That sure sounds like vacuum leaks to me. Low vacuum, erratic tuning, issues that come and go. I just pulled my intake (after nearly pulling all my hair) because of a bunch of symptoms I couldn't tune out. A smoke machine revealed intake gasket leaks at the lifter valley. Oil and water traces were evident all along the bottom, and between the water port, and forward most intake ports. Don't make the mistake of spraying carb cleaner around and assuming there are no vacuum leaks if it doesn't run different. It can still leak from the underside.
Thanks ken! Mark(carmantx) built this qjet for me. I originally had the screws at three turns out. Checked my plugs and they were ghost white. One actually broke on exit. Per the guys here, yesterday, I hooked up a vacuum guage to the manifold vacuum port on the front of the carb and turned the screws to achieve the best vacuum in park at 1k rpm. That yielded 10-14 hg (it fluctuated) with the screws at 4.5 turns out. I checked the secondary blades for fuel and didn't see any. ---------- Post added at 10:51 AM ---------- Previous post was at 10:49 AM ---------- Think it could be a fuel issue. When I had the Holley on it, the pressure guage read b/w 5&7 psi. The needle bounced all over. Would I benefit from a pressure regulator or is that unrelated?
You could have a fuel pump delivering an intermitent amount of fuel, if your fuel pressure gauge was not faulty and your fuel pressure is indeed jumping then yes replace the fuel pump. Have you used a timing light on the engine? If the timing also bounces then you may be dealing with a worn out timing set. If TA said your cam is fine with stock pushrdods then you are fine there as long as you did not mill the heads or block.
If TA told you the stock pushrods are fine for that cam then you are ok as long as you checked them for damage and that they are not bent. Did you also check to make sure where they sit in the rocker arm is not worn or damaged. I know this doesn't necessarily coincide with the original post but thought I'd throw that out there since you asked.
I'm really surprised at some of the things people say they heard from TA. If they told you your stock push rods were fine with a new cam, that's wrong. Anytime you change a cam, you need to check push rod length and lifter preload. That's just good mechanical sense. The stock Buick valve train is non adjustable. Using adjustable push rods is the best and least costly way to get adjust ability. I've used them for over 10 years and never had a problem. There is no reason for the idle vacuum to fluctuate between 10 and 14". You have a problem, and it's basic. The first thing to check is compression. You can rent a gauge and check each cylinder. Warm the engine up. Then remove all the spark plugs. Block the throttle wide open. Run the starter for each cylinder until the gauge reading tops out. Record the compression reading for each cylinder.
I'll definitely change the fuel pump. Hell it's less than $30 so that's easy. I figure at best that would stabilize the idle some but I still may be a bit low on the vacuum piece. Certainly a fuel pump isn't going to increase hg would it?
I changed the timing chain and gears when i put the cam in. Under the light, the timing mark is steady. Is the lack of vacuum any way relayed to the camshaft? Is Having low vacuum robbing my power? I've read that some cars have a vacuum canister. Is this an oem part? Am I supposed to have one? I noticed a cylindrical shaped container with two hoses coming off of it located on the drivers side right behind the head lights. The two hoses aren't connected to anything and I assumed it was air conditioning related as I don't have mine hooked up. Any thoughts?
No, the cam will lower vacuum some. I would expect about 15" of vacuum with that cam. The issue is it fluctuates, and that isn't normal. It should be steady. Something else is wrong. Generally, the more valve duration you have, the lower engine vacuum will be. Some cams can lower vacuum so much (below 10") that they require a vacuum canister to run the power brakes. That was never original equipment. Your cam should make 15" or more, plenty for power brakes. The container you refer to is the charcoal canister. It's an evaporative emissions device. Nothing to do with vacuum.
Thanks Larry. What are the benefits of a fuel pressure regulator? do fuel pumps work intermittently as a sign of failure?
Not saying I do, was just wondering what the bennies where of having one. Stock fuel pump(probably the original one), rebuilt qjet(by carmantx). Other than that, pertronix, 288h cam, walker longtubes.
You need a fuel pressure regulator when the fuel pump you have puts out too much pressure, and needs to be regulated. That isn't true of the stock fuel pump.
Gotcha-I was thinking the opposite. That a fuel pressure regulator would keep the system pressurized to compensate for a lackluster pump. Learn something new everyday!!! pump is ordered. I went with a stock replacement mechanical type. Hope that fixes me up.
The intermittent idle was definitely a faulty fuel pump. The new one is in and the idle is steady. Well, thumpy but steady. My next question is how to adjust the adjustable vacuum canister. I originally had the screw all the way clockwise and had a stumble under light throttle. The crane adjustable canister directions are confusing. Should I just keep backing the screw out until the part throttle ping stops?
I edited my last post to fix grammatical errors and add clarity(silly smart phones). The crane adjustable vacuum advance is what I was talking about.
The allen key through the nipple only adjusts the spring pre load. It doesn't adjust the amount of advance in the canister. To adjust the amount entails mounting the black cam on the canister arm. I have pictures of that in the Power Timing thread( Page 16, Post # 389). You need to limit the advance in the canister to 8 or 10*, otherwise, you will get surge, ping, and less power.
