The top picture is a picture of the carb on my brother 68 big block as an example. The second pic is his.

 

thanks, deleted my comment

 

Gotcha, I see what you have now. With 22 inches of vacuum on your motor the original Brawler power valve IMO is too small.

I’d wait to get some input from Jebby or some guys that know carbs better than me but I’d be looking at moving up to a 8.5 possibly 9.5 valve. In short the power valve is kinda like a third jet that lets fuel into the carb when vacuum falls below the rated number of inches IE a 8.5 valve adds fuel sooner than a 6.5 on accel/cruising. Conversely though you might need to change up your accelerator pump cam or squirters. The “lean pop” your hearing could actually be a rich pop of you have an exhaust leak. An AF meter would be helpful here.

 

Holley Tuning Specs:
Use Street
CFM 650
High Speed Air Bleed 28/28
Idle Air Bleed Size 70;70
Primary Main Jet 70
Primary Power Valve 6.5
Primary Pump Nozzle Size 31
Mechanical Secondary
Main Jet 74
Secondary Pump Nozzle Size 31

Kossuth may have a good point. A lean part throttle bog could be the power valve setting. My LT-1 idled at 10.5" vac so I ran a 6.5 " power valve. And that's the PV you have now. You probably need higher.

The way you can tune a power valve is with a vacuum gauge. You have one, so get a long hose and have it inside the car while driving.
Write down your vac level at cruise speed. Then very slowly push the throttle down more (to eliminate the accel pump effect) and see what happens as you near / hit 6.5 and the installed power valve opens. Lean bog? Sudden pickup at 6.5? Lean AFR? Lean at what vac level? Then try a a 9.5 and repeat. The power valve # should be set at least several inches below your cruise vac. And not kick in too easy, only on moderately aggressive acceleration, like 1/2 throttle. IIRC 3-4-5 below is usually a good spot. There should be no surge, or hiccup, it should be a smooth increase in power as the throttle goes down to 5" vac. If your cruise is up around 16-18" you may want to go higher like a 10.5 or more. To keep it from going too rich too soon, use an AFR, or lean it out by lowering the PV#, until you get a bog, and then go higher until the bog just goes away.

Once you get the slow-throttle PV set to where the engine likes it, then you move on to the fast throttle Accel pump tuning.

All Holleys seem to like to be tuned to your cam-engine combo. There are tuning techniques to check each circuit if needed: Idle screws, main jets, PV, and accel pump.

 

Ok, been awhile, but put a bunch of mileage on to see what's what. Lol. Pulled plugs, generally not to bad but some were a bit black with some carbon. 2 had a good amount of carbon build up on the plug tips, but still nice brown color. Rim of plugs or end of threads exposed on cylinder were black and a bit fuzzy so had carbon. Cleaned plugs real good, like new. Checked gapping, and the 2 bad plugs had lost there gap? Can't figure out how, unless maybe I banged the tips some how installing them. So re gapped all the plugs and opened them slightly to try to get more heat. Have a 40k coil so should be ok, I gapped to 37 instead of 35 so not much opening up. I then decide to check the timing again even though I went through all that in another thread, but because I changed the gaps I wanted to check. It was out if wack? How did it change without moving distributor? It was too high at total timing, and at base timing it was way high at 22! So I redid the total timing to 36 and base came down quite a bit to around 16. I was by myself do very difficult to hold throttle at 3000rpm and read and adjust gun. Keeping I mind I have that short water pump so have to get real low next to the alternator to even see the marks. So took awhile re checking several times to be sure it was at 36. Forgot to mention during testing I was making small mixture changes trying up reduce the high rpm deceleration popping. So it's a bit richer than totally leaned out were I had it. It's almost a full turn on all 4 screws, up from 1/2 - 3/4. So timed and bit rich probably I took it out for a good run. Before all this it ran good except for popping decel, which was worse with a/c on than not. Why, don't know. Lol. Some other stuff I noticed piling mileage on this last month is it would shudder when taking off, car would shake if I didn't get rpm up, and deceleration it would trailer hitch. Almost felt clutch related although clutch and transmission are all new. And on low rpm cruising in 4th gear and 3rd, maybe 1500 rpm there was a real slight miss but not every rotation of the distributor just a real small almost not there cough. Another reason I checked plugs for carbon. Ok up to date now the test run retimed and plugs cleaned up and gapped. Holy crap, it was super smooth, all popping gone on decel and trailer hitching gone, real smooth gear downs now. And taking off is smooth too, no shaking. Amazing change. Only thing now is if I stomp on it it bogs a bit then starts winding up. So think it's rich at 1 turn open. My vacuum there is down from 22 to 19-20, so I'm thinking today I'll put the vacuum gauge on and adjust it back leaned to 22 inches again. I'm thinking timing was the issue being too high and I should be able to lean it out. Quick note my fuel mileage is up as well. So I'm getting real close. Lol. Hoping it's still smooth and no popping after I lean it out too. Cross your fingers, I'm real close. I think the bit of carbon and black was timing too, so will check plugs again after some mileage to see if that improves. Don't seem to be burning as much oil either? Level has been stable since I adjusted timing. Odd since I think these heads need redo. Was getting a puff of blue from time to time if idling along time hot. But not driving or regular idling. Could that have been timing too? Crazy. Will post results of leaning test.

 

Not sure without reading through complete thread what distributor but one option is to remove one advance spring so you don't have to hit 3k for full advance. With a aftermarket coil. 045 gap is acceptable.

 

 

Alright. Put vacuum gauge on today to lean it a bit. Got fronts to 1/4 and rears to 1/2 turn open. I was surprised that the vacuum had dropped to 16 after retiming it and going plugs. After adjustment it was barely under 20, but that's as high as I could get it. If I rev it slightly it goes to 25 then drops off loses all as it should. Test drive and still no popping , and even smoother than yesterday. Still a slight big on the hit but not bad at all. Think I'm leaving it there for awhile , then I'll check plugs again for carbon. Think they'll probably be better . If not I'll open gap a bit more. And try that.

 

from your descriptions I would say a couple cylinders are Oil fouled.
I would run a hotter plug in those cyl's. ONLY the fouled cyl's.
take note those cyl's are worn and nothing but overhaul will fix.
unless the valve seals are the issue.
problem comes when cylinders allow too much oil and hotter plugs can't burn it off.
Like I told you many threads ago.
It is perfectly fine to have different heat range plugs in different cyl's.
nothing says all cyl's must have the same heat range.

 

Thanks for that. It's definitely the heads that are bad. When I first got it it would smoke pretty good for a few seconds every morning. Was definitely valve guides leaking over night soaking cylinders. I think those 2 were the worst. I Band-Aided it wth some positive valve seals and it greatly improved. But still burns about a litre per month, ish. Lol. Just trying to fix all this stuff then will probably rebuild it in near future. Finally got it running real good . We'll see how fouled the plugs are in a couple weeks testing it out. Been putting 20/50 in it for now, makes a huge difference in oil consumption. Motors tired. Can hear a bit of timing chain rattle too, so it's due. Actually torn which way you go. If I rebuild this motor I can do it myself. But I know a builder that will build me a high rpm 400ish hp 350 with aluminum head for 4500 Canadian. Cost me about 1000 to rebuild this one myself. Not sure which I'll do. Money will probably settle that one. I'll either have enough for the good motor or not. Just did my 351m so a bit tight right now. It was pricey being a rare motor and upgrading it to efi and bigger cam etc. Efi was expensive. Mainly the residuals like fuel tanks, pumps, filters ,lines etc. I actually have another efi set up for this motor(850cfm one) but didn't use it because I'm having a tough time learning how to tune them. Self learn is pretty basic. Anyway. Will do the plugs after I see what happens on these adjustments. Think I got it best it's gonna get.