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+--- Thread: Mag Engine - Misfire & parts source (/showthread.php?tid=6565)
Mag Engine - Misfire & parts source - JohnD - 29-08-2021
This weekend i have pulled the cover off the GE Cup for next weeks, Bo'Ness Hillclimb - Ive had it out for a run and it develops a misfire which comes and goes under load. Speaking with a forum member briefly they suggested it could be the condenser, so i have removed the mag and end cap to reveal the bellow pictures.
Two questions:
- Where is the best place to source mag parts that will have them with me for Thursday at the latest.
- Does anyone have any other suggestions to the cause of the problem.
RE: Mag Engine - Misfire & parts source - Ivor Hawkins - 29-08-2021
The black wire at the bottom doesn’t look to be in brilliant shape!
As far as getting parts on a bank holiday ready for Tuesday, I think it’s a case of begging from a local club member...
RE: Mag Engine - Misfire & parts source - Steve Jones - 29-08-2021
Agree, the black wire doesn't look good. An easy replacement. The condenser is a common Lucas type. See:
https://www.ebay.co.uk/itm/Ignition-Condenser-Lucas-DCB101C-Replaces-1463027-2798667-105E-12300-/324733735778?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338268676&toolid=10044&customid=EAIaIQobChMIuL_HivPW8gIVh-_tCh05WAh-EAQYASABEgJn3fD_BwE
Mags don't like damp and the surface rust on the fixing screws etc. suggest it might have been stored in a damp environment. In the absence of a substitute mag, replace the black wire and the condenser and store for a couple of nights in the airing cupboard.
Hope you get it going.
Steve
RE: Mag Engine - Misfire & parts source - Parazine - 29-08-2021
New condensers for the SR4 magneto are suspect at best, although available from:
Lucas RS1 & SR1 Magneto Replacement Condenser (stationaryengineparts.com)
also various eBay suppliers. I haven't worked out a suitable answer to a reliable replacement yet.
Misfire under load could also be due to faulty spark plugs, might be worth a try.
RE: Mag Engine - Misfire & parts source - "Slack Alice" Simon - 30-08-2021
I buy condensers like that from my local car spares shop - I ask for condensers with a wire coming out of them and they produce a selection.
H------s, the big car and cycle chain store would have them, too.
RE: Mag Engine - Misfire & parts source - Parazine - 30-08-2021
(30-08-2021, 07:26 AM)Slack Alice Wrote: I buy condensers like that from my local car spares shop - I ask for condensers with a wire coming out of them and they produce a selection.
H------s, the big car and cycle chain store would have them, too.
But what value (in uF and voltage) are they? "Modern" coil capacitors are usually 0.1uF but Magneto capacitors (apparently) should be between 0.1uF and 0.22uF (100 to 220nF), depending on whether they are rotating magnet or rotating coil types. 0.22uF is recommended for rotating magnet types, like the Lucas SR series. ( Magneto condenser theory (themagnetoguys.co.uk) ).
The other issue is that many of these odd capacitors are for supressing noise on in-car radio/stereos, heaven knows what capacitance values they will be and can they with stand the back emf generated by the magneto coil?
Using the advice on: Magneto condensers - practical (themagnetoguys.co.uk) , I'm trying to build a suitable replacement for my SR4 using the recommended RIFA capacitor, 0.22uF, 275VAC, which equates to about 600VDC. Having pulled one of the modern replacements apart, I was shocked at the poor design and workmanship, it's no surprise they're doomed to early failure.
RE: Mag Engine - Misfire & parts source - "Slack Alice" Simon - 30-08-2021
Good points - no pun intended.
I'm not sure voltage has much to do with it.
I didn't know mags had a greater value, so I would buy three: one to replace the one in the mag, one to run externally to give you double the value, one as a spare.
I haven't checked where my local shop's came from, they may be Lucas old stock. Still working after a few years, though.
At least one bought locally would get you running is the short term - assuming the condenser is the problem.
RE: Mag Engine - Misfire & parts source - JohnD - 30-08-2021
Thank you everyone for your comments, i have sourced two condensors and will give it a try again tonight.
Could points bounce be an issue on a high reving engine, as its typically happy on idle and pottering about, It tended to get worse when the needle on the speedo was back around at 0mph!
"Parazine" if you are succesful with a higher capacity capacitor please let me know as i would be interested to find out your results.
RE: Mag Engine - Misfire & parts source - Parazine - 30-08-2021
Yep, I'll certainly share my findings on here.