When I unplug the distributor, am I to put a plug in the carb port or on the distributor vacuum advance?
To all those who've shed some input to this thread I say thank you sincerely! Larry, I followed your directions step by step and the car is a totally different animal now. It actually chirped second gear. That's a huge milestone for what I once considered a lame duck 350. Talk about a foot in the mouth! Lol. Seriously guys, I appreciate the time u took to help me get it right. Heading to the auto skills center on post to do the can swap tomorrow with a smile on my face! I'm sure it'll really wake up w the 284!
I got the cam installed and broke in, and when I went to powertime the car again it just didn't perform like I thought it should. The lopey idle is nice and the butt dyno did notice a slight bump but I don't feel like I have the timing right. I replaced the cap and rotor as well as the wires and plugs(gapped .50, too much?). The car has the pertronix conversion and flamethrower coil. Went with msd street fire 8mm wires so I figured the increase in gap was warranted. I tried several different adjustments on the carb idle mixture screws bc it seemed like I was too rich (thick gas smell at idle). Tried manifold and ported vacuum. The car Idled better in park with manifold but I had to have the idle mixture screws too rich to sustain idle in gear(1k park/750 drive). So here's the questions-with the aftermarket setup I have, is ported or manifold better? Next, with the powertime complete, I'm at 20* advanced at idle. Seems way higher than any other post I've read. Issue or no? Lastly, is this Holley 750 too much carb? I still have the stock Rochester but the back butterflies don't open. Better to keep the Holley 750 or have everyday performance rebuild my 650 qjet?
First, if the springs in the distributor are too light, you will have some of the mechanical advance in at idle speeds. If you have the original distributor in your 350, it only has about 16* of mechanical advance. To get the total up to 32*, your initial timing will be up around 16*. idling out of gear at 1000 RPM, you probably have some mechanical advance in, so 20* isn't out of the question. Nothing wrong with that as long as you have no problem cranking the engine to start when it is warm. When you put the transmission in gear, you lose some mechanical advance, so there is a bigger RPM drop. Sometimes stiffer springs give a more stable idle, and less RPM drop. With the Pertronix, i wouldn't go above .040 plug gap. Whenever you change a cam, you bump the power range up. you gain the ability of the engine to breathe at higher RPM, where it can make more HP. You also lose some bottom end, hence the lopey idle. A smaller engine will be affected by a cam, more than a bigger engine. the same cam will be milder in a 455, than it is in a 350. It's very common for guys to think that bigger is always better, so they over cam an engine. Fact is, for a street driven car, smaller is better. You may need to change the torque converter, and/or gears to complement the cam. You may also need to re jet the carburetor. 750 CFM is not too big. The factory Q-jet was 750 CFM. the Q-jet uses air valves up top on the secondary side. If you are expecting to see those open when the gas pedal is floored, you won't. The secondary air valves only open when the engine actually needs the air flow. The secondary throttle blades should always open when floored, as long as you have the correct throttle cable. It's easy to check this with an assistant. With the engine off, have someone push the gas pedal to the floor, while you push the air valves open, and check to see if the throttle blades are fully open. Ported or manifold? try both, see which choice feels better. If you chose to use the Q-jet, I'm sure Ken can build it for you, and recommend some jetting changes. The Holley will need to be tuned also. I like the Q-jet for a street car, hard to beat once they are calibrated correctly. I think you might have been happier with the stock or a smaller cam.
Great post Larry! I think I have the two silver springs in. I just reread an earlier post of yours that said one blue one silver is best for the street. Correct? I'll reduce the gap in the plugs tomorrow and see if I can recoup some power. I think you are on the head of the nail with the springs tho! Hope to make some progress in the morning!
Hey Larry, in reference to the qjet I got two questions-first the seller said the Rochester was original but also said it was a 650. How do I confirm or deny? Also, you mentioned air valves on the carb. I'm going to reinstall the qjet tomorrow to see if it performs better. Only thing is I'm not tracking whether if I have my wife floor the car (engine off) am I to expect the rear blades to open with out me doing anything or should I be actuating an air valve (location unknown) to see if the rear blades open as advertised?
And one more thing, I put a 1inch 4-hole space underneath the Holley. Should I leave it when I put on the Rochester or discard? Was it a waste of $ or something that i actually benefit from?
Usually, one blue, and one yellow, OR, one blue and one silver will be optimal. Try them both and see which one gives you a stable idle. What I mean by stable is, as you go from neutral to drive, and back to neutral after driving awhile, the idle speed in Park/neutral stays constant. It doesn't creep up. The spring choice will depend on what weights are in the distributor. Heavier ones have more leverage on the springs. Experiment and see which spring combo works for you. The Rochester Q-jet that came on your 72 350 was a 750 CFM model. All Q-jets were either 750 or 800 CFM. Some later ones that came on smaller engines were still 750's, but the air valve rotation was limited, thus limiting carburetor capacity. There are primary and secondary throttle blades on the Q-jet. They are both visible if you flip the carburetor over. Those are the blades I am talking about when I ask you to check that they are opening, when the pedal is floored. If the secondaries do not open, it is because the throttle cable is wrong. They were different between 2 and 4 bbl. On top of the carburetor, on the secondary side, are the air valves. They are NOT connected to the throttle cable. They operate by vacuum. They are spring loaded (adjustable), and also linked to the front choke vacuum break. The air valves will not open unless the engine demands the additional air flow. That happens when enough vacuum is present under the air valves from the opening secondary THROTTLE valves. The air valves will tip in gradually as the engine demands more and more air flow. The air valves are also slowed down by the primary choke vacuum break. It holds the air valves tightly closed at idle. At large throttle openings, vacuum drops, and the choke vacuum break releases it's grip on the air valves allowing them to open when conditions, described above, are present. You may not see the air valves open at all even if you wing the throttle, with the air cleaner off, and the hood up. Hope that is clear. The Holley and Q-jet have different bolt patterns, and throttle blade patterns. The Q-jet is a spread bore and the Holley is a square bore. The 4 hole spacers are usually worth some low end power, but not always. You have to experiment. There may be jetting changes required to realize the gain. Gaskets and bolt patterns are different between the two carburetors. If you have an aftermarket intake, it will be drilled for both bolt patterns, but the intake carburetor pad will either be spread bore shaped, or square bore shaped. The spread bore shape will flare out at the back, the square bore will be nearly square. You can run a Holley carburetor on a spread bore opening with a thin adapter plate. Running a Q-jet on a square bore opening will require a thicker adapter plate. i would think that you would need a spread bore 4 hole spacer to run one on the Q-jet. The Holley 4 hole spacer won't work.
Swapped the springs(blue/silver) and gapped the plugs to .40. That alone have me more off idle pep and smoothed out the power curve. I have a sputter at about 4k at WOT though. Figure it's probably trash in the carb or something. Seems as if my car likes manifold over ported vacuum. All in all, I'm happy with it. Thanks for the suggestions!
Update: the car sat for two weeks while I was away for a military training exercise and I've noticed a few issues. When I replaced the wires recently, I didn't cut them to the proper length as I should have. An issue that I'll fix this weekend. The excess wire is currently ziptied together. Is that harmful in anyway? The reason I ask is because theres an uncomfortable sound that comes from my car at low rpm when it's cold. It's sounds like a metalic clapping sound. Like its coming from the bottom end somewhere. When I fire the car up, it makes a wired noise like a banging or clapping (metalic) sound. Their I raise the rpm it goes away. When I was setting the idle mixture screws on the carb, it made a similar sound as I screwed them in and the engine was dying. I thought I had it worked out though. There's still a potent exhaust stinch from the car. Could the metalic clacking sound be a result of an improper carb/ignition tuning? I powertimed the car, or so I thought. I followed the powertime thread and got it set at 34* in at 2400 rpm. I don't know why my vacuum advance is at though Nor how to find out. After normal engine temp tuning to these specs, the initial is at 19* which I think is rather high. How do I find out what my vacuum advance is at? I have the crane adjustable version and can turn the screw counterclockwise to reduce it. Just not sure what to do here.
The closer the wires are together, the more chance of crossfire, but this is unlikely with new wires. It's best to separate them some, especially the #5 and #7, as they follow each other in the firing order. Your noise could be a cracked flex plate, or loose converter to flex plate bolts. It can sound like a knocking that comes and goes. It can change to a ticking when in gear. It will be more obvious when the engine is running rough, like when it is cold. Your 350 distributor only has about 14-16* of mechanical advance in it, so 19* initial and 34 total, sounds right. That's fine as long as you have no hot cranking problems. Have another look at my Power Timing thread. There are pictures on how to adjust and modify the Crane canister. You want to limit the vacuum advance to 8- 10* maximum. You do that by mounting the cam on the canister arm. This is different than what Crane instructs you to do. The adjustment through the vacuum nipple adjusts the canister spring preload. That adjusts the rate of vacuum advance not the amount. If the exhaust is irritating, you are either too rich or too lean.
Is the exhaust stench att the tail pipes or under the hood? If you smell exhaust under the hood when the engine is cold perhaps you have a header gasket leak which could also be the cause of the noice you hear.
i think you're right on Larry. i thought the noise was specifically coming from the torque converter area as i was under the car while it was running today. how do i check the bolts to see if they are loose, or to confirm/deny that the problem is infact there? transmission need to be removed? since the 284 cam, i have been contemplating putting a higher stall converter in but have been dragging my feet. several people have said that it's a welcomed addition but i've just been lazy since i know it's a fair amount of work. is this something i should take care of now de to this issue that's come up? if so, what speed stall converter and do i need to replace the flex plate too?
Start by removing the inspection cover for the trans. Next put a wrench on the bolts that are visible from the under side and use a dab of white out on them to mark that you have checked them. Next rotate the engine over by hand or with the starter till the un marked bolts are visible. While you are doing this also look very closely with a light for any cracks. Go with something like a 2500 rated stall or a 2800 rated stall. Only replace the flexplate if it is cracked.
Went under the car today. Three of the four bolts were loose. After tightening them, I started the car and still had a clacking noise. Albeit, not as bad, yet it was stpl there. It did go away under throttle. I found No cracks in the flexplate, but I did notice that w the eng off, the flexplate would move left/right about 1 inch. Normal? Or should it be no play as I'm thinking?
