Carb. Question

[86GMC4x4]

How much of a difference is there between a Q-jet carb from 305 to one from a 350. I compared the settings and adjustments for the 2 carb numbers and don't see alot of differneces,or is it just the size of the metering rods??

Thanks

[VileZambonie]

Metering rods and jets are different sizes. The carbs are the same. On feedback carbs the MC solenoid duty cycle is controlled by the PCM so it is essentially the same thing.

[86GMC4x4]

I pulled a carb from a 85 Chev Caprice yesterday while we were in the junk yard.Checked the carb number when I got home and found out that it was used for 305 engines. It looks to be in fairly decent condition, I am thinking of trying it on my 86 4x4 that has a 350 to see if it will work any better then what is on there now.Looking at them they look identical other then whats inside.The price was right so I don't think I have alot to loose if it don't work.

[VileZambonie]

Are they both feedback carbs?

[86GMC4x4]

How do you tell??

[DnStClr]

86GMC, I'm far from being an expert, but maybe this can help explain about feedback carbs. In the 80s, the govt. wanted to find ways to control as much emissions as possible that were coming out of exhausts from vehicles. So electronic feedback systems were installed on carburetors. The feedback originates at a sensor in the exhaust pipe called an O2 sensor. It compares how much oxygen to how much unburned fuel there is in the exhaust, and then turns the comparison into an electrical signal that is sent to a computer. The computer then tells the carb how much fuel/air mixture to add to the engine by electrically controlling the position of the metering rods in the jets in the carb. A solenoid at the carb relays this computer signal, and the higher the voltage from the computer to the solenoid, the deeper the rods go into the jets, so there's less fuel flow.Thus, the term, MC, or mixture control solenoid. At least, that's my understanding of what's going on-    After these  types of carb control systems were developed, then tbi, or, fuel injection, was developed, and the carb was discontinued.
Hope I got most of it right anyhow.  
Now if someone can just explain pulse width...
( After re-reading my post, I edited for spelling errors)

Edited by: DnStClr at: 5/29/06 10:10 am

[86GMC4x4]

Thanks for the replies,both of the carbs don't have any eletronics except for the electric choke.I did some checking on the carb #'s and they came up as the M4ME types. I think I will put a kit in the one that i just picked up and try it to see how it will work.

Thanks again for information

[86GMC4x4]

Installed the carb. on my truck and the only thing I did was clean it externally and cleaned the varnish off with some spray type carb cleaner where I could spray and then bolted it on and she fired up.I was going to put a kit in it but decided to try first to see how it would operate.I  increased my mileage for sure 2mpg if not more,I will know by the end of the week as I drive it more but it seems to be running better then my other carb. that had a kit installed not long ago.