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Collection, Preservation and Display of Old Lawn Mowers

Suffolk engine misfire under load

Hello. 

I have a Suffolk engine on a qualcast commodore misfiring under load. It does it when I engage the rear roll.

I have cleaned the points and set them.

I had replacement points I bought from recently but they were not as good as the original. So left the original in place. Has anyone bought any good quality Suffolk points? Wondered where to buy them from?

The misfire has improved but is still present.

I wonder if it could be the condenser ? If so would anyone know where I might purchase one ?

I have never had any issues with Suffolk ignition systems before so wanted to hear you experiences. If a Suffolk condensers is likey to fail.

Thank you for your help, I have been using suffolks for over 40 years and this is the first time I have ever removed the flywheel and set the points. So figure they have a good ignition system?

Or have I just been lucky.

 

Forums

wristpin Mon, 09/05/2022

Before going any further , try a new plug and a new plug cap/ ht wire connector, check that the ht wire is firmly screwed into the coil and that you are not using a suppressed plug cap with a suppressed / resistor spark plug.

Failing condensers can give rise to a variety of symptoms so unless you can find someone with a proper condenser tester , substitution is the only way to prove the point. However, beware of “ new old stock” which although unused may be as old as the one that you are replacing. I have a proper tester and always test “ new” ones ,and sometimes reject them. The other issue is that it’s becoming difficult to find ones that physically fit the space. In a worst case scenario, the condenser does not have to be within the magneto, it will work just as well hung outside the mag with a wire through the back plate and connected to the points.

Possible sources for a condenser are

Jon Cruse at the Hailsham Mower Centre

George Shead at Villiers Parts

Series3boy Wed, 11/05/2022

Thank you for your advice. I have soldered a brass spark plug connector onto the HT lead. Hope that's not the cause of my problem?

I am not sure about resistor and suppressor plugs types would you be able to explain that to me.

Is it possible to replace the HT lead on a Suffolk? Or are they moulded into the coil ?

I wonder if you can still buy a condenser tester?

wristpin Thu, 12/05/2022

Providing your soldering is up to scratch , your brass connector will be fine. Normally the ht lead is screwed into a socket in the coil. At the bottom of the socket there’s a tapered male screw; push the lead in and onto the point of the screw and then rotate the lead clockwise and it will be pulled down into the socket. On very early coils there’s a bare metal tag for the ht lead to be soldered to.

Fly wheel magnetos with contact breaker points can create Radio Frequency interference . Those of us of a certain age will remember when certain vehicles passed by,  the wireless set or 405 line black and white TV would react to the RF interference. To combat this, engine manufacturers would fit a small “ suppressor” plug connector. On Suffolk’s this usually took the form of a small black cylinder that screwed onto the plug end of the ht lead and had a springy loop that fitted over the nipple on the top of the plug. Later on the spark plug manufacturers developed “ resistor “ plugs  that had built in suppression and did away with the need for a separate suppressed plug cap/ connector. Such plugs could often be identified by an R in their part number; for the older cast iron Suffolk engines, a plug from NGK would be BR6S.