Acceleration rough L-82 350 help

[Charles P.]

I just got back from a show here which I had to drive about 75 miles each way. On the way to the show the car acted great.

On the way back as I quickly accelerated away from a toll booth the car lurched and bucked until I pushed in the clutch. I revved it slightly and let out the clutch and smoothly accelerated with no problem. As I got up to speed and tried to accelerate the car repeated this pattern at speeeds of 60 to 70 miles an hour (ie seemed to cut out) until I pushed in the clutch which reduced speed and smoothly accelerated and kept my speed down.

It had about 1/8 of a tank so I stopped for gas (V-power Shell prem.) but the problem remained in various degrees the rest of the way home. Sometime it would act like it wasn't present at all then I would accelerate abruptly from 60 and it would cut out and lurch until I brought the speed down. As I said the car was running very well. Also the distributor was recurved by Lars which had the car running great. I say this because I don't think it has anything to do with timing or distributor.
Any ideas?

[Clem Z.]

Re: Acceleration rough L-82 350 help

sounds like a dirty fuel filter

[Michael W.]

Re: Acceleration rough L-82 350 help

Or a weak spark/bad points.

[Duke W.]

Re: Acceleration rough L-82 350 help

How about telling us if it's a single point or HEI ignition, or at least the model year, so we can figure it out which one it is.

Duuke

[Joe L.]

Re: Acceleration rough L-82 350 help

sounds like a dirty fuel filter

clem and Charles-----


I agree; it's definitely the first thing to check. On a 1973, there is no in-line fuel filter; the only filter is the one in the carburetor inlet fitting and that's the one you need to replace.

These filters are easy to find in an auto parts store. They are either of paper construction with metal end caps or sintered bronze material. Either type can be used interchangeably although folks might have preferences for one or the other.

If one of these filters gets plugged in any way, you WILL have problems. They are so small that any plugging will create a serious impediment to fuel flow.

[Joe L.]

Re: Acceleration rough L-82 350 help

Changing the fuel filter is easy, so do that ASAP.

If a new fuel filter doesn't solve the problem, it could be a HEI issue. When the modules go south they will sometimes give you this warning - intermittent cutting out of the ignition.

The other problem could be the lead wires from the pickup coil. They are stressed by movement of the base plate by the VAC, and can eventually break with vibration causing them to go intermittently open until they finally go completely open for good.

Free revving the engine may duplicate the problem when it gets into the correct RPM range, and a timing light can tell you if the spark goes away when the engine stumbles. You could also exercise the VAC at idle with a Mightly Vac and see if that causes the ignition to cut out. If it does you should remove and overhaul the HEI with a new module and pickup coil ASAP before it strands you. Parts cost is about $100 including a new cap and rotor.


Duke

Duke-----


HEI was not used on Corvettes until the 1975 model year; I believe the car in question is a 1973 model, so it would have breaker point ignition. The ground wire on the breaker plate could be a source of the problem, though.

[Duke W.]

Re: Acceleration rough L-82 350 help

Duke-----


HEI was not used on Corvettes until the 1975 model year; I believe the car in question is a 1973 model, so it would have breaker point ignition. The ground wire on the breaker plate could be a source of the problem, though.

Where did he say it's a '73.

Duke

[Joe L.]

Re: Acceleration rough L-82 350 help

Where did he say it's a '73.

Duke

Duke-----


In the "signature" section of the post Charles lists the two 1973's he owns. So, I presume the car he's talking about is the 1973 L-82.

[Charles P.]

Re: Acceleration rough L-82 350 help

Sorry, 73 L-82 completely stock (ie as delivered sans smog pump) with original single point distributor. I was thinking fuel also since I was at the end of a tank when it started. After I filled up it remained pretty much the same. I will start with the fuel filter in the Q-jet.

[Duke W.]

Re: Acceleration rough L-82 350 help

Duke-----


In the "signature" section of the post Charles lists the two 1973's he owns. So, I presume the car he's talking about is the 1973 L-82.

Okay, if I squint I can see 1973 1974, which probably comes from the profile we filled out. But what if the question is about another model year or the profile is wrong or not updated for a new acquistion?

The point I am trying to make is that the model year/engine option should be clearly stated with an engine related question or the type of transmission if it's a transmission related question, etc.

We know the L-82 is a 350, but the configuration details changed over the L-82 run depending on the year iincluding the ignition system.

It makes it a lot easier on me, and most others if basic information like the model year/engine option is specifically stated with an engine related question or any other salient information that is necessary to identify the specific system or component based on model year and option configuration.

Duke

[Martin N.]

Re: Acceleration rough L-82 350 help

CLEM-
Did these cars have a fuel tank "sock", or was that later on in GM production? I was a Buick line mechanic in the late 70's early 80's and those things with collapse with a droplet of water. Just a thought if it applies.

Marty

[Joe L.]

Re: Acceleration rough L-82 350 help

CLEM-
Did these cars have a fuel tank "sock", or was that later on in GM production? I was a Buick line mechanic in the late 70's early 80's and those things with collapse with a droplet of water. Just a thought if it applies.

Marty

Marty-----


Yes, they did have a fuel strainer ("sock") on the in-tank fuel pump pick-up. The strainer is replaceable and remains available in SERVICE.

[Duke W.]

Re: Acceleration rough L-82 350 help

If the fuel filter is clogged the engine will stumble as fuel flow demand increases, so inspecting/replacing the fuel filter is a first easy step.

It could also be an ignition related/vibration issue, so basic checks like point resistance and dwell angle should be done along with connectors. On C2s the body connector at the cowl which contains the 12V ignition circuit to and from the ignition switch is often the culprit. Usually the terminals just need a decent cleaning.

An intermittent ignition circuit open caused by vibration can sometimes be verified by free revving the engine with a timing light attached. If the light quits flashing when the engine stumbles the problem is likely somewhere in the primary ignition circuit.

Duke

[Joe L.]

Re: Acceleration rough L-82 350 help

Okay, if I squint I can see 1973 1974, which probably comes from the profile we filled out. But what if the question is about another model year or the profile is wrong or not updated for a new acquistion?

The point I am trying to make is that the model year/engine option should be clearly stated with an engine related question or the type of transmission if it's a transmission related question, etc.

We know the L-82 is a 350, but the configuration details changed over the L-82 run depending on the year iincluding the ignition system.

It makes it a lot easier on me, and most others if basic information like the model year/engine option is specifically stated with an engine related question or any other salient information that is necessary to identify the specific system or component based on model year and option configuration.

Duke

Duke-----


In this case, you don't need to strain your eyes to see the left margin icon. The cars Charles owns are contained in the signature section at the bottom of his original (and subsequent) posts. It includes model year, engine RPO and transmission. Same style and font size seen in the rest of the post.

What if he's talking about a car other than those shown in the signature? Well, I suppose then he'd better state exactly what he's talking about.

[Jim T.]

Re: Acceleration rough L-82 350 help

A quick check at night or a dark garage with a strong flashlight inspecting inside the tank for any water pooled in the bottom of the tank will be easy enough to check.