Author Topic: Concentric 928 on A10 Super Rocket  (Read 301 times)

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Concentric 928 on A10 Super Rocket
« on: 17.06. 2020 12:37 »
I have just bought a 1962 Super Rocket with a brand new Concentric 928 carburettor which has never run yet. Although I have to overhaul the engine after at least 30 years of standstill, I am interested whether this type of carburettor is suitable for this bike. I am completely new to British bikes and Amals. Main jet is 180 and pilot jet is missing.
Can I use this carb with this main jet or will it need a bigger main jet? What pilot jet does it need?
Would appreciatie any advice

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beezermacc

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Re: Concentric 928 on A10 Super Rocket
« Reply #1 on: 17.06. 2020 13:29 »
Whilst not the standard carb there are plenty of A10's with concentric carbs which owners have tuned to suit. Somebody else on the forum may be able to offer jet sizes they use on the same bike. 180 main jet could be OK but my advice would be to start with a bigger jet, say 230/240, and work down as you're less likely to cause damage starting with a richer jet. Concentrics suffer from tight slides which is usually caused by overtightening the manifold bolts which, in turn, distorts the body.
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Online JulianS

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Re: Concentric 928 on A10 Super Rocket
« Reply #2 on: 17.06. 2020 13:34 »
If it is a stanard concentric, rather than the premier version, it will have a non detachable pilot bush not a detachable pilot jet.
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Re: Concentric 928 on A10 Super Rocket
« Reply #3 on: 17.06. 2020 13:38 »
Thanks Guys, this already helps
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Offline Billybream

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Re: Concentric 928 on A10 Super Rocket
« Reply #4 on: 17.06. 2020 16:39 »
For a Super Rocket, carb should be 930 if Concentric type fitted which has 30mm bore to match cylinder head porting, 928 has 28mm.
Regarding main jet depends alot if air filter fitted.
Difficult to advise on jetting when smaller carb  used, best guess you should be looking 300 size as starting point
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Re: Concentric 928 on A10 Super Rocket
« Reply #5 on: 17.06. 2020 21:03 »
G'day Racker.
I had two (twin carb head) 932's on my A10RR+ Cafe racer. The main problem I had was the fuel height in the bowls due to the downdraft angle of the manifold. The recommended float height is between 90 and 140 thou. I had to lower the height to about 170 thou to stop them flooding, the float was hitting the roof of the chamber before cutting off the fuel.
I changed to PWK's.
Cheers
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Re: Concentric 928 on A10 Super Rocket
« Reply #6 on: 08.07. 2020 14:52 »
For a Super Rocket, carb should be 930 if Concentric type fitted which has 30mm bore to match cylinder head porting, 928 has 28mm.
Regarding main jet depends alot if air filter fitted.
Difficult to advise on jetting when smaller carb  used, best guess you should be looking 300 size as starting point

This probably means that top speed is limited as the maximum flow of fuel/air mixture is limited by the cross sectional area. Would you agree? I am less interested in the higher performance settings than in a smooth running engine.
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Re: Concentric 928 on A10 Super Rocket
« Reply #7 on: 08.07. 2020 14:56 »
G'day Racker.
I had two (twin carb head) 932's on my A10RR+ Cafe racer. The main problem I had was the fuel height in the bowls due to the downdraft angle of the manifold. The recommended float height is between 90 and 140 thou. I had to lower the height to about 170 thou to stop them flooding, the float was hitting the roof of the chamber before cutting off the fuel.
I changed to PWK's.
Cheers
Although I am not interested in updating my bike to twin carb config this is good to keep in mind in case I will exeperience flooding. Thanks for the advice.
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Online RichardL

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Re: Concentric 928 on A10 Super Rocket
« Reply #8 on: 08.07. 2020 15:57 »
Racker,

Pardon my referring you to one of my own posts, but those are most easily recalled. I did some testing a while back to view fuel level in my 930 float bowl. The link I'm pointing to isn't the whole story, but there is other discussion in that thread you may find interesting. Check out the May 4, 2017 service bulletin post from Julian.

https://www.a7a10.net/forum/index.php?topic=11619.msg89007#msg89007

Richard L.
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Re: Concentric 928 on A10 Super Rocket
« Reply #9 on: 14.07. 2020 21:59 »
Thanks Richard , will check this out

Regards Ron
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