Hi,
C15 trouble again - sorry. I am getting a persistent misfire at all revs. I have changed the plug (NGK B7ES 23 thou gap),plug cap, condenser. Points ignition fitted with a regulator/rectifier from Rex Caunt racing. I have set up the points to the correct gap and set the tappet adjustment (although I struggled with getting the piston in the right place). I'm not sure about the ignition timing - I can't see how the procedure described in the manual (knitting needle down plug hole etc) can be very accurate. Any ideas would be gratefully received.
Phil
How old is the fuel?
The only thing left is the coil , which can cause a misfire , or the petrol . My guess would be the coil .
forgot to ask is it distributer or side points ignition .
Hi,
Distributor ignition, new fuel, bike starts very easily.
have you another coil you could try then .
no I'm afraid not - I'll see if I can get one
Is it set too rich?
Is it flooding?
What does the plug look like?
No flooding. Plug looks OK
Have now fitted new coil but has made no difference. Looking for ideas.
Phil
is the ignition timing retarded, if the bike starts easily but doesn't want to rev it may not be correct, does adjusting the timing make any difference to misfiring?
Does the engine idle ok or have you got to keep it going with throtttle?
cheers
derek
Hi,
Idles OK. Altering the timing by turning distributor body makes no difference to misfire. I've uploaded a video to Youtube - VBO977. I thought this would be better than trying to describe what it's doing.
Phil
90% of all ignition problems are carb related
I've just had the carb off and cleaned it out again. All looks good but no difference.
I know you have already changed it but was it the same with the old condenser in . Does sound like the condenser is breaking down on your youtube link.
Hi, yes - same with old and new condensers
Unfortunately, these types of misfire can be hard to sort out. It sounds as though you have changed everything on the electrical side and so that tends to now rule out that as the source. What is the actual state of the engine, especially the valves and piston/bore. If these are all in good condition then it might be worth substituting the carb to rule this out.
Quote from: ANDY HIGHAM on 21 Jun, 2018, 10:49
90% of all ignition problems are carb related
how true that is!
Does the bike pull ok through the gears or is it down on power?
compression test?
trying to think of possible causes sorry if you have been told all this before.
cheers
I had a quick shot on a Triumph Tiger cub today, i know its a different bike but bear with me. It was i think restored a few years ago and doesn't get used much but runs well and may have a slight misfire but pootles along well and is a joy to ride (especially in the sunshine and not going anywhere in particular!)
It got me thinking maybe sometimes too much is expected from these old machines and they might not run perfectly well all the time, but that to me is part of the attraction.
regards
derek
OK, the problem was with the carb. Took it off again for a more careful look - cleaned everything again and changed position of needle to 3 down from top. Ran a lot better. Noticed when it was apart that the body is marked 375/31 when the book says 375/34. Also the needle was a 'C' rather than a 'B' as per book and the needle jet 105 rather than 1055. The body and throttle slide looked good so I just got a B needle and 1055 needle jet. Running nicely now but probably needs some final tuning. One more thing ticked off the list. All good fun!
375/31 means it was off a Bantam D7. However, unlike the Concentric carbs, I don't think the 375 Monobloc carbs were separated into 2-stroke and 4-stroke carbs.