Sunbeam scooter 250cc

[TTJOHN]

Hello there, can anyone let me know  what carburettor they are using on the 250cc scooter now just wondering whether I should try out one of those cheap Jap thingy's. One of my ideas was to do away with the intake manifold and fit a Amal 363 flange fitting, straight to the head and as this would put the float level above the bottom of the tank fit a electric pump, similar to the mini, wired up to the ignition. any sensible input would be appreciated.

TTJohn

[Spaceman]

Out of interest, what's wrong with the original AMAL 363 Monobloc which I assume is fitted? One of my 500 cc single cylinder bike's originally came with a Concentric but many people fit a Mikuni because it makes kick starting easier. However, if this is an electric start Sunbeam, this benefit would probably not be that apparent?

[TTJOHN]

The original  one is a Zenith 17mm clamp fit and the inlet manifold from the head, goes down below the petrol tank level, the elbow on this  gives room to have the carb just below the tap level, the distance between the carb intake and tank is limited, with a push on fit, which is why I thought, if I did away with the manifold and just use a flange fit carb, direct to the head, using a heat shield spacer. However, this would mean the carb being above the petrol tank level, hence the idea of a electric pump to get the correct float level, it's just an alternative idea at present and wondering if it would work.

TTJohn

[Dean Southall]

I fitted a Mikuni from Allens Performance, all set up for the Sunbeam (well, they list it as for the Tigress actually).
I have been having other issues getting the bike roadworthy but it runs fine on the Mikuni

[TTJOHN]

Dean.
I looked at Allens to see what they were sending out and it seems like they were doing Delorto carbs jetted for this machine, so I trawled around e-bay and saw the same one they were selling for £92 and that was £27-50 or make an offer, so I offered £20 and they counter offered £22-50 which I took.
Anyway, the result was, I purchased a Chinese Dellorto 18mm copy, which was jetted the same but I had to lift the needle one notch to get it running okay but now it starts and runs as it should, I have not road tested yet as it is not registered yet but she is all ready to get registered, I just have to get a retention for the original number from our Steve.

[Dean Southall]

Hi John
thanks for the update. I am glad you got the carb sorted and the bike running. Have fun!
The carb listed by Allens is a Mikuni. Mine starts very easily and dyno shows good mixture but starts playing up when I put it under load. I've to get round to checking of its ignition or my decision to open up the inlet port.
cheers
Dean

[Spaceman]

One of the bikes I ride uses a Mikuni VM32 from Allens but some of their settings were not quite right including the main jet size that needed tuning. The advantage I've found of the Mikuni is that it delivers better performance although this tends to be at the expense of fuel consumption. I have another version of the bike fitted with a PHF Dellorto carb and that also performs pretty well overall and also gives 20% better fuel economy.

[TTJOHN]

Still having a few issues with carburation, I just need to experiment with the jetting and needle position, starts up and runs fine but after trying a run down the road found it wasn't correct, spitting and banging under load, so I am still working on it.

[Dean Southall]

Hi John
just the saem I am having with mine.
Rechecked ignition (Boyer) and recalculated timimng I don't know how many times.
Tried alternative needle positions and jst in the Mikuni.
All any of these attempt would achieve was to make it even worse!
Out of ideas so I'm letting it collect dust to see if that helps.

(last autumn I bought a brand new popular motorcycle for less than I have spent on this BSA project!)

[TTJOHN]

Dean.
I believe that it's a ignition problem now, I have just advanced my original setting, only by about 1 degree but it has made quite a bit of difference, not road tested yet but it certainly starts and runs better. I will let you know later what I have, carb & jetting wise but I am using a Dellorto cheap copy from land of the rising sun, it's a PH BG 17.5mm, I did have to remove the plastic sleeve as it wouldn't fit on the inlet manifold intake, at the moment it is on a standard set up, just as I received it. 40 slide, W6 needle, 85 main, 262 atomiser, 50 idle jet, 55 choke jet. I think this carb only cost me about £28-00, so if I can get it running on that, I will be pleased.
Let you know how I get on later.

TTJohn

[Dean Southall]

Hi John
perhaps we can catch up at Mallory this weekend

[TTJOHN]

Well, I believe I have cured the bad running on the scooter, just an update of what I've done, as you know I fitted a cheap Jap copy of a Dellorto 17.5, to get it running correctly I have reduced the idle jet to a 40 and raised the needle down to the second notch from the top, It now starts very easy on the choke and once warmed runs and up pulls very well.