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Try adjusting the idle mixture screws. One at a time. Screw IN until rpm drops, then OUT until you have max rpm/smoothness. If nothing changes, then that indicates a blockage/malfunction with that side of the carb.

Clogged pick up screen.

Every engine is different & all have a 'sweet spot'. It is quite possible to have a larger engine get better mileage than a smaller engine if the bigger engine is operating in it's most efficient range.

Agree with RRR, that is a bit tight. Far more power will be lost by ring ends butting together [ too tight] than will be lost by gaps 0.005" too big.

In Australia [ [post #47 ], before litres, we used Imperial gallons. Not sure if James is using Imperial, or converted to US gallons which are about 7/8 of an Imp gallon.

She was a good Mama.....

Probably work well. Pontiac used the QJ on a 230 in line six in 1967.

Doubt it would be 390 cfm. D. Vizard tested Weber/Dellorto carbs. Didn't test 38s, but tested three 40mm carbs: 342, 350, 364 cfm.

A trick that I have used in the past for carb heat insulation when you do not have room for a spacer or do not want to use a spacer: - drill out the carb mounting holes to 7/16" - use some insulation over mounting bolts/studs. Heat shrink, or some spark plug lead sheathing often works well - fit...

Most likely carb float/fuel level: - too high, fuel sloshes into carb throat - too low, fuel uncovers the jet on L turns.

I have no experience with E fuel in our old cars, but I can tell you this: it has no place being in a metal carburetor. I keep E10 in the shop for parts washing because it is cheaper. A few years back I left some in a container overnight, very mild weather. Next morning there water drops in the...

My headache just got worse....

15* of vac @ WOT suggests the carb is not getting anywhere near WOT.

He stated the dwell was 45*. This could be so many thinks: - water in fuel - sediment blocking jets in carb - cam lobes going flat - ign/electrical. I am leaning towards electrical. It is also external. Check: plug wires & spark plugs [ or replace ]; inspect dist cap, rotor for carbon...

Do not delete the PCV. It keeps the engine clean internally. All carbs that use PCV are designed for the air flow they add. Make sure the PCV is not gunked up. It should rattle when you shake it. If blocked with gunk, it might let in excessive air & be contributing to the problem. Have you got...

I doubt 0.003" of wear is causing any problems. You have an adjustable air+fuel supply [ the mixture screws ] to compensate for variations. That is why it is adjustable. I tuned my first carb in 1964 & I am still learning..... I never use a vac gauge for idle adjustment, I tune by ear & feel...

Although it is hard to tell from the pic, I doubt that that amount of wear is causing the problem. I have always found 4 bbl Holleys to have a lot of shaft clearance, even when new, compared to other brands, so 2 bbls probably the same. Worn shafts [ if they are worn ] do not cause fuel to...

I once saw a Falcon with a 6 cyl engine, where the owner made an intake that took Amal motorcycle carbs, six carbs from memory. It went like really well....

Patented with 'dryseal'. In the decades since the engine was made, maybe new substances have been invented that seal without additional sealer. I would install it without additional sealer.

450 is a bit optimistic. A 40 FAV1 [ 2 bbl carb ] flows about 342 cfm according to D. Vizard 40 DCOE flows 350.

If you have a choice, use leaded fuel.

Another company that has intakes for the slant 6 is Redline Performance. [ www.redlineauto.com.au ]. They also have a good variety of linkages etc.

Most Webers come with steel needles & seats. Redline in Hollywood, Calif sell Viton n/seats which are more forgiving & less prone to flooding for street use. Not sure if they have them for all models.

Would probably work vey well.....

It is not ign. If you can screw the idle mixture screw in until it seats & the engine does not stall or at least run very rough, then the engine is getting fuel at idle from somewhere else. Check the PCV valve; it should rattle when you shake it. If that checks out, remove the carb & see how...

If it is a down draft, probably a 38DGAS. If side draft, a 38 DCOE.

If you already have the carb, run it. The worst that can happen is it doesn't run properly...& then you can move to plan B.

Ign coils rarely use the available secondary voltage. But the fools fall for the big numbers, such as 60kv must be better than 48kv, right, even though the spark plugs will only ever need 28kv to fire them. Very unlikely that a coil rated with a 3kv higher sec voltage provided a 'better' spark...

Unfortunately, the term 'elec ign' covers a wide spectre of suspects. Same applies to ign coils. There is nothing secret about ign coils. If you want the longest/best life/best spark from any coil , follow the instructions as to whether it needs a bal res.

I recently rebuilt a 455 Pontiac engine with the same problem. The top rings on 7 out of 8 cyls were broken, in pieces. The ring pieces were carboned up, obviously been running this way for a long time. Engine ran reasonably well, just had this oil problem.