I have a 1960 Super Road Rocket engine which came with an Amal 928 concentric carburettor (no choke), 190 main jet and 3.5 cutaway. According to the Amal website this would originally have had a 389/46 Monobloc carburettor (30mm bore).
I'm having a lot of trouble starting the bike. When it does start the mixture seems very rich (black, sooty spark plug). I think this is because the float level is too high (level with carburettor flange instead of 1 -2mm below. Before I mess around with the carburettor, can the Super Road Rocket run properly with a 28mm carburettor or do I need the 930 (or is it better to put a Monobloc on)?
In principle, the smaller choke will reduce the maximum power (full throttle) slightly but most people will not notice the difference.
The concentric should be fine for the Super Rocket, I used one on the alloy head a few years back no problems.
I think a 190 main jet is far too small for the bike..
The early concenrics used a different needle/needle jet/jet holder to the later ones, easy to mix early and late parts and if mixed you get problems. It may be worth checking the parts fitted - see below bulletin.
The Super Rocket with a 389 Monobloc with a 1 5/32 choke had a 420 main jet.
Hi,
Using a 28mm Conc. on RR spec. A10 for many thousands of miles and it goes fine.
Main jet 230
Needle jet 106
Slide 3
Mid slot on needle
Pilot jet 20
No air filter
Your float could have taken in a bit of fuel thus affecting the fuel height. 'Stay up floats' available and they are ethanol proof.
Otherwise clean the carb and start with the pilot mixture screw at about 1 1/8 turns out.
Dave.
Quote from: DAVE BRADY on 15 Aug, 2022, 09:13
Using a 28mm Conc. on RR spec. A10 for many thousands of miles and it goes fine.
Your float could have taken in a bit of fuel thus affecting the fuel height. 'Stay up floats' available and they are ethanol proof.
Otherwise clean the carb and start with the pilot mixture screw at about 1 1/8 turns out.
Thanks for the great information Dave. I'll persevere with the 28mm :)
The plastic float doesn't have any fuel in it. It seems that the float height on the old Mk1 is set by knocking the inlet insert up or down. Perhaps mine has been set incorrectly? I'll get a stay up float and recheck all the jet sizes.
I had a K&N type filter on but have just bought a pancake type filter to replace it. Why do you run without a filter? Is there any advantage?
Hi,
No real advantage to not having a filter but the bike has plunger frame and originally the carb would probably have been an Amal 276. The original filter housing was made for this. The 28mm Conc. is bigger and there is little room to fit the original filter and no room for a pancake type as the oil tank gets in the way.
I think it is always best to fit a filter if you can.
Dave.
i hate the concentrics. especially the fixed pilot jet that blocks up.
with the monobloc you have the correct inlet sizes, factory jetting [which can be way off ] but most importantly with a neat socket tool , remove and clean out the pilot jet in minutes.