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Personal Viewpoint:

Turning a stock Yamaha RD 250 or 350 LC into a Forgotten Era race bike.

This story has been put together to help and encourage guys wanting to get into "Forgotten Era" class roadracing on a Yamaha RD250 or 350 LC.


Picture: Brett Metcalfe's RD250LC racer.

Brett has had great success on the bike winning the South Australian period 5 State Titles for the past three years in a row,  finishing third in the 2006 Australian Classic Championship at Mac Park, Mount Gambier, as well as finishing second in 2007 Victorian Historic Championship for Forgotten Era up to 600cc.


Obviously, some of the modifications will not be allowed by other countryís Post Classic Racing governing bodies, but there should still be enough useful information contained here to assist you no matter where you live and race

Always be aware that modifying a motorcycle, of any type and in any way,  almost always reduces it's reliability.

Do not attempt any of these modifications to a road-going RDLC or any other motorcycle used on public roads. The improvements are designed strictly for motorcycles used in closed course roadracing competition.

Remember, motorcycle racing is dangerous. If you undertake it it is invariably at your OWN RISK !!

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Read about other guys' race setup tips

Click on the links for information:


Yamahaís early LCís are the best road bikes to use to create a Forgotten Era racer in my opinion. Period.

They are simple, relatively light, handle well and, above all, with the correct modifications, they are both fast and reliable. If youíre smart, they can be really cheap to buy and set up, though depending on the level of development you want to achieve, there can be a hell of a lot of work involved to reach anywhere near their limit.

Picture: Brian Donovan's LC with grinning son aboard !!

This article was written from a personal viewpoint,  using my own experience as the "data-base", as well as information given by other LC racers I have spoken to. It is by no means the "be-all to end-all" definative description of how to build an LC racer. Other guys will no doubt disagree with some of the stuff I've mentioned here. All I know is all this stuff certainly worked for me. I'm certainly no "guru" when it comes to LC's, TZ's or whatever, I just like to do things myself and spend the bare minimum I can.

The main theme of this article is "budget racing". Obviously, if you have lots of money to waste you can buy everything you need new from Yamaha and have specialist tuners spend days on your bike. This is something I never did when I raced LCís. I always took the cheapest way out and did almost everything to the bikes myself. Itís up to you, maybe this article will be of no use to you, you might have money to burn.

Itís divided into separate sections devoted to different aspects of the bike.

Enjoy !!

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  • Have a look at the frame and work out which lugs and brackets you can afford to lose and which ones will be needed. Things like the lugs for the stands, the battery holder etc. can usually go, but obviously lugs like those that mount the radiator etc. need to stay.

  • Get the white paint and a small brush out, mark the lugs to be sacrificed, strip the bike back to the bare frame and get the angle grinder out !!
  • Around 1 to 1.5kg can be saved if you put enough thought and effort into it. Save all the metal you remove and weigh it all when youíre finished. You might be surprised !!
  • Check you swingarm bushes while youíre at it, theyíll more than likely be seized in there and will need to be broken to be removed.
  • New ones are available through your Yamaha dealer, but a much cheaper alternative is to turn some up on a lathe out of nylon bar, which can be bought from any good bearing service.
  • Your steering head bearings could probably do with attention as well. Some guys replace them with tapered needle roller bearings but I never bothered. Just clean and grease them and stick them back in, unless they are badly corroded. If they are, once again, go to the bearing service for replacements.
  • Consider a steering damper if you find you are experiencing disturbing amounts of headshake. They mount easily to the lower triple clamp and a bolt welded to the frame.

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  • Suspension:

  • Check your rear shock to see if itís leaking any oil, or thereís corrosion on the centreshaft. Most suspension reconditioning companies these days claim to be able to rebuild any motorcycle shock. Put them to the test if youíre keen to spend money. As a precaution, ask your friendly Yamaha dealer to check his "Factory Service" information, if he still has it for the LC. It should list the standard gas pressure, give this figure to the shock rebuilder, if he doesnít already have it.
  • Aftermarket shocks are available from companies like White Power, Ohlins, Whitepower, Hagon and Maxton etc. if you are real keen to spend money, but donít lose track of the fact that your bike is a 20yo. plus dinosaur and you are racing in a low cost category of competition. Can you justify the expense? Donít forget thereís usually no prizemoney in Forgotten Era racing.
  • As far as forks go, check for leaks around the seals and replace them if necessary with cheap, aftermarket seals. Remember, you wonít be commuting every day on this racer, so you will probably never wear a set of seals out.
  • Closely inspect the tubes for rust specks and clean these up with fine "wet and dry" sandpaper, then oil them, let it soak in overnight and clean the oil off in the morning. This oiling/cleaning ritual will need to be kept up regularly, every couple of months, or after every time the bike is exposed to moisture. The other alternative is to track down a pair of tubes that have no rust and look after them.
  • Pull your forks right apart and clean everything in kerosene. Check the free length of your springs and replace if under spec. There are some good non-genuine springs available for these bikes, check the English bike mags for ads.
  • Run 15W oil, at 5mm higher level than stock to begin with and increase this if you still find you are bottoming out.
  • In my opinion, patter is the biggest handling problem with LCís. I have experienced it at both the front and back ends on LC's !! Play around with spring rates on the front end, this is usually the source of patter problems. Riding position can have an effect as well. Even consider "Gold Valves" from a KX80 ( I think they are the ones that apparently work in LC forks ) as a last resort, some guys have claimed this improved their patter problem. But the cheap options first !!
  • Oh, and donít neglect your tyres and make sure they are actually balanced correctly and round. Youíd be surprised how many top brand tyres for these things arenít round.
  • You can make your own "rule-conforming" external pre-load adjusters by drilling each fork cap and tapping a 6 or 8mm bolt into them, with a lock-nut. Put 10cent pieces on top of your springs, or a circular piece of metal to give the adjusting bolt something to press on.
  • Another good idea is to put an O-ring around one fork tube prior to fitting the forks back into the bike as a "travel monitor".
  • Donít worry about wasting your time with a fork brace, they do virtually nothing except add unsprung weight in my opinion. If you reckon your forks are twisting then find wheel bearings with a bigger ID and fit a bigger diameter axle.

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    Picture: Mark Boddy's LC racers.  ( Photo: Mark Boddy )

    A hell of a lot of development has gone into these bikes over the last 5 or 6 years and it has paid off with results for him.





    A word of warning: remove all rubber seals and plastic parts from your brakes before baking. I left the little window in a master cylinder once and it turned a lovely golden brown. You have been told.


  • Check your wheel bearings. If thereís any "notchiness" or "binding" pop them out of the hubs and clean and grease them. If this doesnít improve them then go to your local bearing shop and buy new ones, they are cheap.
  • I once fitted spoked wheels to one of my LC racers. To be honest they were almost identical in weight to the stock "mag" wheels and offered no real advantage except to allow wider tyres. But if you can be bothered, old air cooled RD wheels can be made to fit quite easily.

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  • Controls.

  • Fit "clip-on" handlebars. You can make your own out of steel tube if you know how to weld well enough. Your master cylinder will sit on an angle and you will have to lean the bike over to top the oil up but thatís no big deal..
  • Ditch the stock footpegs and brackets, they scrape on the track all the time. Get hold of some 10mm aluminium plate and make up your own rearset brackets using the two bolt mounts on the frame to secure them to the bike. For footpegs, buy some of those "trick" pegs kids attach to the axles of their BMX bikes. Mount your new pegs and levers to the rearsets using greased HT. bolts and washers for spacers.
  • Be careful not to go to radical on the rearset position because they can induce patter in the bike if they are too "jockey-like". Start with say 60mm back by 25mm higher than the stock position and work from there. Youíll need to extend your gearshift lever rod to reach the gearbox rose joint.

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    Picture: Lech Budniak's two LC racers, NSW Post Classic Championships, Eastern Creek, 2001. ( Photo: Mark Boddy)





    Return to the "LC Corner Page"


  • Pull the top end off the bike and check the conrod side clearance. Also, after removing the pistons, carefully check the big end wear by delicately holding the conrod perfectly vertical at BDC and gently twisting it, as well as trying to move it up and down vertically. No movement is ideal, very, very slight is ok, but any more means rebuild time. If in doubt, ask an expert.
  • Some guys have their cranks welded during a rebuild to prevent them spreading. I feel this is un-necessary, Iíve rebuilt a few in my time, never welded one and never had one spread on me. I just use a Loctite on the pins and check the conrod side clearance after each race meeting.

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  • Engine mods.

    ( Bet you looked at this section first !! Come on, admit it !! )

  • Firstly, check the condition of your top end, ie. clearances, wear, carbon build up etc. Itís no good modifying a worn motor.

  • Porting: Get hold of a Dremel or die grinder and carefully raise your exhaust ports by 1.5mm over stock, checking and measuring constantly. Remember, thereís no turning back if you take too much metal away. If youíre keen, polish the exhaust duct (between the bore and exhaust boss.) to help prevent carbon build up.
  • While youíre at it, sharpen the bridge between the two transfer entries, but donít over-do it and also carefully trim your base gaskets to match the barrels.
  • Some two stroke heads even go to the extent of marking the outline of the transfer inlets on their pistons at BDC and die grind the excess piston skirt sides away to provide the maximum fuel flow into the transfers. An obvious problem here is matching piston weights. I really donít think itís worth the hassle to be honest.
  • Compression: All I ever did with my LCís compression wise is remove the head gasket. I canít recall the figures, but I know it did seem to provide a noticeable improvement in "seat of the pants" pull out of corners.
  • When using this method, you need to lap the barrels onto the head by turning them upside down and using valve grinding paste to ensure a good seal. To seal them, use plain old Selleyís Silastic. It's cheap and it works.
  • It pays to keep an eye on squish clearance too. Bend a short length of 2mm soldering wire at 90 degrees and thread it down through the spark plug holes so that it touches the bore. Turn the motor over by hand, squashing the wire between the piston and the head. Measure it, the thickness should never be less than 0.7 to 0.8mm.

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  • The original Yamaha items are the best, though very expensive, something like $100 Aus. each or more. You can buy aftermarket pistons from a few companies which are well worth trying. Wisecos can be used, but being forged they require a larger piston/bore clearance and a lot of warm up time to be reliable. Saying that, a lot of guys fit them to TZ750ís with success, but it's best to stick to cast pistons if possible with LC's.
  • Some guys enlarge the transfer holes in the back of the pistons or even cut the back apron right out to increase flow/ inlet duration. This is a bit risky, obviously it can weaken the piston and lead to high wear and failures. The best thing to do is just measure the orifices and ensure that all four   ( two pistons ) are identical with a little light filing.
  • You can leave the lower piston ring out safely as well to minimize drag on the cylinder wall.
  • After each race meeting , pull the top end off the bike ( a 15 minute job, Iíve timed it) and gently rub any score marks off the pistons with fine "wet and dry". Marks on the back of the piston can indicate too small a pilot jet, on the exhaust side, too small a main jet.

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  • Exhausts.

  • If youíre running a 250, get hold of some good race chambers like those dimensioned below. This is the single, biggest power increase you will get with these bikes. The stock exhausts are very restrictive.

    LC Race Chamber Dimensions.

    Below is a layout/cutting list  for  race chambers to suit a 250LC.

    (Click on the thumbnail to enlarge the "cutting diagram".)

    Please note:  1.  You'll notice the stinger section of the table is divided into two sections. Ignore this and treat it as one length.

    2.    The stinger length includes the muffler. For the record, the muffler body itself is 220mm long.

     3.    The header cone section is measured from the flat mounting face on the cylinder.

     4.    They are suited to a 250 LC and would best be described as "peaky" LC chambers. But saying that, being an LC, the thing was still dead easy to ride and had heaps more midrange than a TZ.

    Youíd be amazed how many sizes of main jet you have to go up to compensate for the improved

  •  breathing. You'll need to run approx. 340 mains in the stock 26mm carbs with the mods listed in this story.

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    RD350LC Race exhausts.

    Finally we have a design for performance RACE ONLY exhausts to suit the RD350LC. Sincere thanks go to Greg Sims for providing these dimensions. Greg actually manufactures exhausts here in Australia so if any of you Aussie LC racers want a set of race pipes that actually work contact him via email by clicking here!

    Greg's website is located here:

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  • The stock 26mm Mikunis are fine for a 250LC. Maybe 28ís, but not much bigger. For a 350,  28ís or 32ís would be better.
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    Reed Valves.

  • Keep a close eye on the condition of your rubber inlet manifolds, hold them in your hands and bend them slightly, looking for splits and other damage. The slightest air leak can cause seizure.
  • File your reed cages out to maximize flow, try to aim for a total effective area 80% of the carby bore area, ( refer to your better two stroke tuning books ) but donít remove the centre rib unless you are running single leaf reed petals.
  • Closely monitor all four orifice sizes (two sets of reed valves) and keep them identical.
  • "Boyeson" and other two stage reeds are great and definitely help with midrange, but who needs midrange power on an LC racer? They already have heaps to begin with. Go for some single leaf, single stage reeds, which allows you to remove the centre rib of the cages for improved flow.
  • Bend your reed stops outwards to allow a petal lift of 12mm.

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  • "Boost Bottles"

  • Never tried them myself, but by all accounts they do actually work, though apparently the size of the chamber and length of tube is important.

     Sorry, I have no information on this. Have a surf on the internet, Iím sure youíll find something eventually.

  • Ignition.

  • Iíve only ever run the stock LC ignition. You can have the lighting coils removed if you feel the need, but itís a bit expensive and achieves little in the way of acceleration, if anything.
  • Some guys machine a little off the outside of the flywheel to reduce inertia and get the motor to spin a little more responsively.
  • A mate of mine "cooked" a few LC ignitions and ended up drilling horizontal holes on the ignition cover to allow it to breathe and stay cooler. He never cooked another ignition, though it was probably more of a  coincidence than anything.
  • Keep your ignition advance to around 1.8mm BTDC and run B10 or 9EV plugs. If you have trouble starting the bike then use 8's to get it going and change over to the colder plugs once it's warmed up.
  • Obviously you can buy aftermarket ignitions if, once again, you want to spend some money. I feel they are un-necessary, don't forget your bike is a 20 year old dinosaur.

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  • Oil Pump and Kick-Starter:

  • Remove the pair of them and plug the holes with brass "welsh plugs" from your local auto spares shop.
  • Donít forget to plug the little brass oil inlet tubes in both carbs once youíve removed the pump.


  • Dyno graph of theoretical power improvement with all the above modifications:

    Left  is a comparison of power output between a box-stock RD250LC and one modified in the way described above..

       ( Click on the thumbnail image to enlarge )    

         ("Muddy" now owns the bike all this work was done to. You've got yourself quite a bike there mate !!)

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    If you have anything to add or dispute, by all means let us know. Email the Webmaster    

    This article is exists for one reason and one reason only, to assist those guys wanting to convert a stock LC into a racer. Any external help or advice is most welcome, it can only enhance the story.

    Click here for an article on hotting up a 350LC.

    Click here for an article on hotting up a 250LC   A lot of the ideas above cross-reference here as well !!

    Click here for page 1 of another RDLC performance article. Click here for page 2, Click here for page 3, Click here for page 4 .

    Please accept my apologies for the poor quality scans. I can't find the original articles and could only locate these photocopies to scan. If anyone has scans of the original documents could they please email them to me and I'll upload them in place of these hard-to-read documents!

    Ever wondered just how fast your LC racer is going?

    Click here for a speed calculation spreadsheet that you can input your own specific data into...

    Email the Webmaster

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    12/04/09 04:23 AM +1000    

    This article and website © Greg Bennett 2002.