feetupfun

Kimpybugalugs I just remembered something else about 2 stroke oils that might influence what you use. While full synthetic premix oil generally provides the lowest smoke and engine deposits formation rate, it does not protect the rolling element bearings from corrosion during non-use periods as well as semi-synthetic and straight mineral two stroke oils do. So if you only ride your bike once in a while and store it exposed to high humidity, or if you are not able to run the motor after washing your bike, you may want to consider using semi-synthetic oil. If you ride at least every week and keep your bike in a low-humidity environment, it probably doesn't make any difference in this regard which oil you use. David

Don't forget the effect on the brakes If your little blasts include much sustained downhill riding under brakes, you will certainly be overheating the brakes. I've seen them overheat after only about a minute of serious downhill high speed riding. Blue discs, boiling fluid etc. Braking into turns on the flat or only short downhills the brakes will be fine.

If your jetting is good, you can run as much oil as 20:1 and still not have oiling up problems. If your jetting is too rich, you can have oiling up problems with much less oil in the fuel. Where I live, Castrol TT is not a synthetic oil. Maybe you mean Castrol TTS? I have been using mineral based, full synthetic and semi-synthetic two stroke oils in the premix for my TY175 since 1976 and all my other twinshock trials bikes since I got them (ranging from 4 to 13 years ago). I have consistently run 33:1 fuel:oil with all three types of oil and have never had oiling issues. My sparkplugs last many seasons and never foul. I eventually replace them because of electrode wear. I have noticed that modern synthetic oils produce an almost invisible exhaust plume while the mineral based oils from the 1970s produced a more visible plume at the same ratio. I'm sure people have run their bikes on less oil and also not had problems but I'm just telling my story. David

Matthew Yes it sounds like unwanted air is entering your 247 motor. Don't assume it has to be the fault of the AMAL (but it may be). Because you have been diligent with your meintenance of the carby and have taken the trouble to avoid the usual pitfalls relating to air leakage and flange mounted carburettors, and that you know the history of the bike, you would know if the crankshaft seals have been replaced recently. If your bike has the original seals, they would be quite hard by now and susceptible to leakage when combined with any wear in the crank bearings (main bearings). Because you didn't mention heavy smoking as the performance deteriorated, it may only be the magneto side crank seal leaking at this stage. If on the other hand, you have replaced these seals in the past few years, the leakage may be the result of another issue. Here are some other possibilities: Cylinder base gasket leaking - would be visible as an oily deposit somewhere on the gasket joint. Body wear of the AMAL. You mentioned rebuilding the carby but didn't say if it had been resleeved. The slides wear very fast and you may have replaced the slide many times. The slide contact surface in the body also wears but at a lower rate and can cause leakage. Yes it is fine to fit a Mikuni carby. Mounting flange adaptors are available from Mikuni suppliers so you can fit a spigot mount carby to your 247 barrel. Suggest Hugh's Bultaco, Craryville, New York state as your Mikuni supplier. If you want your 247 to continue to look original, you can still buy new standard AMAL carbies. David

I just had to add my two cents worth. The forks and front wheel on the bike in the photo were used on all 348s and the first two models of the 349; the 1980/81 red tanked model 349 with the sight guage tube in the side of the petrol tank and longer swingarm, and the 1981/82 white tanked model). During the white tanked model run, 349s started to come out with the horrible (prone to failure of the spoke flanges) conical Honda design hub. The fork tube spacing was narrower on the white tanked model 349 compared with the 348s. This doesn't really matter but may help with identifying which model triple clamps you have. Not sure about the first red tank 349 fork spacing. If you intend riding the bike in competition, compare the swingarm length of your Monties. You may have the swingarm from the first model 349 which had a longer swingarm than the 348 and the later 349s. The long swingarm is great for hillclimbing and the shorter one is great for tight stuff.

Yes it is important for older style riders. I don't hop the front or back so the tight turning characteristics are important to me. I find when riding a Beta Rev3, tight turns are a breeze. The other modern bike I like to ride is the two stroke Scorpa, but it does not seem to have quite the same turning circle as the Beta.

I think that Dan was suggesting that the kill switch might have been working unexpectedly. They can do that even if they won't stop the motor when you want them to. If you're having plug cap problems, make sure you are using the correct plug top for the cap. The standard Beta cap requires you to remove the aluminium nut from the top of new spark plugs. If you don't, the cap won't stay put.

Just because the float height is set right, doesn't mean that the fuel level is right! Possibilities include: Floats not floating high enough in the bowl (usually due to a float containing some fuel) Float needle valve not sealing off fully A good test for the fuel level being too high is to turn the fuel off while you are riding around. If the symptoms disappear for a while before the carby bowl goes dry, you have narrowed it down to fuel level being too high. The other info you have not given us is: Has the bike has just developed this problem while you have had it or was it like this when you bought it? David

If it was your plug cap jumping off, you would have had to put it back on again to get going again wouldn't you??

If you are not yet an accomplished rider, a newish bike will help you improve your riding faster than a twinshock as the stronger feedback you get from a modern bike trains your brain faster to do the right thing. If you are an accomplished rider, there are few things better than riding a twinshock against modern bikes and winning. Most people who have enjoyed riding and owning a twinshock (or classic) bike and then sell it, later wish they hadn't.

Montesa did make some dark green-tanked trials bike models (Cota 172 maybe) but not the Cota 348 model. Have a look at your frame and engine numbers and Jared Bates' excellent website if you want to work out what you are looking at. http://www.southwestmontesa.com/montesa/gallery.htm David

Nigel Dabster You've got a good memory and eyes like a hawk. Yes the black painted bit on the ribbed section and spoke flange has to wait till next weekend. The conical polished bit is standard though. That reminds me of something. The brochure shots of my M198 look quite drab with the black motor and black fork sliders compared with the preceeding shiny models. I do like to maximise shiny bits but am keen to have it look like it did from the Bultaco factory. OTF what's that about no TLS front brakes on twinshocks? It's OK here in OZ with rules only specifying "drum brakes" for twinshock class. Don't see too many TLS brakes though. Maybe it's the travelling backwards fright factor? DabDab the linings for the M198 are relinings of the original shoes by an automotive brake company using a very high friction coefficient material. I've recently fitted a set to my KT250 (after machining hub and shoes) and it is a revelation. I'm in the process of fitting a set to my 250 Majesty too and expect to be assembling the wheel this weekend. Will post results.

Thanks guys. I agree with your suggestions. I think I gave the impression of being a bit of a yokel with those photos. They are "before"photos of a bike which came in boxes and had been sitting around for about 20-25 years, judging by the age of the tyres (Japanese trials universal Dunlop on front as fitted to TY twinshocks when new, and Pirelli MT13 on rear). I've attached a photo of the front wheel in the process of being restored as a reference for the standard of the restoration I'm aiming for. By the time I get to ride this bike it will: Have had high friction linings fitted to the Bultaco shoes, and machined back to exactly fit the drum, while in position on the backing plate. Have had both drums lined with steel (front drum already lined when I got it and has just been machined to remove slight grooving and rust) (cast iron liners not available where I am getting the rear drum lined). Be using a rod and left brake pedal. Have the backing plate centralised when tightening the axle nut. Have a lubricated cam and bush and brake pedal pivot. Have a high tech, low friction front brake cable. Be using the original AMAL brake lever. Have a lengthened brake arm on the front. Bushing the pivots as suggested by Nigel Dabster will get rid of 99% of my issue with the design so I'll probably go that way. Thanks David

The offset pivot arrangement for the brake shoes in both wheels of my M198 had me wondering if there were brake shoes from a different bike that would fit and not have the offset pivots. I'm trying to maximise the performance of the brakes by avoiding the eccentric loading against the drum that the standard bultaco pivot arrangement creates. I have looked in the EBC catalogue and there were a few alternatives that looked like possibilities. Fantic 240 shoes appeared the closest in the catalogue. They are for the same diameter drum and are the same width shoe and use a standard pivot arrangement. I know I can have the existing shoes modified by welding and machining then relined but it would be a lot easier if some other shoes fitted. Has anyone tried something like this? Thanks David Photos added

TLM 50s are a good choice for sub-adult size youngsters wanting to ride twinshock class as they are a bit smaller all over than a full size bike and quite light for a twinshock. The motor performance is very good for a 50. Standard size trials tyres, while not leaving much clearance at the swingarm, can be fitted. As far as I know they were only sold new in Japan, but there are quite a few now which have been imported second hand (to Australia) from Japan. Motor parts (not that they usually need them) are not too hard to get as the motor is shared with a Honda moped or scooter. Body parts are scarce. The photo is of a youngster in our local club on her TLM50.

Yes, good quality industrial and automotive rubber hose bought from the reel nowadays is usually ORTAC (oil resistant tube and cover). It's not too bad with high temperatures either. I have had some on an exhaust join (main section to muffler on a 2 stroke) for 5 years now without any problems either.

It's not just a bigger piston job to get to 200cc. You need a bigger cylinder sleeve, head machined and also crankcases machined for the bigger sleeve. Various pistons are available. Some pistons require a spacer under the barrell. Some pistons need the gudgeon pin holes bushed down. It's a big job. Are you still keen to do it?

What is a Razor?

There are options for getting the old oil out. You can drain the gearbox through the filler (inverting the bike) but it is a lot of trouble and quite messy. You can drill out the remains of the plug. You can drill a small hole in the plug and use an easy-out tool. You can work on loosening the plug by tapping against the sealing flange with a pin punch. On the 348 the clutch/primary drive oil is seperate to the gearbox oil and usually has a decent drain plug so you should be able to change that oil without any hassles. By the way, there are many species of snakes here in OZ that are more dangerous/venomous/aggressive/poisonous than the US (or Mexican) rattlesnake. It is a well developed habit here to look before you put your foot down when riding or walking.

Our local club doesn't include twinshock class ie they only run rider grading classes so I ride on my twinshock against modern bikes. Most open trials include a twinshock class so I usually ride that. Some other open trials are for twinshock and classic bikes only. Last year my wife sold her modern bike so whatever trial I ride now it is on a twinshock bike. Before that I sometimes rode the modern bike.

You can do whatever you like with the clutch. It is whether the bike stops or not that counts as far as scoring goes. If you are a died-in-the-wool stopper, you might find that to start with you will do less accidental stopping if you leave the clutch alone. Personally I find it so much easier to ride using the clutch that I prefer to use it and pay close attention to keeping the bike in motion.

Your message was a bit hard to work out, but it sounds like where you ride, the twinshock class rules include a stopping penalty while the modern bike class rules allow stopping. Contrary to what are saying about the rules in the 1970s, events then were almost exclusively run to no-stop rules. If you were allowed to momentarily stop and balance in the 1970s, you were riding under different rules to the convention at the time. There are reasons for using a stopping penalty for twinshock class nowadays. Depending on the nature of the sections, a bike with poor clutch action by nature of it's design may be disadvantaged by allowing stopping. If the organisers are trying to attract riders, it is useful to make the playing field more level by reducing the advantage gained by having good clutch action. To replicate the feel of the events of the time the bikes were made, orgainsers sometimes like to use the same rules as those used at time. Yes it can be tricky and sometimes quite amusing riding to the no-stop rules after years of stopping and balancing. We have one (twinshock and classic bikes only) event a year that runs to no-stop rules and that is one of the reasons it is such fun to ride. And yes lots of us ride twinshock bikes in modern bike classes (with great satisfaction too)

I have no experience with the Castrol 747 but do know that if you use Castor oil (Castrol R40) as the pre-mix oil in your two-stroke trials bike, the carbon formed on the piston crown and in the head will form very quickly and be extremely hard. To remove it will require emery tape/grinder rather than the usual wiping with a 3M scouring pad that removes the carbon formed when using modern oils. Another consideration is that switching from one type of two-stroke premix oil to another without washing out the motor internals can cause accellerated wear rates until all the old oil has worked its way out of the engine. The concentration of Castor oil used as an upper cylinder lube or odour agent in the fuel for a 4 stroke should be kept much lower than what you would use in two stroke premix - mainly to avoid causing carbon buildup in the exhaust ports and valve/s.

I thought this might be the right time to show a photo illustrating how popular Cota 348s are in our local trials club. Photo taken before a club trial October 2007.

Those fork caps are standard on some model Cota 348s. I have 3 sets of 348 forks and thay all have those caps but I have also seen 348s with plain fork caps. It was a popular thing to do at the time. It provides another way to adjust the front suspension. There is a drawback though that increasing the pressure inside also increases fork seal drag.