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yamaha mark

yz400f 1998-1999 carb issues

15 posts in this topic

hi guys and girls im having some issues with my 1998 yz400f carb and its really getting to the point where i want to sell the bike.through constant problems with jetting i have now cracked the bowl from removing it so many times (over tightening it probably didn't help) but any way to the point. really what is the difference between 98-99 model carbs.yes i now they have different part numbers and the 99 carb is a lot cheaper to buy,but physically are there any differences?or does someone even know where i can just buy a new/second hand bowl?please help i love my bike and dont want to practically give it away coz of this problem. thanks guys.:thumbsup:

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Remove the carb and place it in your work shop in a prominent place where it can be seen as a reminder of past battles fought with machinery.

Then go on eBay and/or the TT Classifieds and find a carb from any year YZ450, preferably an '05 or later, and adapt it. It very nearly bolts straight on, and makes a huge difference in the amount of cooperation you'll get from the bike.

You will need to have as much of the hot start cable/lever/plunger assembly as you can get with the carb, so look for that. You will also need to block the port on the head that your current hot start tube connects to.

Makes a very worthwhile upgrade.

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ok thanks to you grey i will look into it.even a yz450 05 carb is still cheaper than a yz400 98 one.

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I got mine off of an 07 and will never look back. Best fix ever. struggled with hanging idle, non-idle, idle with only choke etc...was totally over it after multiple re-jets.

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I sold a spare '06 carb to a member here who installed it on a 426. It had 100% stone stock '06 jetting, and he said the bike had never run that good as long as he owned it before that.

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sorry maybe i should clarify.

on the old one i had all those problems. and tried all the fixes. even lost the accelerator pump rod once. ($30+)

on the new one it was almost perfect with stock jetting just a bit rich on the pilot jet. plus it came with a Boyeson QS2 :smirk:

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it took me about 30 minutes to take the old throttle tube off. connect the new one. run the cables. attach the carb. had someone stretch the boot with me. at first it had bone stock jetting, 45 pilot, 160 main, 4th needle position. ran incredible right off the bat.

now I'm using a 42 pilot.

It is the most basic change you can do. Perfect fit really. my carburation is soo good i can putt in first on just the idle speed. I can coax the bike into a roll on flat land just by feathering the clutch out...

You'll be thrilled if you take the plunge.

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The pull cable is different. The one i ordered came with complete throttle cables with throttle tube and grip already attached. I just used the new stuff replacing my old tube instead of putting the old tube and grip on the new cables which could have just as easily been done.

had to stretch the boot maybe a 1/2in. to an in.

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On the boot, it seems easiest to me to clamp the air boot to the carb, then pull the carb forward into the intake stub and clamp it.

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On the boot, it seems easiest to me to clamp the air boot to the carb, then pull the carb forward into the intake stub and clamp it.

this is the winner.

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