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Old 04-01-2004, 01:52 AM
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Sputtering starts and knocking during idle

Hello All,

My lovely 68 Buick Skylark has developed a couple of little problems with starting and idling. I know there are many threads covering similar topics. However, the many different options are somewhat confusing to me. So, I thought I would post my particular situation in the hopes that someone might be able to suggest a specific course of action.

Problem # 1: When cold starting, I have to tap the gas pedal and then she turns over. No big deal. However, during warm-up, she sputters and falters. There's a little shaking going on as well. Since it sounds like she will stall out, I give her gas to help it along. As the car revs up, the sputtering clears out more and more until it finally goes away (I have also just let the car run until it warms up on it's own. The same thing happens, just slower. It goes from sputtering, to full high idle.)

Problem #2: When the car is warmed up and at curb idle, there is an intermittent knocking sound. It is not a steady pattern. It is faint enough that I can only hear it when I have the hood open (Although I believe that it has been going on for a while, I only discovered it recently.) As someone suggested in a post, I went all around the car listening for the exact location of the knocking. As far as I can tell, it seems to be coming from the front passenger side of the engine.

Here are some specs on the car. 1968 Buick Skylark Custom convertible. Approximately 4500 miles on a rebuilt Buick 350 engine (I found the serial numbers on the block under the #1 plug. The first two letters indicate that it is a 68 Buick motor). Stock intake and exhaust manifolds. A nice new K&N air filter. A "never used" Q-Jet carb purchased on eBay. (It's the proper model for my engine. The one that was on there was for a Buick 430. Probably didn't make a difference, but for for $50.00, why not?) Stock points distributor and coil. Stock rear-end (I assume..) Dual exhaust with glass packs. Unfortunately, I have no specs on the cam, or other internal aspects of the rebuilt engine.

Now, a short repair history. When I purchased the car, it had no pick-up and really crappy mileage. Plugs and wires were changed (the old plugs were gapped to .045. I gapped the new ones to the book spec of .030) My mechanic installed new points, timed it, and installed and adjusted the "new" carb. While he didn't give me an exact number, he did say that he had to really advance the timing. He also found that the heat riser was stuck closed. This might account for the exhaust coming out of the right pipe being much cooler than the left. (I am getting the exhaust system replaced soon. The Muffler guy said he'd deal with that) As the weeks wore on the sputter-start developed. However, the car ran well when warm. Mileage was about 12-14 mpg. After researching on this site, I decided to replace the points with a Pertronix Ignitor 2 and Flamethrower coil. (I thought the extra spark energy might help with the sputtering starts and maybe boost mileage a litle) I also upgraded the wires to Accel 8.8mm spiral core wires. The Pertronix unit went in two days ago without a hitch. The car started right up and the timing was exactly where it was before the upgrade. The oil was also changed last sunday.

This is where I am at currently. Before working on the points I checked the timing (vacuum advance disengaged and the hose plugged). My advance timing light said it was at 25* BTDC. Running the engine to about 2500 rpm put the timing at about 50*. ( I know some feel that those advance lights can be way off. ) To try and stop the knock, I filled up on 91 octane and tried bringing the timing down to 20*. The knock didn't stop and the engine started to falter. Also, the Ignitor and beefier coil didn't help the start-up situation either.

I am not sure where to go from here. As you can tell from all that I have vomitted up here, I am a novice. I feel confident doing some of this work, but obviously, I need to learn MUCH more. My ultimate goal is to make this car a daily driver that gets decent mileage and has enough "oomph" to pass someone on a freeway (no racing here) Any suggestions would be greatly appreciated.

Thanks!

(Apologies for the LONG post. I have just seen too many people complain about not being given enough info. Maybe I over compensated....)

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Old 04-01-2004, 02:20 AM
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First off, it was a very wise move to invest in the pertronix unit over the points, the best place for points is in the trash. It sounds to me as if the choke needs adjusted, and if the heat riser passage is blocked off, there is no extra heat until the engine is fully warmed which results in a cold start problem since the carb needs heat to help keep fuel suspended in the stream and not fall out and puddle on the intake floor. it sounds as if it`s too rich when cold, which is likely the choke staying closed too much for too long. I`d also advise you move the spark timing back to where it was. the knock your hearing could be spark knock from carbon build up, if so, it shouldn`t be present at idle when the car is cold, if the knock is present at start up, then I would search that area of the engine until I found it, remove the valve cover and check that side, check the rocker arm, the pushrods etc. a bent pushrod or loose rocker can cause it to knock.
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Old 04-01-2004, 04:48 AM
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1/ Choke, as noted.

2/ Does the knock come from the top or bottom of the engine? Is it a ticking sound or a deeper knocking sound.

The ticking could be a rocker, lifter etc, even the fuel pump.

The deeper knock could be a rod or main bearing.
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Old 04-01-2004, 01:00 PM
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Thanks for the advice! I'll check out the choke straight away.

I actually hadn't noticed whether the noise was there immediately upon start-up or not. Today, I will start the car and listen for the noise as it warms up naturally. If it is there from the start I will try to pin it down more specifically. I also wanted to pull the plugs and re-gap them a little wider to take advantage of the Pertronix unit (their site says I could up the gap about .005 more than factory specs.)

Another thing I neglected to mention is that when I changed the oil, I changed it to Mobil One. A friend seemed to think that I could benefit from the synthetic oil. He didn't think I would have the old engine/thin oil problem since it was a "recent" rebuild. The previous oil was rather thick (It surprised my mechanic. He thought it probably had some kind of additive in it) Could this be a potential cause of noises, or has the new oil just revealed a problem that was already there?

Something tells me the new exhaust system just went on hold. The money is headed someplace else I think...
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Old 04-01-2004, 02:50 PM
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if the buick only has 4500 miles on it oil weight shouldnt play a difference in the tapping knocking noise youre hearing from the motor.sounds like a bigger problem than oil,although if youre using synthetic oil now i have heard of older model engines tapping more than with regular oil. to listen to the motor i always use a round piece of wood like a 12"broom handle or a big screwdriver to listen to the motor my putting the handle to my ear not the sharp end lol and putting in on different spots on the motor.

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Old 04-01-2004, 09:36 PM
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Okay, following the excellent advice I was given, I went out and listened to the car. It started easily. Instead of hitting the gas to blow through the sputtering, I let it warm up naturally. It took some time.

During that time, I noticed that the car was idling somewhat smoothly with no knocks to be heard. As the car warmed further, the sputtering subsided, what little vibrations eased, and the RPM's increased. Still no knocks.

Then I tapped the pedal. The car dropped down to curb idle. At first I didn't hear anything. Then, very subtly, the knock appeared. It stayed relatively faint. There was a discernible pattern. Every few seconds the knock would fade in with a "clack-a, clack-a, clack-a" and then, fade out. This repeated regularly. Also, the car had a slight shake, like it was on the verge of stalling. This shake seemed to fade in and out with the knock.

I listened the best I could to pinpoint the source of the noise. It does seem to be coming from the front, passenger side of the engine. It is best heard from the top of the car. I had my head right over it, so I am pretty sure of the location.

Does any of this help prove your theories? Again folks, thanks for all your advice. I am learning!
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Old 04-02-2004, 04:35 AM
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I/m thinking exhaust leak....crack in the exhaust manifold. Buicks are prone to cracked manifolds.
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