feetupfun

Yellow or orange or red means weak spark. A good spark is blue. It can have a weak spark and still run OK but start poorly because the spark voltage drops off with reducing RPM and kickstart RPM is lower RPM than running RPM. Problems with the HT lead or cap will reduce the spark voltage. The spark when you look at it with the plug out of the cylinder will always be a better spark than what happens inside the combustion chamber because the pressure in there is higher (a higher voltage across the plug electrodes is required for a spark when gas pressure is higher) Another way to test for a weak spark is to reduce the plug gap and see if it makes an improvement to starting. Try about 0.5mm gap. This makes it easier for the spark to jump the gap but is only fixing the symptoms not the problem. What I've written here about the spark is just for diagnosis. The fact that it starts better when up to temperature makes me think that your starting issue is more likely a fuel/air ratio issue. If it revs up a fair bit with the choke on when starting cold, that can mean that the starting circuit is not letting in enough fuel. The "leaning the bike over" test is good for diagnosing this. You can also see what happens when the bike is up to temperature and idling then you put the choke on without touching the throttle. If the motor stops or runs very rich then your choke is working OK but if it revs up or runs normally with the choke on and throttle closed when at running temp, there is too little fuel going through the starting circuit for cold starting.

Here are some possible things you didn't mention Air screw maybe set too lean Spark plug cap failed inside Spark plug wire failed inside Colour of spark Reeds sitting against seats What you are doing with the throttle as you kick it Is it any easier starting hot or cold The SY250s I've been involved with won't start unless they get spun over fast enough but run fine once running.

If the parts are clean, smooth and lubed the aluminium part will slide off the damper rod under it's own weight. No thread, no need for anything. It is held there between the damper rod and the slider by the screw that holds the slider on.

Yes the tapered aluminium tapered piece has to come off for the damper rod to come out the top. It could be stuck on by gunky old oil sludge

A common cause for slow fan is fan rubbing against something. You didn't say if the 2 Volts is with the fan connected or not. Test for open circuit voltage to see if it is a fan problem or a power supply problem.

The length of the spacer is not particularly critical, as long as it is a bit longer than the distance between the bearing seats, which you should be able to measure. The thin disc near the middle is not important. It is there for when you are fitting bearings. You can hold a plain spacer in position with the axle while you fit the bearings.

You will need to say where you are because rules are different all over the world

Maybe the clutch plates are a bit thinner than normal

TY175 push rod 122.4 mm TY175 mushroom 62.5 mm Have you got enough clutch plates in it?

If you do go the honing route, there are imperial-sized big end rollers made for Harleys that are slightly bigger diameter than the Bultaco rollers. I'm not surprised that there are a few things wrong with your motor because I have never encountered a second hand Bultaco engine that didn't need extensive internal attention before being re-birthed. One I bought recently the crank was so chewed up on the magneto flywheel taper, that half of the crank is unusable. The other side of the crank had the nut welded on, but should be OK to use. Another Bultaco I bought had the primary drive chain welded together. I figure someone couldn't work out how to get it apart so they ground the end off two chain pins, then welded the cover plate back on the chain afterwards. I haven't pulled either of those motors fully apart yet (saving the fun for a rainy day) At least the price of Bultaco conrod kits has come down in the past few years. I remember doing up a 350 Alpina engine about 15 years ago and back then, the piston kit and conrod kit cost about twice as much as the same parts cost for a M49 Sherpa T motor I did up recently.

Are you sure that a 1W1 pushrod is the right length? The 1W1 series motors have a different clutch camshaft and a different clutch to a TY175. I'll measure the TY175 parts later to tonight if I can find them

If you are serious about saving money, the big end hole in the conrod can be honed out and oversize diameter (imperial sizing) rollers can be used to refurbish it.

OK thanks. The TY175 I rode that had a TY250 mono front end also had a standard TY175 tank and it had a huge turning circle. If the owner had modified the stops to get a better steering angle then the fork tubes would have hit the fuel tank. I can see that if you use the right type of Majesty style tank then there might be clearance for the fork tubes and have a decent turning circle.

Yuk

Seeing the corrosion damage on the one-way valve in your photo, I suggest you also have a good look inside the tubes where the damper piston runs. The swept area in the tubes may have corrosion damage that will affect the damping performance even it you make or buy replacement damper pistons

Is see that the photo shows a Majesty frame. What did you do to the steering stops to restore the steering angle?

That aluminium part with the taper on it is a hand-slip-on fit on the damper rod when there is no corrosion. This part is the anti-bottoming cone.

The forks you bought are from a TY250 mono which is a completely different bike to a TY250 twinshock. The brake plate on a TY250 mono engages with the lug on the LH fork slider on the forks you bought. Those triple clamps will not match well with your TY175. They will have very limited steering angle side-to-side unless you get a different fuel tank and modify the bottom triple to suit the TY175 frame. TY250 twinshock models forks and triples can be interchanged with TY175 forks and triples without modification. TY250 twinshock forks look a lot like TY175 forks but have bigger diameter tubes and sliders. TY250 twinshock forks are also slightly shorter (about 20mm shorter overall) Your new forks have tubes that are too big in diameter to fit TY250 twinshock triples without modification, and your forks are leading axle, so the steering geometry will be wrong unless you also use the TY250 mono triples.

That seal sleeve is normally a light push fit. I haven't had to heat one up to get it off. Yes the big end should not have that much side play. Should be more like 0.5mm. Might have had the wrong conrod kit fitted. Some Montesas do have the conrod kept central by the top end of the rod, but Bultacos like yours use the bottom end of the rod to guide the rod and depending on the piston used, also may have centralising spacers on the gudgeon pin. Fairly standard Bultaco failure to shear the drive side key when something goes wrong. One Bultaco I bought recently had that nut welded to the crankshaft! Being a Sherpa T it was a slow process grinding the weld away inside the drive side flywheel recess. It's hard to see how much clearance there is on the outsides of the crank wheels in your video, but is it possible that the crank wheels have moved apart to cause that side play at the big end?

Also when you tighten the shock mount screws, do it in a way that avoids the shock mounting rubbers being gripped. The shock mount rubbers need to be free to rotate on the mounting pins to avoid side-loading the shockie oil seals as the swingarm goes up and down. Falcon shocks and many others have mounting rubbers that are wider than the Yamaha mounting pins are long. For this you can use spacers to effectively lengthen the shockie mount pins and tighten the screws up against the spacers, or don't bother with spacers and just Loctite the screws in the position that allows free movement.

If you are never going to dent a steel tank, then a stiff tank sealer that is compatible with modern pump fuel (epoxy resin) is OK. If you do dent a metal tank that has a stiff tank sealer, the lining will probably crack away from the steel and you won't be able to get the dent pulled out with heat and you won't be able to reseal it with epoxy again. So for a bike used on the road an epoxy lining is probably a suitable cheap fix. If the hole is in the tunnel it should be able to be welded or soldered up without the repair being visible when the tank is on the bike and won't damage the paint on the pretty parts of the tank. If you use a flexible tank sealer in a steel tank, it will eventually swell, go floppy, come loose and cause you lots of dramas while you try and get the liner out through the filler hole. I have had to do this in a TY80 (steel) tank and it took hours. The tank didn't leak, so it looks like someone had lined the tank just because it looked a bit rusty inside. You can find metal tank leaks by slightly pressurising the tank (lung pressure is usually enough) and brushing soapy water on while looking for bubbles. Using work shop air pressure or tyre filling air pressure can cause the tank to go way out of shape (permanently).

Can also use a bottle jack to push the tubes down. Push against the junction of the frame tubes near the front of the seat (to avoid bending the top frame tube) If you do it just right the mounting holes will line up nicely too. It's a common maintenance job on twinshock trials bikes that get ridden in trials.

Fabulous looking bike there Gary. Thanks for the photos. M27s are not often seen on the forums and I've never seen one in real life. I did look at an M49 that was for sale nearby years ago (pre-digital photos) that still had the original triples with the U bolts and the welded-on control levers on the bars. I'll see if I can find the photos I took at the time. I remember the seller had some parts that went with the sale, including spare crank seal carriers. He told me it was routine maintenance on the bike to change the crank seals every couple of months, so he bought spare seal carriers so the bike would be pulled down for the minimum time. I'm glad that crank seal life has improved since then.

Here are a couple of photos showing two of the types of top clamp that are being discussed. The upper photo is an M80 and the lower is an M49

If you have standard TY250 fork tubes and they are positioned with the top ends of the tubes flush with the top edge of the top triple clamp, the fork seal will get to 57mm from the underside of the lower triple clamp on full compression. I've put a black pen mark at 57mm in the photo