2004 CRF450R - Won't idle, low-end bog

Hey all,


Bought the bike a couple months ago and it has never been able to sit and idle (will BARELY stay alive with choke on). Within the last 5 hrs of ride time I've completely disassembled the carb and cleaned every piece, nook, and cranny. Reassembled and bike was running great. Still no idle, but low-end wasn't bogging. It should be noted that during the previous 5 hrs of ride time, the weather was in the 50s/60s and relatively dry air conditions.


Went trail riding this past weekend (so majority of day was spent in first or second gear). It was cooler (40s, low 50s) but very humid. Adjusted the pilot screw slightly thinking it would accommodate for this change in conditions. However, I spent the whole afternoon struggling to keep the thing running. Low-end was bogging pretty bad. It has NEVER backfired on me before, but started doing it later in the afternoon.


Fire it up last night (24 hrs after riding) thinking things may be different since the weather warmed up, etc, but had the same issues. Hard to start, wouldn't idle, low-end bog, and backfired once.


I realize this could be caused by a lot of different things, but wanted to open it up to discussion. My first guess was, since it's a high-geared track bike, that the slow trail riding was flooding it? Or maybe the change in weather was enough to require a different main jet being put in (even though that wouldn't necessarily help my low-end issues)? Did some research and changed my mind to it being the leak valve possibly needing changed or retimed? Now my head is spinning.


Any suggestions on where to start, or what to consider? Thanks in advance!

Edited by xxCHUMxx

Buy a new pilot jet. Not just a 'clean' one.


Ensure the fuel screw and its parts are there an undamaged.


Ensure the hot start fully seats and works properly



Get the idle right BEFORE you misadjust anything else/ One step at a time.

Soak that carburetor in some carb cleaner. That's should clear out all your hoses and jets. And all your gaskets will fit better because they're cleaner.

Soak that carburetor in some carb cleaner. That's should clear out all your hoses and jets. And all your gaskets will fit better because they're cleaner.


No DO NOT do this. Never ever submerge an FCR carb in carb cleaner! 


They have internal rubber gaskets that will be destroyed.


You just need to maintain the carb, replace the pilot, service the hot start, get an R&D remote fuel screw and learn how to use it.

Thanks for the suggestions. New jets (main and slow) and hot start assembly are all in a cyber shopping cart awaiting shipment. I'll try to remember and post the outcome after the bike is reassembled.

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