C15 misfire

[phill]

Hi, yes - same with old and new condensers

[AWJDThumper]

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.

[DerekAnderson8]

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

[DerekAnderson8]

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

[phill]

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!

[AWJDThumper]

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.