T120 missfire

[triman65]

Help I have a 1973 model OIF T120r Bonneville which is missfiring and poping on the L/H cylinder.
It is fitted with a new Boyer electronic ignition and the timing has been double checked. Have also fitted complete new ignition cables, new plugs NGK 7es, New Battery, New jets and needles in concentric carbs and both coils.

 The only thing I can think of is a top end decoke, as it looks a bit carboned up looking through the plug holes. It has been restored at some time and the clock shows 13000 miles. I do not know how much work has been done on the engine, but a Haywood belt drive has been fitted.

Any help will be appreciated

Mick

[Rex]

Was all this work done to cure this problem, or has the misfire been only since the work was done? Do you still have the points and could you refit them to prove a point (hoho)?

Boyers are notorious for needing a good 12V (or near enough) and it always seems that one cylinder is affected before the other. If you rig a wire straight from the (freshly charged) battery to the Boyer,  this should check out this aspect.

[Justin_Faithfull]

Another possibility might be that there is an air leak on the inlet side between the carb. & the head. Worth checking out.

[triman65]

Thanks for your help.

I have made an extra earth lead from the battery to the engine head steadier and changed a lead to the coils which was on the wrong coil and I think I have cured it. So it maybe down to the plonker who shall remain nameless, who put the lead to the wrong coil.

Many thanks again.

Mick