feetupfun

This is a B model bottom end. I looked at an A model as well and it looked very similar

http://bikepics.com/pictures/646837/

I bought a TY175 once that had a Gunnar Gasser twistgrip (huge cable pulley diameter) fitted which made it about 1/8th turn from closed to open on that carby. It worked fine. Maybe on a more zippy trials motor it might have been a problem. It's also possible that you can train your mind and body to ride with just about any setup.

if you can post up photos of the bike it may help with suggestions

It may also just be the spring is weak and the shaft needs relubing. Either way it is a 2 minute job and springs are readily available

I use a multimeter for this and watch for a voltage spike in the LT wire

what's an LT spark?

The two different 125 Scorpa four strokes sold here (concurrently) had different forks. One of them had the same forks as the SY250 while the other had something not quite as flash - non-adjustable perhaps. There was a difference in the seat department too, one had a seat the other not. Other things like alloy rear sprocket vs steel also spring to mind.

I know that some people modify their TY airbox by removing the lid and fitting a flat piece of foam across the top instead of the foam sock-on-core that is standard. One weakness with this is that the velocity (and pressure drop) of the air through the foam is increased by the reduction in surface area of the media. Another consideration is that the smaller a filter is, the quicker it becomes clogged with dust, in dry conditions (very important where I ride). The modern trials bike filter in Woody's Majesty photos is a basin shape which increases the surface area compared with a flat piece of foam

Patrik, there are some errors in your explanation. I noticed the following straight up and stopped checking the rest: 175cc is 0.175 litres, not 0.0175 litres 2.3 m/sec is 8.3 km/h, not 83 km/h I also think that the proof of the design of the TY175 airbox lies in the fact that the standard competition version of the TY175 has a wonderful free-revving characteristic. From what I understand of what you are saying about your bike, there is a rubber snorkel on the airbox. Please be aware that the standard competition TY175 as sold around the world as model 525-xxxxxxxx, did not come with that snorkel, but road-going Ty175 models such as the 1N4-xxxx did have the snorkel, and the snorkel probably does cause a bit of additional drag to the airstream.

probably depends which majesty tank you are talking about and which TY frame. There are quite a few different majesty tanks

Riding with peeling chrome will not make the hub irrepairable, it will just have poor braking and will chew up the shoes faster than a good drum would. Just inspect the shoes for thickness after each trial to avoid going metal to metal

The ball is the same diameter as the rod whatever that is (5mm maybe). You can file or grind the face of the cam flat again, just make sure it ends up smooth where the rod end contacts. I've successfully built worn ones up with mild steel weld and machined the OD back to size when the pit in the cam was too deep. I don't think the cam face needs to be especially hard, but smooth is important

modern trials bikes overheat if you flog them along a road. the cooling system is only made to cope with intermittent high load operation.

You can generally run a lower preload on the clutch springs with the plates that have friction material, so you can achieve a lower lever pressure without any slippage. In my experience they are only a real benefit in a 325cc motor, because the 238 and 250 motors can be set up with a nice light lever pressure even with all steel plates and not slip.

I think naichuff is saying that a Bultaco will run backwards even with the timing set quite a way before TDC. I agree with this and add that advancing the timing can increase the tendency for the motor to run backwards, because at very low RPM (when kicking over, or when motor on verge of stalling), the motor is more easily be stopped and reversed because it fires with the piston further before the top of the stroke. A different factor that can muddy the waters in discussions is that the motor will run better in reverse the more retarded the timing is. Some bikes have a diode in the primary circuit to prevent ignition when the motor is rotating backwards

In case you are wondering why it is OK to have no retaining circlips, it is just that the internal pressure when the forks are compressed is not enough to cause them to slide upwards. Some Bultaco forks have vented caps, which limits this pressure, but the odd thing is that there are many Bultaco forks without vented caps and also without circlips. A bit of a mystery so far to me. Anyway, I run (non-standard) unvented caps on my 1968 M49 (the bike in my avatar) and do not use circlips and despite quite a hammering, the seals have stayed put.

I did mine similar to Guy's

The SM kits I have seen do not require removal of the original mounts

It was to avoid scraping one's boot edge on things, which (once upon a time) used to earn the rider a point. I'm used to the standard peg position on all my 1970s bikes and after trying out lower pegs on one of my TY250s, do not want to lower the pegs on any of them.

Depending on how long your legs are, lower pegs mean you may get hit in the bum more often by the rear frame loop when unweighting on obstacles. I lowered the pegs on one of my TY250s a little bit more than the SM kit pegs and while the bike was easier to balance, it made it a bit more restrictive to move about on the bike (I am 174cm - 5' 10")

If you have the front hub as used on most 247s and all 348s, then yes the front spokes made for TY175/250 front wheel will fit. Would you like a photo showing my 348 front wheel recently respoked with genuine TY spokes?

also do you mean the end that goes through the cover? or the end that turns in the gearbox casing? I found that I needed to rebush both on one engine,

The tank looks long because the top shock mount and associated frame joint is further forward then standard

No they are a very good clutch if working properly Things to check: edges of basket fingers need to be completely smooth not ridged steel plates need to have a rough finish (not polished smooth) cam surface smooth end of pushrod smooth newish friction plates (originals would have lost their frictional properties by now) suitable oil in good condition