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For what it is worth, I have headers on my 75 and no heat riser. My choke is the same setup as you have and it works perfectly fine. On a 60 degree morning after a cold start I am on the road in 5 to 7 minutes. Once you get your choke working right you may have other problems with the mix and match unit you are running. I would suggest asking Lars for a Qjet summary of jet and metering sizes and make sure you have the right parts for the carb you have and not the year car. A good setup and the right APT setting does a world of good in these old Qjets.
Good luck, Jerry
If it's running rich, is it as simple as turning that dial towards "lean"?
It is NOT as simple as that.
What is the carb number??
Knowing what you have can help. And the reason I am asking is that just because the number is not what the car came with does NOT mean that that carb can be built correctly to work on this engine.
In the photo you posted that is below...the two tubes you see that are made into a plate that is bolted to the intake is where the heat from your exhaust is being directed to your choke housing. That area...if you had a heat riser...would heat up quickly and allow the choke to pull off. You can crank your engine and see either by an infrared temperate gun or carefully touching it to see how long it takes to get hot.
And are you 100% positive that the heat riser spacer has no shaft in it that would thus let you know that you have a flapper in it??? The heat riser for your engine is not like that of earlier Corvettes where you can see that big square weight coming out from the side.
you heat riser would look like this:
And the rich smell of fuel can be attributed to ignition/timing issues and not always the carb. You might be having a weak spark on a few cylinders which can also be a cause for it running a bit rough at idle.
It's hard to see the number with all of the grime, but what I see is 17084502.
There is absolutely no riser. I just replaced the entire exhaust system last weekend and it's just a spacer.
On the drivers side, there is a small metal hose coming off of the air cleaner that went to the heat stove which isn't there. Not sure if that contributes to the choke performance or not.
Does this help?
Would a weak spark be due to the distributor? It seems as if the PO did all the right things with the major items (short block, heads, brake lines etc) but may have skimped on the bolt on's like the carb and the distributor.
Thanks Dub.
Steve
Last edited by Norcoastal; Aug 30, 2017 at 07:20 PM.
Thanks for all for the GOOD photos. They were a really good help. And also THANKS to 'bmotojoe' for posting a photo of where to push down to get your choke to go off and idle.
NOW....I think this is not the correct carb due to I ahve never seen a Corvette of your year model with that other pull off on the right side rear of the carb.
Can you post the carburetor number???
Below are images on where to look for the carb number and they might be lightly stamped in the main body so take your time when you are looking at it.
I can say that I now need to see the heat riser or at least the exhaust on the right side...especially where the exhaust pipe attaches to the exhaust manifold. It may be possible that IF you still have a heat riser..it may be able to be controlled with a cable....OR....
Possibly take off the choke on that carb and install an electric one.
I know why it takes so long for the choke to finally pull off and you have an idle... and that is because I can see that you do not have either two of the temperature vacuum switches in your intake/thermostat housing. One of them if for your EFE system..which is what allows this type of choke design to function. Which is why I really need to see what you have going on a the exhaust on the right side.
DUB
Good point DUB..I have a 78 a/t with no rear pulloff????
Wonder what's all about Dub????
mike
Here's a question. IF I need a new carb, would it make sense to replace what I have with an aluminum high rise and a holly carb?
You have to be kinda careful on what you put on your engine due to underhood clearances. It does get tight ...and with other modifications to fuel supply lines and air cleaner and so on...you can open up a can of worms. Not saying that it won't work...but it is not going to be as easy as clicking 'Lego's' together.
Your carb is definitely made in 1980 or after. 'Google' that number and it will prove what I wrote.
In the link below...go down to '1975 and later carbs'
The tube on the left side exhaust that goes to the air cleaner is to provide heated air when it is really cold. It is not part of the choke issue.
With you having no heat riser..I am curious on how fast the tubes I showed in your one photo get hot when you have the engine running???
It is hard to say if your ignition is needing to be freshened up. but a rich condition of excessive fuel smell in the exhaust is either timing or weak spark or the carb..there is NO way in knowing unless I am there. I have had numerous engines in the past that were built and supposedly tuned by a performance shop and what they did was 'tune' it to run like a bat out of hell...but it would not idle on the street for crap. NOT saying that is what they did...but I am only saying what I have had to fix and make 'street-able'.
You have to be kinda careful on what you put on your engine due to underhood clearances. It does get tight ...and with other modifications to fuel supply lines and air cleaner and so on...you can open up a can of worms. Not saying that it won't work...but it is not going to be as easy as clicking 'Lego's' together.
Your carb is definitely made in 1980 or after. 'Google' that number and it will prove what I wrote.
In the link below...go down to '1975 and later carbs'
The tube on the left side exhaust that goes to the air cleaner is to provide heated air when it is really cold. It is not part of the choke issue.
With you having no heat riser..I am curious on how fast the tubes I showed in your one photo get hot when you have the engine running???
It is hard to say if your ignition is needing to be freshened up. but a rich condition of excessive fuel smell in the exhaust is either timing or weak spark or the carb..there is NO way in knowing unless I am there. I have had numerous engines in the past that were built and supposedly tuned by a performance shop and what they did was 'tune' it to run like a bat out of hell...but it would not idle on the street for crap. NOT saying that is what they did...but I am only saying what I have had to fix and make 'street-able'.
DUB
Good advice. I think what I should probably do is find a Q-Jet that was made for the car and be happy with that. I don't want to do a lot of mods to this car.
I just put in a true dual exhaust with no cats and I need to redo the interior and give it a paint job. I think that will be it. I don't think it's a very desirable car. There were a lot of 1978 SA cars. This one doesn't even have an L-82.
The only thing special on this car is that it's a 4 speed.
My goal is to get it looking great and mechanically sound and sell it and find a chrome bumper car.
But who knows. I may change my mind tomorrow. Haha
Last edited by Norcoastal; Aug 31, 2017 at 07:18 PM.
From: At my Bar drinking and wrenching in Lafayette Colorado
The carb is a 1984 heavy duty truck carb. The trucks used the rear pulloff, but it can be removed if the front pulloff is used. Just like the '75 Vette carb. I can see that the choke is out of adjustment. It should be aligned 2 notches clockwise from the center mark on the housing, and yours is rotated almost 45 degrees from the correct position. This will cause the choke to stay on way too long with fast idle not wanting to come down. Adjust your choke to the correct setting and verify your pulloff operation to make it work correctly.
The carb is a 1984 heavy duty truck carb. The trucks used the rear pulloff, but it can be removed if the front pulloff is used. Just like the '75 Vette carb. I can see that the choke is out of adjustment. It should be aligned 2 notches clockwise from the center mark on the housing, and yours is rotated almost 45 degrees from the correct position. This will cause the choke to stay on way too long with fast idle not wanting to come down. Adjust your choke to the correct setting and verify your pulloff operation to make it work correctly.
Lars
This is very helpful, but can you be a little more specific? What center mark? And will I be able to use this carb as is?
Last edited by Norcoastal; Sep 3, 2017 at 07:44 PM.
This is very helpful, but can you be a little more specific? What center mark? And will I be able to use this carb as is?
Loosen the three screws on the choke housing. Your current position of the choke (Line In Red) should be moved to the second mark to the right of the center-line of the choke housing (Line In Yellow). Just rotate the plastic part of the choke to align the two marks. Tighten the three screws.
Loosen the three screws on the choke housing. Your current position of the choke (Line In Red) should be moved to the second mark to the right of the center-line of the choke housing (Line In Yellow). Just rotate the plastic part of the choke to align the two marks. Tighten the three screws.
That's terrific thank you. This was very loose. I guess that's why it could have moved. The idle seems to have calmed down and sounds terrific!
Thank You!!!!!
Will this carb be ok for this car? When I step on the gas there seems to be a hesitation but that could be timing I assume.
I'm glad that the idle is good.
Thanks again!!!
Last edited by Norcoastal; Sep 4, 2017 at 10:09 AM.
There is nothing "wrong" with that carb on your engine. The Q-Jet was standard on nearly all GM cars for almost 20 years, and it has all the capacity and capability you need.
However, ALL carbs get 'worn' and need to be rebuilt so that they can perform as expected. Since yours "stumbles", it is very likely that the seal on the accelerator pump is worn or is no longer functional. Very common for ANY carb with 10 years of service (or more).
Getting one rebuilt properly is a bigger issue. No offense, but it doesn't sound like you have the needed skills for doing the rebuild yourself. If you think the carb needs that kind of work, I suggest that you send Lars (Grimsrud) an e-mail to: V8FastCars@msn.com , and ask him if he would be able to rebuild yours, what it might cost, and when he might be able to do that work. He is the best one for this job and he is very reasonable.
If you can 'adjust' your carb to work satisfactorily, you should do so. When you feel it needs to be rebuilt, send an e-mail to Lars.
Loosen the three screws on the choke housing. Your current position of the choke (Line In Red) should be moved to the second mark to the right of the center-line of the choke housing (Line In Yellow). Just rotate the plastic part of the choke to align the two marks. Tighten the three screws.
Originally Posted by 7T1vette
There is nothing "wrong" with that carb on your engine. The Q-Jet was standard on nearly all GM cars for almost 20 years, and it has all the capacity and capability you need.
However, ALL carbs get 'worn' and need to be rebuilt so that they can perform as expected. Since yours "stumbles", it is very likely that the seal on the accelerator pump is worn or is no longer functional. Very common for ANY carb with 10 years of service (or more).
Getting one rebuilt properly is a bigger issue. No offense, but it doesn't sound like you have the needed skills for doing the rebuild yourself. If you think the carb needs that kind of work, I suggest that you send Lars (Grimsrud) an e-mail to: V8FastCars@msn.com , and ask him if he would be able to rebuild yours, what it might cost, and when he might be able to do that work. He is the best one for this job and he is very reasonable.
If you can 'adjust' your carb to work satisfactorily, you should do so. When you feel it needs to be rebuilt, send an e-mail to Lars.
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by Norcoastal
Will this carb be ok for this car? When I step on the gas there seems to be a hesitation but that could be timing I assume.
The carb can be set up to run fine on your engine. I'm not a big fan of using the late model truck carbs on Vettes, and suggest using a pre 1980 passenger car carb. But what you have can be set up to run well. The hesitation is likely caused by a worn or failed accel pump, a low float level, or a lean condition. From the looks of the carb, it needs a rebuild and a good setup. But timing is always the place to start.
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by Norcoastal
Thank you Lars. I think the best course of action for me is to find a carb that is correct for my car.
I know for a fact that this carb is a frankencarb built by a bunch of parts. The guy I bought this car from told me that.
I understand that the correct carb for this car is a 17058203. Do you agree that this is what I should do and that this is the correct number?
Or do you recommend that I get an aluminum intake and a Holley carb? Aluminum intake and Quadrajet?
I'm debating whether I keep this car pure stock or modify the engine. I keep going back and forth, but now I'm leaning heads, cam intake and exhaust.
Thoughts?
Thanks a lot!
Steve
Based on your apparent level of experience, I'd suggest you stick with the correct parts and put the car back to its stock configuration. This will be the easiest approach, and will assure that you get it running well. Swapping over to a Holley will involve some custom fabrication work and it's not a simple direct replacement bolt on. Unless you're concerned with "numbers matching" you can use any 1976 to 1979 Chevy passenger car carb for an excellent level of performance. Do not get a commercially rebuilt carb.
Based on your apparent level of experience, I'd suggest you stick with the correct parts and put the car back to its stock configuration. This will be the easiest approach, and will assure that you get it running well. Swapping over to a Holley will involve some custom fabrication work and it's not a simple direct replacement bolt on. Unless you're concerned with "numbers matching" you can use any 1976 to 1979 Chevy passenger car carb for an excellent level of performance. Do not get a commercially rebuilt carb.
