Hi all.
I've recently taken on a 1960 A10. It's in a pleasantly non standard trim, and runs well, although it spent a few recent years quietly hiding under a sheet in a garage. As a result, I'm gradually going through it. Naturally, a part of the process has been cleaning the fuel system (including the tank). On inspection of the carb it appears to have a 420 main jet, and a No3 slide.
The bike picks up very well, and I have a feeling it may have a slightly "hot" cam. So, here's the thing, will the 420 serve me well, or should I return to the standard 250?
I've assumed that the larger main will of course affect mpg, but will the return to a 250 require anything other than refitting?
My thanks in advance for your replies.
Leave the jet alone and go by the plug colour. And only make changes of one increment at a time, then check again. If it was rich it would not run well and the most likely outcome of going from a 420 to 250 is a holed piston or scored bore.
Hi,
It may help to know what carb. is fitted. If it has a the sporty 357 cam it may also have larger carb.
Dave.
Has it got an alloy head and a 389 carb? If it has and it it is up to Super Rocket spec then a 420 main jet is correct.
Hi all. Thanks for your contributions.
It has got an alloy head and a 389 carb and I had begun to think that it has been modified towards S.R spec. I will leave the 420 jet in place, and give an update in the near future.
Oh, and the plugs are a healthy tan colour.
I have fitted an air filter, as the thought of fine particulate entering the low mileage rebuilt engine felt a bit uncomfortable. The P.O said that the engine had only done about 700 miles from rebuild.
I'll treat it as a new mill, and do my best to run it in with some sense and understanding.
If you are fitting an air filter, bear in mind that it will run rich. You might find that you will need to drop the main jet to a 350.
Thanks for that. I had wondered if I might need to, as I was aware that the filter would have an effect. I'll keep a keen eye on the plugs.
I thought this may be of use.
I'd wondered if my bike had a sporty cam. This info (service sheets, 701) confirmed it. My engine number is higher.
As its "from source " it provides a useful point of reference (though i realise that subsequent work by others over the years may have brought changes).
Good to know though.