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JonnyWobbles

Help! 198A poor starting and runs backwards!

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I refurbished my Sherpa over the winter. No changes to the engine which started well and ran ok before and after initially the full nut and bolt refurb. I’ve not had chance to use due to lockdown, but recently struggled starting her. She fired but died and when eventually she ran I found she was running backwards which I know they can do sometimes. I’ve check all the fuel side out (new fuel as well) and reset points and timing, setting to 2.6mm BTDC (as advised by InMotion) with dial gauge etc. to the Bultaco method (which it was before). Spark is good etc. But starting remains a real problem and on the one occasion she did run, it was backwards! I’m a bit of a loss as nothing changed from running and starting well to now. Help please as my calf muscles have taken a battering with her kicking me back! 😩

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Please check the ignition again, the timing and the points distance, too how the points look like

That happend to my Sherpa too after a winter hibernation time and waking up the bike again and the issue was a wrong timing.

Don't ask why it happend and how it just showed up and starting backwards was the main issue. 

Edited by pschrauber

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Hi, I would also check the woodruff key just in case the flywheel is slipping on the shaft.

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Cheers, can certainly say the woodruff key is ok, as I had the flywheel on and half a dozen times checking the timing. Thing is it was only a couple of weeks from running ok to current problem?

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2 hours ago, pschrauber said:

 

Don't ask why it happend and how it just showed up and starting backwards was the main issue. 

I believe any dampness in the timing cover causes slight rusting on the cam, this quickly wears the heal of the cam throwing the timing out.

Edited by b40rt

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The only thing that will cause or allow running backwards is points setting/timing setting - you need to check it again, carefully.....

1 hour ago, JonnyWobbles said:

Cheers, can certainly say the woodruff key is ok, as I had the flywheel on and half a dozen times checking the timing.

but did you start and run the engine half a dozen times between checking ?

 

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Hi Lorenzo, no checking timing point done before reassembling and then trying to start. Have to say given the method of using the DTI to set distance before TDC infers accuracy, but given the problem and feedback it seems rather suspect! 

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Running backwards😮. As others say: Your ignition is most likely  way out of timing. I would check that the flywheel key is there and is in good condition. If so, check the ignition point again and that the breaker plate can be tightened and everyting else ignition related is OK. I have got the information that modern breakers are ment for Lambretta, not Bultaco and that make correct timing difficult......but running backwards🤔

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I would assume you might have misinterpreted the “before top dead center” through turning the flywheel in the wrong direction.

I made the same mistake because I had worked on a Ducati motor immediately before setting the timing on the Sherpa and Ducatis have a reversed crank turning 🤪

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Jonny -

+ 1 on DonMoto71's comment.  

D.T.I. will accurately set  piston position, but how did you determine the point at which contacts open ?  Visually, or other ?

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Points opening checked with a multimeter, connected to (disconnected) black feed wire to coil. Also disconnected green from earth to prevent path to earth via magneto coil. Obviously this will detect when points first open, not when fully open. Is this correct. Not sure what difference in mm this would make without measuring, but setting when fully open would effectively retard ignition. Which is what I think is required! 
lorenzo with regard to the modern points, I’ve none to compare but can say that a brand new set I purchased were faulty and intermittently went short circuit. Very poor quality when you look at the riveting etc. 

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Set  points to the correct gap The spark will occur at the point when the points start to open This is 2.5 mm BFTDC if too advanced the engine will kick back and run in backwards Set up a lot of points been in the motor trade a long time so set a lot in my time Still run my Bulto on points 

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10 hours ago, JonnyWobbles said:

Points opening checked with a multimeter, connected to (disconnected) black feed wire to coil. Also disconnected green from earth to prevent path to earth via magneto coil.

Was the condenser in situ in the stator plate, and still connected to the c/b points ? If so, this will provide a path to earth, as it's wired in parallel, i.e. across  the contacts.

I wonder if your multimeter would be sensitive enough to give a worthwhile result.......

Timing figures are always given for the point at which the contacts open, which is when the spark occurs, as stated by naichuff . If your contacts are fully open at 2.6mm. before TDC, the timing will be substantially over advanced.

10 hours ago, JonnyWobbles said:

 with regard to the modern points, I’ve none to compare but can say that a brand new set I purchased were faulty and intermittently went short circuit. Very poor quality when you look at the riveting etc. 

I'm unable to comment on "modern" points, as all I've ever used are these :-

1263545637_Femsacontactsets.thumb.jpg.cdf684ca9aaa2ba4fd875921c64baf82.jpg

which I believe are o.e.m.

If the contacts you purchased were as bad as you claim, you should return them to the seller for replacement or a refund

Edited by lorenzo

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My points were obviously a copy and I’ve emailed the supplier today (Feked) Where do you get the Femsa points from? I relocated the new condenser as recommended when I rewired the bike. Multimeter is a good bit of kit, I used to be a proper hands on electronics engineer in my youth before becoming a desk bound email answering ‘engineer’ 😀!

But thanks everyone, you’ve confirmed what I suspected that it must be the timing. So I’ll get some proper points and start again checking everything as I go! 

I report back! 

Cheers

  • Like 1

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If you want to bypass all electrikery , after setting the points , stick a fag paper between the points , it will pull out/ fall out when the points just start to open .

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