Documented Effective & Affordable XR100 POWER upgrades

I've often read the question here 'what is the best affordable power upgrade is for a relatively stock XR100?'.

Many different answers are usually generated. Very few have a verified answers (not to say that the response is incorrect, just not verified); BBR notably does acknowledge a modest 2 HP gain over stock with their 120 BBK though if I recall it's not stated as to what pipe and carb are used in concert with the BBK to generate the extra 2 ponies.

Aside from uncorking the intake & exhaust/jetting (yawn) I'm betting the best bang for the buck on a stock XR 100 is a lightened flywheel. While this won't show an improvement in horsepower generated by the engine, it does reduce the weight on the crank and provides a great improvement on acceleration. Inner rotor kits for the venerable 100 are currently anything but affordable. I'd also be concerned that they sacrifice flywheel effect much more than a lightened stock flywheel, making the bike more difficult to drive.

In the coming days I will be putting together a comparison of my stock, uncorked (and very tired) engine, then with the lightened flywheel only.

I thought I'd set a steady idle speed with the engine hot with stock flywheel, then see what the change in engine idle rpm is with the lightened flywheel. Yup, I do have an inductive tach, though it's for 4cyl engines. The reading will not be accurate to true engine rpm, but for the purposes of comparison reliable.

Lightened flywheel is the first step; I have also laid hands on a 120 BBK, camshaft and pipe. I'd like your input as to how comparisons or 'real' numbers could be done to show the results (sorry folks, no access to a dyno) of each of these items as individuals. I do have access to an array of tools / equipment, so don't be afraid to ask for a technical result.

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On the flywheel, I did not notice any difference. There's not a whole lot to take off like a TTR125 flywheel. It's really hard to say what is the overbest this. Obviously, I feel a BBK is problem number one, but without a pipe or airbox mods then it's pretty negated. But we've dynoed things like spacing out the carb, multi stepped pipes, meg pipes vs. straight pipes, carb manifold angle, there are alot of varibles. We did a ton of things just a get to 11hp or so (using a knobbie on the dyno). But the Kitaco kit was the overall best combined with other stuff. That was until it blew up. But my friend just bought some guys National Flat Track number one bike that Frank Nye built that is just stupid fast. He said it's way faster than his kitaco motor.

I'm not so sure about how much there is or isn't to be taken off on the XR flywheel; It appears to have been put on a serious diet as it's had material removed from the face as well as radially. The Purolator scale at work will tell the tale. You can't lose taking weight off of an already heavy crank ass'y (by comparison to the XR80). The idea is to provide some idea as to how money can be spent effectively on a basically stock engine; To most, Kitaco is the antithesis of affordable.

I think on a stock engine the lightened flywheel will be much more noticeable than one with other mods, being that the stock XR100 engine is a asthmatic low revving slug.

dont forget the ATC200X 24mm carb, the bore kit will increase low to mid power, but the larger carb will increase the top end power to widen the powerband. If thats a TB cam dont expect a whole lot from it, pretty mild, You will like the white brothers pipe, good all around pipe with a larger headpipe diameter than most of the other aftermarket pipes.

Edited by dumbdotdog
dont forget the ATC200X 24mm carb, the bore kit will increase low to mid power, but the larger carb will increase the top end power to widen the powerband. If thats a TB cam dont expect a whole lot from it, pretty mild, You will like the white brothers pipe, good all around pipe with a larger headpipe diameter than most of the other aftermarket pipes.

The weigh scale at my local Purolator depot indicates the stock CDI XR100 flywheel is good for 2.45 Lbs as removed from my bike. The Firepowerminis lightened flywheel is a svelte 1.75 Lbs. This is gonna be interesting :thumbsup:

The cam is a 'surprise', I'll save that for later. Yeah, I'll need a 24mm carb to get the most out of the BBK and cam. I'm trying to track down a PE24, but will most likely end up with the more plentiful (and cheaper) ATC200X carb. Pretty sure I read in one of SoCal's posts that a CR80 cable and throttle are required for the ATC200X?

As with anything bikes, boat, cars whatever , its usually a combination of alot of things working in tandom that gives the greatest results , your going to get all kinds of opinions on what one thing works best , because everyone has a different idea of what they think can be improved depending on the application , and the money they have to throw at it, personaly i liked the lightened flywheel it would rev up quiker on a mx track and help clear jumps i couldnt before , im 200pds though , my 10yr old son would probably benift from something else

after rereading your title , as far aspowewer documented ? i guess a dyno is the only why to prove anything,the 100 has been around so long that , anyone can read threw old posts ,and find the same info

most popular /reliable bbk is the bbr120 kit ,for a carb which i did before the kit atc200 , cam,there are a few web,mega,tak ''that actually'' work , an oil pump i feel is essential ,some clutch work if your heavy,pipe thats another 4-5 avalable the best? ive never seen a dyno , anything stepped probably best

,the flywheel ,talked about above i feel is worth it ,firepower does em cheap , another mod is when you bbk and have your head off firepower does some porting/blending cheap, matching the intake boot helps too, you might as well put a coil on that has some stronger voltage to help burn that gas up, bbr also has a cdi , all in all , all these things together ARE proven to work, and compatable , Ithing when you leave this combination of things , your going to start to spend big dollars, and you might want to give consideration to different bikes 150r cr85 etc , both my 100's have everything , example we did a practice day at lodi cycle bowl short track , and i watched cr85's blow by me on the strait aways and i had the 100 hammered .

but on a small mx track , that bullet proof electric powerband of the 100 is great

Fgrote

I agree with most of what you brought forward (not sold on the CDI or coil). A Dyno will come into it at the end of my build ($80 for 3 pulls isn't cheap when there are multiple steps) just to prove out the final HP #. Going further than a BBK carb/cam/exhaust and the costs start become exponential.

The intent is to provide as much honest info as possible using commonly available and affordable parts (the WB pipe is a bit of a stretch on the affordable, but Terry @ firepowerminis.com made me a deal I couldn't refuse).

If BBR says Dyno proven 2HP for their 120 BBK, I believe it. I'd really like to know what pipe/carb they used to extract that number, I sent them an email; we'll see if they respond.

The intent of this post overall is to provide real numbers without bias so that folks will know what they are buying in each instance. Engines only and Yoshimura are the only BBK builders that I've found that openly post their BBK results; unfortunately EO doesn't list for either of their XR100 kits that I could find and now can't find Yoshi's # either (not that they are overly affordable).

If you or anyone else comes across published numbers, post them here, I'm sure people would appreciate it.

BTW, the firepowerminis lightened flywheel was good for a 50 -75 rpm gain at idle vs. stock flywheel - Documented, here http://www.youtube.com/watch?v=R8FNrH5ie5s

Doesn't sound like much but the proof is in the pudding; first riding impression of the lightened flywheel; some loss of flywheel effect but can still crawl and accel in first, throttle response is fantastic (well, comparatively).

i have the wb pipe on both my bikes too they were blown out on ebay a yr or 2 ago.

terry did my flywheels i would recomend him , he's reasonable and does good work .

the other way people can judge performance is with a gps , i think a stock 100 does like 50 somthing? both my bikes do 65+ before the bbk and cam and port like 61+62mph plenty fast enough to give you road rash :thumbsup:,

i did alot of playing with parts /gearing and a gps

ps i think the coil/ cdi made the bike crisper but not on the top of the list for big gains for sure

i have the wb pipe on both my bikes too they were blown out on ebay a yr or 2 ago.

terry did my flywheels i would recomend him , he's reasonable and does good work .

the other way people can judge performance is with a gps , i think a stock 100 does like 50 somthing? both my bikes do 65+ before the bbk and cam and port like 61+62mph plenty fast enough to give you road rash :thumbsup:,

i did alot of playing with parts /gearing and a gps

ps i think the coil/ cdi made the bike crisper but not on the top of the list for big gains for sure

Pretty much what I was thinking for the coil & CDI, however a $5 C7HSA plug will do the same. Pretty much have to be running race fuel compression to get any tangible performance out of ignition components, even then it's more for quench than power. From a stock perspective Mph studies with my XR are a little tainted due to 14" CR rear wheel and sprocket selection (more grunt than go). I have noticed since installing the FPM flywheel that I seem to run out of gear quicker (on accel), so +1 tooth countersprocket is en route. But that doesn't mean I can't do comparisons.

No word from BBR.

BBR big bore kit ...complete with big finned cylinder...high comp big bore piston kit....camshaft...spring kit...and complete gaskets...

is VERY hard to beat on power for $$ spent

cut a few airbox vents and add a pipe with a stepped header so you don't lose throttle response

you can get all that for about the price of just an exhaust system on a fullsized bike

VERY fun and reliable setup

Suggestions on a hiugh comp piston kit brand? I haven't actually seen a high comp kit to match the BBR 120 kit before.

Suggestions on a hiugh comp piston kit brand? I haven't actually seen a high comp kit to match the BBR 120 kit before.

Yoshimura has their kit on sale @ $270. Rated ~ 12.5 : 1 compression, it should kick a$$ and take names. You will have to pony up for a carb, full exhaust (their exhaust is on sale too @ $180ish) and a cam to get full benefit. Yes, the BBR does come with a cam; no it's not noticeably better than stock as mentioned by Fgrote.

Tally that up and your over $800 for a BBK, not really 'affordable' as you can buy a pretty nice late model 100 for that money, or a slightly tired CR80 that'd still walk all over an XR loaded with Yosh goodness.

BBR hasn't gotten back about their claimed 2HP BBK carb/exhaust combo either, though I did read in their instruction set that they recommend a 105 main jet in the stock carb for their 120 BBK...

Interesting.

BBR hasn't gotten back about their claimed 2HP BBK carb/exhaust combo either, though I did read in their instruction set that they recommend a 105 main jet in the stock carb for their 120 BBK...

Interesting.

Hmm, only a 105 main? Is that assuming a stock carb and airbox? Seems rather small. I was running a 102.5 on my stock bore, but then again I removed the airbox long ago.

Anyone have any idea on the compression of the BBR kit?

The BBR 120 kit is 10.5 to 1 CR

Wow that yosh kit is a sizeable jump in compression. I would suspect that would make more power even at the 5cc disadvantage, and at that price not far off from the bbr.

the BBR kit measured in at 12.5:1... not sure where you got the 10.5:1 numbers...

the difference in the BBR kit...along with cutting the airbox and re-jetting...but still using the stock pipe.... was from having to yank on the bars in first gear to do wheelies on stock machine.... to wheelies on throttle alone in first 2 gears and slight tug on the bars for third gear wheelies....

the cam is an excellent midrange cam that comes with the kit...

anyone who has installed and correctly jetted the kit will tell you that you can't beat the power for the money spent.... unless the goal is to just spend more money to say you had it to spend :smirk:

the BBR kit measured in at 12.5:1... not sure where you got the 10.5:1 numbers...

the difference in the BBR kit...along with cutting the airbox and re-jetting...but still using the stock pipe.... was from having to yank on the bars in first gear to do wheelies on stock machine.... to wheelies on throttle alone in first 2 gears and slight tug on the bars for third gear wheelies....

the cam is an excellent midrange cam that comes with the kit...

anyone who has installed and correctly jetted the kit will tell you that you can't beat the power for the money spent.... unless the goal is to just spend more money to say you had it to spend :smirk:

Where did you get the 12.5:1 CR? Wiseco is 12.5:1, but BBR doesn't list their's and when they did, it was 10.5:1. Plus Gman mesure's everything himself and is the best source for number's for the XR100. Yes, the BBR kit is a good kit for for the XR100, but for serious power, you need to step up and spend money. There's just no way around it.

i measure everything in my own shop myself.... actual measurement was 12.47:1 so i just rounded up thinking they intended it to be 12.5:1

the small combustion chamber combined with not the highest cylinder filling efficiency , makes the small engine have good resistance to detonation... this setup still works well with premium pump fuel as delivered...

Thanks Socal!

Ya- I've sunk my teeth into the BBR kit (CC the head, piston molding/cc'ing, etc,etc) Including degreeing the BBR cam- have to disagree with your CR findings, but To each there own-it is what it is...

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