what carburetor for 1959 super rocket

[peter small]

Hello everybody this is my first post

I have a 1954 Road Rocket which has been fitted with the more powerful Tongue in cheek 1959 Super rocket engine,
The carburetter fitted is a 376/97 Monobloc.
The bike lacked power and poor starting when hot so i decided to fit a tufnol spacer which it didnt have fitted.
checking the bore diameter of the head it measures 1 13/64 which is well over the size of the carburetor which has a 1 inch bore.
Ive looked at the tables and it recommends a 1 1/16 bore carb
I have a feeling the carb i have has been stamped incorrectly and should have the bigger bore

Any thoughts  leave it as it is or change it

Pete

[chaterlea25]

Hi Peter,
According to my maths thats equal to 30.55mm 
What number is cast/stamped on the underside of the inlet manifold ? this would identify the head type
My opinion is that the 1" carb is waaaay too small
My SR is fitted with a 30mm carb to match the 1571 head,

A bigger carb is only one part of the equasion, what pistons and cam are fitted?
What condition are the valves / seats and bores in?
Is the ignition timiing correct? and equal on both cylinders
Poor hot starting is most often down to a failing magneto

HTH
John

[Greybeard]

Hello everybody this is my first post

Are you sure about that? 

[beezermacc]

If the Super Rocket engine is correct spec you should have a 1 1/8 389 monobloc.

[peter small]

First post in three years should have said

The engine is now in good order new rings all bores in tolerance flat top pistons plus 20 thou, valves replaced guides all new/ springs,
 Ive also fitted with SRM pump
The MAG is new
I havent checked the timing
I will check the head tomorrow for numbers
I havent took the motor down as far as the cam as it was rebuilt by PO just before i bought it and shows very little wear.
It does start first kick when cold but seems sluggish and is very lumpy running not as smooth as it should be its a new carb
I will check the head number tomorrow.
I have a 376 1 1/16 inch carb body on the way
Im not after a performance bike i leave that to my Triumphs i just want a good working bike.

Thanks John for your constructive reply

Pete

[East_Coast_BSA]

My 59' SR has an Amal 389/31, which is 1 1/8" carb.  One kick starter hot or cold.  When my motor would act up (good starter cold, not so good hot), the valves needed to be re-adjusted because they had gotten tight.  I adjusted them three times within the first 1000 miles.  Everything starts to take a "seat" over time, this includes the rockerbox gaskets.  If you're using the thick paper gaskets, they will crush a lot.  Be sure the rockerbox nuts and bolts are all tight and check the valve lash (it's easy enough to do).

[Rocket Racer]

1 1/8" on the road rockets and 1 5/32" on the super rockets, 1 3/16" on the RGS

1" way too small, something in the 28 to 30mm range but not bigger.

[trevinoz]

RR, how about 1-1/16" TT on the Road Rocket, 1-1/8" on the Super Rocket until 1960 and 1-5/32" thereafter. Option of TT.
RGS used exactly the same engine as the Super Rocket. 1-3/16" specified for some markets.

[peter small]

chaterlea25

The cylinder head identification mark is 67-1459
I Have located a engineer that will bore the carb out to 1 1/8" he also sleeves carbs
I just want to confirm i am doing the right thing
a 1" bore is no good at all which everyone agrees.

Ive read the posts with interest thanks everyone for their input.

Pete

[peter small]

should have said bore out to 1 1/16" not 1 1/8"

[chaterlea25]

Hi Peter,
The 1549 head is the late type Super Rocket,
I have seen these with different size inlet tracts ? the ones I have looked at  seemed to be "factory" and not home ported
So it should at least have a 1 1/8in. carb, I  wouldnt bother boring out the 376
I would buy and fit a correct size carb
All this may not help hot starting if theres another problem???

HTH
John

[peter small]

What size main jet should i use in the 389 1 1/8"

[kiwipom]

hi Peter, work it out and take your pic, cheers

[RichardL]

As is often the case with carbs, I'm confused. With 1-13/64" bore in the manifold, the 1-3/16" (1-12/64") seems the natural fit. Is there any reason this would not be true? As for running rough, I could envision where the diameter mismatch could be responsible for that. The air velocity will change from the carb to the manifold.

Edit: Yes, I know there is venturi action through the carb that draws up fuel, but I don't believe the throat mismatch should be part of the venturi.

Richard L.

[peter small]

Amal 1 1/8" bore Looks like a 290 or 250 jet as per spec 389/31 or a 48 which run 3.5 slide with a 30 pilot it take your pick time

Im currently running a 250 main on a 1" carb  and a 25 pilot same slide 3.5

so if i put the colour tune on tick over it will give me an idea re pilot size the rest will be plug colour at different throttle settings

thanks for download Kiwipom

Thanks again for input

Pete