The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Amal, Carburation, Fuel => Topic started by: peter small on 14.10. 2015 14:56
-
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
-
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 *problem*
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 *doh*
HTH
John
-
Hello everybody this is my first post
Are you sure about that? *smile*
-
If the Super Rocket engine is correct spec you should have a 1 1/8 389 monobloc.
-
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
-
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).
-
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.
-
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.
-
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
-
should have said bore out to 1 1/16" not 1 1/8"
-
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
-
What size main jet should i use in the 389 1 1/8"
-
hi Peter, work it out and take your pic, cheers
-
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.
-
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
-
Hi Peter,
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
Those are the sizes with air filter
400 or 420 without
Modern fuel has a different specific gravity to what was recommended back then so some experimentation is mostly required
HTH
John
-
Im using a Pan cake filter and its jetted 240 as a matter of interest
-
Have the Amal 389 1 1/8 fitted started up no problem ticks over like a good one had to lower the needle as it was far to rich.
Used a colortune to check the mixture burn and it seems ok although it does hesitate when you blip the throttle.
I would have to adjust the settings when i fit a filter.
if you accelerate smoothly it is fine and it feels like more power is being developed, haven't road tested as the weather at the moment is rubbish.
The old pancake filter doesn't fit anymore so do i buy a new Pancake or go for the original anyone have a view on it
Thanks for your input great site
Pete
-
Been out for a 50 mile run at a constant 50 mph and the plug colour is spot on.
starts OK when hot so the Tufnol spacer has done the trick.
Much more responsive with the bigger carb
Cant really check main jet as the motor has a few more miles before it run in
-
If you have a late SR head, get the 389.
If everything is set correct, you will get a crisp throttle responce with the correct carb:
http://amalcarb.co.uk/cf/vehicle/list/?manufacturer=B.S.A&vehicle=A10+Super+Rocket+%28Export%29
-
Just for the record my bike is fitted with a large valve head. Carb is a 389 bore 1 and 5/32" and the settings are: Slide 3, main jet 420, pilot 25, and 106 needle set on second position from the top. It goes very well!
John
-
Bike was going very well with the new carb running in progressing been up to a staggering 60 mph without a hitch.
Now its the turn of the 6 spring clutch to get binned.
But that`s another story.
Amazing what you have to do to keep them on the road.
Pete
-
yes indeedy , surprised you'd kept it so long , best of luck.
-
Bike was going very well with the new carb running in progressing been up to a staggering 60 mph without a hitch.
Pete
According to the literature of the day (Eddie Dow), safe continous rpm is 6800 and through the gears to 7200.
So 60mph shouldn't be too hard even with the sidecar and caravan attached ;)
-
Hi
The engine is still being run in that`s why i haven't gone over 60 mph.
if i blow it up,Will Eddie Dow be round to fix it NOT.
Pete
-
It sounds like your new carb is giving it some performance potential *smile* but if you're still running in a bit of restraint initially won't hurt.