BS EJR2 factory racer - 50cc twin50cc Factory racerBS Factory Works Team
50cc Factory racer
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Description: Picture of a 50CC Single Cylinder Racer.  Note - left hand carburator.
 
Sent in by Paul Dunne
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Posted by: Richard Clark BS parts 
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Guest
June 19, 2011, 08:49:06 AM
1963 might be too early.
Guest
June 19, 2011, 08:48:00 AM
Our Japanese member Kotaro says this is 1964 engine in his comment  post. I think the single would be before the 1965 twin.I think this single  is a race shop only project with little kinship to the BS90/BS50 4 speed production engines.
disc_valve
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June 17, 2011, 06:44:34 AM
Sounds like there is a fair bit of confiusion around the "EJR" racers. The figures for power output were taken form a Japanese book "The History of Japanese Racing Motorcycles", published back around 1980. Although the book is written in Japanese (which I can't read) the quote of 13.5 HP at 16000 rpm was taken from the caption on a photo said to be of an EJR1. That bike has a different shaped fairing compared to the EJR2 pic alongside it, and no sign of a radiator, so I assumed it was the single.

The 50cc twins appeared in two colour schemes (1965 and 1966) with identical shaped fairings.  I believe the early twins had a 10-speed box, later changed (I think) to a 14-speed unit. Presumably that accounts for the two versions of the twin that you mentioned.

When the roadster BS50 Sport was released in 1965, Bridgestone did produce race-kitted versions and raced them in the Japanese National series. These produced around 10.5 hp at 13,500 rpm. Of course these would have had a right side carb, and the motors would have been clearly derived from the road bike.

Maybe Bridgestone did produce some early prototypes singles with left-hand carbs, but I wonder if they really would have produced them as early as 1963. After all, at that time the BS90 hadn't yet appeared, and their main product was the BS7 and Homer (both piston ported motors)

Your pic was the first time I'd seen a pic of a left hand carb air cooled single without a fairing, but it seems there is much more to these Bridgestone racers than meets the eye.

Thanks for your reply.

Graham
Guest
June 14, 2011, 08:55:46 PM
in the beginning, say about 1963-65, there were factory racer  50's that were singles. I have seen pictures of two different air cooled singles with the left side carb. One was said to be a 6 speed and the other I think was an 8 speed. The singles did not rev to 16,000.I dont recall the letter designation.I think there is confusion on the EJR, etc.  There were, I believe, two different twin cylinder  water cooled 50's. The generator/alternator   and  carburetors are different between the early and later 50 twins. I think there may hav been bore and stroke differences between the twins also.
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May 31, 2011, 06:10:17 AM
Hi,

I'm a little puzzled. I've seen photos of this same bike taken from the other side. The frame is the same modified CR110, and it is against the same background (flower bed and silver-grey garage door).  There is definitely no carb on the right hand side and there is only one expansion chamber. So... it must be a single-cylinder lump.

The output figures I've seen for the EJR1 show 13.5 hp at 16,000 rpm - which sounds about right for a well-tuned single. The EJR2 was certainly a water-cooled twin, but maybe the EJR1 was a simple air-cooled single??

Does anyone out there know?
Guest
July 31, 2010, 03:18:40 AM
Paul,

Hello.
Thank you for posting rare photo of Bridgestone factory racer.

This is a 1964  "EJ-R1"  air cooled single cylinder engine with 6 speed gears on Honda CR110 frame in 1990's. I could not find original frame anymore. "EJ-R1" is the prototype of 50 cc twin GP racer. It still remain 3 at least in Japan.

Thank you,

Kotaro
Last modified by: July 31, 2010, 03:19:28 AM



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