yz400f carb swap now wont start

So I got a carb from ebay off the 08 yz450f to put in my 99 400. now it wont start sputter or anything except its kicking back on me every few kicks. I cleaned the carb before installation and double checked the boots to make sure they were not leaking. the jetting appears to be stock with the exception of the pilot #48 and the main #165. the needle is 3rd position from the top and pilot screw is 2 turns out stock pipe in the california valley. could the larger jets be causing this problem? Maybe I need to use completely different jetting since im using the 400 motor? 

How were all your throttle cables?  I just swapped an 06 carb in to mine.  Having some similar issues.  Mine doesn't kick back on me, but it stops short of a full kick sometimes.  It was suggested that perhaps throttle is being given, while kicking.  I am thinking that might be due to cable adjustment.  I am headed to check that soon.

throttle cables not even hooked up

You should check to be sure your pilot jet is not clogged or partially clogged.  It's quite common in carbs that have been allowed to sit and dry out. 

 

The pilot is a little rich, perhaps, but it should start and run on that.  A 45 is probably closer to perfect.

Why is the yz450 carb better then 98-99 carb.

Just because it is newer ?

More modern internal design, and more sophisticated circuitry.  So, yeah, it kinda is just 'cause it's newer.

Check that the idle screw isn't turned in too far (will often cause kick back if slide is up too far).

Check that Hot start and Choke plunger are working.

Like Grayracer said, probably bit too rich at 48 pilot but should start cold.

Check the O-ring on the fuel screw, may be perished or missing.

Check float height.

Check slide valve isn't upside down.

Check Pilot air jet isn't blocked.

:thumbsup:

Check that the idle screw isn't turned in too far (will often cause kick back if slide is up too far).

Check that Hot start and Choke plunger are working.

Like Grayracer said, probably bit too rich at 48 pilot but should start cold.

Check the O-ring on the fuel screw, may be perished or missing.

Check float height.

Check slide valve isn't upside down.

Check Pilot air jet isn't blocked.

:thumbsup:

Done that before and does what you described.  :banghead:

thanks for the help guys I put a 45 pilot in and played with the idle screw a bit fired right up runs great :D

Sorry to bump this thread back up, but it seems my other thread on this topic no longer exists. 

 

A while ago, I put an 06 carb in to my 99.  The bike ran rough at first, then not at all.  It is having trouble kicking.  I kind of gave up and it has sat for a long time.  I just finally tore apart the carb to see what was what.  Dirty inside, but who knows if I got it like that, or it's from sitting for a year or so.  Here is what I found.

 

Main jet- 170

Pilot Jet- 40

 

I backed the pilot screw out 1 1/4 turns.  Bike has a full Dr. D exhaust, No-Toil air filter, no airbox lid.  I will be trying to get the bike running at sea level, temps around 80. 

 

I haven't put fresh gas in the bike and tried starting it yet, but what do you think about that pilot screw?  And any pointers on where I should set the idle screw?  How much a gap should there be between the carb and slide valve?

Thanks good info, going to do same ! Where did you guys get the carbs ?

Change the pilot jet to a 42 and the main to a 165/168.

 

Set the screw at 1 3/4 out as a starting point.  About a 3/32 - 1/8" lift on the slide should be close.

Shawbridge, I got mine off eBay.  Make sure you get the whole kit and kaboodle.  Carb, throttle cables, throttle, hot start.  Makes it easier.  I had started a thread last year sometime that people contributed a lot of good info to.  Sad to see it isn't around anymore :doh:

 

Grayracer, as always, thank you.  One thing I forgot was what to do with the stock hot start.  Just remove it and plug the two holes that the hoses go in to?  And I can use a decompression lever handlebar mount to mount my new hot start?  Hoping bike will run (and run well) by this weekend.  Probably will leave stock hot start on bike and new one zip tied to handle bars until I can finish it up properly. 

Edited by SpceSpff

 

How on earth??? I thought of myself as a capable forum searcher.  I searched honest to goodness for 25-30 minutes.  I used the forums search engine and google.  I could not find that thread.  I found older threads I started and posted in, but that thread was nowhere to be found.  Thanks for finding and linking it!

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