lemans 2 misfire issue

Having just rebuilt my lemans 2 engine I have had a problem which as yet can not resolve
Tappets set, points gap set, engine timed using strobe- ran lovely for about 10 miles. Then started misfiring which has increased in frequency usually under load. Harder to start and at one time couldn’t get a spark at all which I think turned out to be failing ignition key barrel which has been replaced (lot of burn smell coming from the worn contacts when pulled apart). Thought this would sort it all out. but no

I have new condensers, coils, Points and plugs. Carbs have been over hauled by me with new main jet, idle jet choke plungers - I think they are OK and considering it ran beautifully for about 10 miles I thinks it feels electrical. Could it be HT leads which are probably original. Any other suggestions?. Checked tappets again which are fine - 0.22mm inlet and exhaust Getting desperate as I am due to go on a bit of a tour in a week or so. I have ruled out any cylinder head leaks as the whole engine has been checked- rebuilt with new bushes, shells, rings valves, guides etc. I am stumped. have new HT leads to assemble and fit - any suggestions welcome


coils and leads,plug gaps

will check coils, gaps and plugs again. Leads to replace tomorrow. All test well on in terms of voltages etc but I guess under load this may be skewed. What NGK plugs are people using. There seems to be a lot of variation of opinion on this. I think I have NGK BP6ES at present fresh from Guzzi bits.

We have had brand new condensors fail…pop the old ones back on maybe …?

I have had a brand new coil fail!
All the best,

I’ve had similar issues on my S3, and have replaced points/HT leads/coils/plugs (NGK BP6ES)/plug caps. Two weeks ago following running issues, I bought two new condensors, one doesn’t work, put the one back on which has been on the bike since I bought it back in 1990! Not sure on a Le Mans 2 or if you have installed a modern reg/rec but if you have the old diode board type, check the wire that takes current directly from the battery + terminal to the large tab on the rectifier, should have a large 35 amp spade connector. On my bike, the connector was splitting but couldn’t be seen from above so I didn’t notice it. I replaced the connector which was singed badly with the resistance. Check that, and check all the connectors to the the rectifier, I had at least a couple loose or making tenuous connections. Have sorted these, and with the old condensor back on, it is now running perfectly (touch wood…)italianmotor2014-07-16 09:17:37

Have the plug caps been replaced? I find NGK LB05 good. Also are there any leaks on inlet manifolds?


The NGK BP6ES is not what is recommended by Guzzi bits. They supply NGK BP7ES which I have sourced locally. Not sure if difference is significant. The HT leads supplied are to be made up and they are the silicone type. The metal plug that fits on the coil end of the lead seems a bit flimsy. The core presumably wraps back over the outer core and is clamped by the terminal. Hard to get the crimping even and round in order to slot into the coil socket. What are peoples views on these. Many seem to prefer the older copper cores.

Plan to :
replace the HT leads and try.
Replace plugs and try
replace coils with old ones and try
check condensers
Check all my gaps again
By a new bike

Just got to keep systematically keep eliminating.

I’ll post the results


Some of the newer plugs seem to give a lot of troubles, if you have an old pair, try putting them back in.In my opinion, the old copper plug leads last for ever, just cut a quarter inch off the end and screw the plug caps back on.

BP6ES is for my S3, which has a short stroke 750 motor, BP7ES is right for a Le Mans 850 motor. This is a good explanation of plug grades by NGK: NGK. I personally only use copper core HT lead.italianmotor2014-07-17 07:51:54

New rubbers on manifolds and tight. Plugs changed for BP7ES. Has anyone used these Iridium plugs. Are they worth it? - supposed to save fuel etc

With regard to latest progress, changed left HT lead for new silicone plus new cap and coil terminal. no discernible improvement. Following eve changed back to old coil left hand side. Bike started with a little choke and ran smoothly on tick over in garage. Thought I had cracked it. Swapped back to new coil and it still ran smoothly on tickover in garage. Can only assume there was a dodgy connection or perhaps there is a dodgy connecting wire leading from the coils. I did undo and check the connection to the after market regulator located next to the coils so this may have been the culprit but no sign of split of damage. Need to test run today weather permitting. Thanks for the suggestions.Will report back.

I am using Iridium plugs at present and they are performing satisfactorily. I had lots of problems with ordinary NGK plugs and have stopped using them. I have a pair of Bosch plugs waiting in the wings. I bought my bike as many boxes and bags of bits and, thinking back, the previous owner had saved lots of plugs of different makes and types so he may have had problems too.

Thanks for that

by way of update, bike starting on the button and ticks over nice but directly loaded or reved starts getting lumpy and misfiring. Going to go through everthing again tomorrow. Thought I had sorted it with one of the old coils but sadly no.