As of right now timing is set at 18 btdc. I'll most likely bring it back a little bit so total isn't 40+ish. Didn't check it with a light today but day before yesterday I had the light on it to check things and timing is definitely advancing well. I had advanced timing the other day to see if that helped with the vacuum and got an extra inch by going to 18-19 degrees at idle (700-800 rpm.) Not exactly sure what you mean by internal carb or distributor?


I'm heading out of town with the kids this evening for a couple days. Won't be able to pursue this further until Thursday/Friday unfortunately. I'll double check the advance weights/springs then. It couldn't have anything to do with the choke could it? Graspin' at straws...

 

Internal to the carb would be possibly a gasket that is allowing vacuum to escape internally, but not suck in outside air, so starting fluid wont affect it.
Internal to the distributor would be anything under the cap. The vacuum advance, mechanical advance, etc.
Since it ran well, something has failed to drop the vacuum down this low. Does it bump up the vacuum when you rev the engine, and it drops off? Usually a good vacuum signal will be at it's highest as RPM's drop after revving the engine. If it's not coming up then, there's most likely some place it's leaking.

 

It does bump up the vacuum when I rev it. The video clip on the last page shows it doing that when I rev it. I only do it a couple times in the clip but you can clearly see the vacuum go to zero and then increase and slowly drop back down with revs. I'll stew over this the next couple days until we get back and I've got another chance to look at everything. The carb has 2 new gaskets as I'm using that AFR spacer also. They are both the square holed type. If I increase the idle, the vacuum goes up also but I don't want to idle at 2000 rpms again like last summer in order to achieve decent vacuum . I agree that it did show higher vacuum before so I'm assuming something is indeed not jivin' right now. Having it start, idle and run like it does though is making this tough to track down. I'll get a clip of the timing showing initial and it advancing when I get back. Out of curiosity would a vacuum can/reservoir help with other things besides just the brakes? Not suggesting I overlook the current issue but have been curious about that. I remember way back when we were talking about the cam I'm using (Lunati Streetmaster 295/295 .534/.534) and it was mentioned that I very well could end up needing some help getting the brakes to work. 3-4" is still too low, even with that cam obviously. Just wondered if people use those cans to help with other non-brake help?

 

I've tried vacuum can reservoirs on cars with low idle vacuum, and they only work if the vacuum is a little low. When I swapped cams in my SBC powered Austin, I dropped from 15"-16" of vacuum, to around 12" of vacuum. A friend gave me a reservoir, and it still didn't give me enough brakes to feel comfortable. I swapped to manual master to get things working well.
Just a thought, but I've had gaskets on carb spacers, or adapters that didn't cover the passage ways properly. They didn't leak to outside atmosphere, but didn't seal the base, and even though they worked great at first. Might consider carefully checking the gaskets now to see if they properly fit the carb's passages on the bottom. If they don't, you may need a different carb spacer/adapter, or a different base gasket.

 

I guess I shouldn't be assuming anything as I still can't find what's causing this low vacuum, but I don't think it's the gaskets on the carb. They are both the square hole pattern and both fit well. I've had about 4 different sets of new gaskets on there with having to swap carbs so many times. I won't rule out that possibility but would rather not pull the carb back off there again yet just to check if they're covering passages. I'm going to at least take another video clip to show the vacuum gauge and how it seems to do what it should when I rev it and WOT how it goes to zero, rises and then comes back, but comes back to 3". I'll put the timing light back on it again too so I can show it advancing. I had asked about the possibility of the choke possibly causing this issue "grasping at straws" before and the reason why is that the only thing that I've noticed to be different since the low vacuum started was the fast idle doesn't seem to be working when I start the engine anymore. The adjustment screw is set properly and I've verified the choke opening up after running for a few minutes but no fast idle at initial start up. I'll try to get that on video also. I am completely unsure what's going on still but really feel like it has something to do with the carb. The second brand new one.


Appreciate the insight on the reservoirs, I don't want to get one if it won't help that much.

 

Sorry I never posted the clip that I said I'd post. I did check everything that I was talking about however. Vacuum gauge shows that aside from the low reading, when I rev the engine the pointer drops to zero, rises and slowly comes back. I put the timing light back on and checked that it was advancing. One thing I found however was that there doesn't seem to be 24 degrees of mechanical built into the distributor as stated by the manufacturer. From what I saw several times, there's 17-18 degrees of mechanical built in. I moved the initial back down to 15 btdc and it stopped advancing at 32-33 degrees. I advanced timing to 17 degrees and it stopped advancing at 36 degrees. Timing is all in by 2800 rpms. I bumped the idle up to 950 rpms and vacuum gauge reads 5" hg now. At this point, I really don't know what else to check. Engine runs really well. I drove about 5-6 miles this evening and it ran beautiful. Only issue still is WOT but I really didn't even try that this evening so who knows? I'm heading out of town until Friday again this week but when I get back I think I'll get the trans filter changed now since it's got a tiny leak around one of the pan bolts. I had used synthetic fluid initially but I don't like that stuff. Smells god-awful and I also read somewhere that synthetic is not recommended for the th350s. Don't have an informed opinion either way but I'm going to use type f this time around. That shouldn't cause any issues if I don't get all the synthetic fluid out, which I most definitely won't will it? I'm not a fan of opinion pieces about what to use and what not but I saw several different people saying they run type f in their th350s as it is a bit stickier fluid. My trans seems to be working superb, which I'm extremely proud to report but I don't want to cause any problems going forward either. I know that's sort of out of left field and not specific to what I've been discussing on here but thought I'd at least ask. I'll still try and get a video clip showing the vacuum gauge and timing, but need another set of hands here in order to do that.


Some good news - I now have all my gauges functioning! Not so sure how accurate the fuel gauge is since it had at least 3-4 gallons in the tank before and never actually showed a reading. I put another 6-7 gallons in there this evening and the gauge moved to just under half a tank. Maybe I needed to get the level up higher before the float moved? Suppose it wouldn't be that bad to have a few gallons left when the gauge shows almost empty. Unintended safeguard, that's fine with me. Also, temp gauge (with fan on) hasn't gone above 180 with a bunch of idle time today and then the drive. Some good news at least!

 

The gas gauge will rarely show anything below 3-4 gallons, as that's your "reserve" once the gauge reads empty. Same on the full side. It reads full for a long time before it starts to drop off the mark.
Type F trans fluid is not recommended for TH350, or any GM automatic trans. You'll need a fluid that says it's specifically for a GM trans. Some are multi use, and work on Ford or Chevy. Most makers have gone to Dexron VI now, but used to be Dexron II or III.
https://en.wikipedia.org/wiki/DEXRON

 

Ever hear of B&M Trick Shift fluid, that "makes the clutches grab better and helps prevent slipping"? Word on the street has always been that it's little more than a Type F fluid by a different color. Why, even in their own description of the Dexron formula... "meets and exceeds Type F requirements": http://www.summitracing.com/parts/bmm-80259.
With that said though, I would go with B&M. But then, I'm more of a blue color person!

 

I understand type F is not exactly recommended for GM transmissions. Just like Dexron isn't recommended for Ford's. Suppose this is all moot now anyway, the type F is already in there. Only half of the fluid drained out as expected so it's not entirely a non recommended fluid. I know there are a lot of people using type F in their TH350's so I'm not terribly concerned about it. Chuck, I had a few guys tell me the same thing about Trick Shift being Type F also. Another guy swore by using Type F and said over 20 years of using it has created no problems in his TH350's. Guess I'd rather use that than these newer fluids that are "universal" as that tells me there can't be that much of a difference between them.

 

If you search online, there are a lot of guys using type F with no issues. And true, you don't want to use Dexron in a trans that requires type F, the switch doesn't go both ways.