solex 31 pict-3 stock jetting question??

[pablovent]

Hi, for my 1303 1973 1300cc manual trans, I need solex 31 pict-3 stock jets size information....

In the picture appear, but is too big jetting for me, and (0) jet without information.......

Really appreciate your help!!

[kreemoweet]

There's some info on this page: http://www.ruddies-berlin.de/solexPICT.htm
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[Aussiebug]

The 31pict3 was the stock carb for the 1300 twin port engine, ( note that the pic says 1300 and "44 ps motor" which is the 1300 engine), so the sizes in your pic should work ok.

The 31pict3 has a larger 25.5 mm throat than the earlier 1300s 30pict carbs (24mm throat).

So my reading of that jetting is that it has a rather large main jet to go with the larger throat, but a large air correction jet to stop it going over-rich at higher speeds ( with open-throat style carbs, the main jet would go over rich at medium to high speeds without an air correction jet).

The idle jet is a fraction larger than I would have thought at 60 rather than 55, but that might be because of the larger throat too.

The aux (power) jet is less critical as it only operates at high speed/ open throttle, so it coul be anything between about 47.5 to 65.
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Rob
Rob and Dave's aircooled VW pages
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[pablovent]

[pablovent]

[glutamodo]

The air correction jet did vary all over the place across the 30PICT-3, 31PICT-3,31PICT-4 ranges in the 1970s... all the way from 110 to 170. Note the vehicle application and the size of the main jet also vary.

-Andy

[francoangellini]

[pablovent]

which is what determines the size of air and main fuel jets in the same engine and carburetor ??
....why differences between Germany chart and USA chart for the same bug and carb??.....110z is too different to 170z!!

Elevation??

[pharos]

Hi,

Carburetor: 30/31 Pict-3
Engine is 1600, Single Port with Engle W100 Camshaft
Cylinder Head Ported and Polished

I just Brake-in the engine, and it run perfect, now I need to make fine tuning for this new carb. and I have AFR. Need your advice for jetting it for the best engine running temperature because of our hot weather climates

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[Aussie63]

Ive just rebuilt my stock 1300 TP engine and am using an original Solex 31, Pict -3. The H30/31 is a direct replacement for this carb.

I have read up on numerous sources for correct jetting and I've never understood the extreme variations on jetting options for this carb listed by manuals and so fourth. The two most common jetting options are:

145 fuel jet
170x air correction
60 idle jet
50 for the aux jet.

VS:

130 main jet
110x air correction
52.5 idle
47.5 aux jet


My understanding is that this carburettor was mated with the DVDA distributors. I'm wondering if that had a bearing on jetting?

For me the 145 option was making the car run way to rich and I was getting a massive flat spot on acceleration, not to mention poor fuel economy. The second option with the 135 main jet still gave me the same result.

I've finally got it jetted to 125 main jet, 125 air correction, 60 idle and 50 aux. It's running near perfect with the mixture now a nice rich grey. It accelerates smoothly. Living in the cooler climate here in the UK and roughly at 300ft altitude.

There's a good read on choosing suitable jetting on Rob and Daves VW Resource. They mention jetting for the replacement H30/31 carb too. Have a read.

http://www.vw-resource.com/jets.html#30

[glutamodo]

Generally, since the air correction jet feeds air to the main discharge arm of the carburetor, and the main jet feeds fuel, the two need to match. Now, once you get closer to full throttle, the high speed enrichment jets also come into play, but in the midrange, you need a match of air correction and main jet. The crux of this is, usually, larger air correction jets go with larger main jets, and vice versa. But having two power fuel (enrichment) jets does skew things a little.

Yes, going by "feel" and by closing monitoring fuel economy works (looking at spark plug condition... that varies, because people pull spark plugs with far too few miles, or with just in-town short hops that can drastically alter what you see there) A tailpipe exhaust gas analyzer is nice, but can also be misleading because just revving an engine up parked at the curb, so to speak, there is almost no load on the engine.

Now the two idle jets (pilot and auxiliary are the two paths of a divided idle circuit) only play into idle and transition.

One thing to keep in mind is that the German 31PICT-3 variants were originally matched to either SVDA or DVDA distributors. My chart shown above lists these.

The Brazil H30/31PICT is set up for a vacuum-only distributor, like the 113905205T, that is, if you are accessing the traditional left side vacuum port. If you hook that up to an SVDA or DVDA, you won't get proper vacuum advance. The port suitable for advance on SVDA or DVDA is the angled one to the right rear of the carburetor and to use it, you may have to get creative to route the vacuum hose in such a way that it doesn't tangle with the throttle arm.
_________________
Andy T.


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[tzepesh]

I need some support on this topic. Helping a friend with a 1.3 dual port, original 31pict3, SVDA. We can not get it to idle, and it backfires in the exhaust heavily.
My main question is if the idle jet and aux positions are actually right in the pictures (pos. 3 and 0 in the first picture, 26 and 24 in the pictures from the ruddies-berlin website). With that configuration (52.5 idle, 47.5 aux) in those positions, we can get it to idle only with the throttle opened quite a lot. If we swap the places of the jets, then it starts to respond to the basic tuning, with throttle closed.
Any ideas, please? It's driving us nuts since months. We tried 3 different carbs, and different ignition...
_________________
'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[Maddel]

[tzepesh]

Valves are adjusted. Heads are cracked, an issue is that replacement 1.3 DP heads are not available... But I had cracked heads in my 1.6 for years and still it ran very well, adjustments were working...
_________________
'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[tzepesh]

Actually my main question here is in order to confirm the positions of the jets, because it seems a bit strange to have the idle jet to an angle, whereas for all other carbs the idle jet is in the "straight" position. Also correlated to the behavior that we could tune the idle when the jets were swapped.
_________________
'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[kreemoweet]

[tzepesh]

Thank you for the link to the German manual. It's clear, the jet going perpendicular is the aux, and side jet is the idle jet.
It's also puzzling us, because it means that with a smaller jet (47.5) we can tune the idle, but not with the larger one (52.5)... Unfortunately I do not have a jet gauge tool to check the real size.
Next: swap the ignition to another known good one.

Could we blame the cracked heads for this behavior?
_________________
'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[kreemoweet]