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Recently purchased a 75. Runs very good except slight hesitation and rough idle. Had a local mechanic replace plugs, wires, distributor, rotor and set timing. Really didn't do any good. He said it needed a new carb and went into why but I can't remember exact words . Anyway, Yesterday noticed gas collecting in areas shown in photo. So I assume the carb does have issues. It's a Holly 600. I would rather get a new one than rebuild this one. I don't need anything fancy, just want the car to run as it should. Holly 600 a good carb? In your opinion what does the photo tell you? Is it ok to drive the car until it gets fixed? Thanks! Sorry I forgot to add the photo. Here it is.
Last edited by ALLEN007; May 12, 2023 at 02:39 PM.
Reason: Add photo
Recently purchased a 75. Runs very good except slight hesitation and rough idle. Had a local mechanic replace plugs, wires, distributor, rotor and set timing. Really didn't do any good. He said it needed a new carb and went into why but I can't remember exact words . Anyway, Yesterday noticed gas collecting in areas shown in photo. So I assume the carb does have issues. It's a Holly 600. I would rather get a new one than rebuild this one. I don't need anything fancy, just want the car to run as it should. Holly 600 a good carb? In your opinion what does the photo tell you? Is it ok to drive the car until it gets fixed? Thanks!
Let me put this into perspective. You call your doctor and say “I’m sick, can you prescribe me some medicine.” Do you think they’re going to say, “just take some cough medicine and you’re good.” You’re thinking, “I don’t have a cough, but ok.” And obviously it doesn’t fix your problem.
Same situation with your engine. You gotta give us more information before we can say a 600cfm carb is good for your engine.
Let me put this into perspective. You call your doctor and say “I’m sick, can you prescribe me some medicine.” Do you think they’re going to say, “just take some cough medicine and you’re good.” You’re thinking, “I don’t have a cough, but ok.” And obviously it doesn’t fix your problem.
Same situation with your engine. You gotta give us more information before we can say a 600cfm carb is good for your engine.
Yes, forgot the important info. It's a stock 350. Anything else?
Assuming the manifold has been changed from a spread bore to square bore to fit the Holley, a Holley style carb is your only option. I personally would go to a slightly bigger 650 cfm carb, not because your engine needs a larger carb, but because your engine will not have to work as hard to pull air in.
For example, you put a “normal” size straw in a glass to take a drink and then put a larger diameter straw and take another drink. Your mouth only holds so much volume so the larger straw doesn’t necessarily allow you to drink more fluid, it’s just easier to drink through the larger straw.
Same for your engine. It can only take in so much air, the slightly larger carb just makes it easier for it to do. Rewarding you in a slight HP increase.
Assuming the manifold has been changed from a spread bore to square bore to fit the Holley, a Holley style carb is your only option. I personally would go to a slightly bigger 650 cfm carb, not because your engine needs a larger carb, but because your engine will not have to work as hard to pull air in.
For example, you put a “normal” size straw in a glass to take a drink and then put a larger diameter straw and take another drink. Your mouth only holds so much volume so the larger straw doesn’t necessarily allow you to drink more fluid, it’s just easier to drink through the larger straw.
Same for your engine. It can only take in so much air, the slightly larger carb just makes it easier for it to do. Rewarding you in a slight HP increase.
Since there is already a Holly 600 on it wouldn't we assume there would be that square bore already?
‘75 Corvettes didn’t come with Holley carbs, only quadrajets. So the factory intake manifold will look like this.. Which is a spreadbore manifold, which also means your engine is not exactly stock/original.
Actually, just took a better look at your picture. You have an Edelbrock performer intake on it. Definitely not original.
‘75 Corvettes didn’t come with Holley carbs, only quadrajets. So the factory intake manifold will look like this.. Which is a spreadbore manifold, which also means your engine is not exactly stock/original.
Actually, just took a better look at your picture. You have an Edelbrock performer intake on it. Definitely not original.
Just got the car a month ago so really don't know what all has been done to it. Is it ok to assume that if a holly 600 is on it now a new holly 600 will fit? Probably a dumb question. Appreciate the help!
Just got the car a month ago so really don't know what all has been done to it. Is it ok to assume that if a holly 600 is on it now a new holly 600 will fit? Probably a dumb question. Appreciate the help!
Without knowing what intake you have, no one is going to say yes or know to that question.
Can you identify which Edelbrock Performer intake is under there? They made both square bore (Holley) and spread bore (Q-Jet), and using an adaptor will make your car run like garbage.
There is no need to buy a new carb when the one you have just needs a rebuild most likely. 600 CFM is plenty for a stock 350 that runs out of power above 4500 RPM.
You should put your man pants on, buy a book on how to rebuild a Holley carb, watch a bunch of YouTube vids, go buy a rebuild kit and rebuild it yourself. It's pretty easy to do, and you can always ask questions here for a quick answer.
I just noticed you have been here since 2012 with over 800 posts.....you must be somewhat knowledgeable about working on Vettes
ALLEN007
Step back some and take some more pictures of the engine. Some where we can see the manifold and the whole engine. If there is a part number on that carb, then get a picture of that also.
Originally Posted by ALLEN007
Recently purchased a 75. Runs very good except slight hesitation and rough idle. Had a local mechanic replace plugs, wires, distributor, rotor and set timing. Really didn't do any good. He said it needed a new carb and went into why but I can't remember exact words . Anyway, Yesterday noticed gas collecting in areas shown in photo. So I assume the carb does have issues. It's a Holly 600. I would rather get a new one than rebuild this one. I don't need anything fancy, just want the car to run as it should. Holly 600 a good carb? In your opinion what does the photo tell you? Is it ok to drive the car until it gets fixed? Thanks! Sorry I forgot to add the photo. Here it is.
There is no need to buy a new carb when the one you have just needs a rebuild most likely. 600 CFM is plenty for a stock 350 that runs out of power above 4500 RPM.
You should put your man pants on, buy a book on how to rebuild a Holley carb, watch a bunch of YouTube vids, go buy a rebuild kit and rebuild it yourself. It's pretty easy to do, and you can always ask questions here for a quick answer.
I just noticed you have been here since 2012 with over 800 posts.....you must be somewhat knowledgeable about working on Vettes
I have my man pants on and there is money in them. I'm going to buy a new one. I have had a C6, C5 and this is my 2nd C3. And yes I can work on them to a certain extent, but sometimes choose not to.
ALLEN007
Step back some and take some more pictures of the engine. Some where we can see the manifold and the whole engine. If there is a part number on that carb, then get a picture of that also.
Also, I'm going to replace the valve cover gaskets. What's the best material to use? I've seen rubber, cork and a mixture of the two.
I like rubber. More expensive but lasts longer and if you take your valve covers off you don’t have to replace them (if they’re not old and dried out).
From: At my Bar drinking and wrenching in Lafayette Colorado
The carb you have is a good (but very small) carb. Any "new" carb you buy will need to be properly set up - there is no new carb that will run correctly right out of the box. You're much better off just properly setting up what you have. I see that you are running your vacuum advance off ported vacuum, which means that your timing is severely retarded. Badly set timing has a much greater impact on engine performance than the carb setup. You have tuning and setup problems that are not related to the carb. Set your engine up properly, give it a correct level of tuning, and adjust/set up what you have. It will run great. Just replacing the carb with another new carb that needs a setup will gain you nothing, no matter how much money you have in your man-pants. If you chose not to properly set up and tune your parts your car will never run well.
...and FYI - the carb list number is stamped right into the choke airhorn on the forward driver's side.
Lars
Also, I'm going to replace the valve cover gaskets. What's the best material to use? I've seen rubber, cork and a mixture of the two.
Mixture of the two. Cork seals the best but is not reusable. Rubber is reusable but does not seal the best. Composit, both materials, is the best of both.
Love Holleys, as shown on my avatar. However, that 600 in my opinion is not correct for SBC. The fuel inlet is on the opposite side of the fuel pump. It almost looks as though the fuel bowls should be swapped for proper fuel connection. But that's not feasible.
Your factory carb was 650 CFM. So, you downgraded. I think I would look into a different Holley, 650, with fuel inlet on the passenger side.
Also, bubba hooked up your PVC Valve so a vacuum line is routed all the way across the engine to the rear of the carb. A better solution is to swap the PCV Valve with the breather. It will be a "short-cut" to the vac port for your PCV.
Which is now plugged with a bolt?
It looks as though the fuel bowl and metering gaskets are non-existent or are smashed down so much that, that is likely your fuel leak. Those gaskets are easy to replace, but get the blue, reusable thick ones. And use only Holley parts, not knock-offs, "fits Holley blah-blah-blah.
Last edited by HeadsU.P.; May 14, 2023 at 08:07 AM.
The carb you have is a good (but very small) carb. Any "new" carb you buy will need to be properly set up - there is no new carb that will run correctly right out of the box. You're much better off just properly setting up what you have. I see that you are running your vacuum advance off ported vacuum, which means that your timing is severely retarded. Badly set timing has a much greater impact on engine performance than the carb setup. You have tuning and setup problems that are not related to the carb. Set your engine up properly, give it a correct level of tuning, and adjust/set up what you have. It will run great. Just replacing the carb with another new carb that needs a setup will gain you nothing, no matter how much money you have in your man-pants. If you chose not to properly set up and tune your parts your car will never run well.
...and FYI - the carb list number is stamped right into the choke airhorn on the forward driver's side.
Lars
A couple days ago I had plugs, plug wires, distributor and rotor replaced as well as timing done. Sure gets confusing. Thanks for the input.
Mixture of the two. Cork seals the best but is not reusable. Rubber is reusable but does not seal the best. Composit, both materials, is the best of both.
Love Holleys, as shown on my avatar. However, that 600 in my opinion is not correct for SBC. The fuel inlet is on the opposite side of the fuel pump. It almost looks as though the fuel bowls should be swapped for proper fule connection. But that's not feasible.
Your factory carb was 650 CFM. So, you downgraded. I think I would look into a different Holley, 650, with fuel inlet on the passenger side.
Also, bubba hooked up your PVC Valve so a vacuum line is routed all the way across the engine to the rear of the carb. A better solution is to swap the PCV Valve with the breather. It will be a "short-cut" to the vac port for your PCV.
Which is now plugged with a bolt?
It looks as though the fuel bowl and metering gaskets are non-existent or are smashed down so much that, that is likely your fuel leak. Those gaskets are easy to replace, but get the blue, reusable thick ones. And use only Holley parts, not knock-offs, "fits Holley blah-blah-blah.
Good idea on swapping the PCV over (I'm still learning). Also, the tube with the screw went to the Charcoal Cannister. That fitting has two ports. One goes to the headlight system (which I just replaced everything) and the other to the Cannister.
Last edited by ALLEN007; May 12, 2023 at 09:01 PM.
Reason: add info
ALLEN007
I would follow this advice from Lars before anything else. He shares all kinds of great info on this forum. I read them all and I don't EVEN have a carb on mine anymore......
Originally Posted by lars
The carb you have is a good (but very small) carb. Any "new" carb you buy will need to be properly set up - there is no new carb that will run correctly right out of the box. You're much better off just properly setting up what you have. I see that you are running your vacuum advance off ported vacuum, which means that your timing is severely retarded. Badly set timing has a much greater impact on engine performance than the carb setup. You have tuning and setup problems that are not related to the carb. Set your engine up properly, give it a correct level of tuning, and adjust/set up what you have. It will run great. Just replacing the carb with another new carb that needs a setup will gain you nothing, no matter how much money you have in your man-pants. If you chose not to properly set up and tune your parts your car will never run well.
...and FYI - the carb list number is stamped right into the choke airhorn on the forward driver's side.
Lars
The carb you have is a good (but very small) carb. Any "new" carb you buy will need to be properly set up - there is no new carb that will run correctly right out of the box. You're much better off just properly setting up what you have. I see that you are running your vacuum advance off ported vacuum, which means that your timing is severely retarded. Badly set timing has a much greater impact on engine performance than the carb setup. You have tuning and setup problems that are not related to the carb. Set your engine up properly, give it a correct level of tuning, and adjust/set up what you have. It will run great. Just replacing the carb with another new carb that needs a setup will gain you nothing, no matter how much money you have in your man-pants. If you chose not to properly set up and tune your parts your car will never run well.
...and FYI - the carb list number is stamped right into the choke airhorn on the forward driver's side.
Lars
Hey Lars what do you mean by "running your vacuum advance off ported vacuum"? Could you be more specific and tell me how it should be? Just got the car and this is how it was when I got it. Also, what size carb should be on the car? I appreciate you help!
1975 Carb question
