Anyone Know the Rochester DualJet?

Status
Not open for further replies.

RustRocket

Master Mechanic
Sep 8, 2014
351
86
28
Las Vegas, Nevada
Hi, I have a 1982 Cutlass 3.8, and I'd like to know how to tune the carb. I really only need to know which screw does what, as I cant tell. I found the Idle screw, and that's it. If I could learn to adjust the fuel/air mixture and whatever else that'd be great. Its says Rochester DualJet 210 with the GM logo on the throttle side. Any info about these would be great, Thanks
 

Bonnewagon

Rocket Powered Basset Hound
Supporting Member
Sep 18, 2009
10,540
14,217
113
Queens, NY
'82 is computer controlled. Not much you can do. Passenger side has a fast idle screw, which sets your fast idle when cold. It should be between 1500/2000 rpm at start up then drop off as it warms up. Adjusting this may require adjusting the vacuum break to compensate so I don't advise it unless it's way off. Driver side screw is the curb idle for when it's at operating temp. Computer adjusts air/fuel ratio so adjusting this too much may upset computer. Down in front are the idle mixture screws, should be capped from the factory so knuckleheads don't mess with them. If exposed, then carb has been played with. They are factory adjusted and should not be touched at all. That said, a slight richening can cure a rough idle and the computer will adjust to compensate, but then may fail emissions testing. They require a "double D" socket anyway, do you have one? What I'm getting at is if the carb is acting up, get it fixed by some one competent, don't screw around with it.
 

RustRocket

Master Mechanic
Sep 8, 2014
351
86
28
Las Vegas, Nevada
Bonnewagon said:
'82 is computer controlled. Not much you can do. Passenger side has a fast idle screw, which sets your fast idle when cold. It should be between 1500/2000 rpm at start up then drop off as it warms up. Adjusting this may require adjusting the vacuum break to compensate so I don't advise it unless it's way off. Driver side screw is the curb idle for when it's at operating temp. Computer adjusts air/fuel ratio so adjusting this too much may upset computer. Down in front are the idle mixture screws, should be capped from the factory so knuckleheads don't mess with them. If exposed, then carb has been played with. They are factory adjusted and should not be touched at all. That said, a slight richening can cure a rough idle and the computer will adjust to compensate, but then may fail emissions testing. They require a "double D" socket anyway, do you have one? What I'm getting at is if the carb is acting up, get it fixed by some one competent, don't screw around with it.
Well, I know pretty much nothing about carburetors, and the car no longer has a computer. It's just running incredibly rich, and I'd like to fix that.
 

jiho

Royal Smart Person
Jul 26, 2013
1,001
508
113
If you have the original "feedback" DualJet that was hooked up to the computer that's no longer there, then it will never really run right without the computer no matter what you try to do. The computer controlled the mixture by pulsing a solenoid that admits extra air (kind of like an anti-fuel injector). With everything properly adjusted, the solenoid would be pulsed about 50% of the time at idle with the air cleaner off, a little more with it on.

You might improve things some by turning the idle mixture screws in (clockwise), that will lean it out. But then it won't be as rich as it should be at WOT, which might cause trouble.

The computer also controlled the ignition advance. Does it still have the original HEI distributor? If so, the ignition is running in a "fallback" mode, with a fixed advance.
 

82Poncho

Not-quite-so-new-guy
Mar 27, 2013
43
2
8
Ontario, Canada
I have the original Dualjet 210 on my 82 Canadian built V8- no computer control. I bought a carb kit for $35 and basically cleaned and resealed the carb. Real simple. My factory adjustment plugs are still in place and the carb works great. Or just buy a new after market carb and stick it on. That will make an engine run great with no fuss.
 

Bonnewagon

Rocket Powered Basset Hound
Supporting Member
Sep 18, 2009
10,540
14,217
113
Queens, NY
No computer? Why? Is it still there, can you hook it back up? If so, do so, then diagnose whatever is wrong. If not, the only way forward is to go with a non-computer carb AND distributor. Preferably a pre-computer Dual-Jet, like say, a '79 or '80 model. HEI same thing, '75 to '80. Aftermarket carbs can work, but since you say you know nothing about carbs, why add more headaches? You are running rich because without the computer the system is in "limp home" mode which means it will run crappy, but get you home, barely.
 

RustRocket

Master Mechanic
Sep 8, 2014
351
86
28
Las Vegas, Nevada
Bonnewagon said:
No computer? Why? Is it still there, can you hook it back up? If so, do so, then diagnose whatever is wrong. If not, the only way forward is to go with a non-computer carb AND distributor. Preferably a pre-computer Dual-Jet, like say, a '79 or '80 model. HEI same thing, '75 to '80. Aftermarket carbs can work, but since you say you know nothing about carbs, why add more headaches? You are running rich because without the computer the system is in "limp home" mode which means it will run crappy, but get you home, barely.
Well apparently the computer was removed because it was shorted and "locking up the torque converter, killing it every time" The car's actual owner is probably in his mid-fifties, but the last 10,000 miles were by his teenage son, if that has anything to do with it. The son drove it for a few years without a computer, it was parked in a field two years ago when the brakes disappeared, and now it sits in my driveway. The whole car is a mystery
 

darbysan

Master Mechanic
Apr 3, 2007
287
10
18
Las Vegas, NV
X2 on the limp home mode:

Just to clarify a couple of issues. The Dualjet uses a solenoid (Mixture Control Solenoid, or MCS) to adjust your fuel to maintain as close as possible to 14.7/1. It does this by moving the main metering rods up and down inside the jets, essentially switching from full rich to full lean 30-50 times per seconds. With the ECM removed ( or failed) the default position of the solenoid is full rich. There are small springs on the rods that hold them there. So running without the ECM you are in full rich mode. On top of that, the Distributor is also controlled by the ECM, so no spark advance signal is going to the distributor.

The Torque Converter lock up is most likely a bad solenoid in the trans, not a bad ECM. When the lock up is signaled, the solenoid locks up the converter, but then doesn't "release" the converter as you slow down. The result is the converter being locked, and the car stalling as you come to a stop. You can test this by just unplugging the ECM from the trans and driving.

So before doing anything else, plug in the ECM, unplug the trans, and try driving it.
 

RustRocket

Master Mechanic
Sep 8, 2014
351
86
28
Las Vegas, Nevada
darbysan said:
X2 on the limp home mode:

Just to clarify a couple of issues. The Dualjet uses a solenoid (Mixture Control Solenoid, or MCS) to adjust your fuel to maintain as close as possible to 14.7/1. It does this by moving the main metering rods up and down inside the jets, essentially switching from full rich to full lean 30-50 times per seconds. With the ECM removed ( or failed) the default position of the solenoid is full rich. There are small springs on the rods that hold them there. So running without the ECM you are in full rich mode. On top of that, the Distributor is also controlled by the ECM, so no spark advance signal is going to the distributor.

The Torque Converter lock up is most likely a bad solenoid in the trans, not a bad ECM. When the lock up is signaled, the solenoid locks up the converter, but then doesn't "release" the converter as you slow down. The result is the converter being locked, and the car stalling as you come to a stop. You can test this by just unplugging the ECM from the trans and driving.

So before doing anything else, plug in the ECM, unplug the trans, and try driving it.
Well you see there's my next problem, I don't have the ECM, and neither does the previous owner...
 

johnson350

Greasemonkey
Oct 4, 2013
173
2
18
Florida, USA
Since you have no computer already, you could find a regular non-computerized DualJet from around the 78-80 year, that should work. I had an old '79 DualJet that came off a 305 that I threw on mine.

The older ones (like that 78-80 model) are super easy to rebuild, but can be kinda tricky if you've never rebuilt carbs before.

I myself have done the ECM delete, its very simple to do. Also you are going to need a new distributor, I bought a remanned unit from autozone for around 85 dollars. Its for a '78 model, which had vacuum advance. The vacuum advance replaces the computer input going to the distributor.
 
Status
Not open for further replies.

GBodyForum is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. Amazon, the Amazon logo, AmazonSupply, and the AmazonSupply logo are trademarks of Amazon.com, Inc. or its affiliates.

Please support GBodyForum Sponsors

Classic Truck Consoles Dixie Restoration Depot UMI Performance

Contact [email protected] for info on becoming a sponsor