Magneto failure ?

[Duncan R]

Hi All,

Just got the bike back on the road after a gearbox overhaul, which was carried out by Dave Flintoft to a very high standard. The bike has been running perfect with all the harshness from transmission now removed. After a 10 mile stretch on an A road of between 60 -70 MPH the engine was running spot on. I then stopped for 15 mins or so after which the bike became very difficult to start and was cutting out on 1 cylinder, it became progressively worse and would only run at a set throttle position equating to a speed of about 35 MPH in top.

I have changed the plugs and checked the carb which was a bit grubby inside and was refitted after a good clean, nothing seemed amiss inside the carb. This made no difference, so I assume I am getting intermittent sparks from the mag. The magneto was rebuilt in 1998 and has only done about 4000 miles (bike was in storage for quite a few years) It has always been a good starter and I have never had misfire issues before.

Grateful for any advice.

Engine spec is 650 cc with an A7SS alloy head, concentric carb and flat top pistons

Thanks for your time

Duncan

[TT John]

Duncan, Have you checked and cleaned the pick ups? also the carbon brushes, these can also give problems when  worn down.

TTJohn

[groily]

For a few basic DIY mag checks you can do - and some more complicated ones if you're up for it - you may find some of the stuff here useful: http://www.brightsparkmagnetos.com/DIY/index.htm.
18 years is quite a long time in condenser-speak, even with careful storage, as deterioration can be a factor of time as well as of usage, so that has to be one possibility.

[Duncan R]

Thanks guys, Just read your replies as I have been away. Just before I left I cleaned the pick ups, one had a crusty coating on it like corroded battery terminal and the other was rather oily. I fitted new plugs and it fired up right away and idled spot on. I didn't have time to test ride it so will do that ASAP

[Duncan R]

Update is took the bike out yesterday and put about 60 miles on it and got it nice and hot. It ran fine with no misfires and started ok when hot so I am hoping all is good with the magneto and it was the dirty pick ups causing the issue.

Thanks again