2001 xr400r bogs

I have a recently purchased 2001 xr400r. I'm fighting a hesitation from idle. Bike starts easy, idles fine, mid and upper range seems fine. I know there are threads on this, I've read all I can find. I understand this is normal, but I have found that some have eliminated this bog.

Stock carb, uni filter, snorkle removed, supertrapp with 12 discs installed. I live at 1000' elevation.

The carb has been cleaned.

I have tried many combinations of 2/3rd needle clip.

I have tried jets from 52 up to 65 on the slow jet.

I have tried 148 up to 160 on the main jet.

I've experimented with the fuel screw in small increments.

I have 65/160 in it now, 2nd clip, 2.5 turns out. Bog still present. The bike seems to run better with half choke. This tells me I need to go up on the pilot. 65 seems like a lot though.

Suggestions are appreciated. I'd like to get it close with this carb, without going the pumper carb route

First, we need to verify that you're using the choke correctly. Choke off is with the lever all the way DOWN. Full choke is all the way UP. Be sure you don't have this backwards. If you do, that could be why it seems to run best at half choke.

There are a lot of variables that have determined how well others have eliminated their bog. Not just jetting, but how the intake, exhaust are configured for a specific bike, elevation, air temp, humidity, valves, compression, etc.. All play a part. Don't get hung up on it. Tune it for best response and go with it.

Edited by Trailryder42

If it runs better with half choke check your float level , It may be low . Do you still have that door on your choke ? 158,159,160 should be a good place to start for the pilot jet.


pilot controls Idle and just off idle . main jet controls mid range .the needle is the last thing to adjust after the main is very close.


 if the pilot screw is more then 2 turns out, then you need to go down on the pilot . less then 1 turn go up on the pilot.


take your carb off put it in the vice put a clear hose on the bowl drain, rig a way to get fuel to the carb if the float bowl is full you should see fuel in the clear tub to the parting line . You can do it on the bike, I like to take it off . If the float is wrong nothing can be adjusted to make up for it and it will never run right.


watch this video to get a better idea of what I mean



Thanks for your comments. I do understand that there are a ton of factors involved in tuning, which make it frustrating to say the least.

To answer a couple of the questions,

I'm using the choke correctly, full is up, off is down. I have other xrs (250r) similar set ups.

Float height was measured to be right on. I think I'll try that clear tube method as well. Does the level of fuel need to be level with the bowl I assume?

The choke door is still in place, spring is functional. I will purchase the replacement if I can work out these bugs.

I have a fuel screw, further out I've been going up on the pilot, right?

Thanks again.

Just for fun take off end cap on supertrap.See if it gets better,or more bog.BTR

fuel level check with clear tubing has level of fuel right on the bowl with the bike level.


I bought the bike a month ago, not running as is.  The muffler had no cap at the time.  It had similar bog without cap.


Heavy black soot around the muffler cap and on the discs.  Too rich, I assume? 


Crazy confusing at this point. 


It seem rich by the muffler signs and plug, but runs better half choke like it needs more fuel.

Edited by unplayable

Did you remove the fuel screw and clean that passage and check o ring condition?

Unlike a pumper, you can't just whack the stock carb and expect instantaneous bog-free rpm. If that's what you're looking for, get a pumper carb, otherwise tune your best and learn to roll it on.

65 is too big.


I'm betting on a clogged fuel screw passage


The pilot circuit is not affected much by breathing mods because you're running at lower RPMs with less volume on that circuit.  Breathing mods affect the main jet size mostly at WOT and the needle position. Try the needle at three or one notch richer.


Remember that the engine needs to be fully warmed up for best performance.



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