30 pict 3, or 30/31 on a SP

[ruckman101]

The 30/31 has an adapter plate I assume so that it can be fitted to the intake of a DP. I think the '70 SP was originally fitted with the 30 pict 3.

Anyone have any experience or preferences between the two on a stock SP?



neal

[sped372]

I've got the 30/31 on ours and have been happy with it matched with the stock vac-only dizzy. No experience with a pict-3. The 30/31 tunes like the later carbs with the air bypass.

[Amskeptic]

I've got the 30/31 on ours and have been happy with it matched with the stock vac-only dizzy. No experience with a pict-3. The 30/31 tunes like the later carbs with the air bypass.

Any Pict3 carb is by nomenclature an air bypass carb.
The first number is the venturi size.

Neal, generally you want the velocity of a smaller venturi with a stock singleport, i.e. the 28/30/31 carbs.
The 34Pict3 wants a dual port manifold under it. It is also calibrated for the vacuum retard and lower compression pistons.
Colin

[ruckman101]

Currently have the 30/31 on there. But got a 30 pict 3 cleaned up and gone over yesterday, sitting on the bench. Been meaning to go over the 30/31 currently on there, but haven't yet. I will if this thing continues to give me issues. Have to take a look at the exhaust, too. Conditions returned on Cheryle Wednesday, dropped idle, backfiring, but seemed fine today on a short test run. Cheryle is out and about on a similar run today, so anxious to hear if conditions again return.


neal

[DjEep]

I roll a 30/31 in the 1600sp in Maybelline and 30-pict-1 on Betsy's 1300. Both run fine, but I like rolling the 30/31 w/ an SVDA and the 30pict with a vac-only.

Been toying with the idea of fabbing some dual carb manifolds to fit the teeny 40horse ports and linkage to fit a pair of 28's or 30's, just to see what would happen... Got a pile of old 40horse manifolds with hopelessly plugged heat risers and buckets full of 28s and 30s...... what's the worst that could happen?

[Amskeptic]

Currently have the 30/31 on there. But got a 30 pict 3 cleaned up and gone over yesterday, sitting on the bench. Been meaning to go over the 30/31 currently on there, but haven't yet. I will if this thing continues to give me issues. Have to take a look at the exhaust, too. Conditions returned on Cheryle Wednesday, dropped idle, backfiring, but seemed fine today on a short test run. Cheryle is out and about on a similar run today, so anxious to hear if conditions again return.


neal

Ran like a champ, you said, before I deleted your last post with its wandering reference to brake work, now then.

Intermittent symptoms, like you describe above, often relate to lousy sloppy wiring connections to the electromagnetic cut-off, or an electromagnetic cutoff that is not getting a secure ground. Checkitout. Instead of waiting for symptoms, get in there and wiggle wires and touch the cut-off to see if you can imitate the symptoms, even jiggle the key at idle to see if it de-energizes the cut-off which sometimes refuses to re-open even as the rest of the engine barely registers that momentary loss of electrical power to the coil.
Colin

[ruckman101]

That was a weird freak tic of what the? My current theory is that the rubber O-ring on the big screw idle bypass some such bit was so brittle and shot, that I got a similar running much too lean symptoms as when the idle cut off solenoid assembly was loose enough to snug up by hand. Sucked wads of air.

The first time I took screwdriver to it I couldn't find the slot and then realized I had and was spinning it in real quick. Every other one I had tackled had a fresh O-ring on there and some resistance. So after Cheryle had issues after confirming the solenoid was still tight and hadn't loosened, I pulled it out and filmed that O-ring with a bit of axle grease.

Since then no issues. The plan is still to swap carbs and brave my fears of not being able to have the skills to adjust. A cleaned up 30 pict 3 instead of the 30/31 currently running. If that works, then I can go over the carb I'm running and decide.


neal

[ruckman101]

Currently have the 30/31 on there. But got a 30 pict 3 cleaned up and gone over yesterday, sitting on the bench. Been meaning to go over the 30/31 currently on there, but haven't yet. I will if this thing continues to give me issues. Have to take a look at the exhaust, too. Conditions returned on Cheryle Wednesday, dropped idle, backfiring, but seemed fine today on a short test run. Cheryle is out and about on a similar run today, so anxious to hear if conditions again return.


neal

Ran like a champ, you said, before I deleted your last post with its wandering reference to brake work, now then.

Intermittent symptoms, like you describe above, often relate to lousy sloppy wiring connections to the electromagnetic cut-off, or an electromagnetic cutoff that is not getting a secure ground. Checkitout. Instead of waiting for symptoms, get in there and wiggle wires and touch the cut-off to see if you can imitate the symptoms, even jiggle the key at idle to see if it de-energizes the cut-off which sometimes refuses to re-open even as the rest of the engine barely registers that momentary loss of electrical power to the coil.
Colin

Oof. Simplicity. After the prior post of navel gazing egoisticism. A bad wire.

neal