Xr 4 throttle respone ?'s

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#1
I'm posting this for my brother who has an 01 xr 4 with a stock front sprocker (14t ?) a 52 t on the back Stock jet of 142 and has lowered the needle one notch from the stock setting.

The throttle response off idle is too abrupt for his liking. When in tight twisty stuff he has to blip the throttle. Kind of like hitting a light switch off and on. He is trying to get it so that you can roll the throttle on smoother. If a motocrosser or hare scramble guy got on the bike they wouldn't know what the problem is. My bro prefers to "tractor" through the woods, trail or no trail. any suggestions on carb set up for this type of riding keeping the stock pipe.
 
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#2
I've never heard this complaint about a stock XR4. They're about as tractor like as you can get. Maybe he would have been better off with the XR 250. He could try going one tooth smaller on the front sprocket, to lower the gearing.
 

TR

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#3
14/52 gearing ! Standard is 15/45 and you should be go anywhere with that.
I run 15/44 and if the hill is at all rideable than I can usually get to the top in 2nd.

I would try experimenting with the gearing. The differences are noticeable and you might suprise yourself.

Regards
TR :eek:
 
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#4
I had 14:53 on my XR6 when I bought it ..... WAY TOO LOW for what the trails I ride!! A couple of people I know were quite happy with 14:46 for their XR4's
 
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#5
mmmm I knew this wasn't going to be easy!! It's not the gearing It's already low enough to pull stumps!! It's the way the gas comes on when you twist the throttle. It's like the initial spurt of gas is too much. Admittedly it's being a little knit picky but my old xr did the same thing and it bugged me a bit. Plus my drz doesn't do it. As i mentioned above it's like the gas hits all at once you can't really roll into the throttle. No it doesn't go into full throttle or anything like that but it is kind of irritating. I guess we are trying to fine tune the throttle response off of idle. What inside a carb would you screw with to do that???
 
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#6
Could it be that you are experiancing the XR400 off idle stumble and go?
 
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#7
I think he's just trying to smooth out the initial surge of power off idle. Easiest thing I can think of would be to use the clutch a little bit.

Jeremy
 
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#8
Ahhh!! now we are getting somewhere!! vintageguy talk to me about this stumble and go.... describe it...... is it an xr thing you have to live with or can it be fixed

H-xrguy a couple of riders have told my bro just to slip the clutch. But that sounds like a real pain when your doing psuedo trials-trail riding. Although i know nothing about trials riding.... do they work the clutch like madmen or stay away from it or just the usual clutching you'd expect??
 
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#9
Hey,
The 400's have a flat spot right off of idle, then the fuel surges, and you get a little hit. Check out bajadesigns.com, they have an XR400 section on their menus. It tells about the dual tapered needle, slide, and jetting, as well as the airbox mods. Supposedly, it fixes the flat spot problem. The needle and slide are relatively cheap also, so it's worth a try either way in my opinion. On the other hand, you can spend ~$400 for a Mikuni Pumper carb which also, supposedly, works wonders for the 400's. In the near future I will be trying the Pumper carb on my 400. I've got an Xr's Only pipe and jetting and I'm not displeased, even at low speed, low RPM riding. However, I think I understand what your friend is complaining about. Search around these forums for XR400 mods, Mikuni Pumper carbs, and check out bajadesigs.com. Good luck.
 
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#10
I had an '00xr400. If you really crack the throttle open at low rpm they will bog. Correct me if I'm wrong but I think they have a CV carb? So it has to build a little pressure before it lets the gas in. The richer the jetting the more the bog, the leaner the more it goes away. The answer is to clutch a little or give it a little roll before you snap it open. W/O changing to a pumper carb you won't get the response of a yzf or a 2-stroke.
 
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#11
Skid

Everything I know about an XR4 I posted in this thread, click here . I know it's not much.

Also, I don't think the stumble is cause by a rich condition. At least in my experience it's been due to a lean condition. I went to a richer slo jet and improved the off idle throttle response. Also, you didn't say what year your XR is (at least I didn't see it), I know the newer ones came with the dual taper needle, just don't know when that started.

One more thing. If your engine idle speed is set to low, you'll notice the stumble is worse.
 
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#13
I had a 98 XR400 with the same stumble problem. Although I never thought the hit was excessive.

It is ussually caused by a Lean condition when opening the throttle suddenly from idle. I think this is a 4 stroke thing that the YZs solve with an accelerator pump giving a shot of gas.

A quick check tha proved to me it was too lean was to engage the choke 1/2 way and try it. It ran much better without the stumble for me. Then, a richer idle jet helped but never completely eliminated the problem.
 

mtngoat

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#14
This is a tough one. Most XR4 jocks complain about the hesitation, not the hit off throttle.

Here's a link that describes what-works-when:

http://john.rushworth.com/Motorcycle_Co_UK_archive/xr4faq/

Trying some reverse logic, you may want to richen things up to dull the off-throttle response. To do so, return the needle clip to the middle position (assuming you didn't really "lower the needle", you lowered the clip) and go one size bigger on the pilot jet. BTW, beware of too lean conditions if any mods (exhaust changes, open airbox) are done; explained above.

If the "hit" occurs when rolling and coming off idle, consider encouraging the use of the clutch to finesse the power.
 
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#15
Thanks for the replies guys!! Certainly enough here for my bro to play with so he really screw up the carb!!