feetupfun

Here's the other side of DabDab's 348 brochure. Sorry if its upside down or sideways - remember it was uploaded in the Southern hemisphere!!

These are scans of a 348 brochure I am posting on behalf of DabDab. They are in pdf format so I'm not sure they will display properly.

1 The brand/size that you personally find easiest to ride. For me it would be a toss up between Scorpa SY250 and Beta Rev3 250. 2 It wouldn't be a factor because the all the brands are well supported by their distributors here.

Stripping paint from fibreglass tanks is easy if you use an electric heat gun to heat the paint and then scrape it off with a paint scraper. I've successfully done fibreglass Spanish trials bike fuel tanks this way. The latest was an OSSA MAR tank that had three layers of paint and lots of spray putty. Warnings: Make sure you have removed all the fuel fumes before you use the heat gun Don't overheat the fibreglass (or it may catch on fire). Just heat the paint surface to about 50 degrees C - about as hot as you can stand to touch with bare hands.

The head on the bike in the photo from the France Trial Classic website looks like a DT175 head.

Clark Maunfacturing in the USA make high quality plastic tanks for old MX and mini MX bikes. Some of them would fit the KT but the look is nowhere near as sleek as a steel KT tank.

I like the way you show what you are doing to the bikes as you go. I'm usually too keen to finish to stop and take photos along the way but your show and tell webpage has motivated me so a current resto (M198 Sherpa T) is getting the progress photo treatment. When you put the front guard back on the TY, please put it on the other way round even if it means ending up with holes where the mudflap was. Yes you should use tank stickers that look right - even if they are for a different model TY250. You have invested lots of effort already in the paint job and it would be wasted if the tank ended up looking strange. If those stickers in your "goal" photo are too expensive, the yellow and white TY250B paint scheme looks great and the correct stickers for that would only be about 5 pounds and the pinstripe less than 1 pound.

I've tried running a Rev 3 200 Beta on AVGAS which is high lead petrol made for piston engined aircraft. Once I adjusted the float height for the big difference in fuel density (AVGAS is very light), it ran beautifully, and was probably a bit less powerful overall than when run on you guys across the Pacific would call 98 octane "pump gas". No problem with lead deposits on the sparkplug either. The only problem here is that for competition use we must use (unleaded) "pump gas" or homologated unleaded ELF racing fuel so unless you never compete, here it pays to stay away from the user-friendly leaded fuels. About the ethanol content, I have never heard it promoted here as a performance improver in fact the fuel suppliers have to keep the price about 4 cents/litre below the cheapest non-ethanol "pump gas" to sell it (we have a choice of buying "pump" fuel with either 0% or 10% ethanol). "Pump gas" of all types is still very cheap in Australia (approx $1.15US to $1.25US per litre). Most trials riders use the highest quality 98 octane non-ethanol "pump gas" they can get.

Knobby tyres are terrible on anything that has hard surfaces like rocks and logs.

I would expect that if you have a standard pinky it will have needle roller bearings with rollers that will stay in position within the bearings until you slide the bearing inner bushes out ie you should be able to slide the swingarm axle out and remove the swingarm from the frame without having rollers fall out.

The chain will slowly wear the swingarm away unless there is a protector. The protector is sacrificial and wears out slowly. It is no big deal in the short term to have the chain touching the swingarm. Pinkys have steel swingarms so the wear rate will be slow. Yes the swingarm has to come out. I expect it would take a motorcycle mechanic about 30 minutes to replace a protector on a clean bike. Sounds like you haven't done much work on bikes yet so it would probably take you a fair bit longer. You will need tools to fit the swingarm pivot axle and both shock mount bolts. Make sure you clean the bike well before you start or you will get dirt in the swingarm pivot bearings. I would suggest buying a new protector and fitting it when convenient ie when you have to take the wheel out next to clean the brakes or replace the tyre.

Ah the fun of buying a bike in pieces! A standard TY175 head has only one plug hole and there is no place to fit a second plug or decompressor. Your TY175 probably has a head from some other model Yamaha. There are lots of interchangable parts between Yamaha bikes of the same era as the TY175. Having a different head may not be a problem. You may have a few other non-TY175 components so if you want to know, I suggest you start off by checking a few things; Have a look at the number cast into the barrel between the bottom two fins on the right hand side. It should be 52500 if it is TY175. Have a look at the engine number stamped into the top of the right side engine casing. It should start with 525 or 1N4 if it is TY175. Have a good look at a brochure photos of TY175s and post a photo on the forum of anything you are not sure about.

It may be something as simple as a ring stuck (with gum) in it's groove.

Maybe it was just the execution of the idea in the case of the Rotax jetski motors that was crap. The most successful 250cc road race GP bikes in recent years (Aprilia) have rotary valve induction. They are noticably faster than their reed valve competitors (Honda and KTM). In the case of bikes for Joe Public, yes they are a bit more complex than reed valves but do produce the goods. In twinshock trials the SWM with the rotary valve Rotax motor is a beaut and the SWM enduro bikes of the late 1970s with similar Rotax rotary valve motors were at the top of the performance tree at the time.

Regarding the lack of throttle position input to the oil pump on your Jap import TY mono, the amount of oil sent the carby does not have to match the quantity of oil required on such a short time scale as you are imagining. The intention is to match demand and supply over a timescale of a few seconds rather than a few milliseconds. For this reason it is not essential that throttle position is a control input on an off-road motor. Yes it is a compromise and would probably put the motor at risk if you used the bike for a application where the speed and load did not vary for long periods ie road riding.Yes it is not as technically sophisticated as the system on the TY twinshock bikes but there is also less to go wrong. I have lost count of the number of friend's bikes that have had the engine ruined when the autolube system stopped autolubing without warning. If you want oil metering with the highest reliability and the rate well matched to the demand, I recommend using pre-mix fuel.

I couldn't resist having a bit of a giggle reading this string about the merits of different fork springs for a 35 year old motorcycle. For many years I wanted new fork springs for some of my TY250s and could find no suppliers for them anywhere. In about 2001, I finally found a supplier and was very happy to be able to buy something somewhere (B&J Racing Products - Tenessee USA). Now a few years later again we have people arguing about whether German made TY250 fork springs are better than UK made TY250 fork springs!! Things are looking great for supply of Twinshock trials bike parts when we see arguments like this cropping up. The debates about which are the best shockies for twinshock bikes are a similarly good sign. By the way, for quite a few years (not sure if it is still the case now) if you bought a new BMW car in Australia, the suspension springs on it were made in Australia - something to do with the German springs being too soft for the spirited driving BMWs are subjected to here in OZ.

When you say owner's manual, do you mean the parts/service manual? The one I mean starts with drawings of all the special tools and then has specs including all the usual things like oil types and quantities, fastener torques, crank runout and piston clearance then good quality exploded view drawings.

Yes I remember having to go searching for those springs for one of my Cota 348s but it was so long ago I can't remember the details of what I tried but did end up finding enough of those strange montesa springs on another bike. I seem to remember that TY175 shoes are the right diameter and will fit the 1970s Cota trials front brake backing plate but can't remember if the TY175 brake springs have clearance to the outside of the bearing housing. If you don't get enough useful info on this from someone else, I will do a test fitup of Ty175 shoes (in a Cota 348 hub) to see how it goes. David

You may not have a tyre slip problem. The tube can get pulled around without the tyre slipping on the rim. I was obsessed with rimlocks for a while till I painted marks on the rim and tyre to prove to myself that the tyre wasn't actually moving relative to the rim. Don't ask me how to prevent the tube moving though. Powder on the tube works OK until water gets in between the tyre and tube. I've found that the tube will always move one way as far as it can in the stem hole and will then generally stop the tube moving further without getting the stem pulled out. I use Thai, Malaysian and Taiwanese tubes of a smallish tube size (3.50/4.00 x 18) in Michelin and IRC tyres.

I suggest you get the 16. My 6 year old 17kg (38 lb) and small-for-age son is well sized for his 16. He would be cramped on the 12.5.

If you use Barnett brand friction material clutch plates, the clutch spring preload can be backed off quite a bit further than with the all steel plates before slipping. You may even need to machine the spring nuts shorter so they don't rub on the casing.

The things that sounded a bit dodgy to me in your story are that: TY backing plates don't normally have slotted holes (maybe yours has been modded or is from a different bike). There is an ideal range for points gap that has nothing to do with the capacity of the motor. It is chosen to give the best spark. For Yamaha motors/ignitions like yours the ideal gap range is 0.3mm to 0.4mm, and you should be able to get the timing right without going outside that range. If the backing plate is moved too far away from the ideal position in either direction, the flywheel magnets won't be in the right spot relative to the ignition coil when the points open (causing weak spark). I suggest you set the timing from first principles ie using piston position and measuring the advance when the points open and also make sure the backing plate is in the right spot. If you have a picture showing the position of the backing plate on a standard TY250 you could probably get yours close enough to the right spot to eliminate that as a possible issue. To start with I would try somewhere between 2 mm and 1 mm BTDC with that motor. The ideal clearance for the coil laminations is as close as you can get without anything touching. If your bike has been sitting around for a while it is possible that there is now a bit of movement in the crankshaft bearings which could have caused the magnets to hit the laminations and maybe even loosen them and the flywheel. It would be pretty unusual for the not-revving issue to be caused by the timing being set a bit too far either way. Much more likely to be: Blockage somewhere (air inlet/filter, exhaust pipe/muffler, carbon buildup in exhaust port/ inside head) Worn rings Broken or bent reed/s Something wrong in the carby (some OEM TY carbys have an o-ring that seals the main jet into the needle jet and when this o-ring leaks, the bike will run very rich above low throttle openings)

Suggest you have a look at www.trials.com.au

What a strange question The internal flow resistance of the motor will limit the RPM to well within the mechanical strength limits of the motor. A standard 315 motor with throttle held open in neutral may rev up to 8000 - 9000 RPM. The upper end of the useful power range is probably around 6000 RPM.

Problem solved. I found a small pine leaf/ needle in my carb. It is amazing what you sometimes find in there. It's easy to get stuff into your float bowl. It can fall into the fuel line downstream of the filter when the hose is off the carby. It can get in via the air intake when you are cleaning the air filter. If you are really clever you can get it in through a float bowl vent line using a high pressure washer or compressed air. It can even fall in just as you are refitting the carby bowl. The most common pilot jet blockage item I've found is grass seed. Just the right size. The most common main jet blockage item I've seen would have to be water.