cvgmmartin

The ability to run longer is dependant on the AMP/hr capacity of the battery and the current draw of the ignition circuit, for example if both the 12v and 6v batteries are say 4 Amp/hr capacity and both the 12v and 6v ignition circuits draw the same current then there is no gain, but if the 12v system draws less current then you will get a proportional increase in running time. I would guess a 12 volt ignition cicuit may draw slightly less current than a 6 volt system but I don't know. If you use electronic ignition circuit components (which are probably all 12v) then you would probably get a bit more life since the current draw on these is less than that of an old coil/contact breaker arrangement. I run a 12v total loss system on my 500 triumph and have made up an ignition cicuit using an ignition box and coils from a Yamaha twin (i think)and by making a trigger circuit that fits where the contact breakers go. It works fine for our trials which are short all on closed land but I doubt if it would work on a road trial. I also find that when the battery is low then I get miss fire on one cylinder so the performance of the bike now has another variable (battery condition) as well as all the other problems one has with old engines. I would suggest you change to a charging system, it will be a lot less aggravating.

Hi Bob, I don't know how helpful this will be but the Mikuni I have was put together from bits and pieces I had in my box of carb bits so I don't think you can replicate it. Anyhow, this is what I have, it is a 26mm VM type carb, with a 140 main jet, a 30 pilot jet, a 5DJ19 needle (which I believe is from a Kawasaki triple) with the clip in the middle position, the needle jet has the numbers 284 0-2 stamped on it and I can't find these numbers in any Mikuni jet table. This needle jet is a bleed type (for 4 strokes) but it has the extension into the throat that is the same as the primary type (i.e. for 2 strokes)!. I doubt if this extension has any merit, it was just what I had in the box, the important part I think is to have a bleed type jet and not a primary type. Also the needle has been filed down over most of its length to make it richer throughout its range (again it was what was in the box). The slide is a #2 with the cut away increased to a height of 4mm (another piece in the box). This mixture however seems to work quite well with good plug colour throughout the range. I do find that this engine doesn't run well if it is too rich unlike my Bultaco that seems to run on almost any settings. A lot of other people run Mikunis so hopefully someone will tell what mix of jets they use that are easily available.

You said your clutch rod was 5 inches long! the rod on my 500 is 9 1/2 inches long and I would expect the 3TA to be the same, also the rod sticks out about 5/16 inch out of the mainshaft at the clutch end. If your rod is 5 inches long then I would expect there to be another 4 1/2 inches still in the main shaft. A long rod can have a tendancy to bend when the clutch is actuated and this results in a heavy clutch action due to friction between the rod and the bore of the mainshaft. Some people cut the rod in half and put a ball bearing (same dia as the rod) between the 2 pieces, the shorter rods don't bend so easily and therefore there should be less friction and hence give a lighter clutch action. regards Martin

There is a brass thrust washer on the lower gearbox shaft that goes against the needle roller brg and a small peg is used to stop this washer from rotating. This sounds more likely to be the piece of metal. regards Martin

I have a B25T engined bike that I first built into a BSA frame (the later version than yours) and that was so heavy and the weight distribution such that it was hard to lift the front wheel like a more modern bike. I later built my own frame which improved matters considerably. I also tried a 22mm carb but although it pulled like ateam engine it didn't seem to accelerate very quickly, I now use a 24mm mikuni which seems fine. There may be an issue with your timing aswell with insufficient advance, it is easy to adjust so I suggest you try playing with it. If you don't have any automatic advance/retard built in then you will probably be stuck with a compromise setting which is neither good at either end, i.e. it will stall too easily at low rpm and not rev out as quickly at larger throttle openings. Try playing with the timing first before changing any equipment.

I didn't read your first comment closely enough, you did say it was the same diameter as the rod so it couldn't have been clutch roller. Your comment said it was 4m long but I assume you meant 4mm. Have you owned this motor from new or did you get it second hand. It sounds most likely that somebody put it in as an extension to the rod for some reason. My engine is in the process of being rebuilt so I will measure the rod tonight and let you know. I don't think there is any difference between the 500 and 350.

It sounds like one of the clutch roller bearings. The clutch is mounted on a set of loose roller bearings which have to be assembled onto the clutch hub. It is not a caged bearing as you might expect. If you take the clutch plates and the centre hub off then you can see these rollers and you can tell if one is missing. The manual should tell you how many you need (20 I believe is the correct number). You can usually replace a roller using a pair of tweezers without taking the whole clutch apart. If you look at the exploded view of the clutch in the parts manual, the roller is item 4 and the centre hub is item 6. Hope this helps.

You can get answers to most questions on Triumphs if you Google www.classicbikes.biz It has manuals, maintenance info, and parts diagrams for a number of different engines. Other than part numbers, there isn't much difference between 3TAs and the 500cc engines. The manual will tell you 20/50 oil for engine and primary chaincase although some people use ATF oil for the primary. To get the bearing out you will have to get at it from the inside of the gearbox. I think there is a circlip holding it in place but the manual in the above. regards Martin

I agree with your idea of a set of sensible rules that makes it less expensive and easier to build a complying bike. However as totalshell says there is a lot of "free" in the initial concept that this will result in even more specials, for example by only specifying rear shock length it stiil allows room for unique non 1970s rear suspension designs. So if the intent is to cut out the specials and maintain a 1970s look then your going to need a lot more detail in the rules. If the specials are welcome then the rules are fine. There are lots of riders and builders out there who will want to stretch the boundaries as much as possible to either win or just because they enjoy building specials, so at this stage I think it is important that besides defining what is to be allowed, you sort out in more detail what you don't want this class to become.

Since you have checked all the obvious likely problems, it sounds as though it may be something a little out of the ordinary. Is it the same whether the engine is hot or cold or does it get gradually worese as the engine gets hotter? I had a a grass track JAP engine once that was fine for the first half of a meeting but as the engine got hot the tappet clearance closed up such that it ran fine up to half throttle but would miss fire at full throttle.

If you google www.odgie.com and open "me in the dirt" you will see a picture of a cotton trials bike that has a twin down tube and the rest of the frame looks like yours. regards Martin

Be grateful you have such a large choice. Back in the bad old days (1960s)we used to wear reconditioned leather firemen's boots with metal studs hammered into the sole to give a bit of grip. Painful when worn with ingrowing toe nails.

I ride a 500 triumph in trials and use the normal 18 tooth on the engine and have made a 12 tooth sprocket for the gearbox by welding on a sprocket onto an old sprocket that had the teeth machined off. The rear wheel sproket from talon is 54 teeth giving basically the same end result as beno41. Even so top gear is a bit low for green laning so I certainly wouldn't go to a 60 tooth rear.

On my 500 Triumph and BSA trials bikes I just use clear plastic (fuel line type) tubing since there is no significant pressure on the supply and return lines and it makes it easy to see that the oil pump is working and the colour of the oil. The tubing does eventually go hard but it is cheap to replace. I was also able to buy clear braided tubing from my local hardware store but the amount of braid was minimal and I doubt it would take much pressure. What bike are you using it on and what sort of pressure will the tubing see?

If you have a weak back then consider getting a proper orthopaedic support belt (looks like a corset with steel ribs in the back). I have had to wear one for years and it makes the difference between riding and not riding. I am surprised that more people don't wear them since they wear all sorts of other protective equipment. Even when my back feels O.K. I wear it as a prevetative measure. When you are getting old you can't always exercise your way back to your youth, you just have to accept a few compromises if you want keep riding. Hope your back gets better (alcohol is one of the best muscle relaxants when taken internally and is kinder on the stomach than many of the pills).

Where did you order it from in the US?

If you go to www.classicmotorcycles.org.uk will find some useful technical information and there is blown up dwg of the gearbox cluster that maybe helpful.

I had a similar problem once with a B25 g/box. I had somehow assembled the box such that the output shaft was shimmed too far towards the clutch and I could only engage gears 1,2, and 3. Check the primary chain alignment i.e. clutch teeth aligned with the engine sprocket, if the clutch is too far out then this may be the problem, otherwise hopefully someone else has a better suggestion, good luck.

Hi Zippy, That is exactly what I had done, chopped the existing bone a few inches above and below the joint and fitted stainless steel inserts top and bottom plus a plastic/teflon pad under the knee cap. I have the X rays in pdf form if anyone wants to see what it looks like. They make an incision about 6 to 7 inches long down the centre of the knee to open everthing up and then get the saws out. There is obviously a lot of skill (capentry type) in making the fit between the bone and stainless steel and I was told they are glued together so the joint has full full strength almost immediately. It is the soft tissue such as ligaments and tendons that takes time to get back in shape, also there is a general numbness around the knee ever after so they feel strange for quite a while. I rode last Sunday in a trial on my 500 Triumph, fell off several times but otherwise no problems other than hard work kick starting this engine after it has been on its side and flooded the engine. There is no reason why you shouldn't ride normally after such an operation, the key is, as several people have mentioned, you must do the exercises to recover good mobility of the joint. It is hard work to start with and for the first few months it can be very frustrating, but there is no option but to get proper Physiotherapy help to get the knee bending to around 135 degrees.

Hi Vinnied, I had both my knees replaced at the same time in January just over 3 years ago and I ride a 500 triumph (weighs 245 lb) in vintage trials in Canada. I first rode the bike about 5 months after the operation but not seriously (just messing around), whenever I felt the bike going over I just let it drop. It wasn't till the next year 18 mths later) that I rode in a trial and although a taking it easy, it didn't cause too much trouble. This year I have been falling off, hitting trees, etc quite happily with no knee problems. You may want to use knee pads for a while since although the knees are somewhat numb, they are still very sensitive. The one thing you don't want to do is twist them so if in doubt bail out. Don't feel it will stop or limit your riding but it is critical that you do all the prescribed exercise and get that 135 degree of knee bend. Hope this helps.

It seems a little curious that you have the needle in the leanest position (top groove) and you have a large #4 cutaway on the slde which should also make it lean yet it runs rich at 1/8 to 1/4 opening. It makes you think there is something odd happening. Could your needle jet be worn? You say you have a number of spare jets and slides so perhaps try a few substitutions. It would be very helpful if some member with the same engine/carb combination could tell you what they are using.

It sounds as though you have the right pilot jet with the 25 jet, but as soon as you open the throttle it runs rich (and the needle is already in its lowest position), so perhaps you need to try some other needles that have a slightly larger tip diameter to lean it out at small openings.

All the comments about stretching and excercise are absolutely correct, but even with all that I still wouldn't last 5 mins on a trials bike if I didn't wear a proper orthopedic support belt (looks like an old fashioned corset with steel ribs in the back) I wouldn't be riding anymore if I didn't have it. Much as we would all like to be able to completely cure ourselves by various sorts of treatment, it isn't always possible. I fell off too many grasstrack bikes in my early twenties and flattened 3 of the lower discs. Excercise is absolutely necessary just to be able to keep do the normal things, but it seems common sense to me to protect the lower back as much as possible when I ride, so regardless of how I feel, I always wear this bullet proof belt. I don't know why more people don't use them as a preventative measure especially as they get older. I'm 61 and ride a 500 triumph trials bike, but I wouldn't even be riding a Bantam without the belt.

Thanks for the advice and the problem is now resolved. I lowered the float level slightly, dropped the needle one notch and readjusted the air screw a little further out. Engine now runs smooth as silk.

The slide seems O.K. there is some discolouration on the bottom of the slide skirt matching the choke dia but there is no wear ridge that I can feel when running my fingernail over it.