[Teej]

Yep, accelerator pump had a torn rubber seal. (light blue) Replaced that. Get good spray now. But it definitely stumbles off idle. Idles nice at 700, but as I tip in, at say 1000 rpm, it definitely stumbles.

[Tom Vaught]

If you get a good spray from the Accelerator Pump (when the engine is OFF) then you will get the same spray when the engine is running as the Accelerator Pump is a mechanical device hooked to the throttle and does not care if the engine is off or on. You are talking a MINIMAL throttle change here.

Take the center carb off, take the base off. spray some carb cleaner in the progression holes in the bores of the carb (where the throttle blade moves upward under tip-in modes.

Tom V.

[Teej]

Tom,
Yep, I watched the spray off first. I think the accelerator pump is working correctly now. it sprays pretty much immediately.

But after that spray, I was watching down the bore of the carb and it looked like gas was dripping out of the venturies as I held the throttle open just slightly. After the spray was done, trying to hold it at about 1000 or 1100 rpm. Just seemed like more gas than I would have guessed.

I'll try spraying some cleaner in those progression holes next time I have the carb off. Which, given my latest trials, should be in the next day or so..

[Tom Vaught]

Dripping Nozzles says fuel level a bit high, if off idle.

Tom V.

[Teej]

With all the on/off I've been doing of the carb lid, the idea that my float got bumped or is out of whack is definitely possible. I'll check that next time it's off.

Another member had suggested that my off idle stumble could have been by actually a lean condition. He suggested I back out my idle screws a turn and see if that helps. At about the half way mark on my drive to work, I pulled over and backed them out about a turn. My low speed low rpm cruise (35 mph, 1200rmp) had been a little hesitating and seemed to be better.

Then in the parking lot I sat and watched my AFR. At idle, it was now reading rich (12) at about 600 rpm since I had backed out the screws. As I increased the RPM slowly, I saw that the AFR went consistently lean from about 800-1800 rpm. I tried to hold it at about each couple hundred rpm increase and the AFR was reading about 17 to 19 till i got to about 2000, at which point it kind of broke over and dropped back to 12-13.

Can I use that data? Does the unloaded engine AFR differ significantly from driving AFR at the same RPM?

[Teej]

Couple more things... First off I tested my AFR meter on a new car in our parking lot. It read a solid 14.5 at idle, so based on that I'm going to have to say my meter is reading correctly.

Again I watched and at idle it was rich (12) and as I increased the rpm it went lean (17-19) from about 1000 rpm to about 2000 rpm and it went back to rich. The stumble I was seeing at 1000 earlier is gone, likely due to the increase from the idle screws. Cruise is still rich at about 12.8 at 2500+ rpm Cruise at 2000 rpm is about 13.2.

I have not yet adjusted the float level.

[Kenth]

I think you´ll have to return to square one and start over.

I see a carb put together with incorrect parts and that someone tried to cure a lean idle condition by putting in larger than needed main jets.
Main jet sizes does NOTHING to cure a lean idle condition, larger idle tube restriction does.

Clean the carb good, put the carb together, with the correct parts, and adjust the float level by the book.
If needed open the idle tubes from .035" to .038", idle channel restrictions from .044" to .047" and the idle mixture screw holes from .046" to .070".
This would result in a strong idle and smooth transtition to lowspeed w/o any nozzle drip to ruin the mixture at idle.

[Teej]

I'm not sure I'd say that it's put together with "incorrect" parts, but I will admit that in chasing the issue that things have been swapped around. If you have a list of what's "correct" or what I should change I'm willing to try anything. Both carbs that I've been working with were set up very closely to each other and I was simply trying to identify what area needed work. Both are very clean having been serviced within the past year or so.

The jets were initially changed (by me) to try to help a higher speed cruise stumble. (60mph, 2600 rpm) That was before I dug out my AFR meter and removed the outer carbs. Then after finding it running rich, they were swapped out to try to lean it out. I think I can dial in on those after I get rest going.

I checked the idle tubes and didn't have an .038 pin gauge but they are bigger than .035 and smaller than .040.

Channel restrictions? Not sure exactly what you mean by that. Is that the main well tubes on the venturi cluster? Those obviously have numerous holes in them and they vary in size on the cluster I took out of the carb. (2 larger holes on the bottom/side are .054 smaller holes further up are .040)

i have not measured the idle mix screw holes. Are you talking on the bore side, the idle discharge holes? From the diagram in the link below, it shows three holes. (fig 6b-33) Which hole(s) are you saying should be enlarged?

[Teej]

Different day, same results.

Took it apart again, swapping back to the first carb body. Pulled the accelerator discharge valve ball and spring and everything looked great. Ball was shiny and looked brand new. The seat at the bottom looked smooth and had a very uniform wear pattern that should make for a great seal. I even stretched out the spring slightly just in case it was weak. But it's such a weak spring anyway, I can't imagine that would really matter.

Also checked the float height. According to my paperwork, the center carb said it was supposed to be 1-9/32 Which seemed huge to me and angles the float significantly. If that's accurate, mine was set quite a bit higher.

It's all kind of a moot point anyway though as it still runs rich at cruise. Maybe a slight bit better, but still around 11.5. I can get the idle where I want it, and now it doesn't stumble from the 1000-2000 like it did when I rev it in place. But WOT is also still way rich..10.3. Jets are back to #57.

Checked the idle mix screw holes in the base plate and they were clear. But there is a small groove that goes through all of them. Very shallow, but very precise and obviously intentionally machined. I wouldn't think this is affecting the cruise AFR, but figured I'd mention it. I do not have a spare base plate I've got confidence in to swap out.

Anybody have any other ideas?

[carbking]

At this point in time, it would be interesting to simply install an unmolested original carburetor to see what happens.

No way is a correct carburetor with correct parts and proper adjustment running rich with #57 main jets. Should be so lean the engine is overheating, unless you live at 15,000 feet!

Jon.

[Tom Vaught]

Originally Posted by Teej

Also checked the float height. According to my paperwork, the center carb said it was supposed to be 1-9/32 Which seemed huge to me and angles the float significantly. If that's accurate, mine was set quite a bit higher.

Anybody have any other ideas?

Confused by your post here.

Attached proper way to set float height and float drop on a Rochester.

You set float height with the air horn lid upside down. Float Height is the pic on the left.

Tom V.

[Teej]

Tom,

That is how I interpreted it as well. And the paperwork in the rebuild kit I had said the float height for a 57/58 was supposed to be 1-9/32. (Picture on the left) Which seemed very large to me. That made my float up higher on the left hand side (of above left picture), instead of the somewhat level look it shows.

I just did a search and from the pontiactripower website shows this:

"Typically, the end carbs are set at 23/32" from carb airhorn gasket to seam on brass float, with 1 24/32" drop. Center carbs are 21/32" and same drop, 1 24/32" These measurements are slightly different from factory specs. However, they will result in a bit less fuel in the bowls at all times. I prefer this as it keeps fuel away from the airhorn gaskets and reduces seepage."

This is more of probably what it WAS before I adjusted it. (Darn it.) So if the above is true, it's way high (low fuel level) now. That's kind of what I thought, and I should have double checked, but my thought was, if it's way high (1-9/32 ) then that should definitely stop any fuel drip issues if it was the float level.

[Teej]

Yeah, I'm out of ideas as well. And nope, not at 15,000 feet. More like a foot and a half here in FL.

Obviously I'd like to figure this out from the perspective of how my car was running, but I also like figuring things out to learn how they work. I've definitely learned a lot about my carbs lately and am good at taking them on/off/apart. I just know there's got to be something simple we're missing. Or some detail I've considered inconsequential and not mentioned.

[Tom Vaught]

Set the float level to 21/32 inches or .656" from the gasket to the seam on the float.

The rebuild number is WRONG!

Tom V.

[Kenth]

What needs to be understood here is that the float level adjustment/check is measured from gasket to the top of the upsidedown airhorn/float.
"Gauge from top of float to airhorn gasket"
The specs 1 9/32 is correct for 1957-8 tripower center carbs.

Also, on float drop adjustment: "measure specified distance from gasket surface to bottom of float".

[Tom Vaught]

Not a 57-58 expert just go by info I use that works. I am assuming they used a brass seamed float in 1957-58 Kenth?

Makes sense now. Thanks

Tom V.

[Teej]

Well, that would explain the confusion on the float height. I most likely made the assumption that it was measured to the float seam as that is what I've been familiar with. I'll check the literature again but I'll bet that's right.

OK, first of all, thank you for all the input and thoughts that everybody has had. I know this has been long and probably a bit trying...

Next, maybe I need a little clarification here. I've been saying that it's running rich during cruise. Is that too vague? What's "cruise"? I'm sure that differs based on all kinds of things. I'm running a 4 spd and a 3.23 rear with 15" tires. So "cruise" for me is about 2500 RPM and about 55 mph. (This is where my AFR is mid 11) If I get into 4th gear early through town, say 40 mph and my RPM is 1300 my AFR comes up two points. Mid 13 call it. She's still not smooth, but I'm just trying to make sure that I'm not making some assumption (like measuring the float at the seam) and that's throwing the whole testing off.

My last thing is that I'm going to replace the coil. It's the last part of the ignition system I haven't changed. I hooked up a relay to the distributor feed so that I get a full battery voltage at cranking and on run.

[mgarblik]

I have been following this thread and all the changes you have gone through. To help define cruise rather than use road speed and RPM only, could you tell us what the manifold vacuum is during this period of rich operation. At my school, we define "cruise" as engine operation between 12 and 17" of mercury. Still a rather wide range. Good luck figuring this out, you will get it.

[Teej]

Mgarblik,

While I don't have an exact number, I do know that it was definitely still in the green section of a Pontiac console vacuum gauge during cruise. At idle it says it's close to 24, but I put a T in there and another gauge I had was about 21. So I'd say that at cruise it's probably reading about 19. Might be an actual 15. I'll double check on the drive home.

[mgarblik]

That's a huge vacuum number. Not a problem, but indicates a very sealed-up engine and a very mild camshaft. Typical idle vacuum is 17-21 " . Generally don't see vacuum over 21" except during deceleration. May not tell us much, but another piece of the puzzle. I will say you have some absolute experts helping you on this thread.