C15 performance is like ?

[mcman56]

I finally got my C15 together. Thanks to those on the forum that provided input. So...what should it run like? I need to do some more tuning and I have never ridden a TL125 but it runs like a TL125 sounds. It is super smooth and pulls smoothly and strongly from very low rpms but does not respond quickly. It takes lot of effort to lift the wheel 1/2 foot. (Bultaco front end/ wheel with steel BSA tank) It has the standard cam, big valve/ small port head, Kehin 22 mm carb and an ignition with no advance...set at full (I believe). 18 tooth motor sprocket, 13 tooth trans sprocket and 54 on the rear. I was expecting some quicker response like a TLR200.

[cvgmmartin]

I have a B25T engined bike that I first built into a BSA frame (the later version than yours) and that was so heavy and the weight distribution such that it was hard to lift the front wheel like a more modern bike. I later built my own frame which improved matters considerably. I also tried a 22mm carb but although it pulled like ateam engine it didn't seem to accelerate very quickly, I now use a 24mm mikuni which seems fine. There may be an issue with your timing aswell with insufficient advance, it is easy to adjust so I suggest you try playing with it. If you don't have any automatic advance/retard built in then you will probably be stuck with a compromise setting which is neither good at either end, i.e. it will stall too easily at low rpm and not rev out as quickly at larger throttle openings. Try playing with the timing first before changing any equipment.

[b40rt]

an issue with your timing aswell with insufficient advance, it is easy to adjust so I suggest you try playing with it. If you don't have any automatic advance/retard built in then you will probably be stuck with a compromise setting

Or, get electronic ignition, well worth it in my experience on the B40.

[bobtlr]

I have a B25T engined bike that I first built into a BSA frame (the later version than yours) and that was so heavy and the weight distribution such that it was hard to lift the front wheel like a more modern bike. I later built my own frame which improved matters considerably. I also tried a 22mm carb but although it pulled like ateam engine it didn't seem to accelerate very quickly, I now use a 24mm mikuni which seems fine. There may be an issue with your timing aswell with insufficient advance, it is easy to adjust so I suggest you try playing with it. If you don't have any automatic advance/retard built in then you will probably be stuck with a compromise setting which is neither good at either end, i.e. it will stall too easily at low rpm and not rev out as quickly at larger throttle openings. Try playing with the timing first before changing any equipment.

what jets do you use in the mikuni is it a VM 24mm?

i have the same on my b40 and it responds a bit slow my bike has electronic ignition

mayby my exhaust systhem is holding the engine back a bit ?

best regards bob

[cvgmmartin]

Hi Bob,

I don't know how helpful this will be but the Mikuni I have was put together from bits and pieces I had in my box of carb bits so I don't think you can replicate it. Anyhow, this is what I have, it is a 26mm VM type carb, with a 140 main jet, a 30 pilot jet, a 5DJ19 needle (which I believe is from a Kawasaki triple) with the clip in the middle position, the needle jet has the numbers 284 0-2 stamped on it and I can't find these numbers in any Mikuni jet table. This needle jet is a bleed type (for 4 strokes) but it has the extension into the throat that is the same as the primary type (i.e. for 2 strokes)!. I doubt if this extension has any merit, it was just what I had in the box, the important part I think is to have a bleed type jet and not a primary type. Also the needle has been filed down over most of its length to make it richer throughout its range (again it was what was in the box). The slide is a #2 with the cut away increased to a height of 4mm (another piece in the box). This mixture however seems to work quite well with good plug colour throughout the range. I do find that this engine doesn't run well if it is too rich unlike my Bultaco that seems to run on almost any settings. A lot of other people run Mikunis so hopefully someone will tell what mix of jets they use that are easily available.