Villain's Folly - Ultimate DR350 Supermoto Racebike Commuter

Discussion in 'Thumpers' started by The Villain, Aug 3, 2018.

  1. The Villain

    The Villain Adventurer

    Joined:
    Jul 29, 2018
    Oddometer:
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    'Merica (for now)
    Useful / Inspirational Links up top:

    ADVrider DR350 Index -- not going to link to every individual build thread and piece of info...they can be found here.
    Tiny War Machine Links -- some repeated links from the ADV index but some other fun rantings, ideas and tracker-related stuff, too.
    This Old Tractor -- Also in the above links but worth having up top for the factory service manual and Greg Bender's excellent O-ring kits alone.
    '91 Dirt Bike Magazine Article -- if a stock bore 350 can be fast...
    DR350 Supermoto Thread -- definitely NOT the end-all-be-all DR350 thread, as the title proclaims, but some inspirational images and another source of info on running sportbike wheels on a DR.

    Happy to be here, folks. Long time lurker, but not really a dirt guy so didn't register until it became time to make this build thread. I've benefitted from a lot of build threads over the years, and now I'll attempt to give back.

    Why post this to ADVrider, instead of say a supermoto forum or my local board, the very active BARF? Because here lies the ultimate lore of all things DR350. And because, frankly, this forum is possibly the most well respected of the moto boards in all the english-speaking net.

    What this thread is...

    A chronicle of how the bike I have came to be, and how it will transform once more, along with (no doubt frequent) pleas for help and advice from the moto-geniuses who frequent these parts, and questions answered when I'm qualified to answer them.

    What this thread is not...

    An invitation to tell me why the DR350 is not the platform I should be using (I'll address the alternatives just once, below), why I shouldn't waste time and money polishing a turd, that there's no replacement for displacement. Because, of course, there are several. To proactively hurl an idiom in retort, there's more than one way to skin a ferret. And I happen to know that's factually true.

    Goals...
    1. Have reliable 2-wheel transport for short trips around town that won't overheat at stop lights or suffocate during brief highway blasts.
    2. Have a fun and approachable toy for the twisties and occasional mid-range day trips.
    3. Roadrace at least 2 events next season, plus one or two track days.

    That's right, I want all those things in the same machine. Finding the balance will be a major theme of this build. But the 3rd goal (race bike) is of vital importance and some compromises to the first two goals will likely have to be made.

    What we're starting with...

    [​IMG]
    #1
  2. The Villain

    The Villain Adventurer

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    1994 DR350 - dirt model. Plated with Baja Designs kit, back when you could still legally do that in California (no more). Stock TM33 pumper carb (already jetted per Jesse), airbox top cut (per Jesse), White Bros. muffler on stock header pipe. KX500 front end grafted on (vintage unknown). Shock worked on at some point by someone. Clarke tank. Fat tapered bar.

    Purchased for $750 in dirt trim from a cool dirt guy in So Cal about 8 years ago. Instantly 'Tarded. (That is, Supermotarded...don't get touchy). That entailed...

    GS500 wheels (acquired for free by agreeing to haul off the frame and parts box too...guess not everyone has a dumpster).

    [​IMG]

    Spacers for fitting the rear wheel.

    [​IMG]

    Not sure how, but the axle for the KX500 forks fit perfectly with the GS front wheel. Pirelli Rosso II tires were fitted, 110/140 (currently sits on Bridgestone S20 Evos, same size).

    A custom brake caliper relocation bracket was fabricated.

    [​IMG]

    This was welded up from sandwiched stainless sheet. It has worked well, but will be replaced.

    It held a Nissin 4-pot caliper (common on Honda CBR 600 / 900 / 929 / 954, among others). Swapped on a 5/8" sportbike Nissin master cylinder for the stocker (too big...was eventually changed for 1/2" off a TRX quad).

    To make the gearing a bit less ludicrous I had Sprocket Specialists cut this rear sprocket.

    [​IMG]

    That's it.

    Within days of the sumo conversion being completed the DR was taken for a thrashing around Laguna Seca.

    [​IMG]

    In an Intermediate track day group I was humiliated down the front straight and up the Rahall straight, but made mince-meat of sport bikes in the tight stuff (look out on the inside into T2!).

    [​IMG]

    In all, I managed a bit of passing myself and when asking a control rider if I should bump down a group because of my low power I was told "No way, stay put."

    Since then it's been to Laguna 3 more times (riding to the track from SF, riding the track, riding home), played in canyon and forest roads around LA and the Bay Area, handled highway, urban and suburban commuting and also sat forlornly at times in garages and storage units when I wasn't using it.

    Now it will move into its next incarnation.

    The Elephant in the Room...

    Why the hell would I build up a DR350? Or (gasp) roadrace one???

    The answer verges on the personal but I'm going to put it out there once so I don't have to hear about it again. The DR is what I have. It's one of my modes of transportation and needs some money put into it to make it run better, which leaves less money available for a stand-alone race bike...which I also don't have room for at the moment, my garage space decreasing as my family size literally doubles all at once.

    {Plus the local SV race grids are kind of small, and I wasn't able to get along well enough with a 450 "Cripple-Triple" in a recent test ride.}

    Why not sell the DR and buy a better platform for both street and track?

    I want to race a lightweight class and street-legal Ninja 300s, SV650s, even Groms are prohibitively expensive...and that's before they get all the race bits they absolutely need to be anywhere close to competitive on track. Plus, regularly swapping street and race fairings (and lights) is a PITA. On a supermoto it's a cinch.

    What about other sumos?

    XR400 - can be difficult to find plated ones in California, 5-speed, most likely needs 'tarding.
    DR/KLR/XR650 - a lot bigger and heavier for only a little more power, larger bore could does put me in different race classes, most likely needs 'tarding. Ditto other large-bore thumpers.
    DRZ400 - 5-speed, plus water-cooled motor definitely puts me in harder race classes*. Ditto other water-cooled thumpers/sumos.
    2-smoke? - I've thought about it. Found a couple plated ones. Na ga do it.

    I suppose a water-cooled 250 single might keep me classed correctly, but finding one that's full-sized, fast, can do double-duty street and track (5-speeds!) and isn't all new and farkley and espensivo (and orange) would be a challenge.

    Besides...I like the DR350. It's fun. I'd rather keep it and make it kinda fast.

    *This turns out to be more club dependent than I thought, actually. While a couple of my old racing orgs used to let air-cooled singles basically get away with anything, AFM doesn't give them any more concessions than water-cooled singles. So I could still theoretically be gridded with, for example, a 63hp Husky FS 450...which doesn't seem particularly fair, but maybe those sort of bikes aren't showing up to play? (Fingers crossed)
    #2
  3. The Villain

    The Villain Adventurer

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    The plan...

    1. Motor. More fresher, more powerfuler, more reliabler...More Motor. (Including intake/carb/exhaust considerations).
    2. Suspension. Rebuild/revalve what I've got, make it better suited to my needs. It's still set up for dirt, for crissakes.
    3. 2nd set of wheels with slicks race tires (slicks look not to be an option in my sizes).
    4. Race legalize. Belly pan, safety wired, etc.
    5. Tweak the little stuff.

    First steps...

    Not going to tackle the motor on my own. I've already spoken to a detail-oriented, home engine builder who came highly recommended on my local forum. He's really an XR guru but is game to put together a tight DR motor if I get him the necessary parts. Machine work will likely be done by Engine Dynamics.

    Design of the motor is already beginning to coalesce, but I could use some advice.

    BORE:
    I'm purchasing an Eiger jug and Wiseco 83mm piston from a local ex-DR rider (and possibly forum member here). So the plan is to go with the small overbore to 385cc. Using the Eiger cylinder that should give me a safely thick sleeve remaining (thanks to the meticulous research of thump!).

    HEAD:
    I need a head. A couple of the fins are cracked on my stock one:

    [​IMG]

    I'm sure that's affected cooling a little, but the bike has run like this for years. Nonetheless, it needs to be fixed. Unfortunately, DR350 heads seem as rare as ever and Eiger heads have shot up in price since this swap was first discovered. Is it possible my head can just be repaired?? I know welding cast stuff can be tricky.

    (Unless you're Rob Muzzy! Speaking of trick and cooling fins, man, would I love the extended cooling fins on this old Muzzy ISDE DR350!

    [​IMG]

    ...Ah, dreams. Link to that whole article at the top).

    GASKETS:
    Can someone confirm for me that I want to use the Eiger base gasket?

    What top gasket do I need if I'm using the Wiseco piston on an Eiger head? What about on a DR head?

    CAMSHAFT:
    If I do use an Eiger head, sounds like the cam is slightly less agressive than the stock DR cam, so I'd want to swap that (I believe they're swappable??). BUT, even if I keep using the DR head, it's hard for me to conceive how I get this bike in racing shape without going to a hotter cam grind! The extra top-end power is probably crucial.

    Unfortunately, this step will probably double or even triple my engine build cost right there. Megacycle's quote, for example -- $300 for the cam, $200 for the R/D valve spring and retainer kit (Kibblewhite kit doesn't have enough lift), plus what sounds like a stupid amount to harden the rocker arm surfaces.

    {By the way, I'm happy to be told I'm wrong and that a cam is unnecessary. If I can break past 35hp with the 385cc bore with rebuilt head, full exhaust, TM36 or FCR37 and a better airbox, I'd strongly consider it.}

    Any advice on my cam problem?

    The available options look to be:

    Web Camshafts
    Mild: .335 lift / 240 duration @ 0.050"* -- Supposedly drop-in, would still replace valve springs as part of rebuild, could just barely get away with the slightly cheaper Kibblewhite kit, or maybe even go OE quality. Maybe too mild an increase to bother??
    Race: .390 lift / 248 duration @ 0.050" -- Needs not only higher lift valve springs but apparently also shortened guides! Nix.

    Megacycle (catalog p.51)
    Mild: .372 lift / 236 duration @ 0.040" -- Pretty good for a "mild" profile! But needs R/D valve spring kit (chromoly only available).
    Race: .402 lift / 255 duration @ 0.040" -- Whoa, getting a little crazy. Not building a Baja bike.

    Stock profile for reference: .328 lift / 226 duration @ 0.040"

    *I'm using the clearance durations since Megacycle doesn't list the full duration in their catalog.

    The White Bros cam is no longer made.

    I'm assuming with ANY upgraded cam I'd be stupid not to have my rocker arms hardened? How much should I expect that service to cost?

    I'll leave that as the starting point -- looking for opinions on my top end motor build. I've got a ton of questions about carbs, airbox and exhaust too, but I'll save that for next time.

    Feel free to ask any other questions this silly project brings to mind.

    Thanks everyone!
    #3
  4. plugeye

    plugeye MC responder

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    #4
  5. Friedom

    Friedom Onward and upward!

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    I'm a fan of your work. "Official" street bikes in this size they I've tried just don't feel as fun and flickable as a tight DR350. I'm working on the gs sumo swap on my 99 dr441SE currently. You are inspiring me to follow through!

    I did the Eiger cylinder/385 swaw on my last DR, and it really woke the bike up! I had pinging issues, but running high octane helped. I ultimately chose to sell that bike and go with a 441 kit with standard 9.5:1 compression ratio as mine is primarily for adventure/camping/going into the deep, and I didn't want to worry about octane. But that 385 sure was fun!

    You don't need to change your cam to go to a 385. Sure, it'll help, but you'll get a very appreciable performance boost with just the 385 kit. Everything else is bonus points.

    I went with the procycle piston and head gasket. MLS would be ideal if you can find it, but I was happy with what it came with.

    In closing, your pictures and story lead me to consider for the first time actually racing when I get my sumo setup finished. Just to eat up the corners and watch people wonder what in the world I'm riding. I go out of my way to remove all badging and identification(legally. I don't touch serial numbers or tags). Last item is the Suzuki logo on the oil filter cover.

    Have fun man, thanks for posting this thread. Sub'd.[​IMG]

    Sent from my SM-G930V using Tapatalk
    #5
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  6. The Villain

    The Villain Adventurer

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    Interesting. So are you saying that the cam for the kickstart model is set to different timing than the electric start model? I'm confused but this sounds important.

    This is nice to hear. I'm still a little worried about running out of steam way too early on race track straightaways, but sounds like maybe the 385 will give me more of a boost on its own than I was expecting?

    And thanks for the support, Friedom! Glad to hear that you're getting your own sumo conversion together. Looking pretty slick already...I like your luggage rack and need your tank. And why are so many GS wheels white? Gets so dirty.

    Something to keep in mind with the GS (or any 17") wheel conversion: your kickstand will now be too long.

    You can live with it (I did for a couple years), but eventually you'll get tired of looking for slightly downhill slopes to park on, or getting nervous that a stiff breeze or dumb kid will knock it over when parked on flat ground.

    There are probably shorter kickstands from other bikes that you can swap on, but if you can weld, the solution is easy...
    [​IMG]
    Now I cannot weld, but have a friend who can and we made short work of this -- me chopping and him MIG-ing. I don't remember how much I cut off but it's now just under 13.5" from the foot to the center of the pivot bolt and that length has been perfect. My front end might put me in a slightly different stance than you but it'll be close.

    Did a little basic repair/maintenance work today. I'd had a worsening high idle problem that was part intake leak and part mixture screw / throttle stop / throttle cable mis-adjustment. Trying to get my carb boot air-tight without having the correct O-ring had led me to over-tightening and breaking it. Got a new boot and popped it on today...
    [​IMG]
    After that and a lot of fiddling with screws and nuts and cables it seems to be running more or less okay now...will do some more thorough testing tomorrow.

    So as it stands the bike looks like this:
    [​IMG]
    Ugly, as is its way, naked of its side plastics (they're in the garage), and ready for more power! I hope to pick up the Eiger jug and piston this week.
    #6
  7. totensiebush

    totensiebush re-tarded

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    What class are you planning on racing that allows a front end swap, big bore, cam, carb but doesn't allow slicks?
    #7
  8. The Villain

    The Villain Adventurer

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    Well I'll be starting a discussion with AFM and possibly WERA folks about my options, but at first glance of the AFM Competition Rules for 2018, could probably choose from Formula 3, Formula 2 (when not run at the same time as F3), Formula Singles, 250 Superbike, Clubman Lightweight and Legacy Lightweight (though I'd probably get creamed), or possibly Legacy 250 if I can get the rules committee on board with air-cooled singles getting to run down a class like in Superbike (probably won't go for it).

    I didn't say I wasn't allowed to run slicks, I'm saying there don't seem to be any 17-inch race slicks on the market period in 110/140 sizes (or even 150, doesn't look like).

    And at the moment my carb is stock equipment. We'll see if that changes.
    #8
  9. The Villain

    The Villain Adventurer

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    Hey Friedom -- since it looks like you don't have tires on your GS wheels yet, could I get you do me a favor and weigh them and post the weights up here? I'm working on some alternative options for my race wheel-set but need to figure out if there would even be any benefit.

    I also realized that I never actually spoke to your comments about racing. It's definitely next level shit and I recommend anyone who has the hankering should try it because it permanently changes you a little. I'm sure it's the same for people who race dirt. Some don't like the added stress and go back to track days, canyons or trails, but you might just find that moment waiting for the green flag to drop surrounded by a whole bunch of other bikes revving their engines brings something out of you that you didn't know was there. To paraphrase Fight Club, how much can you really know about yourself if you've never been in a race?

    As for racing the DR350...good chance I'll get well and truly smoked, but on tighter tracks it might just have the ability mix it up. The rest is up to the rider.
    #9
  10. Bucho

    Bucho DAMNrider

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    Cool!

    The DR350 will always hold a special place in my heart. While not my first bike, it was my first every thumper and dirt/dualsport. For a short while it was my only transport and I used it as a daily fall/winter commuter in MD. Was such a great little bike.
    I finally put half decent knobbies on it and started using it to learn to ride offroad.
    #10
  11. dbarale

    dbarale Squiddly slow

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    My GS wheelset if off the bike right now but has tires on it. Would that help you?
    #11
  12. The Villain

    The Villain Adventurer

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    Thanks for the offer, dbarale! But I want the bare wheel weights (I guess minus rotors, too) to compare against other options. Could use my own but then I'd have to pull the tires off and everything...
    #12
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  13. Friedom

    Friedom Onward and upward!

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    Hmm do you want it minus the bearings as well? And the material that was taken off for clearance? I'm in a good position to get you that for the rear. Front is mounted up already, but I'm running an fzr1000 1990-92 front wheel for the 17mm axle anyways. Looks the same as the white 3 spoke cast gs wheels though.

    Sent from my SM-G930V using Tapatalk
    #13
  14. The Villain

    The Villain Adventurer

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    Verrry interesting on the FZR wheel. Yeah, the rear weight in that condition would be good. Maybe with and without the sprocket carrier? In addition to my internet research I'm going to be making a trip to a couple salvage yards with my axles, dial calipers and a scale. :brow
    #14
  15. Friedom

    Friedom Onward and upward!

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    I have a second fzr wheel, circumstantially obtained by ebay sellers mixing up their stock, should you know anyone who could use it. Tire is pretty decent, but I think it needs bearings. And it's purple.

    Sent from my SM-G930V using Tapatalk
    #15
  16. The Villain

    The Villain Adventurer

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    Was riding the DR yesterday, feeling out the power delivery...I'm becoming more convinced than ever that I have to cam this thing up.

    With the bore and compression increase I'm expecting I think I'll just rip up to 6th faster but still run out of breath up top. If I'm going to race this thing I need to get safely higher into the rev range and keep pulling the whole way.

    If anyone wants to talk me out of a hotter cam (or steer me towards or away from a specific grind), do it soon!

    Which leads right into the next power-making question: whither should I carburate?

    I'm running a TM33 pumper now. I'm not convinced it's completely healthy/dialed in any more, but doesn't seem to have the issue of carb body wear causing air leaks. With a bore increase, hotter camshaft, and full exhaust (and hopefully some sort of upgraded airbox situation), am I moving past the capabilities of this carb? Can it be bored to a more useful diameter? (I know Jesse used to do this).

    Other options...
    1. TM36-68 -- bigger bore, adjustable pumper, not super expensive new, can be made to fit.
    2. FCR 37 (MX?) -- widely available used, roller slide is smoother and won't wear out like a TM, hot start, can be made to fit.
    3. FCR 35? (if I can find one) -- possibly more appropriately sized than 37?
    4. ????? You tell me...
    #16
  17. The Villain

    The Villain Adventurer

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    With thanks to buzzword...
    [​IMG]
    Nice, clean Eiger 400 (really 376) cylinder. Shiny 83mm Wiseco piston ready to compress those gases at 10.5:1. They don't fit together, of course...at least not yet.
    #17
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  18. The Villain

    The Villain Adventurer

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    Okay, I'm making more sense of this now, and it sounds like this is going to be a snag if I replace the camshaft with an aftermarket one. Going to have to call Megacycle tomorrow, but am I correct in assuming that neither their cams, nor Web's, are auto-decompression?

    If that's the case, I'm guessing this bike will basically be impossible to kick start without using the decompression lever...no? And if that's the case...

    I was looking at using an Eiger head as a replacement for my cracked-fin stock head, but sounds like those don't support the manual decomp.

    So if all this is true, then my options are...
    • Don't upgrade the camshaft
    • Have my stock head repaired (possible?)
    • Have an Eiger head modified to accept manual decompression (possible?)
    • Have my stock auto-decomp cam welded up to a hotter grind
    Please, someone tell me I'm wrong and there's a simpler option.
    #18
  19. plugeye

    plugeye MC responder

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    i'd just try to repair the fins & put a manual cable/perch/lever on it.
    then you're free to use whatever camshaft
    #19
  20. Friedom

    Friedom Onward and upward!

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    Agreed. The fins just disperse heat, and you'd be increasing the surface area. Not a precise operation compared to about any other head work you're looking at.

    As for the carb, have you looked at the Lectron? A bit spendy, but I'm giving it serious consideration for my 441.

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    #20