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Sherpa engine stops every 60min riding


dr-alpina
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Hi there, we have a problem since last week we put a second Sherpa 183 back into life . Engine is totally rebuilt incl. new piston, crank etc. Ignition is the old femsa. new points fitted. new carb. clean filters...When you ride, after one hour, the engine suddenly stops. We have ignition spark, but bike wouldn't start again. If you change ignition plug, it starts again but runs only 30 minutes, then the same procedure, but bike doesn't start with new changed ignition plug, although we have good blue spark...do we have to live with an 1,30 hour riding bike? any ideas?

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Have you changed the old condenser? If not that sounds like the problem. Even new ones can be dodgy. If it isn`t that just go through the ignition system and check all of the connections including the end of the high tension spark plug lead where it goes into the sparkplug cap. Chop a bit off the end and have a new end to work with.

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Hi Doc, If it is something mechanical, then it could be heat related, such as the capacitor breaking down at high temperatures...  Or, it could be the contact breakers closing up... but you do say that there is still a good spark.     The simplest explanation is that the tank breather is blocked, and a vacuum is building up in the tank, stopping the flow of fuel.

Does it restart better with the Choke / Cold Start device? which could be a fuel supply problem.

Best of luck...

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1 hour ago, scifi said:

Hi Doc, If it is something mechanical, then it could be heat related, such as the capacitor breaking down at high temperatures...  Or, it could be the contact breakers closing up... but you do say that there is still a good spark.     The simplest explanation is that the tank breather is blocked, and a vacuum is building up in the tank, stopping the flow of fuel.

Does it restart better with the Choke / Cold Start device? which could be a fuel supply problem.

Best of luck...

yes, that is what we thought first...but if you pull off the fuel line there comes a lot of petrol...i will check out that capacitor thing

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I had a similar problem and it turned out to be a brand new set of points that had a poor connection where the wires attach as the hole was not fully tapped through. It took me countless hours to find the problem as I thought the wires were tightened up against the screw, but the screw had bottomed out before putting pressure on the wires. But as everyone has said replace the condenser first [I bought one from a mower shop once out of desperation and it worked fine] and check all your wiring joins as well as the kill switch and your earth.

Cheers Greg

PS    a faulty condenser can still give a reasonable spark when you are kicking the engine over!

Edited by sherpa325
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13 hours ago, sherpa325 said:

I had a similar problem and it turned out to be a brand new set of points that had a poor connection where the wires attach as the hole was not fully tapped through. It took me countless hours to find the problem as I thought the wires were tightened up against the screw, but the screw had bottomed out before putting pressure on the wires. But as everyone has said replace the condenser first [I bought one from a mower shop once out of desperation and it worked fine] and check all your wiring joins as well as the kill switch and your earth.

Cheers Greg

PS    a faulty condenser can still give a reasonable spark when you are kicking the engine over!

thanks for advice. i will check that at the weekend . here is the plug...ngk 5 

IMG_7491.JPG

Edited by dr-alpina
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On 9.1.2018 at 11:22 AM, bullylover said:

One thing I can see with your spark plug is the plug gap looks way too wide. A Bultaco on points need a plug gap of .40mm the same as the points. That would not be causing the problem but it will make it start much easier.

Hi folks :  It really was the condenser. Bike runs unlimited now, tested out today... Thanks for your help.

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...after two days riding without problems ignotion broke down again. We checked ht coil  and there was no blank steel connection. the frame was painted new and somebody didnt want to destroy the new paint... unfortunately the green wire was also fixed to that point. (no real earth) Now the primary coil was killed...in the end the whole thing was a bad earthing fault.

greets dr.alpina

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