White Bros XR4 Rev Kit

mtngoat

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#1
Jay Peters http://www.justxr.com/info/xr4report.html raves about this mod. Seems to make sense that an EPA bike would have retarded timing and a timing advance mod would really work well. I'm not so sure that disabling the rev limiter (or setting it 2K RPM higher) is so great, but the improved advance curve is appealing.

Anyone try the product??
 

mtngoat

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#3
So far, all I have is the price, $329.

The catalog information is pretty weak, making a bigger deal out of extending the rev limit than discussing the advance curve. No dyno testing either, which is unusual for White Bros products.

Jay seems to be pretty informed. I spoke with him last week and he's apparently tried just about every XR4 mod I've ever heard.

Someone out there tried this???
 
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#4
OK, now it's time for me to throw in a bit of wild speculation and heresay! Please don't by any means take this as gospel !! Awhile back I can vaguely remember a comment along the lines of the XR4 Rev Kit that is sold by certain aftermarket retailers here in Australia as being an XR600 CDI unit. Off hand I don't even know if the plug is the same? Or if there is an adaptor lead? Or if it's just innacurate.... but I'd sure be interested to find out... anybody else know?
 

penguin

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#5
I would not waste my money on the rev kit, it is mostly a lot of hype. You would get more performance out of a big bore kit for about the same price. Honda put a rev limiter in the ignition for a reason, you spin the XR4 too high and bad things start happening. ask a DRZ400 owner what happens if you try and rev the motor too high :eek:
 

Wolf

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#6
I am a little reluctant to go into the engine or change anything on the rev limiter. I don't want to loose the reliability of my XR and that is the main reason I like it.....but I am still curious.
 
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#7
Rev kit.

mtngoat.

I have installed one of these on a customers XR. The engine was modified with a cam, ported head, Mikuni pumper carb, WB head pipe and silencer. The bike ripped. Made good mid range power and rev'd to the moon. The XR engines make good power up top if you let them rev. They seem to hold together pretty good also.

IMO, the most noticeable mod was the Mikuni pumper.
 

mtngoat

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#8
Thanks Terry

I thought you'd know.;) Had a lead on a two month old Mikuni and lost it. I'm leaning that direction, but I want to try the rev kit too. WIsh WB would dyno it.
 
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#9
Penguin what happens when you rev a DRZ motor too high?You hit the rev limiter?Most dynos show the DRZ motor making power right to 10k.
 

penguin

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#10
ask the DRZ owners who have gotten the hi rev ignition kits....they blow up, just like the DR350's before them. Unless you want to do serious modifications to the valve train on many of the 4 stroke trailbikes, you are courting disaster if you try and rev them past their designed limits. You can believe it or not but I have 30 years of riding and wrenching to back me up. Unless you fancy yourself a factory pro, a lot of the hopup parts are wasted on us normal human beings. :silly:
 
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#11
It would be interesting to see a dyno chart with this rev kit. I would think that very little usable power would be had up high. But there could be gains in mid range with the advance curve. For the money the Mikuni carb is awesome! I gave mine the altitude test this weekend and I am happy!
 

mtngoat

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#12
I agree. I'm a lot more interested in the advance curve than the rev limit. I'll try to talk to their techs. Ideally, I'd want the curve and leave the rev limit alone or set it lower. Maybe it's adjustable. But, I also believe the Honda valve train can take it and is more robust than Suzuki (no bash intended, just my confidence in Honda engineering).
 

mtngoat

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#13
Spoke to the White Bros tech folks. Apparently, stock XR4 ignition curve is very retarded, especially thru mid-range RPM for EPA compliance. The kit makes the curve linear (flat), which should really improve mid-range response, IMHO. The rev limit is not adjustable. The kit still has not been dyno'd and no apparent plans to do so. The tech had ridden before/after application and claims significant improvement, consistent with Jay Peter's observation. This mod is most popular with the TRX400 quad. No reports of blown motors due to high reving.

The tech agreed to send me the owner's manual. If there's any more good info there, I'll post.
 

mtngoat

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#14
Sorry, bad prior post

Oops, sorry to controvert my last post, but I received more info and talked with Gary Jones in White Bros. R&D and I'm getting a different and IMO a more accurate assessment of the kit.

Gary did R&D on this kit and played with different curves. He says the modified curve isn't that different and this kit is more about extending rev limits than changing curves. To take full advantage of the rev limit really requires a cam change to enable breathing at higher RPMs. He doesn't recommend it for a stock engine. Personally, I want more low and mid-range performance for my riding. This won't help me there.

This really "syncs" with Ol89r's experience.