TZ350 and 250 Website TZ Maintenance Tips

This submission is not meant to be the ultimate bible for piston port Yamaha owners.

It is merely a collection of ideas based on what various TZ owners have read, discussed and experienced over their years of ownership of the bikes.

If you have any ideas or tips, or opposing opinions you want to share with other 2 stroke racers then please Email the Webmaster and share your expertise with us all. Your input is most welcome, it can only enhance the site.

Picture: Gerard Bidu's TD3 camping.

Shouldn't the bike be inside the tent with Gerard sleeping outside? !!!

Thermostat. For southern hemisphere racing, ditch the thermostat, and take your time to warm the bike up. Feel the radiator for warmth, not the cylinder - the later bikes have the temp gauge in the radiator not the engine, I believe. Don't let the temp go high, or it will/will have detonate/d. Opinions on correct temp vary, though you don't want to see more than 85°C or less than 65.

Squish. Big area for personal preference and plenty written about it. Horsepower to be had here, and engine safety (less of a grenade!) Two important things, less squish clearance is better to a point - it reduces the chance of detonation. More than 2 mm is ineffective - as the original A/B heads were. Don't use less than about 0.65 mm or the piston will touch it, especially on the 350! (Kerry Wilton)

They don't work so well full of old carbon. Remedy is obvious!

Early watercooled chambers are often found to be a bit on the long side - 15-20mm - (from those that have played a bit) - possibly part of Yamahas obvious attempts to keep the idiots from getting into too much trouble! (same deal as the extra width in the squish on the heads, lowering the compression.)

Concur that good sealing of the port to the pipe is essential for good power (and it does keep the bike cleaner!). Silastic works, but good to start with fresh tight exhaust sealing rings if you are using Yamaha pipes. These are no longer available from Yamaha, and would cost an arm and a leg if they were. We have a supplier in UK who can provide a good substitute - lasts in the high temperatures, but is a bit tighter on the port than stock. They require a good shove on the pipe to fit for the first time, but the advantage is a good seal. These sealing rings are especially good for barrels that have had the pipes 'fret' on the outside of the port, effectively reducing the diameter and ruining the seal - the extra tightness goes a long way to restoring the seal. For the tight seals, see ( an English supplier ).

Agree that wiring the pipes on is a must 0.032" wire is the go - use stainless, and at least two separate pieces, especially if you are not using 2 springs. Springs lose their tension over time, so check that the wire hasn't stretched or broken periodically - indication that the spring/s are letting the pipe blow off and slip back on. Not required.

Much benefit to be had playing with pipes and modern design. Where do you stop with the money and dyno time?! (Kerry Wilton)

I've found the best way to clean chambers is to use a piece of steel cable, the thickest diameter you can comfortably push down into the exhaust, and a reversable electric drill on a low speed. Be careful as the cable gets near coming out of the pipe though, it flings around a bit. Please be very very careful. Make sure you wear face protection and other appropriate Personal Protection Equipment as required if you decide to try this method. (Greg Bennett)

Tips List

Air. Agree that air filters are a good idea. Even without foam filters, stone guards are surprisingly effective- Have you ever noticed how many small stones there are on the top of the gearbox after a race? Despite the guard in front of the rear wheel the tyre (usually the stickier the better!) picks them up and fires them towards the carbs, which are doing their best to suck in as much air as possible, creating a depression around the intakes - probably felt as far back as the back of the gearbox. The coming of the bikes with airboxes resulted in no scoring on the bores. In the UK - ( an English supplier ) made some stoneguards and the scoring all but disappeared. ( An English supplier ) still makes batches of them up, with special narrow clips, for 34 and 38 mm carbs. Some research went into the size of the gauze, I believe, and it would appear to restrict intake flow and area. I bought a set for the 750 and two pairs for the 38mm 350's. Have yet to establish the exact effect on the 350, but there was an immediate 4hp gain on the 750 on the dyno with the gauzes on....Seems the gauze, though it surely restricts carb area, actually improves the flow characteristics and mixing. All I did to the carbs was lower the needles a notch. Mentioned the power gain to a couple of guys in the UK. No-one was surprised, but no-one had mentioned it before!

Fuel. If there is room in the fuel lines, I suggest running plastic fuel filters. Make sure they are big enough - 5/16" or 8mm diameter. The filters in the tanks are crap, and most tanks have all sorts of stuff in the bottom these days. The filters can even be 'backwashed' - you'll be surprised what comes out of them. Save yourself the grief of rubbish in the carbs and blocked jets, sticking needle valves, etc.

Carburettors. Performance gains to be had here, mostly in setting up what you have. Unless your circuit is very fast, there is probably little need for putting 38mm carbs on a 350, unless it is F/G and came with them. Have not done back to back dyno tests, but have heard of a guy who recently has -he tried 38's on his 350C and went back to the 34's, spending time setting up the mid-range, etc. Apparently a smooth easy starting bike now, and still makes 64hp at the wheel. We have used a pair of 38's that have been bored to nearly 40mm, though couldn't say they were any better - no dyno runs, though one particular bike runs better on them at low speed! Check float height when you set the carbs up. Figures in Mikuni and Yamaha books. When replacing float needle jets (recommended), note that there is a size number on them - 38's have 3.5's and the 34's are 3.0's.

Power jet Mikunis are OK, though not a requirement. They can allow you to tidy up mid-range, though most guys don't seem to have the bikes that close to the jetting edge these days that it matters. There is the thought that the power jet, being quite small, could block up if there is dirt in the fuel, so some guys use quite small power jets and bigger mains (somewhat defeating the purpose) to guard against a seizure. Regardless, the powerjet plus mainjet size added together is about what you'd have to use for a mainjet size in a non-powerjet carb.

The standard 38mm 350F/G needle/needle jet combination is a bit odd. At Pukekohe in Auckland there is a very slow hairpin corner, where it used to be almost impossible to drive a TZ out of without the clutch (the hairpin is preceded by a fast straight - 11000+rpm on 15/35 gearing, so the first gear ratio is quite tall). We fitted a 6DH7 needle (we started at middle needle clip position, or next leanest.) and Q-4 needle jet, with 75 pilot jets and it transformed things - no clutch required and the 350 would pull out from under 5000 rpm (though a bit of clutch slip in a race made it a faster exit). In the end, this was easier on the bike. See Ian Williams Tuning for the stuff you need (Adelaide, South Australia).

Choke. The choke is hard to get at on the left carb, especially if 38mm carbs are used. The early bikes with the thumb lever are better, but the lever and cables are just complication. Fit a standard Mikuni choke lever assembly on the carb, like a motocrosser - it fits straight on under the 12mm nut, and sticks out the left side of the carb. Available from Mikuni, or their dealers (in their catalogue). No more fiddle or trying to start with one choke.

Lectron. Good reputation. Nothing practical known.

Lectron spares are available through ( an American supplier ).

I just thought that you should put a warning for people ordering Lectron metering rods (needles) from ( an American supplier ). They must specify the length of the rods that fit their carbys because they are focussed toward the drag racing guys who normally have much bigger carbys with longer rods.
Also, make sure that they send the parts by air mail rather than courier or the shipping charges will exceed the value of the parts. (Mark Boddy)

Ei. Poor-man's Lectron, made by S&W shock company until early 80's, from about 78. Hard to get parts to set-up these days, though simple and makes a 250 pull well, even with 36mm. Difficult choke set-up. Float bowl on left carb fouls crankcase over sprocket, requiring relieving of crankcase.

Flat-Slides. Generally good, though too modern for most classes.

Balancing Carbs. We have found that a big factor in easy starting and smooth running, particularly at low rpm, is carb balance. It needs doing every time you have the carbs off for changing jets, etc - especially anytime you have the top off the carb - the tightness of the carb affects the balance. Only if the carbs are miles out can you tell by eye or ear (more than one click when the slides bottom).

Tips List

For good carb balance:

1. cut a pair of short lengths of stainless lockwire, or gas welding rod, etc - about 100mm long each (as required to clear fairing mounts, etc).

2. approach the bike.

3. put the end of a piece of the cut wire into the carb, so that it just sits under the bottom of the slide, and rests in the carb mouth. Do the same for the other carb, and have the wires protruding from the carbs at about the same angle and length.

4. very slowly and gently open the throttle while kneeling at the side of the bike, looking across the ends of the wires in the carbs. Note which one moves first. Adjust the throttle cable outer length (with the in-line adjuster, or at the twistgrip) to bring the 'lazy' carb into line or slacken the first-moving carb cable off - depending on how much play there is at the twistgrip.

5. check both open fully.

6. be surprised at how far out the carbs were with your old method.

The reason this works so well is that where the wire rests on the carb mouth is effectively a fulcrum, and any movement at the slide when the throttle is opened is magnified by the extra length of wire on the outside of the fulcrum - it is very obvious to see which moves first. Try it out. (Kerry Wilton)

Bronze clutch plates available in UK ( an English supplier ) - apparently more resistant to breakage. Can use them for all the friction plates, though we used them just for the inner two. We broke them all.

Barnett in the USA do plates at a better-than-Yamaha price. Haven't tried them. (Kerry Wilton)

I haven't bought any recently, so things may have changed, but the older Barnett clutch plate kits used a very thin sheet of aluminium which was inevitably hammered over on the tangs in very short order. The don't break the same way as stock fragile plates, but their ears do get mashed.
Barnett springs are way heavy and dead cheap, so try 3 Barnett and 3 stock. I still have a couple of new sets that I won't use, just taking up shelf space. (Richard Nowson)

Tips List

When you put new plates in, put a mark on the basket where they go and a corresponding mark on the adjacent outer friction plate tab. Number the plates. Do this so that they can go back in the same way - save adjustment and bedding-in problems.

Use 3 x 750 springs and 3 x 350. Bit tougher on the hand. Harden up.

Have heard that a 'face' type roller bearing can be fitted inside the pressure plate, to bear against the head of the clutch pushrod 'tappet' that pushes the pressure plate out. This is supposed to improve the action a lot. Have yet to try it.

Keep the inner nut tight. Having the clutch fall off is inconvenient, damages things and could hurt! Use Loctite and check it often. Use the bell washer under the nut. Have seen many come loose, even when they were near-new.

If the basket has been 'dressed' number of times to get rid of the individual grooves left by the plates, for a smoother take-up, some will take the strain from the plate before others - breaking the plates. Plates are expensive - suggest getting a new alloy basket from UK - about 100 pounds. Clutch will be smoother and won't brake plates - paying for itself. We have seen pieces of broken plate nearly destroy the basket anyway, and hit the rider's leg on the way out! (Kerry Wilton)

A tip: In order to stop the clutch plates of the TZ250 braking or hammering grooves in the outer clutch drum and clutch centre. Fit the primary gears of the TZ350, you should have to alter your secondary gear ratio of course. We used this in our bikes during the 1975/76/77/78 Dutch Championship season in Holland (Rider Kees v.d. Kruijs). We had many road circuits with tight bends at the time a real disaster for clutches. The clutch plates lasted one season without any problem! Of course at the time I had not told anyone and as we had many poles (and wins) other riders came to look for the gearing we used. You can imagine what happened when they used the same gearing as we did. It took them two seasons to find out!!! (Ferry Brouwer)

RG500 Clutch Conversion: Some guys use a conversion which allows the use of RG500 race bike clutch plates. In a RG500 the plates are made of thin steel with a coating of bronze, this coating apparently almost never wears out.
Some tuners have managed to reduce the plates required for a 350 to 4 friction using TZ750 clutch springs so the weight can be reduced.
The inside diameter of the RG plate is slightly smaller than the TZ350 clutch centre hub so by machining 1.5mm from the inside of the plate they will fit over the centre hub no problem.
The big job is making the outer drum which has to fit the standard TZ splined drive plate for the primary gear and accept the RG friction plate. It can be machined from solid and if done this way can be used for years before beginning to show serious signs of wear. The only maintenance usually required is a once a season rub down on a face plate using 600 grit wet or dry paper to keep the plates gripping.
Fit 'em and forget 'em no more broken plates (almost) ever. (Paul Allender)

Tips List

We use Motul gearbox oils. There are a couple of suitable types, though we use the cheaper and change it often in the twins, and the more expensive one in the 750's. When you drain it out let it stand overnight and have a look to see what metal flakes there are on the top of the oil. Look for evidence of failing gears. (Gearbox lock-up is my worst nightmare).

Never use more than 1500 cc - or it'll leak as you say. We usually use 1250cc (Kerry Wilton)

Engine. We use Motul 800 2T for premix, at 30:1 (25:1 for aircooled). It's good and we get it at the right price. A747 Castrol is possibly marginally better, though very expensive, and not so available. At the ratios above, engine wear is good. Latest copy of Classic Racer had Kent Andersson saying that on Motul oils the 125 twin he rode to 2 world championships will go 2500km (instead of 800-1000) at up to 33:1. (By the way, he is also Motul rep for Scandinavia).

Noise. Most places have noise limits these days. A lot of noise can be generated by the drive chain - up to 3 dBA. Lube and adjust the chain. It helps keep the noise meter man off your back.

Flooded engines. NEVER EVER NEVER NEVER take the plugs out and push the bike to clear a flooded motor. It can damage the ignition if the plugs are not earthed, and even if they are the resulting spark can ignite all the gas coming out the plug holes and burn the bike to the ground. I have seen this happen many times - including to one M Dowson in New Zealand in the early 80's, just prior to him becoming famous.

If the engine is flooded, turn off the fuel and push (rollers better!) with the throttle just open and held constant - when there is the faintest of 'popping' from the exhaust pipes pull in the clutch, stop and hold the throttle absolutely steady - when the motor is ready, it will pick-up rpm. Turn on the fuel. Warm it up and change the plugs as required. This relies on having a reasonable ignition and plugs that are not too old/fouled. Maybe change the plugs prior to trying this. (Kerry Wilton)

Do not EVER turn over a flooded bike on rollers. Do not think about doing it. If there is much fuel in the bottom end, the fuel comes up the transfers in such volume that it creates a hydraulic lock. If you are lucky the rod bends and you can feel the tightness. If you are unlucky, the rod has less of a bend and when it fails, and it will fail, it takes out the crankcases with it. How do I know? yes, I rebuilt the same motor two race weekends in a row with bent rods.
So how do you clean the motor out. As suggested, throttle wide open and push - you cant bend the rods that way and the exercise will be good for you. You may be surprised to see how much raw fuel spews out of the
mufflers or pipe joints when it fires up, so keep a fire extinguisher handy
The cure. All the things suggested, but add a pair of 5/16 inch quick disconnects, and always disconnect them every time you come in form a race. (Richard Nowson)

Tips List

Prevent flooding by:

1. Replacing the float needle valves (about A$30 each - see Ian Williams Tuning in Adelaide) - old ones never work properly, and don't heal themselves. Spend the money and save the heartache.

2. Turn the fuel off between races

3. Disconnect the fuel lines (or drain the tank) and drain the carbs after the meeting - much easier starting the next time.

4. When starting the bike use choke (if your bike likes it - most do for the first start of the day) and hold the throttle either shut or ever-so-slightly open. Push and instead of jumping on the seat and releasing the clutch, keep pushing and press your chest on the tank for another couple of steps while slowly opening the throttle a touch - this allows the motor to turn over and get a second chance at compression - it will fire when it has the mix of air and fuel it wants.

Plugs

Whatever plugs you use, several things remain true:

1. Use a new one if you want a good reading.

2. A dark (rich) plug will not lighten up appreciably if it is run leaner (unless damagingly hot!) (from Kevin Cameron's book)

3. Old plugs may work, but take more voltage to fire. Replacing the plugs can add more 'sparkle' to the engine if the ignition is not too hot, possibly giving a wider range of power.

4. Oil collects on the flywheels and in the cases if the engine is not run for some time - say between meetings. The flywheels throw the oil off when the engine is first started, ruining the plugs from a future reading point of view. Therefore, for the first start use old plugs, warm the motor up (less exhaust smoke) and fit a fresh/good set.

5. Slow running while riding back to the pits will nullify the plug reading. Didn't place too much emphasis on this myself for many years, but had it demonstrated to me when a piece of piston let go on another bike (not Yamaha) at max rpm in top gear, as I shut the throttle. Pulled the clutch and stopped. Pushed back, and looked at the plugs. Beautiful, easy readings.

6. Check how deep the plug protrudes into the head. Some heads require a 5/8" reach plug (not common, if available) so a 3/4" reach plug needs a copper washer (there is a pukka Champion part). The racing NGK's are actually quoted as being 18MM reach, as there is no thread on the last piece of the body.

7. Have never used the B10EVX, though have used a lot of the EV/EGV variety. I prefer NGK - had too many crap Champion plugs (at enormous expense then) when the bikes were near new for me to be bothered now. Champion are trying to overcome the crap racing plug image they had 20 years ago (certainly in NZ), and they are apparently good, but not cheap enough compared to the NGK to sway me.

8. B9's ok most of the time. Be sure that you want to go 'hotter'.

9. Never use more than 0.020" gap - it gives the ignition too hard a time.

10. Use decent plug caps. Without resistors. NGK make really good non-resistor ones (also waterproof) with machined connectors for the plug top - far better than the old black rubber 'lodge' style with a piece of bent tin inside. Not too cheap, but you get what you pay for.

The Webmaster's TZ250 C.

Oils:

It's always been thought of as a strict 'no-no' to mix vegetable-based oils and others. I have seen 2 TZ's (350B, 250C) that spent their whole lives on Castrol R swapped over to Motul 800 2T by pouring the new pre-mix in the tank! They ran fine, lasted a reasonable time, and had no ill effects! No stripping the engine and washing out the 'R' and assembling with Motul -just run it! No sludge, nothing. (Kerry Wilton)

When trying to track down TZ parts through Yamaha it is good to check their Motocross parts. The old silencer silentblocks of the TZ's can be replaced by part number 483-14781-02, which is the same. The seal, guard (chain protector) of the old TZ's can be replaced by a modified YZ protector (they have to be cut as the swingarm has a much larger diameter and they are a screw-on type) (Ludy Beumer)

The rear shock of a TZ 250/350 appears to be identical to older YZ monoshocks. I can't comment on damping characteristics, or exact dimensions, but I saw one recently and thought it looked the same as the ones on my TZ's. (Greg Bennett)

Starting. Rollers are not required on any of our TZ's. They will always fire up in a couple of quick steps. If your TZ isn't starting, then it's time to check it out very carefully. Could be the timing is too far out or slow jets are way out of spec, or you may have some sort of air leak. It's possible that the slow coil in the Hitachi has died or maybe you are riding it hard and putting it away too wet, so that it is partly flooded when you try again. (Richard Nowson)

Rear Engine mounting: It's best not to use the top, rear engine mounting, as it has a tendency to break the mounting lug off, taking a lot of the gearbox top with it. There is no harm in running without the top rear mounting as long as the motor is rubber mounted below, but saying that, rubber mounting the lower rear mount is nice but not essential. If the engine IS rubber mounted at the bottom rear DO NOT use the top rear mount. (also, if the engine is rubber mounted at the rear, and even if it's not, really) use an earthing lead from the engine to the frame somewhere to help the ignition - see the comment in the ignition section. ( Kerry Wilton )

Sprocket bolts and tabs: Even though you may be using lock tabs on your rear sprocket, if you haven't swapped sprockets for a while (eg gearing change), knock the tabs down and re-tension your sprocket bolts. They can fret and work loose without coming undone. 18-20 ft lbs is plenty of tightening torque. High tensile cap screws can be quite brittle and would need 45 ft lbs to carry the load correctly which is a lot of torque to apply to a bolt in a magnesium hub.. Standard high tensile bolts (marked 8.8 on the head) should be more than enough (if at the right tension) for the application, if you are not using genuine bolts.
Don't use zinc plated bolts as the plating interferes with the torque loading - causes more friction when tightening up and less force goes into the actual bolt tension.
It's a good idea to lock-wire the bolts and then get a open end spanner on them to check
between races to make sure they are still at least "tight". ( Alistair Wilton )

Fitting a 350 top end to a 250 bottom end: When doing this common modification always ensure you change the 8 cylinder studs in the crankcase to the longer 350 ones. The 350 ones are 8mm longer and the shorter 250 ones will be damaged if forced to hold down a 350 top end. ( Pierre Mazaloubeaux )

The Heidenau 90/90-18 racing tyres (front) have been tried by some Dutch owners and found to be very good for their courses. They are just 85 euro to buy and might be worth considering.
The 4.10 Heidenau rear tyre has also been tried and is not so good. ( Martijn Stehouwer )