Discussion in 'Small Block Tech' started by buicks, Aug 22, 2013.
Drive it like you stole it then let us know fingers crossed
Well there is some improvement but not alot. I'm thinking the secondary air/fuel could still be an issue.
Revisiting this question, the sun was out and low in the sky today, while I was jamming the throttle from a stop I watched out the back window and their is some black smoke, I wouldn't say a lot. There also is what could be described as popping which could be backfire in intake?
ok is the back fire new. I've been following along the best I could today and see that you've changed 2 things I know you've been checking a lot of stuff but so far just adjusted timing and mixture screws. From when Larry stared talking you through the timing process and where your timing is now (Just base timing) don't even care for what the number is right now is the Dist. as we speak/write more advanced, retarded, or same place Just thinking out load but when you had the light on it was the timing mark steady, it wasn't jumping back and forth. just making sure there no play in your Dist. shaft. when you get some time pull some plugs like (Shoot I forget his name the ex GM tech now a ford tech sorry man)
Id say the pop did happen sometimes before, I don't think the timing change made it happen or get worse.
The thing about it is its not always the same. While I was out driving I took the secondary pulloff off the carb and adjusted the alan screw counter clockwise a bit because I thought black smoke meant the secondary flaps were opening too slow. It seemed to help a little. So I braked to a stop and accelerated hard a few times, the bog was still there. I will pull a plug and see what it looks like.
So as I under stand it right now your base number is 0 or close to it and you have the vacuum advance to manifold vacuum just checking because I know you were running it to ported before. You now by now that anything is possible so this carb could have been dropped during shipping rattled while upside down who knows. How much if any do you drive this car. Like in the past 2 years having this problem has it become worse stayed the same ???
The spark plug gap is 40 or 41.
Almost looks like an unused plug.
Here are some pics of a plug. Sorry low quality My wife took the good camera with her this weekend.
---------- Post added at 07:05 PM ---------- Previous post was at 07:03 PM ----------
Right now I have the vacuum advance plugged. This problem has been the same forever, before and after rebuild. I drive the car during summer for fun, I have driven 300 miles to a show, all is fine unless I floor it while barely moving.
Timing with no vacuumhooked to dist, is 1.3 adv at idle and 32 adv at 2500. Lightest springs (yellow).
The 2nd pic looks a little carbon fouled. Pull them all. plug that advance in to manifold vacuum. I think you misunderstood Larry when he said not to worry about the advance right now he meant during the timing adjustment when you plug it back in it might have a little to much total advance maybe ping maybe not. He did tell you about limiting the amount from the can using a stop. (Larry if I'm wrong I'm sorry I don't want to be putting words in your mouth) but if you going to drive it around before making that fix plug it back in
---------- Post added at 06:26 PM ---------- Previous post was at 06:07 PM ----------
Is it just me or does any one else look at the data and say it don't add up. Basically TDC base timing no vacuum advance 500 + - idle and (19 in vacuum) is this a 14:1 engine . Just kidding
The 2 pics are the same plug, theres really nothing but metal on the points.
He did show me where to look to drill a hole and limit the vacuum advance with the crane can. But it looks like I would have to pull the distributor to get it out to drill and put a small bolt and nut on? I did understand him to say I don't need the vacuum advance. Also that if I hooked it up now without a limiter I would get too much timing. But maybe he will chime in.
Your looking at the plugs live and in person but from were I'm sitting the 2nd pic looks dark and sooty could be the lighting the angle. The electrode looks blurry but dark to me. Now I agree your totally right the 1st. pic looks new & clean. The advance can comes out without pulling the Dist.
Yes I did say not to use it until you limit it. It will provide too much advance with your quick mechanical advance. I guess you missed my question about the APT. Cliff builds later model Q-jets with the adjustable part throttle feature. It allows you to dial in the part throttle mixture. BTW, the secondary pull off has nothing to do with anything but the choke. You can adjust it all you want, but it won't affect your performance. Why don't you contact Cliff and ask him about this carburetor? He has a question and answer forum on his website.
APT? My response was this isn't a later model carb. Or shouldn't be, its the one I sent him. I can get the carb number if youd like it.
By "secondary pulloff" (maybe I said it wrong?) I mean the white plastic one that does control how fast the secondary flaps open.
I would have thought one that controls choke would be called a choke pulloff but who knows.
The white plastic one(the primary choke pull off) does control the choke and the secondary air valves. Some carbs have a secondary rear pull off. That is what I thought you were referring to.
I would have called Cliff long ago if I was you
I would like to know the carburetor number
You are right buicks My bad. The posts come so fast it seems as soon as I go to post the conversation has moved back and forth so much It's hard to keep up. I think I might have even responded to my own ? and found out both of me were wrong I'll try my best to double check what has been discussed before I jump in
The carb number is
7041544 and farther over it says IH 1621
Even the early carbs have APT, but it isn't easily accessible. Call Cliff and ask him about it.
I went for another run, the way it is now, the problem is still there, but I have to floor it harder to make it happen.
***I would say we have improved things. Thanks a bunch for that!***
I can at least break the tires loose easy without boggin it. I just have to NOT floor it all the way.
Maybe with some vaccum adv timing, limited to 8, I can get even better low end power.
Some things that may be related. Or just obervations:
When floored should the secondaries round butterflies down inside the carb be vertical? I set a heavy item on the pedal and looked down in, and they do get vertical when the pedal is all the way down. (I know the top flaps only open with air suction and are resisted by the spring and choke pulloff.)
I set up the crane adjustable vacuum advance, hooked up to manifold vacuum, the advance is blocked at approx 1/16" allowed movement.
I rechecked the timing with the light.
Its showing I have 12.5 degrees advanced at 650 rpm, and 38 degrees advanced at 2500 rpm.
Though the initial is more than I expected, this all seems to still fall in a desirable range.
I checked the vacuum again and it is 19. I did notice if I revved up the motor the vacuum took dive before it rose, unless I revved it up slowly, is that normal?
Yes, that is fine. Manifold vacuum indicates engine load. The engine is pulling outside air through almost closed throttle blades, so vacuum is developed. When you open the throttle suddenly, the pressure equalizes inside the intake, dropping the vacuum. When you are driving the car and punch the gas, vacuum drops, and the advance from the canister goes away leaving initial + mechanical. That is what you want. When you are at a steady cruise, the vacuum will be high, and you will have the added advance from the canister. This is all BASIC auto mechanics.