Recent content by Bruno_c

The manufacturer of this bike is FN (Fabrique Nationale). A belgian factory near Liege. They retained very specific front suspensions up in the fifties.

It is not clear whether the problem is related with high revs or with wide throttle opening.

That's what I suggested one week ago.😉

Did you check valve timing?

I think that at the point of your rebuild you should not worry that much about the auto advance device. But, before trying to start the engine, do the static ignition timing with the auto advance in full retarded position and then check the timing in full advanced position. Then you can safely...

My experience is that a malfunction of the auto advance system does not cause the symptoms as described ninitially by Prisondawg The usual consequences of a faulty auto advance are kickback when starting, sluggish acceleration or revs not falling to tickover when releasing the throttle.

I suggest Prisondawg should tell us if the bike did previously run fine with the present setup or was it put together and never ran.

In my opinion, the symptoms as described do not lead to any logical conclusion. If the bike runs ok on all gears except first, I would ride it as it is until better understanding.

AT this stage I would suspect a weak spark. What is your ignition system ? ( Points or Electronic)

I suppose you checked the main jets are not clogged and the level in the bowls is ok.

Do you mean the engine dies as son as you open the throttle?

Low battery can cause kick back with some electronic ignition systems. Charge the battery before trying again.

First I would try to determine which cylinder is faulty or both. Set idle around 2000 RPM then cut ignition on one cylinder and see if you get a regular tickover. Then change side.

You probably have several issues and it is easy to get lost if you are not systematic. I suggest you forget the charging system for the moment. Disconnect it, charge completely the battery and test run your bike. Charge the battery before each test run.Once you get ignition and carbs perfectly...

If, as I understood, the bike ran fine for a while and then died, IMHO, it is not possible that It started to fire the wrong cylinder. Anyway, if you want to check, the easy way is to Switch the HT leads.