SWM's and earlier Aprilia's had the PHBH 26 FS carb that had a petrol screw, later Aprilia's have the PHBH26 FS which appears to have an air screw ? Are they any better, or just different ?

The one I'm thinking of using has a small brass connection which I think was a vacum to remove any build up from the crank case, but didnt work and was usually blanked off. Can anyone confirm ?

Thanks

Ross

Anyone ?

If you ask me ... I believe it's a try out of something:

- maybe of a YEIS system, which was not uncommen back then. But it cannot work here, as the diameter is too small.

- then a hand made separte oil intake, (maybe someone tried to use this carb on a TY 250???

I don't see any real use for the brass "dingi" as the adjustment of the carb mixture for low revs is done by the air screw,

so the gimmick or "dingi" is useless in my personal opinion.

Hi Patrik

The brass connection was to vacuum any build up of Unburnt fuel/oil from the crankcase, during a long downhill on closed throttle. Didn't really work.

I was hoping for any tips on setting up the carb as it and the engine are from a donner bike and I am still discovering "things" on this "ready to ride" bike.

Ross

Hi Patrik

The brass connection was to vacuum any build up of Unburnt fuel/oil from the crankcase, during a long downhill on closed throttle. Didn't really work.

I was hoping for any tips on setting up the carb as it and the engine are from a donner bike and I am still discovering "things" on this "ready to ride" bike.

Ross

Hi Ross,

is it similar to the Yamaha Energy Induction System which was developed for two stroke engines?

Wikipedia Germany translated:

"...The YEIS is a plastic container, which is connected with a rubber hose to the inlet of the engine.

This creates a kind of reservoir between the carburetor and cylinder, in this container the two-stroke mixture will be retained in closed gate positions

(little or no gas) until the slide is opened again.

The system also works as a vibration damper at certain speeds between the combustion chamber and carburetor oscillating back and forth gases.

The YEIS causes a better engine response, more torque at low and medium revs and a lower consumption by up to 10%. ..."

Patrik

Edited December 16, 201213 yr by pschrauber

All disconnected now, am I wasting my time with this carb ?

If the carb is working otherwise well I don't think so. It would be interisting to know how good the adjustment of

the air screw works in comparison to the normally used gas mixture screw.

I know you turn just the opposite to make the mixture leaner or fatter but is it easier to adjust?

btw. If you like to try out the YEIS system I found an technical article in Trialsport from the 80's for installing and

the calculation of the needed volume for the container.

The now disconnected pipe had a bore of approx 2mm, it also had a non return valve between carb and crankcase.

Mmmh so it was connected to the crank case weird ...

The YEIS system was used by some riders and even Montesa and other manufactorys in the mid 80's on works bikes for a period of time but then they abdoned the tests.

Maybe there were better solutions?

Anyway the benefits where heavily discussed back then and some home made solutions where mounted but in the beginning with no success.

In February 1884 the calculation for the containment especially for trials engines where published in the German Trialsport magazine.

Some bikes where fitted with this modifications and it was reported with some benefits.

But this "fashion" was only used for a couple of years and these mods dissapeared again.

Here the article, you need some math and engine spec's to do it right ...:

The formulars works for every two stroke as long as you know the engine spec's.

Edited December 16, 201213 yr by pschrauber