XR400 dies on sudden throttle twist

[xrh400]

I am not sure whether this is a characteristic of thumpers, but when my XR is free or it is running but I hold the clutch, as soon as I give it a hard throttle twist, it dies....

I remember I solved the problem by increasing the idle - but is it just temporary solution of a greater problem or it's just the way these thumpers work?

[Trailryder42]

The XR 4 stroke isn't going to respond to a quick twist to WFO like a 2 stroke motor. The 4 stroke has twice as many strokes to go thru than a 2 stroke to complete 1 intake - ehaust evolution. You can minimize the hesitation with careful jetting and tuning of the fuel screw but don't get hung up on it.

As long as the engine starts and runs good in real world riding conditions. I can think of no instance in riding where you need to snap the throttle WFO from off idle.

[Mxracer776]

do you have any mods done to it?

[Kev_XR]

The dreaded bog. You need to put on a pumper carb to get rid of it.

You can tune the stock carb to improve throttle response, but it won't completely go away.

https://www.thumpertalk.com/topic/98806-xr400-engine-bog-pilot-jet-and-the-fuel-screw/page__p__701328#entry701328

[CRF450XINOZ]

Pilot jet may be blocked too, Hard to say without seeing & hearing it?

[codyp1814]

First off clean the carb good. Blow through everything and such. If that doesn't work try messing with the pilot screw by turning it out. It is bogging because it is lean and is not getting enough fuel with the first crack of throttle. It doesn't bog with it idling higher because it is getting enough fuel when at a higher rpm. My xr250l did that but it was due to the accel pump not working at all. However, when the accel pump works, it is snappy. So if you want it snappy buy a pumper carb.

[xrh400]

Sorry guys but I thought I was following this thread by default but apparently not. The carb is clean - I cleaned it carefully last december, and I dont go dirt riding with it or abuse its engine. I guess I have to try playing with the fuel screw.

Regarding a pumper carb, I have read about its many advantages - how much do they cost on avg?

[jg83]

Congratulations you found the hidden XR kill switch, lol ? . This is kind of a characteristic of these bikes, pumper carbs will get rid of the bog. I would be careful adjusting the idle too high, remember these are air cooled engines. Luckily my 250L came with a accelerator pump carb and was able to get rid of the bog completly. I would just ride it how it is and not worry about it too much. Pumper carbs are not that cheap ~$400 new but I guess it just depends on your budget.

If you do get a pumper carb I think XRs only has the best kit for the XR4.

http://www.xrsonly.com/parts-categories-1/fuel-components/mikuni-pumper-carburetor-kit-36mm-honda-xr400r