1973tr6

Agree on the gearing. 1976 Mod 183. I went down 1 tooth on the front to 11 (a 10 is too small) and up to a 52 (from 46) in the rear for an 18.9% reduction. Made a significant difference. I had to modify the lock washer on the front sprocket as the original was too large and didn't allow the chain to seat correctly. Ratio Calculator: www.sprocketcalculator.com

Sherpated, No I never got the OKO sorted. It is puzzling because the earlier issues I had with the carb, continually overflowing when the motor was warmed up, despite setting and re setting the float many times, were solved by replacing the float needle. The bike was running well one trial and then the next it was fine to start but quickly deteriorated, sounding like it was running too lean, then nothing... no start, no run. I cleaned and fiddled about with the F&%$^@ for weeks and finally gave in. Put on the Mikuni and voila.... not looked back since. The OKO is now in a box gathering dust.

Grind out the cracks with a dremel or similar, hollow out the crack area to make a slight concave using sanding discs, lay in suitable glass mat to cover the crack and thoroughly apply resin, making sure there are no air bubbles, repeat as needed. When you are hollowing out, make sure you go past the end of the crack otherwise it will start again. Fill with bondo and re profile.Plan B wold be to try using some low viscosity epoxy (check out the boat fibreglassing sites) https://www.youtube.com/watch?v=eggAzL9oQxg

A couple of good suggestions there, thanks. I'll contact Talon and also take a look at the modified Yam idea... I'm up for a challenge too (and have access to a lathe !)

I am trying to gear down my' 76 model 183. The current sprockets are 11T front and 46T rear. I'd like to lay my hands on a 10T (or even better a 9T) front from somewhere but they seem to be unobtainable. I could go larger on the rear but to get anything over a 4% reduction I wold have to get a custom sprocket made and increase the diameter which I don't really want to do. A 10T front will give me just over 9%, a 10T/48T will give me almost 13%. Any suggestions ?

My parts book tells me that it is the same for 350 models 159, 183 and 191 and also for 250 models 158, 182, 190. The Bultaco part number is 23.12.007, crank stop. Part 4 on the pdf attached. I only have the manual for 5 speed models 1967 and on. Hope this helps. Nov 14th.pdf

Sounds to me like the kick starter pawl is not clearing the ratchet properly. If moving the kickstart forward on the spline doesn't work, then the fix is probably inside the gearbox. Take a look at the exploded diagram attached, Parts 2,4 and 10. Item 4, the crank stop may be adjustable from inside the ignition cover but I don't know for sure as it is so long since I pulled one of these engines apart. Part 13, the ratchet stop or a broken return spring (part 3) could also be the culprit. Nov 14th.pdf

Thanks for all the advice, It is a Taiwanese, not Chinese carb complete with markings on the jets. I have stripped, blown, poked, immersed in solvent and WD40'd the carb until I am sick of it. It now knows its own way off the bike- I just stand there and whistle and it teleports from the bike to the workbench ;-) I have ordered a Mikuni today having finally given up. It is such a simple thing but so frustrating. What jets have users found work the best ? I am 500 ft above sea level.

Suggestions please; The bike was running well when it was last used, I went into the garage to run it for a while and it starts OK but there is now a large flat spot when coming off idle. The motor stops firing and "bogs down", coming back the life about about 1/3 throttle. Opening the throttle very slowly helps a little, a little choke helps a little. I have had issues with the carb from day 1, overflowing every trial after about an hour but I had got that sorted . Here's what I have done: Emailed the OKO guys and they said look for an air leak. Stripped and cleaned the carb, blowing out all passages / jets etc. Checked the carb for air leaks Checked the rubber connector for cracks (it was new with the carb last fall) checked the inlet manifold to cylinder joint integrity. Checked the spark Replaced the main crank seals 6 months ago Things to check Cylinder base seal ? Replace the main seals again? Dump the OKO and fit a MIkuni ? Reset the float level (for about the 100th time?) The puzzle it that it was fine, nothing had changed and now it's not.

That brings back memories.. I was HMCC club sec in the early 80"s and ran the Hillsborough Trophy Trial (as it was then) for few times along with Donald Brown who was clerk of the course until emigrating. Only rode the Kwai a couple of times as course closer but it was tough. (I only ever aspired to Novice). My avatar is from the HMCC Novice & Veteran trial at Hollowmeadows, can't remember the year but I had hair !. I was riding a demo Fantic from Jeff Hall. I see from recent results that Dave Thorpe, Keith Hobson and Dave Knaggs (Haggis) are still riding.

I didn't want to cut and weld on the stock exhaust if I could help it. Maybe I could get a banana exhaust with the single outlet and keep the clubfoot stock ??? Lineaway, what do the guys with stock clubfoot exhausts do in your area ?

Just found out that spark arrestors are going to be mandatory soon here, Anyone any ideas about how to fit something like this to a clubfoot rear box ?

Looking to replace the rear shocks (13.5" or 340mm) on my 350 Sherpa. Any suggestions in North America ? I spoke to Bultaco UK and they said that air freight was an issue with gas filled shocks.

New (exchange) coil on its way--- and I have invested in a magnetic parts tray !

I have a spark again, traced the wires and there were cracks in the insulation in a number of places so something was grounding out. I have taken out the lighting coil but will still get a new ignition one if only to eliminate the electrical tape that is now covering all the wire!

OK, I an not very smart as I managed to install the ignition rotor with the spring washer inside, yes inside it. I couldn't find the one I took off anywhere so I put on a spare. I thought I checked the inside of the rotor, obviously not well enough..... to cut a long story short, the bike ran well for a while and then guess the washer moved and bang....... no more go ! It looks like the low tension coil is done for as the insulation on the end was broken off. I am puzzled by the wiring, it look like one of the black wires from the points goes to the lighting coil ? is this correct? I am going to remove the lighting coil so can someone help with the correct wiring. The In Motion coils have a black from the LT coil to the points and then a black which I presume goes to the connector under the tank and then to the HT coil, the green is ground to the connector under the tank and the red is what ?

Just out of interest, what size slow jet are you going to fit? I have just put on an OKO on my 350 and find it smooth but sluggish on transition from idle. I put in the largest jet supplied with the carb (55 or 58??) can't quite read the stamped numbers. It cured the flat spot but it was still sluggish. I set the ignition timing accurately (it was guessed at initially) to 2.54mm btdc and promptly lost the spring washer........ went to try and get a new washer and failed.... it was New Years Day after all... got back and then couldn't find the nut either so I haven't been able to check if the revised timing has helped. There must be a parallel universe in my garage... either that or a black hole that swallows stuff. The guy at Hugh's Bultaco had a good laugh at me expense when I phoned to order a new nut and washer. When I told my wife I had lost a nut, she just smirked.........

Thanks for the responses, I think I will leave it as it is. Thanks also for the compliment. Now I just have to ride the thing after a 15 year hiatus!

Is it possible to switch the gear shift with the rear brake on the 1976 183 model Sherpa. There is a boss coming out of the engine case on the ignition side which moves with the shifter but there are no splines. It looks like there is a plastic cover on the spline but I haven't investigated it yet.

You might want to contact Dave Thorpe of the Hillsborough club in Sheffield. He was, I believe the works / development rider when these were introduced. He may just have the knowledge you need.

Thanks for the responses. I got some square foam draft seal and put that on following the outline of the inner box but I am going to try and locate some of the split round foam over this side of the pond !

First of all----- It runs!. Put the new OKO on tonight and started first prod. Seems to be set up OK but I guess I need to ride it to really find out. The real question is what can I use to seal the air box to cover in the 183 model ? The original rubber is rotted away and I can't find a suitable replacement, any suggestions ?

Depends on model according to the Bultaco spec charts. 250 = 150cc 350=180cc of SAE 20 (or ISO VG 68) both models 6.1" of travel. This viscosity is by preference, a lighter grade will give faster compression and rebound than a heavier grade. I use a 10W30 motor oil. I have also seen 30mm dia forks = 100cc of SAE 40 (ISO VG150), 35mm dia forks = 230cc of SAE 30 (ISO VG100) and 38mm dia forks = 250cc of SAE 20 (ISO VG68)

I an taking a bit of a guess here .... but I don't think the slide should look like this.... Plus the pilot jet playing silly buggers and not coming out for cleaning and the needle being rusted up signed it's death warrant..... OKO on order......

OK, with the help of a puller the flywheel came off, replaced the seals and o rings, reassembled and got the pins in with my daughter's help. Fired up right away and better, but not right. Would only run with the choke part way on. and still a flat spot. Tried pressing on the slide - no difference - I decided to take a closer look at the carb and found the pilot jet clogged and impossible to remove....... yes I tried pretty much everything including drilling the jet out............. shouldn't have done that !!!!!! so........... I am now in the market for a replacement carb.