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JonnyWobbles

Sherpa 198a Timing

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Sorry, so many questions...

Could anyone from experience please confirm the correct timing for a 198a? The Bultaco UK (InMotion) Workshop Manual in the 'Model Specification Chart' states 3-3.25mm for the T250 - which is the same as the T125. But InMotion have just quoted 2.5-2.77mm - which is the same as quoted in the Workshop Manual for the T350. This would make sense to me as the T250 stroke is the same as the T350 at 60mm; whereas the 125 is shorter at 51.5mm. Looks like it could be a misprint in what is a complicated spec. table that covers something like 20 different models?

Thanks yet again!

 

 

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My old manual says 2,5-2,7 for 199A/198A, but it is written in Spanish🤔. I think 2,5-3,2mm is good. You may have to adjust later due to personal preferences.

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1 hour ago, carl ekblom said:

My old manual says 2,5-2,7 for 199A/198A, but it is written in Spanish🤔. I think 2,5-3,2mm is good. You may have to adjust later due to personal preferences.

👍The Bultaco engine ignition timing if set too close to tdc there could be an instance of reverse running. This can happen if the kickstart is lazily prodded. For contact breaker systems initial setting at 3.00mm would be a good starting point, listen out for detonation on accelerating in say third gear up a slight incline. You may end up with a final setting at 2.75mm, this is measured piston travel coming up to tdc best measured with either a dti (dial test indicator) or vernier caliper, either can be positioned through the spark plug hole but turn the engine over very slowly so you don’t catch the measuring device with piston. Hope you are successful🙂

Edited by section swept
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It's my experience that they only run backwards when the timing is too far advanced and they definitely run better with the points set at the 2.5 - 2.6 mark, the motor will be more predictable right off the bottom with less chance of stalling.

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I have found over the years that all of the 250s run the best at 2.6mm BTDC. They are a lot smoother at this timing. So I agree with sherpa325

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Thanks everyone. Confirmed my suspicion that the table in the workshop manual is wrong. Following engine strip down and repaint I'd originally set to just over 3mm but I'll strip back down and reset to 2.6mm. 

Cheers

Jon

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