): 55
Fuel screw/Setting: 1.25-1.75 turns out
Needle/Position: NFLR (stock '07 needle) clip position 4 (down from the top)


You won't be far enough off to worry about for a while.

Thank you I honestly got to say you guys are the most helpful people that I've delt with and I'll I'll give it a try I'll take it apart see where I'm as far as Jets then I'll I'll get the ones you suggested and then we'll see where im at and I'll let you guys know then

Thanks again!!!

I concur... I have a 1999 YZ400F and my mechanic and I both tried cleaning, adjusting, rejetting and rebuilding the original carb many many times.  The result was always unsuccessful.  The best mod we've done was replacing the stock carb with a FCR from a 2005 model, and rejetting.  Now it starts easy, with smooth idle and great throttle response.  I don't race and I don't crash too often, so I don't use the hot start hardly at all and wouldn't miss it if it were gone.  It's easy to breathe out a flooded condition using the compression release, and get the engine to re-fire.

Oh my gosh night and day difference so much more pick up and smoother idle plus it put a full yoshi exhaust to top it off and wow has more pull than ever well worth the swap

Hey there.  I realize this is an old thread, but I'm about to do this swap on mine.  Im just wondering if you ended up keeping the yz450 jetting settings, or if to went to someting else. 

Stock YZ450 jetting is an excellent starting point.  Some people stay with it.  Results vary.

Thanks :thumbsup:

Yes, I was able to keep the stock jetting for the 06 carb. In other words... I didn't change a thing.

The deal for the 06 fell through, but I'm bidding on an 08 unit with throttle tube, cables and hot start. I'll use the stock jetting (if I win the auction

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