sherpat250

Many thanks for the reply. When you refer to M8 and M6 bolts, what is that referring to, exactly with regard to the crankcase nuts? What I have here are a bunch of 10 mm nuts with lock washers, and then one allen/hex-type bolt at the front of the engine. According to a chart I found, M8 bolts would equate to a 13mm wrench size. Neither of my fasteners are this size. Please clarify which number refers to which fastener on the engine. Also, how is it that the M8 crankcase bolt has a higher torque setting than the 8 mm cylinder head nuts, which are spec'd at 14 ft pounds per the Chilton's manual? (I realize the larger head nuts have a 25 ft lb torque). I've already snapped one of the crankcase studs previously, and want to get it right this time! Thanks.

Does anyone know the torque specification for the crankcase nuts on the left side of a 250 cc (M91) engine? I can't seem to find this info anywhere. If not an "official" spec, then I would at least appreciate a reasonable figure to use in the opinion of the experts here. Please also indicate if this torque would be the same for the single recessed hex-head bolt at the front of the crankcase. Many thanks!

Hello all, I wanted to do an update on my Montesa that would not start, despite having spark, compression, and fuel. It is now running thanks to the help of two nearby trials enthusiasts who helped me track down the problem this past Saturday. What we found was a significant rust/corrosion deposit in one spot on the cam inside the flywheel. We believe this was making the engine spark twice per stroke, or making the spark erratic/unstable. We polished the cam, put in a new NGK plug and with a push-start down a hill it began running! Oddly, I could not get it to start or even fire by kick-starting numerous times, but it started right away with a push-start. Now after it has run a bit, it usually starts up with just one or two kicks. This was a very strange problem and I wanted to share it here as it might be one for the "notebook." Everyone always says you need spark, fuel, and compression and an engine will run, but here was a case where I had all three in plentiful supply, yet an odd issue kept it from starting. Oh well, at least it was a good learning experience for me! Regards, --Kevin

I had the same thing happen on my '74 TL-125, and it was able to be welded. It took a bit of finish grinding to get it back to original dimensions, but the weld has been holding for about a year now. Take it to someone experienced in aluminum welding and it should not be a problem. --Cheers.

I'd like to thank everyone for the additional tips & comments. I plan to work on the bike over Christmas vacation, and will report back on what I find. One update--I did check the compression with a gauge and it is 90 PSI. That seems adequate, but I don't know if it's as high as it should be. Any further comments would be appreciated. With respect to statement that I may have "talked the previous owner into pulling it off Ebay", that is not accurate, and I have sent an e-mail to the writer explaining the circumstances by which I came to own the machine. In short, I bought it after seeing it offered for sale at a trial event in NY, and my transaction never involved eBay. Best holiday wishes to all.

Thanks for these excellent ideas. I wondered myself about the timing of the engine. I never touched it, but it's possible the previous owner had it way, way off. This might explain no firing at all, even with starting fluid in the cylinder. I will be sure to check it out. One more quick question...how does the decompression kit install on the engine? Does it use the alternate spark plug hole that Cota's have?

Thanks for these helpful tips. I will check them out!

Hi all, Just picked up on non-running Cota 247 (1975-ish), and would like to get it going. It has decent compression, good spark (at least outside the cylinder on the two plugs I tried), and it is getting fuel. I even tried a shot of ether starting fluid in the carby and cylinder, but it won't even pop...nothing at all. Any ideas on what to check?

Interesting starting trick--I'll have to try it sometime! Speaking of starting issues, I've experienced an odd thing just a few times over the years; The engine will actually start and run backwards! On each occasion I started it up, thought all was well, and let out the clutch to find the bike moving backwards! Anyone else experience this, or know what causes it? I have never had it happen on any other 2-stroke machine. The cure was to simply shut it off and restart.

Thanks for the info, guys. I'm glad to hear it's a normal situation.

On my M91, with the clutch lever pulled in, the engine will not turn over when I push the kickstart down. Is this normal? If not, any ideas on what might be causing it? Just to be clear, the kickstart lever goes down (very easily), but the engine doesn't spin over.

Hello all, I have an update on this problem that I wanted to share, in hopes of helping someone else. My carby definitely needed a good cleaning, and my crank seals were in poor shape too, but the major problem here was with the IGNITION. Yes, I found it hard to believe, too, but I discovered that the magneto wiring harness was incorrectly connected under the gas tank (where the barrier strip is). I found the green wire feeding the high tension spark coil, whereas it should have been the black wire, with the green earthed. I really don't know how I was getting any spark at all! It was a weak spark, but I thought it was OK as long as the engine was starting. I was wrong, as not enough spark was being generated at low speeds. Once I got the RPMs up it ran well (magneto turning faster=hotter spark), but it was an inadequate spark at slow speeds, and that was the cause of my problem. So, now I have a new carby, new crankshaft seals, and a very hot spark. This bike is ready to run. VIVA Bultaco!

Thanks for the reply. I can tell you that I installed the Mikuni 28 mm (from Hugh's Bultaco in the US)on the bike and it runs very well. I didn't even need to adjust anything on it. One thing to keep in mind is that you will need the flange adapter kit, and you may need a new carb manifold that angles to the left in order to get enough clearance for the muffler. Mine needed this special manifold, and Hugh's was able to find it for me. Best of luck to you!

Has anyone tried fitting a flat slide Mukuni 28mm carby to a Sherpa T? I ordered one and would like to know what to expect. Anything to watch out for as far as tuning, throttle control, etc?

Hello all, I ordered a Mikuni 28mm flat slide carby for use on a Sherpa T 250. Anyone have any comments/observations on how well this will work on a Sherpa? Any tips for proper adjustment? Will I be able to use the existing throttle cable with it? I'm saving the original Amal 627 for authenticity, but I have not been able to resolve an off-idle problem with it, and decided to just replace with something more modern. I like to stay original, but I also want to ride! Thanks.