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White Bros XR4 Rev Kit
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Posted by: mtngoat---------------------

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??

Posted by: Wolf---------------------

After reading that article I am curious myself. Let me know if you find any info.

Posted by: mtngoat---------------------

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???

Posted by: John K---------------------

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?

Posted by: penguin---------------------

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

Posted by: Wolf---------------------

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.

Posted by: Ol'89r---------------------

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.

Posted by: mtngoat---------------------

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.

Posted by: weekendtoy---------------------

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.

Posted by: penguin---------------------

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:

Posted by: Handl-it---------------------

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!

Posted by: mtngoat---------------------

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).

Posted by: mtngoat---------------------

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.

Posted by: mtngoat---------------------

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.

Posted by: Wolf---------------------

Quote:

Originally posted by mtngoat
[B

. Personally, I want more low and mid-range performance for my riding. This won't help me there.

[/B]

.....Pumper Carb

Posted by: motoman393---------------------

Hello all...I had a 97' XR400 (I still do because it is sooo much fun to ride) but anyway I only come to this site but about every week (I mostly goto thumpertalk.com) since I have a YZ426 now!

Anyway about my XR400 that I had:

engine mods were: ported and polished head, flowed head, new rev cam form WB, JE piston higher compression stock bore (11:1 if I remember correctly), WB high rev ignition, new stainless valves, new "harder" valve seats (this combo allowed the XR to rev the moon and not blow up), WB e series exhaust, FMF powerbomb (sounds just like my YZ), bored out carb by 2mm and polished carb

Body mods were: A-Loop seat and tank, Revalved suspension for MX by JM racing, eibach springs and race tech gold valves (in both the front and rear suspension) CR front and rear fenders, RM front # plate! etc etc

Jetting specs: 168 main, 68 pilot, 2 1/4 turns on pilot screw, needle in stock position, float at stock specs! (They didnt have the mikuni pumper when I did this mod so im sure I could get even more HP from this XR if I installed one)

Anyways about the ignition mine lasted about 2 1/2 yrs and then for some reason my bike started running weird...sometimes it would run great down low and sometimes it wouldnt! I spent hours adjusting the carb (float, jetting, etc!) but it didnt help. One day I decided to put the stock ignition and CDI back on, and that was my problem. Something obviously wasnt the working correctly in the ignition and it caused my bike to sputter! I think the WB ignition is a great deal and allows the XR to "run like it should" after putting the stock igniton back on it just wasnt the same, I couldnt lift the front wheel with ease in 4th and 5th gears!

Sorry to blabber on but I think as long as you have the "normal" hop up mods such as: new exhaust airbox snorkel removed, new air filter, rejetted, etc and your ignition is becoming the "bottleneck" in your performance...then this mod will be great! It allows you to have the mid range hit and you eliminate the bog at the bottom (very similar to a YZ)!

Another <$100 mod which gives you awesome snap is a higher compression piston (I had a 11:1 WB JE piston) you dont have to use race gas and you dont have to bore your cylinder! With these mods I could easily smoke 98-99 YZ400's and it was pretty cool to see everyone at the MX track wondering "is that an XR"? Anyways I hope this helps in your decisions, if you have any questions email me at: motoman393@hotmail.com

Garrett

Posted by: Handl-it---------------------

My Xr is a 98 model 400 and has been the best bike I have ever owned! I can always use more power like the "Toolman" but like to keep it simple. The Mikuni carb makes it start easier and it revs much faster. Power is better across the board, more even with better contol. The power is smooth as before but its there faster. I really think this carb should be the first mod a guy does to the 400, then the rest for more power!

Posted by: John K---------------------

motoman393:
got any pics of your xr? Love to see and hear more about it.

mtngoat:
I suppose this kinda mod depends on your right hand a bit. I'm not
sure if the unit has any rev limit whatsoever. Perhaps it just relies on
the physical limitations of the motor as so many others so / used to.
Perhaps one of these new twin curve units might be the best bet.

Posted by: michman---------------------

Well, I just order the Rev kit for my XR and in should be here Friday and I will give you a ride report. So for what I have done to my XR4:
Al Baker 430 kit
Cams
Pumper Carb
Big Gun Exhaust
A-Loop Kit
SRC Fork Brace

Mike

Posted by: Wolf---------------------

How many miles do you get to a tank ? (A-Loop)

Posted by: mtngoat---------------------

Motoman, thanks for the feedback.
Michman, looking forward to your review.

My 96 XR4 has the 440 kit, but otherwise has typical (filter, airbox, pipe, jetting) engine-related mods. I'm planning a top end re-work next winter, but I'm not considering a cam unless I need it. My preferred riding calls for more low-mid range. All this considered, I'm having a hard time reaching a conclusion that the Rev Kit is good for my situation. But, the carb is sure looking good!

Posted by: biker---------------------

I have the pumper carb and XR's Only pipe on my 96 XR 400. It's an awesome setup for what I use it for, mostly mountains and tight trails. What do you guys think about the SRC fork brace. Is there a noticable difference in the handling?

Posted by: motoman393---------------------

John K,

Yeah I have a few pics on my wesite http://www.scorpius.spaceports.com/~mx393 I just uploaded my site last night and there arent many pics of the XR400 (maybe 3 or 4) but I will be adding some in the next week! The pics are all old thats why there is a FMF exhaust and stock header (now it has fmf powerbomb header and WB e series)

XR Wolf,

I can go about 2 hrs (on a MX track) with my Aloop! When I goto the trails I can do 2 20mile loops back to back and it almost hits reserve! I think the tank size is 2.2 gallons (which is .6 gallons less than stock) but boy does the ALOOP make a difference in how well the XR handles! Later,

Garrett

Posted by: mtngoat---------------------

biker, I ride mostly mtn trails with lots of rocks. The SRC noticeably improves handling for me. It takes a lot fork flex out. Do a search on it. Lots of good posts. Follow instructions to a tee, if you do it.

Posted by: Wolf---------------------

The fork brace really helps. I find myself hanging on the inside of a berm/rut more, since the bike actually turns more accurately. I am trying to get used to that and steer a little less.

Posted by: xrsforever---------------------

The SRC brace is the best single mod you can do to an XR.Be forwarned you will need a fender brace after cutting the front fender cause it flops around too much. I think the SRC brace cost me $ 199,the fender brace $15,buy them both.You need to tap(add threads to the top of the bottom triple crown or drill out the front fender bolts on the fender brace,good support at SRC,

Posted by: michman---------------------

Before all the engine mods, but with the pumper carb I have gotten 55 miles with the A-loop tank not sure with the new mods through only have gotten to ride twice since having done all the work to the bike.

The SRC fork brace is awesome it made the bike handle some much better. No more fork flex when hitting corners with a vengence.

Put the Rev kit on tommorrow will ride Sunday and Monday. Thhis will be the last time I getr to ride my bike until dirtweek. I will fill all inMonday.

Mike

Posted by: Handl-it---------------------

A loop guys, have you ever filled your empty tank to see how much it really holds? Mine holds 1.98 gallons filled to the very top of the rim. Now how far can you go before you run out? I think my Mikuni carb is a little bit better for mileage than the stock carb on the trail. On the advance issue has anyone tried to just advance the stock timing a few degrees?

Posted by: michman---------------------

I put the rev kit in Saturday and rode sunday. First I thought the directions could be alot better than they were but after redaind them about five time over finally got it. One other thing is that the pick up unit looked like it was hand ground to fit the XR4 and had to file and use the dremel to get the air gap correct.

First let me strat off by saying that I only have been able to ride my new motor set up 3 times before doing the Rev kit and I am also trying figrue out my gearing.

I did notice it did take away some of the bottom end that I had before and it did make it a smoother transition to the mid range. Before it was was a massive hit right of the bottom and that I like but I miss so of the bottom end power. I really don't think it makes the bike rev that much higher if at all, just by the seat of the pants of course it seemed to rev out just like before. In the instructions it said it would rev to 11,500 but that is a bunch of crap.

All in all I would make this the last mod that you would do if at all. I would make may first the pumper carb that one thing alone will make the bike in more ways than any other mod you will do to the engine that of course is my opinion. Also some of the others on the subject let me know if there has been anything else that you have done to make your bike better.

One last thing on my A-Loop tank with all the engine mods I lost 10 miles of gas miliage per tank. I used to get around 55 miles now I had to go on reserve at the 45 mile mark and the parking lot was 1 mile away and I am not sure how far I can go on reserve.

If you have any more questions please asked.

Mike

Posted by: mtngoat---------------------

Thanks Michman.

Handl it, I had thought the same thing. On my CJ7, I was able to significantly improve performance simply by advancing timing (but not too far), which is suggested by the manual for higher altitudes. I asked the same question of the White Bros. (what about just advancing timing?). He said that the timing couldn't be advanced without causing serious kick-starter "kickback". That's why the initial advance is left the same and the curve is changed somewhat.

Posted by: Handl-it---------------------

So if you could adjust your timing, you wouldnt have to but a kit? I just cut a gray wire off my Wr250f to make it run better, so why not bump the Xr timing up to see what happens. Now running stock pipe, vortip, Mikuni carb with 127.5 main jet, Uni filter, air box opened up, and 10 to 1 compression piston. Stock tank gets about 60 miles before reserve. We always used to chage timing on the cars up here by 2 degrees for the altitude. The Honda starts so easy now serious kickback sould take lots of timing advancement. Anyway I will give it a try to see what happens. As the Toolman says " More Power"

Posted by: Shaw520---------------------

Guys, having some experience with getting these bikes to make power, IMO the big bore kits will yeild the best HP to dollar ratio, without taxing the valve train, and without exceeding the normal rpm range. And, in the same price range. Changing the cam, and rpm range will put a limit on reliabilty and longevity.
Also,..with the bore kit, the only real necessary item to go along with it would be a pipe and silencer. After that,...a pumper carb and polished ports only make it better!

Posted by: mtngoat---------------------

Shaw, I took the long analysis route, but I'm coming up with about the same conclusion. Oh well, learned something in the process.

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White Bros XR4 Rev Kit

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