amal carbs

[AdeScrivs]

Are there any other Amal carbs besides 375 or 376 suitable for an Arrow 250cc?
Would a 389 from a 250cc Greeves be suitable with appropriate jets fitted?
Wise words or advice appreciated.

[will_curry]

A 389 will fit the Arrow engine but even the smallest choke size will be significantly
larger than even the Sports Arrow's 376 so making it well work with an untuned Arrow engine
will be quite a challenge. Another issue will be that there isn't a cold start device for the 389
like there is for the standard Arrow and Sports Arrow carbs.

[AdeScrivs]

Thanks for that Will, I've got hold of a correct 376 carb now so I'll give the 389 a miss.

[ian williams]

hi Ade;
i have a 626 concentric on my arrow racer , it has the manually operated push down and lock choke kit fitted , you have to flip it off by hand .
not sure what it was originally designed to be used on but it is a 2 stroke version .
sorry i dont know what the main jet size is but it runs a treat and the engine is tuned as per the 1965 motorcycle mechanics magazine so maybe it has some info in that article or perhaps its a d14 bantam carb with bigger main jet .
regards
ian

[AdeScrivs]

Thanks Ian, 376 carb I bought has arrived and looks mint and correct. Can I fit it as a direct replacement for the old 375 carb or does the inlet port need modifying to suit the larger bore?

[will_curry]

Ideally the inlet should match the carb choke size but you may find it's already
the correct size as later Leaders and the 200s all had the same inlet size as
the Sports Arrow. One thing that won't fit is the cold start device from the 375 -
did the new 376 come with one?

[ian williams]

hi ade ;
you ought to open the inlet hole up if yours isnt already that size , its 1 1/16" but if you cant do that then it would still run but you wont get the results as would have been if it had the larger hole .

Will Curry above mentioned the choke , which i hadnt thought about myself , you will need to look at the choke strangler that goes on back of carb and see if it fits or not .

376/277 is the sports arrow carb model number ,

i run my 58 leader on the original 375 carb and low compression heads still .

hope you get some results out of it .
ian

[AdeScrivs]

I measured it up and the bore of the 376 carb is bigger than the intake. Rebuild kit for the 375 carb arrived today so I cleaned and rebuilt it, fitted it back on and she went 2nd kick and seems to run well. I'll keep the 376 carb in 'the stores' and see if I can pick up another set of heads and barrels to modify, or even a complete engine to rebuild for sprinting.

[AdeScrivs]

I've bought a spare engine for my George Brown replica bike and I will hopefully sort it over the winter.
I did also acquire that Amal 389 carb, (from a Greeves motocross bike) and I'd like to use it on this engine rather than go down the twin carb route.
Can anyone recommend jet sizes, needle height etc using this carb, or would a 626 or a Mikuni be a better bet?
Engine will be have high compression heads and a mild tune.

[Roger James]

If you are going to be building a George Brown sprinter replica then the Amal 389 would be the more appropriate carb to fit rather than a Mikuni. I think in the day George Brown would have fitted GP carbs but these are getting a bit expensive to buy these days. I have three Arrows fitted with the 389 carb using the internal choke slide operated by cable and lever on the handlebars, far superior than Ariels Butterfly choke unit. As for jet sizes, they do vary, one has a 500 main jet, another has a 560 main jet (not sure whats in the third one). Best to fit a larger Needle jet, standard is 105 I'm using 107, you can go up to a 109 for hard racing/sprinting. Needle position is 2nd groove from top. This should give you a guide to get you started followed by test running and changes to suit to engine porting etc. I will mention something important so you don't starve the engine of fuel when working it hard, the standard fuel tap should be changed to a 1/4 turn fuel tap that tend to provide a better fuel flow, these are readily available to buy all over the place these days as they were a common fitting to larger capacity British machines. In addition I would highly recommend that you fit a Float Needle seating thats been machined out to take a larger Dope Needle as the standard set up is a also a bit restrictive to getting fuel into the carb, I get my Float Needle Seatings and Dope/alcohol needle suitably machined out from Surrey Cycles. See attached photo, standard on the left, machined out on the right. Photo of one of the Arrows *fitted with 389 carb and ported iron barrels by Fahron engineering out on track at Cadwell. Jess