05' crf450r Carb issue (hopefully easy fix)

My best friend had a crf450r 05' bike. Last time out riding his adjustable fuel screw fell out. Cheap and same day fix we were able to get a tusk fuel screw forl like 10 bucks.. Now I'm not sure if this is the root cause to the problem or not but this is the only thing that changed on the bike...

From an idle (say 1700 rpm) if you crack the throttle from 0 to 25%+ there is a bad lag. ONLY from an idle.. Once you get into maybe 2000rpm just slightly above idle and then crack the throttle no problem it revs out great without any problems.. If you ROLL on the throttle there are no problems.. It's only when you twist it quickly from a dead idle..

I'm thinking perhaps changing the idle screw out for a different brand, maybe I'll put mine in there and see if it makes a difference as mine is brass.

I cleaned the entire lower end of the carb and didn't notice anything abnormal with it.. It boggles me cause it runs great besides that first throttle blip... Which makes me think it's got to be the air/fuel adjustable screw.. Which I've turned it all the way in and all the way out just to see if for some odd reason it fixed it but it didn't. What I figured.. I'll probably just let him try my fuel screw next time I go over there..

Just wanted to see what opinions I could have over looked as nothing has changed before and after he lost if besides the fuel screw..


look up the o-ring mod for the flat spot.and i had the fuel screw fall out on me the first time i rode the bike it cost me 24.00 and lasted 1 min.now i have the r&d that cost 28.00 but it flexes and is easier to adjust and also uses a carb bowl screw to attatch the bracket too.it can't fall off and get lost,it is worth the money and it is easier to adjust

Sounds like the AP might not be pumping. Verify you've got a pump shot when you twist the throttle.

I would check the AP diaphram sound like it might have a tear or not seated right. Also check the little O rings they might be jacked up.

ya, we are going to do the AP mod to his bike... last time he bought the leak jet he lost it so we never did it... it could be all jacked uo cause i was not there when he installed it all back together..

what they said.. and check that the original o-ring was not still in the fuel screw port after the old one fell out?? It is possible you have 2 o-rings in there now. Im not sure that would matter much, other than throw off the adjustments (when you think your 2 turns out, your really much more out on the fuel screw).

fuel screw > spring > washer > o-ring

Make sure all 4 pieces are there. more than likely not

I had 2 O rings on my fuel screw by accident. One was stuck inside the carb. Get a small bit of thin gauge wire (telephone wire)and make a little "fishing" hook at the end. You might be surprised what you find. Blowing the carb out with air doesn't always get things to come out.

true.. I will run through the carb again..

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