Non Mopar carburetor opinion

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This one is a factory 630 AVS off a 440. I actually put it on yesterday and could not get it to idle. So I slapped the Holley back on. I took the AVS apart tonight and double checked everything, blew it out real good...again and ran wire through everywhere.

Then I saw what I believe was the problem. It's called dumbass. I had the choke pull off plugged into the ported vacuum inlet for the distributor. So that means I had the distributor on manifold vacuum, but the distributor is timed on ported, so I probably had 50* of initial timing at idle. LOL

In my defense, it is probably been 15 years since I have messed with an AVS, but I should have paid closer attention to the fact that the port I plugged the choke pull of into was above the throttle plates. LOL

I am gonna try it again tomorrow and see what happens. Worst case is I will have an AVS doorstop.
 
This post is not to Rusty;
Some guys can tune carbs and some guys cant. I have never encountered a street carb I couldn not make work. I almost dont care how grungy, beat up, wore out, mismatched, whatever. Thats not to say Im a brilliant tuner. Just that I subscribe to the 3Ps; patience, persistence, and perseverance.With those 3 and a modicum of knowledge a guy can go far.
And that applies to almost anything. Just look around and see how many guys right here on FABO, who, with limited skills to start with,have, or are in the process of, turning out fabulous projects.
And I dont mean to imply that YOU cant tune a carb.Just that you mighta gave up a little early.
That Holley 750 can be made to run on almost anything with more than 5 cylinders, or 5 liters. Sure it runs better on more and bigger. I wouldnt argue that.But I am 100% positive it could be made to work on a 390.Those carbs are not rocket science, and they are very well,no, extremely well, supported by the aftermarket.
And Oldmopardude I dont mean to come down on you in particular, Its just that this keeps coming up over and over.A guy replaces one brand with another and gets good results, then disses the carb he took off.All the while, very likely with the 3P system, the first carb coulda worked just fine. And no Im not loyal to any one brand. I have my favorites, thats true.But Ill tune anything.Including; lawnNgarden stuff,chainsaws,marine, automotive, motorcycle, snowmobile, just about anything sub-8 liters.
End of rant. I feel better now. Wheres my pills?What does Rusty say? Oh yeah; Drive through.
 
That's "Thank you drive through." you must be polite.
 
Well I can hardly wait to see how this plays out. Im a little confused though cause you mentioned the timing as up to 22* IIRC. It seems to me you woulda noticed the change in idle speed when you reconnected that dist.hose? No matter. I will wait.

Right; Thank you,drive through. My apologies.
 
It would not idle at all with the AVS. I am assuming because it had way too much advance at idle.
 
I dont suppose you tried running the AVS, with the vacuum advance disconnected, then?
I guess, what Im getting at is this; Perhaps the AVS not idleing was for a different reason than the Holley?I guess we will see.
Also, I dont know about yours, but I have seen one AVS with what looks like a a 3rd mixture screw. It sits dead center between the other 2 and about 3/4 of an inch higher then them. I only ever saw one of those and dont recall what it was off or what it was for.It might have been an idle air bypass or a hot-idle compensator. So if you have one of those, set all three of them to 2 turns out for a start,then take it from there. I think actually that third one was baselined at 1/2 Turn out. I have no idea why I would remember something like that!
Sync up your transfer slots, and bring the timing down to get a nice idle speed, then fine tune it.Some engines like the fuel level tweaked to fine tune the idle pull-over. But I think the AVS is pretty good stock.......... All the best 2U.
I gotta go install a hardwood floor in the dining room tomorrow, but I ll check back in the afternoon and see how youre doing.
 
AJ/FormS said:
I dont suppose you tried running the AVS, with the vacuum advance disconnected, then?
Click to expand...

No, because my dumbass assumed it was hooked to the correct port.
 
How'd those slots look when you flipped it over?
Nice post AJ. I couldn't say it any better.
I know that you wouldn't likely overlook this Rob, but hoping the plates aren't drilled
causing this.
 
No the plates are not drilled. I was kinda in a hurry when I did the swap because I didn't need the truck down long. I will take more time and pay attention to detail when I try it again. I will keep yall posted. Thanks.
 
RRR,

Not bad call on the CR. Nominally, Ford called it an 8.0:1 CR.

The 351C-2V and the 351M used very similar small passage heads. The situation on this motor sounds a lot like the 318. It is easy to over-cam and over-carb. Since the M motors are so similar to each other and to the Cleveland engine, suggest considering a 351C-4V heads for the 400 in order to avoid the same situation on your build up.
 
2 Darts said:
RRR,

Not bad call on the CR. Nominally, Ford called it an 8.0:1 CR.

The 351C-2V and the 351M used very similar small passage heads. The situation on this motor sounds a lot like the 318. It is easy to over-cam and over-carb. Since the M motors are so similar to each other and to the Cleveland engine, suggest considering a 351C-4V heads for the 400 in order to avoid the same situation on your build up.
Click to expand...

I had thought of that.......and might. The 4V heads though will require intake spacers since they came on the Cleveland only. Since there was no 4V 351M or 400, there was no 4V intake for them. They are similar to the 440 in that the 351M and 400 are tall deck engines and the Cleveland was a short deck, so to use the 4V heads on the 400, the spacers are required.

That said, I would never in a million years use the upper RPM HP those heads are capable of. Plus, the 70-74 Cleveland 2V heads have much greater velocity in the lower RPM range as the 4V. Also, the 351M and 400 heads have a terrible bump in the roof of the exhaust port. The heads are drilled all the way the entire length with a thermactor passage, so the bumps were required. I had planned on the early 2V heads for the 400. I think they will actually be better suited for the low RPM torque I am looking for with the truck. They do not have the thermactor bump and flow very good.
 
A few things:

1. Not trying to piss off the above poster, but 4V Cleveland heads are the worst choice possible for a truck. The ports are huge and designed for an engine in a light car that can make use of high-rpm power. That is NOT what you need in a heavy truck.

You want torque bias toward the low end instead of sheer horsepower numbers. A lot of people have only a faint grasp of horsepower, torque and seat of the pants feel.

We had a '73 2wd F150 with a 351C and 4-speed. No, I didn't mis-type C. How that engine got out of a car into that truck who knows, but it was the biggest Tee You Are Dee that ever lived. No bottom end, everyone hated driving it.

2. I have one of those 4175's that I've never used. I was GOING to, but I came to realize that for a Holley it has a few shortcomings that I feel limit it's viability on a modified engine. I'm pretty sure it has a weird dual-stage power valve, and you can't adjust the floats externally.

That carb is a OEM-caliber replacement for Quadrajets and Thermoquads...each of which I feel is a better carb than the Holley.

I'm rather confused where you say "will the 750 drown it?" Which 750??

3. Ford engines of that era came with either Motorcraft 4350 spreadbore which maybe 3 people in the country are willing to work on, or 4160 square bore Hollies. I just a sold a Ford Holley 600 cfm core.

4. This is just an observation, but why on earth are you planning to build an engine only 50 cubes larger? I have nothing against Cleveland engines, but they are just not powerhouses and the work put into one can be put into a 460 for the same or less money. 385-series engines are much more plentiful and easy to buy parts for.

5. The questions about CFM requirements are just going to produce guesses and loose recommendations. To actually size and jet a carb for a particular engine takes some formula work and then reading plugs afterward.

[ame="https://www.youtube.com/watch?v=CNOZFFl9Ss8"]70 year old grandpa does huge burnout in Lincoln 460 - YouTube[/ame]
 
The Street Demon 750. I said it by name in the original post.

And I completely agree with your 4V head assessment. Read my post above yours.
 
Ok. We have an update. I put the AVS back on a little while ago. It runs, but not well. It will not idle below I would guess around 1500-1700 RPM with the idle screw backed all the way out. Bad hesitation. If I close the choke about 3/4 closed, it will not hesitate. It also cleans up the "idle" a little. Also, the air mixture screws DO make a difference. It runs best with them back out to the point of falling out. They will slow the idle speed noticeably the more I turn them in. So, all that says to me BAD vacuum leak.

Got some brake cleaner out and sprayed all around the base and got no change at all, so I am assuming it is internal. I left it on for now.

I also looked at the Holley. The transition slots are showing only a little. Looks like they are about right. So, I would guess it may not have a blown power valve, because I would think it would need more air to idle properly and it idles pretty good. Maybe a little opening the secondary side will fix it. They appear to be closed all the way, with no noticeable gap in the bores.

Any ideas on the AVS? I have had the top off three times now double checking everything. It will probably be something stupid I overlooked. Keep in mind as I said, it's been a good while since I had one on the bench. Thanks yall.
 
Put the Holley back on after I cracked the secondaries very slightly. It still will not adjust with the air screws the right way. Same as before. But now it won't idle down far enough. Gonna yank it off tomorrow and turn the secondaries back down and replace the power valve.
 
I think I found the problem with the AVS. I took the top back off. It has a hot idle compensator valve on the secondary side. The purpose is when the engine gets really hot, say for instance sitting in traffic a long time, it opens up and allows a small controlled vacuum leak to help keep the engine from stalling.

However, somehow, it was bent so that it was open all the time by a pretty good bit. The passage it covers goes straight through the carburetor body and exits below the secondary throttle plates, so it WAS a direct manifold vacuum leak. I removed the valve and crap canned it. Drilled the passage out to 1/8 pipe and I will go into town later and get a pipe plug and plug it off. We'll see.

They were problematic to begin with. Not all of the AVS carburetors came with them so I don't feel bad about wasting it.
 
Ok. More update. Got the power valve out of the Holley. I can see a "5" on it but that's all. I got a Holley brand 6.5 power valve and the spring on it is very strong compared to the power valve I removed, so they are definitely different. Perhaps the power valve was coming open at idle a little. Anyway, I have swapped around carburetors till I am sick of it for now. My back hurts and I am takin a break from it. I might try the AVS one more time but if it does not work this time, it's goin in the scrap pile. lol I know the Holley will work.
 
Well, I see you have been busy. Looks like youre making good progress though. Pretty soon you will have 2 good carbs.Sorry about the,tired,hurting,back.Looks like you were up most of the night. Is that normal for you?
 
Well despite my back, I put the Holley back on. Tired of the AVS. Even though I plugged the hot idle compensator and it WAS leaking vacuum, if I put it on one more time and it did not work, I would have beat it to pieces.

Even with the new power valve, the Holley runs the same. I did try cracking the secondaries open. That made no change in the air screw adjustment but it made it run worse so I closed them back up. It runs good, just not as good as I would like. I will live with it for now.

I do appreciate all the suggestions.
 
Yeah, no biggie. It's rare I have trouble with them, but when I do, it's usually mine. LOL I have enough parts to Frankenstein at least 3 or 4 Holley 600s and those are usually pretty good. They won't get the mileage that this 4175 or the AVS will get, but they'll run good.
 
Ok. See what you think about this. This is the hot idle compensator. It is supposed to be closed as the default position. You can see the two outer holes are the mounting holes where the screws hold it on. The center hole is the passage for the "controlled vacuum leak".

The theory was that when sitting in traffic and the engine got really hot that the bi metal spring would push the valve open and allow the mixture to be leaned out to keep the engine from stumbling.

Now, that center opening is about 1/4" in diameter and mated with a similar size opening that ran down and exited under the secondary throttle plates. As you can see, the valve is obviously bent open. I tried to get pictures from an angle so you could see that pretty much the entire opening is exposed. I think 1/4" hole of a vacuum leak would account for the AVS not working properly.

I don't think the valve was designed to be opened but only a crack and it is clearly much more open than that. That's why I drilled and tapped the opening and plugged it. I will try once more with the AVS and see, because if I can get it to work, IMO it will be far superior to the 4175.

So what do you think? You think that's a big enough vacuum leak to keep the idle speed around 1500?

I do.
 

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I agree, and then some. Thats a big hole. Ive never actually seen one open.
But heres what I dont understand; All that extra air should have made it stall.Kinda like when you pull the PCV hose off. Unless it was also getting an appropriate amount of fuel from somewhere. In theory, to compensate for that extra air, you would have to close down the curb idle screw, which would have shut the transfers off, and possibly the idleports as well. With the blades that far closed, theres no way the mains could flow. So how was the engine continuing to run? and at 1500 yet? Hmmm,thats a poser.

Speaking of 600s; yeah I figured out a way to lean those low speed circuits out some. With a 223* cam, and O/D, I got my 360 to go 36mpgUS, on a 12 hour trip to Car Craft Nationals in 2004. It was pretty bush-league though. I popped the brass plugs out of the top of the low-speed wells and found a couple of perfectly sized rubber plugs to fit in there.Then I just started sticking very fine wires into those orifices.I bent the tops of the wires over at a 90*, so I could fish them out of there as was required from time to time.I had a selection of different wire sizes. Yup, bush-league tuning. Cant argue with the results though. Couldnt drive it around town that way though, until I compensated with a loose PV. That was strictly for the trip. When I got to my destination, I slapped the 750DP back on for the weekend. Now yer talkin. Yeh,those were the days....

The AVS has metering rods. Way easier to do the same trick. 3-step rods yet.Wonder why they didnt make them tapered, like motorcycle manufacturers did/do? Hmm.... I just had an idea.
 
It did stall until I backed the air screws all the way to like two threads holding them in. Then it "idled" at around 1500. lol
 
Well it's over for the AVS. It's officially in the scrap barrel.
 
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