keihin PJ carb on a 4 stroke?
hubert
has anybody tried fitting keihin PJ (oval slide)carbs to a 4 stroke?
i was given a set of PJ carbs, but the only reference i can find for these
seems to be for 2 stroke engines.
i have fitted a set of ex-RD350lc VM mikunis to a ducati, and that swap from
2 stroke to 4 stroke was not a big problem.
having said that, i know absolutely nothing about keihins...
cheers
Hubert
CK
Have you studied the Sudco International Catalog? Sudco has an online
catalog with lots of information. Google for sudco.
Slide valve carburetors were used on 4-strokes for years and years
before the EPA mandated constant vacuum carbs.
Mikuni improved 4-stroke throttle response by developing the air bleed
type needle jet. The needle jet is the brass tube that the tapered jet
needle goes into. The main jet threads into the bottom of the needle
jet.
Mikuni 4-stroke carbs had air bleed type needle jets that mixed air
with the gasoline low down in the carburetor, while the 2-stroke carbs
had primary type needle jets without air bleed holes so gasoline and
air had to be mixed higher up in the venturi.
A 2-stroke engine gets lots of turbulence and heat in the crankcase to
mix huge droplets of fuel before it reaches the combustion chamber.
But a 4-stroke engine needs to have the fuel and air well mixed in the
4-stroke's relatively short intake tract.
The flat slide, square slide, and oval slide carburetor is designed to
increase turbulence downstream of the slide and assist mixing fuel and
air better. Some experimental carbs even had needles that weren't
round, they were flat on the downstream side to assist mixing.
I suppose Keihin would be following the same engineering theory that
Mikuni followed in development of their carbs.
The Sudco catalog I have here doesn't even show the needle jet, so you
might want to call up Sudco and ask the tech reps there about needle
jets and whether they have air bleed holes and if it still matters.
hubert
>
> hubert wrote:
>> Hi all,
>>
>> has anybody tried fitting keihin PJ (oval slide)carbs to a 4 stroke?
>> i was given a set of PJ carbs, but the only reference i can find for
>> these
>> seems to be for 2 stroke engines.
>> i have fitted a set of ex-RD350lc VM mikunis to a ducati, and that swap
>> from
>> 2 stroke to 4 stroke was not a big problem.
>> having said that, i know absolutely nothing about keihins...
>
> Have you studied the Sudco International Catalog? Sudco has an online
> catalog with lots of information. Google for sudco.
>
I have the sudco catalogue, they only list the PJ carb for two strokes.
> Slide valve carburetors were used on 4-strokes for years and years
> before the EPA mandated constant vacuum carbs.
>
> Mikuni improved 4-stroke throttle response by developing the air bleed
> type needle jet. The needle jet is the brass tube that the tapered jet
> needle goes into. The main jet threads into the bottom of the needle
> jet.
>
> Mikuni 4-stroke carbs had air bleed type needle jets that mixed air
> with the gasoline low down in the carburetor, while the 2-stroke carbs
> had primary type needle jets without air bleed holes so gasoline and
> air had to be mixed higher up in the venturi.
>
this one has no removable needle jet /mixing tube like a mikuni/dellorto
etc,
so no bleeding holes,
> A 2-stroke engine gets lots of turbulence and heat in the crankcase to
> mix huge droplets of fuel before it reaches the combustion chamber.
>
> But a 4-stroke engine needs to have the fuel and air well mixed in the
> 4-stroke's relatively short intake tract.
>
> The flat slide, square slide, and oval slide carburetor is designed to
> increase turbulence downstream of the slide and assist mixing fuel and
> air better. Some experimental carbs even had needles that weren't
> round, they were flat on the downstream side to assist mixing.
>
> I suppose Keihin would be following the same engineering theory that
> Mikuni followed in development of their carbs.
>
> The Sudco catalog I have here doesn't even show the needle jet, so you
> might want to call up Sudco and ask the tech reps there about needle
> jets and whether they have air bleed holes and if it still matters.
>
Looks like this design does not have a removable needle jet,
I suppose that is the answer i was looking for, without the possibility to
change the needle jet, wich is not suitable for a 4 stroke it will be hard
to set this carb up for a 4 stroke.
the only possibility is to machine a bit off the top of the screen over the
needle jet until is is suited for the 4 stroke.
not the best option, especially on a twin where you want both cylinders
synchronised.
anyway getting fuel and air well mixed might also be a problem,
finding a set of mikuni's is the easyer option.
cheers, and thanks for the help.
hubert