Help diagnose...studder?
Thread Starter
Racer
Joined: May 2020
Posts: 476
Likes: 122
From: Maine
Finalist 2021 C3 of the Year - Modified
Help diagnose...studder?
I'll lead off that I am NOT good with mechanical stuff at all and my current C3 is my first. I've been cruising around with it and everything appears to operate as normal and as it should except for yesterday.
I notice that when I first hit the gas, it won't gradually take off....once the pedal is depressed more, then it kinda jumps a little. At idle, nothing....the tach is pretty steady and it sounds nice and steady. Second, when I'm going 5-20 mph, even with my foot depressed at one location, it kinda bounces a little, but when I depress the gas pedal more to get to 30+ mph, nothing, meaning, it runs smooth then.
Wonder if this is something simple to diagnose and maybe I can do quickly or could it be a thousand different things and I'll need to have my mechanic mess with it.
Carb, fuel, misfire/timing?
Any help would be appreciative...thanks!
I notice that when I first hit the gas, it won't gradually take off....once the pedal is depressed more, then it kinda jumps a little. At idle, nothing....the tach is pretty steady and it sounds nice and steady. Second, when I'm going 5-20 mph, even with my foot depressed at one location, it kinda bounces a little, but when I depress the gas pedal more to get to 30+ mph, nothing, meaning, it runs smooth then.
Wonder if this is something simple to diagnose and maybe I can do quickly or could it be a thousand different things and I'll need to have my mechanic mess with it.
Carb, fuel, misfire/timing?
Any help would be appreciative...thanks!
Race Director
Joined: May 2006
Posts: 18,597
Likes: 2,540
Neither your profile or your post indicate what year and what engine?
How long have you had this car?
If only recently, do you know when it last had a full tuneup?
Do you have a timing light and if a points distributor do you have a dwell meter?
What carburetor is on the car?
Is the engine modified in any way?
How long have you had this car?
If only recently, do you know when it last had a full tuneup?
Do you have a timing light and if a points distributor do you have a dwell meter?
What carburetor is on the car?
Is the engine modified in any way?
Thread Starter
Racer
Joined: May 2020
Posts: 476
Likes: 122
From: Maine
Finalist 2021 C3 of the Year - Modified
Neither your profile or your post indicate what year and what engine?
How long have you had this car?
If only recently, do you know when it last had a full tuneup?
Do you have a timing light and if a points distributor do you have a dwell meter?
What carburetor is on the car?
Is the engine modified in any way?
How long have you had this car?
If only recently, do you know when it last had a full tuneup?
Do you have a timing light and if a points distributor do you have a dwell meter?
What carburetor is on the car?
Is the engine modified in any way?
1977 L48 350
I've only owned this thing a few weeks. My first C3.
I know that it was gone through by the previous owner who owns his own mechanic shop; and I do not know the details of that process.
There is an aftermarket carb and cam in it.
The engine is original to the car and was rebuilt by this mechanic.
I don't have any of those tools....I'm worse than a forum and C3 owner newbie; I'm not even mechanical.
Thanks for helping me out....I updated my forum stuff.
Thread Starter
Racer
Joined: May 2020
Posts: 476
Likes: 122
From: Maine
Finalist 2021 C3 of the Year - Modified
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,033
Likes: 9,155
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
If it’s been sitting all winter, throw some dry gas in it and drive the tank of gas out of it. Depending on humidity, if your tank wasn’t full, condensation will form on the tank walls and lead to water in your gas..... burn through the fuel and see if it gets better in a few tanks. Dry gas theoretically binds the water to the fuel to get it out of your tank.....in reality its probably just time and a full tank that helps. You could also just drain it so you get it all out
Race Director
Joined: May 2006
Posts: 18,597
Likes: 2,540
If it happens again are you in a position to go back to the seller?
Either you have to take it to a shop or start learning and investing in tools and equipment.
It also would be to your benefit to know exactly what carburetor and camshaft and any other modifications were done to the engine.
Either you have to take it to a shop or start learning and investing in tools and equipment.
It also would be to your benefit to know exactly what carburetor and camshaft and any other modifications were done to the engine.
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Thread Starter
Racer
Joined: May 2020
Posts: 476
Likes: 122
From: Maine
Finalist 2021 C3 of the Year - Modified
If it’s been sitting all winter, throw some dry gas in it and drive the tank of gas out of it. Depending on humidity, if your tank wasn’t full, condensation will form on the tank walls and lead to water in your gas..... burn through the fuel and see if it gets better in a few tanks. Dry gas theoretically binds the water to the fuel to get it out of your tank.....in reality its probably just time and a full tank that helps. You could also just drain it so you get it all out
If it happens again are you in a position to go back to the seller?
Either you have to take it to a shop or start learning and investing in tools and equipment.
It also would be to your benefit to know exactly what carburetor and camshaft and any other modifications were done to the engine.
Either you have to take it to a shop or start learning and investing in tools and equipment.
It also would be to your benefit to know exactly what carburetor and camshaft and any other modifications were done to the engine.
Thanks...really appreciate the advice!
Thread Starter
Racer
Joined: May 2020
Posts: 476
Likes: 122
From: Maine
Finalist 2021 C3 of the Year - Modified
I adjusted the accelerator pump to give it a larger squirt and it made a huge difference....almost like you wouldn't notice anything was wrong unless you were really paying attention....this makes me happy, but if it was running fine before and then this happened, I'd hate to think that the problem isn't fixed yet.
I think the next step after chevron tech fuel cleaner or seafoam, is to have the carb rebuilt and a new fuel filter.
I think the next step after chevron tech fuel cleaner or seafoam, is to have the carb rebuilt and a new fuel filter.
Melting Slicks
Joined: Jul 2006
Posts: 2,266
Likes: 478
From: Salmon Arm, BC
Be sure to get the Camshaft info from the previous owner as this is vital info to have if you plan on doing any further modifications to the engine.
Thread Starter
Racer
Joined: May 2020
Posts: 476
Likes: 122
From: Maine
Finalist 2021 C3 of the Year - Modified
This sounds like you may have a little too much timing advance in at that RPM, if you search here you'll see it referenced as "trailer hitching." Limiting the vacuum advance could help this for you, but we'd need to know where your at first before recommending a fix. You should send Lars an email as I think he has a paper on this subject.
Be sure to get the Camshaft info from the previous owner as this is vital info to have if you plan on doing any further modifications to the engine.
Be sure to get the Camshaft info from the previous owner as this is vital info to have if you plan on doing any further modifications to the engine.