Solex 40 PII-4 (Solid Shaft) Jet Question

[tjbates]

I am trying to get to the bottom of my spitting carbs, I have checked the valve clearances and timing (set at 3500RPM to 33degrees and the 022 distributor is a rebuilt unit from Glenn Ring).

I set the idle mixture screws as per the Porsche Service Manual 1.5turns from fully in and it runs pretty rough. It's not until I back the idle screws out to 2.5 to 3.0 turns when the engine start to run more like it should, but still spitting a little.

The downside, apart from the spitting, is that at idle it now smells pretty rich. I have cleaned both carbs and checked that the idle circuits are not blocked, the carbs are all well balanced and the float levels and set just below the Float Inspection Port.

I then check all the Jet sizes and noticed that the Idle Jets are G50? This is too small right? The Service Manual states G57.5? Could the be the problem?

Would the 7.5 increase make this much difference? If so can anyone think of a reason somebody would want to install these other jets? Modern fuels?

Any jetting advice for these Solex carbs using modern fuels, would be much appreciated.

Thank You,

Tom

[Dave357]

Hi Tom
Any engine fuelled by carburettors will need to have larger jets to compensate for fuels with Ethanol added (which is now up to 10%)
Ethanol burns hotter,so you need to increase the flow of fuel.
I have a 1950 350cc Douglas Mk IV sport, flat twin. I have had to increase the main jet size in both carbs from 75 to 90 (this is with 5% ethanol)
On my 500 BMW R45 (1979) responds better with 98 RON (Shell V-Power or the BP equivalent, but this has Bing constant vacuum carbs.
My Chesil 356 Speedster with twin Solex carbs only runs well on Shell V -power. It is understood the 98 RON fuels will not exceed 5% Ethanol.
Some Supermarket fuels have different additives, and on test and older engines with carburettors, do not respond well,(fuel consumption is not as good)
Modern fuel injected cars just compensate for poor quality fuel
Also on older vehicles this stuff eats fuel lines,gaskets and seals!!!

Hope this helps

Dave

[tjbates]

Thank you for the info.

I just spent a while researching Ethanol in fuels.

It looks to me like TOTAL filling stations are my best bet of getting E0 fuel.

[Dave357]

The advice from a air-cooled engine specialist is Total Shell BP only

Dave

[tjbates]

Dave,

Thanks great gen.

Thanks again,

Tom