Has anyone fitted an American made JRC carburettor to a Commando. My 1976 Commando has a single Mikuni fitted and although it has been set up on a rolling road it gives me a lot of problems when starting up? The JRC carbs look good and the chap from Brill Bike Bits assured me that they were good.
Do you have a link to JRC?
Try this as a starting point.
My sympathies with the Mikuni. On my VM36 I found the choke to be too much of an on/off jobbie and a pain to cope with. You had to use the choke starting from cold, always started fine, but you had to keep it on until warm or the engine would die if the throttle was closed. Then it would be horribly rich in slow traffic until the engine was warm enough. I had the handlebar choke lever but I should have fiddled with the choke jetting to try and fix it. Back to twin Amals now.
You could try fitting a single Amal? I found the single Mikuni lovely for pottering about (suits my age?) but the 2 into 1 manifold strangles the engine from 5,000 rpm. That occasional roar from twin carburettors is worth having! I know you can get twin Amals to run beautifully but it is an art I am still chasing. Last year I drilled my Amal fixed pilot jets out from 0.016" to 0.019" (40% flow increase) and it is much better. Otherwise, buy the new replaceable pilot jet Premiers.
Apologies for not seeing anyone at the rallies this year, but every date has clashed with other plans. Will have to do better with diary planning next year.
The JRC carbs are a Chinese copy of a Keihin carb modified to fit British heads, they are a flat slide design so give a faster response to an opened throttle. You can get the same effect on an Amal by filling in the hole in the bottom of the slide and leaving room for the needle to do its thing. The jetting will change as you are altering the depression created by the airflow.
Not sure that a single carb manifold strangles an engine above 5000 rpm. My brief racing career was quite successful on a single carb Domi. More than happy with the single Monobloc on my Atlas.
Thanks Norm, yes I am getting very similar problems on starting up as it will not run properly at all until the bike is warm and then it runs well. I hope that you are both well.
Thanks for this John, I am sure that the chap from Brill Bits told me at the last Kempton Park autojumble that the JRC carbs were made in America?
Thanks Tony, very good information. Has anyone fitted a JRC carb they look well made?
Hi Mike, have a look at the Brill Bike Parts website.
I am sure that the chap from Brill Bits told me at the last Kempton Park autojumble that the JRC carbs were made in America?
Define made in America, the whole carb or just the flange adaption so it fits Brit flanges made to suit Amal's and the fitting of Keihin jets (as the Chinese ones can be dubious size wise).
The Chinese copies is sometimes sold under OKO brand but they are also with any logo you want if you order enough. Google OKO carb and compare.