1? 2? 4?

[mikeoverland]

Yep, it's me again. Still working on the basket case (1981 250 I6) and for the life of me i can't figure out what carb should be on this thing. RIGHT NOW it has a 2 bbl varijet 2 that doesn't look like it belongs on the intake since it seems that someone made an adaptor out of sheet metal to put this carb on the intake. there is no code factory code sticker in the vehicle that list what the truck came with so i don't know if this engine is supposed to have a 2bbl or a single bbl carb. the air cleaner assembly fits the existing carb but tht means less than nothing. I have to pull the carb since it is leaking out of the bottom gasket and the bowl is full fo some sort of nastyness that can't be described. I refuse to rebuild the carb if it is the wrong one for this vehicle. Someone out there in net land has to have an 81 250 I6 integrated head motor or has seen a stock 81 intergrated head motor and knows what type of carb should be there. Please let me know.

thanks

Mike

 

[mtnmankev]

If memory serves me right from my old six banger days, it should have a Rochester one barrel, and they used a fairly good sized one.
Many guys would get an adaptor and install a staged two barrel, that gave some better fuel economy running a single primary barrel in light throttle applications, and when the secondary kicked in, it dumped enough fuel to out perform a one barrel carb.
If you really want to get carried away, they also had adaptors for a 4 barrel.
Damn, you made me sweep some dust off the old memory cells in my brane !!
If you can find a really good deal, get a divorced head and manifold set and install them, those integrated ones had a bad habit if cracking, besides being a pain to work with when doing R&R with the added weight.
The only real benefit I ever saw from the integrated set was the manifolds could not vibrate loose from the hold down clamps, but that problem isn't hard to overcome with a divorced manifold.
I may be incorrect as to some of the info as I am digging back purt near 40 years, so I am not going to be insulted if one of our GM gurus comes along to correct me.

 

[Turbo4whl]

I owned an '81 4.1 (250) years ago. I don't remember either. Both the 1980 auto sticker and the 1981 3 speed sticker shows a two barrel in the diagram:

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[SirRobyn0]

@mikeoverland If you have the ability to take a picture and upload it of the current carb and the sheet metal thing it might help us out.

I know the older I6's ran the rochester 1bbl for sure. I guess one question is do you want to run the factory carb, or is just feeding it fuel effectively so it runs right good enough?

Ok, so I just looked it up. According to my reference info, there was only two carb option for the 81 C10 I6 either the rochester 2SE or rochester R2-2SE either way your looking at a 2 barrel rochester as the original carb. Could the sheet metal thing be a home made heat spacer of some sort? Could it have the wrong manifold on it, and the right carb?

 

[AuroraGirl]

Depending on the option and the year youre looking at one of these, generally

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Rochester Monojet off a 250 I6 from 76(nova)

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Rochester Varajet 2 off either a truck v6 or an inline 6 MOST LIKELY but it could have come from any number of GM cars, usually 4 to 6 cylinders

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Rochester 2jet, they came in oogles of sizes options shapes of base features cfm etc

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This is a shape of the varajet 2s base on a lot of things. Varajet II were used usually where a 2jet would be that wasnt already taken up by a Dualjet which is the front half of a Quadrajet which could have taken the space of 4 barrels or they had revisions of smaller bases but they still kinda took a fair bit of space and you couldnt get the throttle cable in the right spot my guess without doing more work.

2jets mostly fell out of use to my understanding for EPA reasons but I could be wrong. 1979 cars to my understanding went to Dualjets. Trucks used a Dualjet till 1980 I THINK but I forget for sure

 

[SirRobyn0]

@AuroraGirl If my reference material is correct then it should be your second picture varajet 2SE or R2-2SE.

 

[AuroraGirl]

@AuroraGirl If my reference material is correct then it should be your second picture varajet 2SE or R2-2SE.

sounds about right. assuming its not a 1 barrel intake with one slapped on and thats what he meant by adapter

 

[SirRobyn0]

@AuroraGirl hopefully he'll post up pics, then we'll all know.

 

[Ellie Niner]

@mikeoverland All truck 250's used some flavor of Varajet from 1979-84; I believe the car applications hung onto the one barrel for 1979, their last year in US production. I've never been inside of one before, but from my experience driving a couple of cars and an S10 equipped with a Varajet, they seem to work quite well... though I've heard some people gripe about them- usually the models that are computer controlled.

@AuroraGirl The Varajet is a progressive two barrel, with one primary and one secondary... sorta like a Q-jet sliced in half the other way. You're correct. Both it and the Dualjet replaced the old 2G/2GC carbs due to emissions regs and fuel economy. I've never liked the Dualjet, as it feels exactly like a Quadrajet with the secondaries stuck shut (imagine that?!). Progressive two barrels are a lot more flexible over a wider range of operating conditions.

 

[AuroraGirl]

@mikeoverland All truck 250's used some flavor of Varajet from 1979-84; I believe the car applications hung onto the one barrel for 1979, their last year in US production. I've never been inside of one before, but from my experience driving a couple of cars and an S10 equipped with a Varajet, they seem to work quite well... though I've heard some people gripe about them- usually the models that are computer controlled.

@AuroraGirl The Varajet is a progressive two barrel, with one primary and one secondary... sorta like a Q-jet sliced in half the other way. You're correct. Both it and the Dualjet replaced the old 2G/2GC carbs due to emissions regs and fuel economy. I've never liked the Dualjet, as it feels exactly like a Quadrajet with the secondaries stuck shut (imagine that?!). Progressive two barrels are a lot more flexible over a wider range of operating conditions.

"cut in half the other way" is a good way to say it even though i knew that, thanks lol. also it explains the shape more if you think about it that way

 

[AuroraGirl]

@mikeoverland All truck 250's used some flavor of Varajet from 1979-84; I believe the car applications hung onto the one barrel for 1979, their last year in US production. I've never been inside of one before, but from my experience driving a couple of cars and an S10 equipped with a Varajet, they seem to work quite well... though I've heard some people gripe about them- usually the models that are computer controlled.

@AuroraGirl The Varajet is a progressive two barrel, with one primary and one secondary... sorta like a Q-jet sliced in half the other way. You're correct. Both it and the Dualjet replaced the old 2G/2GC carbs due to emissions regs and fuel economy. I've never liked the Dualjet, as it feels exactly like a Quadrajet with the secondaries stuck shut (imagine that?!). Progressive two barrels are a lot more flexible over a wider range of operating conditions.

if they werent known as to be unreliable, the heated gaskets would be a cool and good thing to use in my climate range .but they go out like hot cakes apparently. EFE heaters

 

[SirRobyn0]

@mikeoverland All truck 250's used some flavor of Varajet from 1979-84; I believe the car applications hung onto the one barrel for 1979, their last year in US production. I've never been inside of one before, but from my experience driving a couple of cars and an S10 equipped with a Varajet, they seem to work quite well... though I've heard some people gripe about them- usually the models that are computer controlled.

@AuroraGirl The Varajet is a progressive two barrel, with one primary and one secondary... sorta like a Q-jet sliced in half the other way. You're correct. Both it and the Dualjet replaced the old 2G/2GC carbs due to emissions regs and fuel economy. I've never liked the Dualjet, as it feels exactly like a Quadrajet with the secondaries stuck shut (imagine that?!). Progressive two barrels are a lot more flexible over a wider range of operating conditions.

I agree the varajet was a great carb. though a lot of guys did not like the computer controlled carbs, like with TBI, the reason guys did not like them was lack of understanding. It was a very simple system really, with the computer only able to vary the size of the main jet at cruse. Coolant temp sensor, O2, and TPS were the main sensors. Back then I was running around in a 1985 Chevrolet Celebrity, 2.8L with a computer controlled varajet and regularly got 26 - 28mpg on the highway.

 

[Ellie Niner]

if they werent known as to be unreliable, the heated gaskets would be a cool and good thing to use in my climate range .but they go out like hot cakes apparently. EFE heaters

Yeah. I've seen those EFE heaters in some parts lists, and my only takeaway was that they look like they might restrict airflow quite a bit... I wonder if those were used in all applications, as it seems like it would be easier to just route an exhaust passage under the intake manifold on something like a 2.8 V6, and operate it in a conventional fashion. The EFE setup on my 1986 uses a Thermal Vacuum Switch on the thermostat housing which operates a vacuum motor on the heat riser valve, instead of the old school bimetallic spring. FWIW- It still works great. The EFE setup on my 1975 GMC back in Montana went away when we put headers on it many years ago, and yep... It could be pretty miserable for a few miles after a cold start.

But yeah... I just looked at some prices, and those electric EFE heaters are pretty damn expensive.

 

[AuroraGirl]

Yeah. I've seen those EFE heaters in some parts lists, and my only takeaway was that they look like they might restrict airflow quite a bit... I wonder if those were used in all applications, as it seems like it would be easier to just route an exhaust passage under the intake manifold on something like a 2.8 V6, and operate it in a conventional fashion. The EFE setup on my 1986 uses a Thermal Vacuum Switch on the thermostat housing which operates a vacuum motor on the heat riser valve, instead of the old school bimetallic spring. FWIW- It still works great. The EFE setup on my 1975 GMC back in Montana went away when we put headers on it many years ago, and yep... It could be pretty miserable for a few miles after a cold start.

But yeah... I just looked at some prices, and those electric EFE heaters are pretty damn expensive.

cold weather packages only. it helps driveability a lot esp on an engine that doesnt make a lot of heat fast or for the size of that carburetor
im unsure of them using THERMACS or not

 

[AuroraGirl]

cold weather packages only. it helps driveability a lot esp on an engine that doesnt make a lot of heat fast or for the size of that carburetor
im unsure of them using THERMACS or not

Did you by chance know any Monsanskys out in montana? My gpa is from there and he brought with him, to wisconsin, his 75 GMC and thats the one that now sits in my dads driveway with a hole in the TH350

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