TheSamba.com :: View topic - H31/30 Angle v straight jet and idle mixture

Mon Aug 31, 2020 5:53 pm

There are multiple sources that cant seem to agree on what jet is the power jet and what jet is the idle jet. Sole say the angle jet is the power and some say it is the idle jet on the H30/31 carb

The carb is on a 1600DP engine with a 1300DP manifold( I have no idea why but that is how i bought the car, I will probably do duals at some point but for now there are bigger fish to fry with the car).

The jetting as i revived the car was 120 main, 65 angled and 50 straight in jet. It was running lean so i rebuilt and jetted it to 125 main, 65 straight in and 55 angle. This per several sights means the angled jet is the pilot jet and the straight in jet is the power jet.

With this the car was running rich at idle. Even with the volume screw all the way in it was still idling rich.

I swapped the straight in jet from a 65 to a 55 and the idle leaned out and idles best with around 2 turns out on the idle adjustment screw.

So it seems to me the straight in jet IS the idle jet and the Angled jet is the power jet. It has to be. Only the straight in jet was changed and it affected the idle mixture.

Has anyone else came to this same conclusion?

I ended up swapping the angle jet (power jet) to 65 and the car runs fine.

Mon Aug 31, 2020 6:48 pm

Oh my Lord.

You got me started.

THERE IS NO SUCH THING AS A POWER JET. THE POWER FUEL JET IS IN THE UPPPER HALF OF THE CARBURETOR FOR HIGH SPEED ENRICHMENT.

On the PICT-3 and PICT-4 carbs, you are talking about TWO idle fuel jets.

"He Said, She Said" :roll:

VW didn't know exactly what to call them, and translation differences may have led to some thinking one was about "Power" but IT IS NOT.

VW split the idle circuit into two different pathways, TWO idle fuel jets, TWO idle air jets, one sometimes considered, "extra" "excess" or "auxiliary" for more precise mixture control for emissions. NEITHER OF THEM ARE FOR POWER. I think the most common translation is "Auxiliary" which is what I go with, but remember, it's just half of a split idle circuit.

](*,)

In the following photos, I provided some the German translations (well, with help of applications like Google Translate)

Now as far as asking which one goes where on the bastard-child H30-31, I'll go with this (my photo)

The True Power Fuel System (high speed enrichment) jets are here, they do NOTHING at all at idle.

Mon Aug 31, 2020 10:48 pm

Thanks that is the best explanation I have heard yet! What are the odds getting bad information off the internet..LOL thanks.

Ok, so there are 2 idle fuel jets (idle jet and auxiliary jet) and 2 idle air jets.

My assumption is one affects idle fuel flow mostly with the throttle blade closed and the other affects off idle fuel mixture at part throttle operation.

Would my assumption that the straight in jet is the aux jet be correct?

The angle jet would be the Pilot jet?

So at idle with the throttle blade closed the transition ports are covered, so most of the fuel is supplied by the aux jet, The air from the Bypass screw mixes with fuel from the Aux jet, Now the Volume screw feeds from the idle jet and supplies addition fuel to this circuit to tune the idle mixture.
Hence why when it had a 65 jet straight (aux jet) in the volume screw was completely closed because it was suppling to much fuel at idle and did not need any addition of the volume screw making the system out of balance.

after the throttle blade uncovers the transition ports addition fuel is pulled from the idle jet to give more fuel at part throttle.
So, it is a balance of both jets, if you want to tune off idle response or part throttle operation the idle jet is the one to tune, The Aux jet mainly controls the fuel flow at idle with the addition of the volume screw.

Is this correct?

Tue Sep 01, 2020 8:14 am

Magnaman53 wrote: So it seems to me the straight in jet IS the idle jet and the Angled jet is the power jet. It has to be. Only the straight in jet was changed and it affected the idle mixture.

Has anyone else came to this same conclusion?

I ended up swapping the angle jet (power jet) to 65 and the car runs fine.

On the H30/31 carburetor, there are two brass jets on the right side (right is right of car). The angled one (points slightly towards the rear of the car) is the idle jet (should be the 50). The other one (pointing straight out to the right side of the car) is the power jet (should be the 65), which feeds additional fuel at high throttle/high rpm. The power jet is needed to correct a tendency for the air correction jet to work TOO well at max airflow - it leans the mixture off too much and the power jet corrects this.
I initially mixed these up on my own carb when I rebuilt it, their threads are the same, and I initially did not notice they were different sizes (stamping on the side, use a light and magnifying glass).

My own 30-31 carburetor has 50 idle jet and 65 power jet

See http://www.vw-resource.com/jets.html and look down at the 30/31 section, states this as well. Their diagram looks pretty official even if for 31PICT3.

Tue Sep 01, 2020 10:18 am

Cusser wrote: Magnaman53 wrote: So it seems to me the straight in jet IS the idle jet and the Angled jet is the power jet. It has to be. Only the straight in jet was changed and it affected the idle mixture.

Has anyone else came to this same conclusion?

I ended up swapping the angle jet (power jet) to 65 and the car runs fine.

On the H30/31 carburetor, there are two brass jets on the right side (right is right of car). The angled one (points slightly towards the rear of the car) is the idle jet (should be the 50). The other one (pointing straight out to the right side of the car) is the power jet (should be the 65), which feeds additional fuel at high throttle/high rpm. The power jet is needed to correct a tendency for the air correction jet to work TOO well at max airflow - it leans the mixture off too much and the power jet corrects this.
I initially mixed these up on my own carb when I rebuilt it, their threads are the same, and I initially did not notice they were different sizes (stamping on the side, use a light and magnifying glass).

My own 30-31 carburetor has 50 idle jet and 65 power jet

See http://www.vw-resource.com/jets.html and look down at the 30/31 section, states this as well. Their diagram looks pretty official even if for 31PICT3.

This is what i read but after experimenting if the straight in jet was the power jet it would have no effect of the idle mixture. When i swapped the straight in jet from a 50 to a 65 the idle mixture went very rich, Hence i do not think this site is correct.

Tue Sep 01, 2020 1:52 pm

My 1970 runs pretty good (30/31 PICT on adapter on dual port manifold, 1600cc) so I'm staying as I have it.

Wed Sep 02, 2020 7:47 pm

The angled jet on mine is a 65. Straight jet is a 50. If I switch them the engine runs like crap.