Suggestion/experience, Need a new Carb

[Rust_never_sleeps]

Originally Posted by MySons68C20

Like Pbfut said you weld in the bung and route to the gauge. I mounted my gauge in the original cluster in an unused hole.
I can get a pic if you want but its on the lower passenger side of the cluster.

You can find clamp on bungs if you don't feel like welding. Most likely, nobody will ever see it

[Kalums]

Originally Posted by HO455

It's my opinion that using a carburetor that was actually engineered to pass emissions will help. Qjets would be my first choice for your situation. I have very little experience with the AVS Edelbrock's but they seem to be an improvement over the rest of their stuff.

To do this you're going to need to find someone who is experienced and has the jets and parts to set up your carburetor. The next step is getting a accurate emissions test. This can be done at many shops but, they need to have maintained and properly calibrate their equipment to give you an accurate test. Most states have equipment that is far more accurate than what your average shop has.

Here in Oregon it's $25 bucks for the first test and the rest are free. So many shops will get a baseline on there equipment then run it through the QEQ test station and make changes based on that. Then run it back and forth until the vehicle passes.

Your also going to find that the tune that allows the truck to pass will not be the tune that allows the engine to run well. For example my unmodified 91 S10 4.3 would never pass emissions with the factory timing specs. Each time I would have to back the timing back to 4 degrees, disconnect and plug the vacuum advance, and pull the PVC hose plug it with an ear plug and then reconnect it. Once it passed I would undo that and drive it until the next time.

You may find that you need an "emissions" carburetor and a carburetor to drive it everyday along with different timing. This process should help make your yearly testing much less arduous.

Having your distributor spun on a distributor machine will also show any defects that may be in the distributor that are affecting the emissions. As an example we had a customer bring in a all original 70 Corvette that did not idle as smoothly as the owner felt it should. He had taken the car to several other places but the problem was never located. Once the distributor was spun it was very apparent the point lobes on the shaft were mis-machined from the factory. They were not equal distance apart from each other on the shaft. (About 4* different) This prevented about half of the cylinders from firing on time. Once a good used shaft was installed in his number correct distributor the car performed much better and idled as expected. This sort of thing would prevent a marginally clean engine from passing the test.

Can you post the results from the test that failed?

I will add that a A/F guage can help get your engine get better mileage but it only measures the fuel to air ratio whereas the emissions testing breaks down the air into its different components and that's what makes or breaks you.

The truck is currently just registered as a "classic" here in AZ and as such is exempt as long as I do not drive it more than 5k a year. The truck currently has no other emissions equipment on it. It has not "failed" emissions yet. It will have to pass when I re-register it for use with my livery business.

[1970-CST]

6 mpg is ridiculously rich. Most tend to "over carb". The beauty of the quadrajunk was the tiny front side. Gave a great vacuum signal and metered well.

I ran a Holley 1850, 600 CFM on my 70' 402 for years. Snappy, crisp and made plenty of power.

What are you running for a distributor? Timing plays a huge part in this question and trying to get a carb dialed in is pointless until you have a distributor map dialed in.

[Kalums]

Originally Posted by 1970-CST

6 mpg is ridiculously rich. Most tend to "over carb". The beauty of the quadrajunk was the tiny front side. Gave a great vacuum signal and metered well.

I ran a Holley 1850, 600 CFM on my 70' 402 for years. Snappy, crisp and made plenty of power.

What are you running for a distributor? Timing plays a huge part in this question and trying to get a carb dialed in is pointless until you have a distributor map dialed in.

Stock distributor, only cap(MSD) , ROTOR (Delco) and module (Delphi/Delco, got it from the dealership, sold as Acdelco, came in a Delphi box *shrugs*) are new. Did not adjust or change weights or springs on this one(since new motor). Vacuum signal is pretty good, timing is currently 12* advanced. Again 6 mpg is mostly my fault as I did not realize the 9895 was a reverse idle circuit carb and what I thought was full lean was actually full rich.
My understanding is that the Quadrajet(s) were mostly 875 cfm carbs and the reason they got good mpg is the tiny fronts were less than 400 cfm of that equation... But I'm definitely no expert, just what a few guys near me have said.
My understanding also(correct me if I am wrong please) , is that I will need a 0* advance to pass emissions, so timing is iffy till the emissions part of the equation is handled.

[1970-CST]

Points type or HEI ? Is there a vacuum advance module in place and what are its specifications ie, when does it begin to deploy in inches of Hg and at what inches of Hg is it fully deployed?

What are the centrifugal weights adding for timing? What RPM and how much additional timing is delivered? These must be figured out or you will chase your tail getting the new carb dialed in.

I think you're on the right track.

I'm up north by Anthem, where are you located in the valley?

[Kalums]

Originally Posted by 1970-CST

Points type or HEI ? Is there a vacuum advance module in place and what are its specifications ie, when does it begin to deploy in inches of Hg and at what inches of Hg is it fully deployed?

What are the centrifugal weights adding for timing? What RPM and how much additional timing is delivered? These must be figured out or you will chase your tail getting the new carb dialed in.

I think you're on the right track.

I'm up north by Anthem, where are you located in the valley?

Every thing is stock HEI, it is all in at 32* advance at about 28-2900rpm. I have no idea about when the VA kicks in, it again is a stock distributor and VA module.
also PM sent

[1970-CST]

Originally Posted by Kalums

Every thing is stock HEI, it is all in at 32* advance at about 28-2900rpm. I have no idea about when the VA kicks in, it again is a stock distributor and VA module.
also PM sent

The centrifugal sounds in the ball park. For older style (pre fast burn) 36* WOT advance was the optimum. Are those fast burn, vortec heads?
There are dozens of vacuum advance modules to fit every application. The vac can you have now should be tested to identify its characteristics and that they match your engines vacuum, and timing needs. Many run in circles trying to get a good idle, fix an idle overheating issue, and suffer poor gas mileage and it all comes down to that vacuum can.

[Kalums]

Originally Posted by 1970-CST

The centrifugal sounds in the ball park. For older style (pre fast burn) 36* WOT advance was the optimum. Are those fast burn, vortec heads?
There are dozens of vacuum advance modules to fit every application. The vac can you have now should be tested to identify its characteristics and that they match your engines vacuum, and timing needs. Many run in circles trying to get a good idle, fix an idle overheating issue, and suffer poor gas mileage and it all comes down to that vacuum can.

My overheating issue hasn't resurfaced since I trimmed the fan cowl so that my fan peeks out like it is supposed to, but I also put the truck in park if I know I'm going to be sitting for awhile. It has the standard TBI "swirl" port heads from the 90s TBI 350s "192" I believe. It ran great at 60(ish) on the highway (101), just man-o-man 6 mpg is in the "cry each time you stop for Gas" range...

[1970-CST]

I'd research what timing those TBI engines accepted. Do you have a mighty-vac hand vacuum gun with gauge? Hobo-Frieght has them for around $45.00 or you could rent one from orieley's.

With a timing light hooked up, engine running, unplug the vacuum advance. Plug the mighty vac into the vac can. Begin to pump up the tool to get 1" of vacuum, and note where the timing is. Do this in 1" Hg increments until you note at what vacuum the can BEGINS to add timing, and at what inches of vacuum the timing is maxed out. The number should be 2" less then what ever engine manifold vacuum is at idle, in drive gear for an automatic.

So if the engine makes 20" of vacuum at idle, and 18" in drive gear, then you need a vac can that is fully deployed, adding at least 16* of advance at 16" of manifold vacuum. This is called the two inch rule.

If you have a vac can that is not fully deployed until 22" of manifold vacuum and your engine only makes 20" at idle, you will have idle instability as the timing is always changing with any flux in vacuum.

You also need to hook the vac advance to a full time vacuum source, not a "ported" one.

To pass emissions, you may need to unplug the vac can, and retard the timing. This will delay burn in the combustion event, and continue flame burn out the exhaust valve and the result will be a more complete burn out the pipe for emissions. But this is by no means a desired engine tune. It wasn't in the 70's when GM did it either. That catalytic converter came along and did the "final burn" to clean up tail pipe emissions, and a more reasonable "power" timing curve could be used.

['68OrangeSunshine]

An old ''Indian Trick'' to sneak thru Emissions was to pour a pint of alcohol in the tank before testing. HEET was preferreed.

A Bouncing Vacuum gauge needle indicates Valve issues. My 292 L6 is nominal at 17.5''Hg.

I had a '67 K/10 Suburban with a 454/TH350/NP205/3.73 Posi. It burned 6 MPG City, and 8 Highway. It had an engine fire in 1998, and because insurance Totalled it and gave it back as Salvage, I have not been in a hurry to rebuild the BBC. Gas cost less than half today's prices.

A 350 in a '71 GMC K/2500 Flatbed [Rigger's Truck] should not be overburdened. But I don't know anything about a '93 L44.

[MARKDTN]

I see no reason why that truck won't pass 1971 emissions with either an early Quadrajet or a Holley 4150 (600 vacuum). If you have no air leaks and the timing is close it should pass. For what you want to do I would favor a Qjet (actually I would put TBI on it but that ship has sailed). You should be able to find a professionally rebuilt Qjet for a 69-73 350 truck, Camaro, Chevelle, Impala, Corvette, etc. and it should be close enough to run pretty well out of the box. You have a brand new GM engine with a later cam that will have good vacuum and smooth idle.

Back in the day the Carb Shop in Ontario CA was the place to get carbs, but I think the dad died and the son does not have the reputation that the shop once had.

The Holley rebuilds from AutoZone used to be good 20 years ago but I don't hear good things lately.

I see Amazon has a new offshore '68-'73 Qjet for $194. I've run some offshore carbs on a Flathead V8, lawn mowers, and a couple of tractors. Mixed results. You can almost buy 4 for the price of a new Holley 600 though. I might roll the dice.

I can remember when Auto Shack had Holley 600 or 750 Vacuum for $99, your choice. But that's been a while

[Kalums]

Originally Posted by '68OrangeSunshine

An old ''Indian Trick'' to sneak thru Emissions was to pour a pint of alcohol in the tank before testing. HEET was preferreed.

A Bouncing Vacuum gauge needle indicates Valve issues. My 292 L6 is nominal at 17.5''Hg.

I had a '67 K/10 Suburban with a 454/TH350/NP205/3.73 Posi. It burned 6 MPG City, and 8 Highway. It had an engine fire in 1998, and because insurance Totalled it and gave it back as Salvage, I have not been in a hurry to rebuild the BBC. Gas cost less than half today's prices.

A 350 in a '71 GMC K/2500 Flatbed [Rigger's Truck] should not be overburdened. But I don't know anything about a '93 L44.

So the "bouncing" vacuum isn't consistent in any way and it goes completely away when I run it full rich and vacuum is steady at 22 hg, if I put my Edelbrock 1407 on the truck runs like poop but vacuum is steady at 16 Hg...(I can't get it to run smooth on the eddy for Any reason, probably needs a rebuild it didn't work on the old engine either) *shrugs* this tells me it is the carb and I agree the 350 is definitely not "overburdened" in any way I can see/feel/tell.

[Kalums]

Originally Posted by MARKDTN

I see no reason why that truck won't pass 1971 emissions with either an early Quadrajet or a Holley 4150 (600 vacuum). If you have no air leaks and the timing is close it should pass. For what you want to do I would favor a Qjet (actually I would put TBI on it but that ship has sailed). You should be able to find a professionally rebuilt Qjet for a 69-73 350 truck, Camaro, Chevelle, Impala, Corvette, etc. and it should be close enough to run pretty well out of the box. You have a brand new GM engine with a later cam that will have good vacuum and smooth idle.

Back in the day the Carb Shop in Ontario CA was the place to get carbs, but I think the dad died and the son does not have the reputation that the shop once had.

The Holley rebuilds from AutoZone used to be good 20 years ago but I don't hear good things lately.

I see Amazon has a new offshore '68-'73 Qjet for $194. I've run some offshore carbs on a Flathead V8, lawn mowers, and a couple of tractors. Mixed results. You can almost buy 4 for the price of a new Holley 600 though. I might roll the dice.

I can remember when Auto Shack had Holley 600 or 750 Vacuum for $99, your choice. But that's been a while

I say this as nice as I can... But I have had terrible luck with the scamazon/fleabay look alikes and don't want to waste anymore $$ on that poop. The carb shop here told me to look for an 80s Quadrajet with an electric choke as he would be able to tune/tweak it better for my set up ( his apparently is almost identical except he has a 2wd, non flatbed) found one off a 82 Corvette earlier I'm supposed to go look at later (according to him it originally came with TPI and he swapped to a qjet and now has swapped to EFI)

[Kalums]

Originally Posted by 1970-CST

I'd research what timing those TBI engines accepted. Do you have a mighty-vac hand vacuum gun with gauge? Hobo-Frieght has them for around $45.00 or you could rent one from orieley's.

With a timing light hooked up, engine running, unplug the vacuum advance. Plug the mighty vac into the vac can. Begin to pump up the tool to get 1" of vacuum, and note where the timing is. Do this in 1" Hg increments until you note at what vacuum the can BEGINS to add timing, and at what inches of vacuum the timing is maxed out. The number should be 2" less then what ever engine manifold vacuum is at idle, in drive gear for an automatic.

So if the engine makes 20" of vacuum at idle, and 18" in drive gear, then you need a vac can that is fully deployed, adding at least 16* of advance at 16" of manifold vacuum. This is called the two inch rule.

If you have a vac can that is not fully deployed until 22" of manifold vacuum and your engine only makes 20" at idle, you will have idle instability as the timing is always changing with any flux in vacuum.

You also need to hook the vac advance to a full time vacuum source, not a "ported" one.

To pass emissions, you may need to unplug the vac can, and retard the timing. This will delay burn in the combustion event, and continue flame burn out the exhaust valve and the result will be a more complete burn out the pipe for emissions. But this is by no means a desired engine tune. It wasn't in the 70's when GM did it either. That catalytic converter came along and did the "final burn" to clean up tail pipe emissions, and a more reasonable "power" timing curve could be used.

On sale for scamazon "prime" days, will be here Thursday. Thank you for this info I will report back with results.

[MS66]

Originally Posted by Kalums

I say this as nice as I can... But I have had terrible luck with the scamazon/fleabay look alikes and don't want to waste anymore $$ on that poop. The carb shop here told me to look for an 80s Quadrajet with an electric choke as he would be able to tune/tweak it better for my set up ( his apparently is almost identical except he has a 2wd, non flatbed) found one off a 82 Corvette earlier I'm supposed to go look at later (according to him it originally came with TPI and he swapped to a qjet and now has swapped to EFI)

Very best move you could make. The guys(me) that can make a Qjet work know what's up. I've had them all, I always go back to the Qjet for all around best performance.
6 mpg!!?? something is bad wrong there. Release the E brake why don't you?

[Kalums]

Originally Posted by MS66

Very best move you could make. The guys(me) that can make a Qjet work know what's up. I've had them all, I always go back to the Qjet for all around best performance.
6 mpg!!?? something is bad wrong there. Release the E brake why don't you?

Hahahahaha! I needed that laugh. And why did I think about that, stupid parking brakes... . BUT yes I'm thinking the Q-jet will be the best "fit" but to each their own, I've got no reason to judge. *shrugs*

[Rust_never_sleeps]

You can swap an electric choke onto a q-jet quite easily.
Any time you transplant one, it's good to check that the jets and rods are sane for the motor you're putting it on

[MARKDTN]

Originally Posted by Kalums

I say this as nice as I can... But I have had terrible luck with the scamazon/fleabay look alikes and don't want to waste anymore $$ on that poop. The carb shop here told me to look for an 80s Quadrajet with an electric choke as he would be able to tune/tweak it better for my set up ( his apparently is almost identical except he has a 2wd, non flatbed) found one off a 82 Corvette earlier I'm supposed to go look at later (according to him it originally came with TPI and he swapped to a qjet and now has swapped to EFI)

There is/was no carburetor on an '82 Corvette. They all had Crossfire Fuel Injection with 2 throttle bodies. There was no '83 Corvette. All '84 Corvettes had Crossfire then '85-91 Have TPI. TPI (Tuned Port Injection) is EFI. I have a lot of experience with TPI.

I'm skeptical of wanting an '80s Q-jet. There is going to be electronic controls on those besides the choke unless it is a heavy truck model. It will have a bunch of vacuum ports that you don't need/can't use. I still say if you want a Qjet you want an early one that is professionally built. But I don't know who that is anymore.

[1970-CST]

Lars Grimsrud in Colorado is a corvette forum trustee and Rochester expert. I can think of none better. I won't give out his details, but he is easily searchable . I would reach out to him and see if he has or will build a qjet for you.

[Kalums]

Originally Posted by MARKDTN

There is/was no carburetor on an '82 Corvette. They all had Crossfire Fuel Injection with 2 throttle bodies. There was no '83 Corvette. All '84 Corvettes had Crossfire then '85-91 Have TPI. TPI (Tuned Port Injection) is EFI. I have a lot of experience with TPI.

I'm skeptical of wanting an '80s Q-jet. There is going to be electronic controls on those besides the choke unless it is a heavy truck model. It will have a bunch of vacuum ports that you don't need/can't use. I still say if you want a Qjet you want an early one that is professionally built. But I don't know who that is anymore.

You are correct, this guys Q-jet did have a few electric plugs, so I politely passed, he kept using cross-fire and TPI inter-changably... *shrugs* I'm definitely no Corvette expert or even a fan, never been a "go fast" type. Carb shop here has a late 70s Q-jet but wants 400$ for it...

[Kalums]

Originally Posted by 1970-CST

Lars Grimsrud in Colorado is a corvette forum trustee and Rochester expert. I can think of none better. I won't give out his details, but he is easily searchable . I would reach out to him and see if he has or will build a qjet for you.

I literally just emailed him *laughs* he already said he has one built waiting for someone to purchase but I need a core*thumbs up* I'll probably buy from him. I've heard great things about his carbs.

[1970-CST]

Originally Posted by Kalums

I literally just emailed him *laughs* he already said he has one built waiting for someone to purchase but I need a core*thumbs up* I'll probably buy from him. I've heard great things about his carbs.

I wouldn't think too long and just buy it. There is no other human walking the face of the earth that I know of that has Lars reputation and knowledge of the QJet. He doesn't perform "rebuilds" he does restorative precise surgery. It will be better than new.

[Kalums]

Originally Posted by 1970-CST

I wouldn't think too long and just buy it. There is no other human walking the face of the earth that I know of that has Lars reputation and knowledge of the QJet. He doesn't perform "rebuilds" he does restorative precise surgery. It will be better than new.

From what I have read, and heard... I don't doubt it. Thank you for the input. Now I have to find a core -_- good luck to me

[Rust_never_sleeps]

Would you post a contact for Lars, last time I mentioned him in a post I found nothing

[Kalums]

Originally Posted by Rust_never_sleeps

Would you post a contact for Lars, last time I mentioned him in a post I found nothing

I've actually been asked not to share it, you can find it in a different "GM specific/go fast" forum though... Sry best I can finagle