Has anybody got any ideas on this because i am running out of straws to grasp at. My 71 lightning has a severe misfire at 4000 revs changed plugs several times replaced electronic ignitions twice for ones i know are good because they came of my 71 firebird changed the coil and caps changed the carbs again off the firebird all made no difference. The misfire is so severe that it wont ride through it and the banging and coughing makes the whole bike shake and shudder. Checked the compression and it was a bit low so i took the top end off de glazed the bores and fitted new pitons and rings genuine bsa reground the valves checked for broken springs but found nothing untoward the sprins are srm and have only done 500 miles but still severe misfire. Ive even dis connected the alternator because i thought the solid state regulator might be interfering with the ignition module. Ive wired the ignition direct to battery to try that but still misfiring badly. Ive been at this for the last month and am getting nowhere. If anybody has had this sort of problem before i would appreciate any advice or ideas to try because ive just about run out.
Does the misfire happen on both or just one cylinder? If its the one then it could be the carb on that side. I've got a pair of Lightning carbs you are welcome to try if it helps. I don't know the condition of them as they were handed down to me from someone else, but maybe worth trying each one in turn to see if it makes any difference.
Send me an email on editor@bsaownersclub.co.uk if that could be of help
Chris
Ive tried a nother pair which i know to be good as they are off my 71 firebird and they made no difference and as for which side or both cylinders mifiring i cant really tell but i think its both. Ive tried both richening and weakening, running without air filters but couldnt try playing with air lever because once it goes into misfire i dont want to take one hand off the handlebars, the misfire is that bad
fuel flow? are the carbs getting enough fuel? what about breather on tank.
Sorry if its too obvious.
cheers
derek
Tried lifting and lowering float height. Fuel flow is good and have also been running on both taps and one tap but still the same
and up to 4000 all is well?
Does it not want to rev out at all? i had issue with needle position but i guess you have tried that.
What colour are the plugs?
derek
Try it with the petrol filler cap loosened off.
Up to 4000 it pulls like a train, the plug colour anything from light grey to black dependant on the different setting ive tried filler cap loosened makes no difference. It usually starts first kick but just wont go over 4000
The springs are definitely ok and correct for the job? seems strange after all the changes it wont go past 4000 and still has same symptoms.
Sounds like a real pain, it can put you off a bike for good until you get it sorted or sold! :-\
good luck
derek
Is it advancing enough at 4000 ?
Quote from: ROYC on 15 May, 2018, 19:40
Is it advancing enough at 4000 ?
That was my guess too whilst reading the earlier posts .
With the strobe you can see it advancing as you rev it to the correct timing mark. I have played with the timing setting more advance and more retard to see if i could break the 4000 barrier but again made no difference. What i cant get my head round is its 4000 give or take revs no matter what settings its on
have you tried changing the condensor and points . Thats the only things left .
Its on electronic ignition and i have tried 3 different ones which i know to be good as they came off my other bikes and 3 coils. At the moment im torn between the canal or a box of swan vestas
What petrol are you using, supermarket or a branded one? I have a Spitfire that had a similar misfire, it disappeared when I started using Shell V power. BP do a similar type of fuel, but empty your tank first. Also have you tried changing the plugs?
Rob
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
You could try a larger main jet, or smaller?
A plug chop after it happens could give you a clue.
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
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
Couldn't be a valve spring, or tapped clearance issue could it?
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
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 !
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)
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
Peter,
Take a look at my previous post further up the page. If you have such switches, worth checking and re wiring accordingly.
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...
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
excellent news!
Silencers eh, who would have thought that!
Anyway glad its sorted.
;)
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.