Misfire

[Shedman]

Its on bp super unleaded and its been on champion n3c and ngk b7es and b8es the ngk b8es seems the best but only marginally

[Caulky]

You could try a larger main jet, or smaller?
A plug chop after it happens could give you a clue.

[ChrisG]

Shedman,
I may have the answer! Many years ago (20yrs I think) I was advised to disconnect the kill button on the RH Handlebar switch as vibration causes the contact to 'make' intermittently and cause a misfire at, guess what, high revs! (This advice came for a former Lucas employee).
This button is connected to the coil by a White/Yellow wire. From memory, this connects to the ignition circuit (White) under the tank where all the wires come out.
Assuming yours is wired up as per the wiring diagram, this may still be connected. If so, it should take 5 mins to locate and disconnect and then see if it cures the problem.
You may also find a White/Red coming out as well which I dont think was used for anything. Really, this switch it really is only needed for the indicators, so there is only a need for the Green/White, Green Red and Green/Yellow to be connected. You dont even need the white (live) connected to it.
Worth a try! Let us know how you get on.
Chris

[Shedman]

Ive tried main jets from 180 to 230 and none of these showed any obvious problems on plug chop.
I will disconnect the kill switch wire but im not hopeful of this because ive had the ignition circuit connected direct to battery seperate to all bike harness wiring but it made no difference, ive even put a new battery on it just to make sure of a good supply voltage

[Triumph2000]

Couldn't be a valve spring, or tapped clearance issue could it?

[Shedman]

Springs are new srm and have only done 500 miles but i have checked them and they are ok and the valve clearances are correct

[peterS]

Shedman

What was the outcome of your problem ?  Or are you still limited to 4000rpm ?
I am experiencing a similar mysterious misfire / spluttering and, after checking and changing all the usual bits, I have sent the electronic ignition unit to Boyer for testing.
If they say it is working ok, I'm stumped !

[Shedman]

I traced mine eventually to a new pair of oil in frame silencers which i bought from armours and found the only 'baffle' as such was a washer tack welded inside the silencer with a 25mm hole in it and nothing else inside the silencer body. I knocked those out and it imprved it significantly but not completely so i enlarged the holes in the perforated plates et the back of the silencers and again this improved it and now i just get a stutter at 4000 rpm but the bike will go through it. The next stop for me is a new set of pipes and silencers that will work without choking the motor. The ones from armours looked the part but in my case clearly didnt do the business. The bike now is a bit loud (but it does sound sweet)

[peterS]

Thanks for that, Shedman. 
A bizarre reason for the misfire !   I shall check the silencers on mine.
Boyer have returned the ignition box and say it works OK.  They suggest the ignition switch could be causing the problem.  This bike is new to me,  and has never run properly since it was bought.  I'm wondering about the valve timing......

peterS

[ChrisG]

Peter,
Take a look at my previous post further up the page. If you have such switches, worth checking and re wiring accordingly.

[Cyclops]

Hi Shedman, had a similar problem on my Matchless G80S which was running Boyer Electronic Ign. Lost power quickly,  backfiring in exhaust and ate plugs. Stripped  carb etc, all perfect so changed the plug (NGK B6ES). The only replacement i had to hand was an NGK BR8ES (Resistor type) from my S/Rocket which was running Lucas Rita at the time. G80 has been running fine since. I assume you're still using elect. ign. so might be worth trying a resistor plug. As Mr Tesco says, every little bit helps!!! Good luck...

[Shedman]

I tried every plug and cap combination from monday to saturday and it made no difference whatsoever and different electronic ignitions. It was when i took the silencers off and sneaked it down the local bypass, knocked 7 bells out of it  and realised that it was the silencers that were causing the misfire. It took me weeks of clutching at straws but got there in the end

[DerekAnderson8]

excellent news!

Silencers eh, who would have thought that!

Anyway glad its sorted.

[peterS]

Thanks for your help and suggestions. 
Editor,    - Interesting thought, but kill button has been removed, so that solution is ruled out.
Boyer returned the black box and said it is OK.   In desperation, I tried a temporary wire direct from battery negative to white connection on ignition box, and......   Hey Presto.    It runs a whole lot better - hardly any misfire, more revs, much smoother.  Not quite perfect, but a huge improvement and very encouraging.   Which indicates a problem in the ignition switch or somewhere in the existing wiring.
I now feel like I'm making progress.