littleblackflash

Thanks

Quick question, Is the flywheel nut or the primary drive nut a LH thread? What torque should they be done up to?

Thanks all. At least I know I don't have to take the engine and box apart. I did correct my original post from 11:46 to 11:42T after I double checked once I got home from work. The engine is quite amazing really. With electronic ignition it really does pull from almost zero revs. In fact I think it pulls stronger at low revs than my ex-works sherco 290. Maybe it is my riding? Again - thanks for the help and advice, I'll let you know how I get on.

Woody - I think our post crossed over. I just corrected my original post with the ratio 11:42T but using a 520 chain. (Came in the box of bits). I just looked on bultacouk's site and they only sell a 52T sprocket which will fit my wheel (6bolts with 3 studs) using a 428 chain. Maybe this is what I should be running? In my excel sheet I've made, a 52T sprocket will bring the speed down from 8.7mph to 7mph (1st gear @4000rpm). It will also make my 2nd gear the same as what my 1st gear is today. I'll see if I can borrow a 428 setup from someone.

1st gear gives 34:1 Crank to Wheel after the sprocket ratio is applied. So maybe it's correct, just far higher than other Bultaco at the twin shock trail I went to last week. All the observers commented on the fact I was in too higher gear, so something needs to change. I have a single chain primany drive, and googling for the gear ratios, my ratios match the sherpa's perfectly. I'm going to change the rear sprocket as a start. I am concerned about going to low on the gear. It still needs to pick up to jump logs / streams etc (I don't ride the easy routes). I've rebuild the engine with a new piston, carb, bearings and seals so it tick's over really smooth and pulls strong from low revs. So fine tuning and playing with sprockets is needed.

Puzzle is still not solved. I took the flywheel cover off and checked my gear ratios and found Primary Drive - 2.375:1 Gear.................... Ratio.................. Overall Ratio (Gearbox out) 1st....................... 3.8:1....................9.025:1 2nd.......................2.92:1..................6.935:1 3rd.......................2.26:1...................5.368:1 4th.......................1.38:1...................3.278:1 5th..........................1:1.....................2.375:1 With a sprocket ratio 11:42 means at 4000rpm (mid range) in first gear I'm doing 8.7mph (4m/s). It feels much faster but if 8.7mph is my slowest speed, it is geared too high. I have found out that my wheel is off a Pursang, which has sprockets ranging from 40T to 48T. If I change to a 48T is will bring my speed down to 7.6mph (3.4m/s) @4000rpm. I'm thinking this is still too high, but probably worth a try. Anyone else know what ratio's they are running? PS - I think my previous estimate of speeds were a little too high.

Thanks. I guess there are different primary drive ratios. I'll remove the side case tonight and count the engine revolution for one turn of the output shaft. That was I'll know for sure.

I agree with what you are saying, but in 1st gear with the clutch out I'm doing 15mph on tickover. I have to slip the clutch in the section to avoid stalliing it on turns. Other Bultacos at the same event were much lower geared, despite having the same sprocket ratio. The over gearing is not a couple of teeth on the rear sprocket, it's out by a factor 2 -3. In my village, there is a flashing sign warning you if you exceed 30mph. I can set this off in 1st gear.

I did my first trial on my M92 bultaco yesterday, and the gearing in first is way too high. I'm running a sprocket ratio of 11-42 (corrected from 46) which sounds about right. But 1st gear is like being in 3rd on my mono. The bike has been built form a box of bits so who knows where the parts came from. Is there different primary drives / gearboxes or anything else I should look out for?

I've just changed the oil on my 2009 Racing Sherco and now the front end is awfull. I refilled both legs with 330ml. Should I be measuring 60mm on the right leg from the top? Surely when the suspension is fully compressed (more than 60mm) the damper will go solid because the oil can not be compressed.

I can't think of anywhere else the water could mix with the oil (Unless the crank case has a crack). Have a good inspection, re-assemble and try again.

Mine were so tight I couldn't push them out with 10t. Tried heating them but still no luck. Ended up melting them out.

The bike has been starting first time, every time if I press the tickler once and DON'T turn the fuel off each time. If I do turn the fuel off, the bike won't start after being left over night. No sign of a fuel leak and in both cases, the bike had not been moved.

Thanks all I brought one of Wayne Weedon who sells on ebay as fdosdisign. Just need him to finsh a needle roller bearing conversion for it.

Hi, I need a 12mm swinging arm spindle to complete my 1972 Bultaco Sherpa. Bultaco UK don't have any and don't know when they will make any? Alternativley, any one know someone who could turn down a 14mm spindle?

I'll give it a go tomorrow. Cheers

I'm using a Mk1.5 Amal Carb. 627 from memory. It is a cold start problem. I've cleaned all the carb out but I'll have another go. The choke is a primative button that pushes down on the float to flood the engine. When I push the choke plunger down, some fuel leaks out around the plunger. Is that normal?

Hi All. I have a 1972 Bultaco which has a fully rebuild engine with electronic ignition. But I can't get it to start as it should. If I use Easystart (or brake cleaner) it will fire up and run well. I can turn it off and it will restart 2-3hrs later first kick. But if I leave it overnight, it won't start. I'm using a new BP5ES plug with a 0.7mm gap as per the ignition instructions. What should I try now?

That could be the solution. I was trying to see if I could get it running just to test the engine rebuild. I'm thinking now, the best thing to do is call Dave Renham and buy an electronic ignition. Thanks for all the help.

Many thanks, that's great. My Bultaco is a barn find under going a nut and bolt restoration (like many) and I have a bit of house hold flex going into the back of the stator plate. Is it important to get the Green and Red wires connected to the tight coil the correct way round? And how can I tell if it is the right way round? My Right coil (loosly wound) is not conected to anything which seams to be correct (yellow wire). Was this used for the horn? I'm mising from my box of parts, the connector block. Is it just a white choc-blok electrical connection or something special? Final question of many, What should the points gap be set too? Thanks in advance.

Hi all I'm just finishing the restoration of a M91 Bultaco and I've got as far as doing the wiring. The stator plate I have has 2 gold coloured coils, points at the top and a condensor at the bottom. The problem is I have no wires. What should I have and where should they run too?

Anyone know how much these upgrade parts cost?

There's 4 wire fromthe stator. For the ignition you can measure the resistance across the brown and red wires. If it's not open I would connect it all back up and measure the red wire to earth (frame). Again should not be open circuit. You can measure the voltage across the red and brown wires when you kick it over. Should read about 7volts if its ok, anything below 3v is nackered.

Ok, thats the same as mine, its the coil covered in white resin thats gone. If it was the other I would be able to make one out of the two. If you find a place to repair them let me know. cheers

What's broken on it? Its either the coil that produces the spark or the 3 open coils that power the fan / lights. I may be able to help.