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Rochester 4 barrel carb questions

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ChadS

03-21-2008 06:45:03




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Any Rochester carb fans/mechanics out there?? I have a 4 barrel, model E4ME. These are found on later Chevys,, they had a few emmisions plugs on em,, TPS and Something else,,,, the engine starts and runs great, but wont idle down.. The linkage will not come to a rest against the stop. Its internal,,,,, checked the usual gasket bind,, nope,,, anyways,,, Im thinking the TPS sensor, that rides the shaft,, has slipped and blocking the shaft from letting it rest against the idle screw. Question is,,, can I cut the little tab off the bottom of the TPS and fix it that way, or does currect have to hooked up to let it idle down??? They used a computer off these carbs for IGN timing chages,,,, seems to me they are nothing more than input sensors,, and not have any mechanical moments by themselves. Im thinking the sensor is holding it open,,,, can these carbs be used without the computer??? carb is off a 84 trans AM with a 305,,, put on a 78 elcamino with a 355. Carb operates great,,,, just doesnt idle under 1000 rpm,,,, no vacuum leaks,,, something is holding the front linkage off its resting postion,,,, any thoughts??? Confused?? Id like to make it work without the computer,,, cant find any wiring diagrams,,, thanks,, ChadS

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Bryan in Iowa

03-21-2008 10:35:50




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 Re: Rochester 4 barrel carb questions in reply to ChadS, 03-21-2008 06:45:03  
Hiya ! Tps will not cause throtle shaft to hang open, it is actuated by the accel pump arm . Sound like you either have fast idle cam adjustment /choke, or secondaries are hanging open .



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Kentb of SWMO

03-21-2008 08:40:22




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 Re: Rochester 4 barrel carb questions in reply to ChadS, 03-21-2008 06:45:03  
Be sure you do not have a throttle plate that is loose.

Kent



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jdemaris

03-21-2008 08:11:03




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 Re: Rochester 4 barrel carb questions in reply to ChadS, 03-21-2008 06:45:03  
I've never had to mess with the later electric Quads myself - but I have a large Rochester manual here that has a section for it. It shows that carb first being used in 1981 - and mentions that the TPS is very easily bent when working on the carb. If it were mine, I'd check the obvious - i.e. bent TPS stem, warped carb body against plate, or throttle plates binding and out of alignment. I've got a 4GC on my bench right now - from my 59 Chevy. It's much simpler.

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Davidj

03-21-2008 07:37:40




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 Re: Rochester 4 barrel carb questions in reply to ChadS, 03-21-2008 06:45:03  
If there"s an electric heat coil for the choke then you may need to run power to that and see if that does it. It"ll take a minute or two to do the trick. I used to run into that problem when the connection would get dirty. Drove 305 GM"s for 20 years or so. I"m glad they invented fuel injection. Good luck



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gab

03-21-2008 07:30:02




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 Re: Rochester 4 barrel carb questions in reply to ChadS, 03-21-2008 06:45:03  
I have'nt worked on one of those in years but two things come to mind. The choke has to come completely off and the fast idle cam has to be loose. There's probably two choke vacumn pull offs and one or two versions of a choke heater that have to work. Also there's a rod a couple inchs long low on one side of the carb that fits in a slot on the secondary throttle shaft. It has to be loose in the slot, any tension at all will hold the bottom throttle plates open enough to increase the idle. Jim

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Allan In NE

03-21-2008 07:12:17




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 Re: Rochester 4 barrel carb questions in reply to ChadS, 03-21-2008 06:45:03  
Hi Chad,

I've been into every blessed carb that GM ever used from '46 on up.

CCC didn't start until about 1986 or so and I'm wondering if this is actually an 84 carb?

"Usually", they hang on that fast idle cam adjusting screw over on the passenger side. Back and underneith of all that linkage.

Are the secondarys closing?

Does this carb use a heat stove or the electric coil? Got a picture of this rascal?

Allan

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ChadS

03-21-2008 08:31:47




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 Re: Rochester 4 barrel carb questions in reply to Allan In NE, 03-21-2008 07:12:17  
Allen, I can get a picture soon,, best "Visual description" is when your facing the engine, looking at the throttle linkage side, there is whats called a TPS, and its made into the housing,, you would have to remove the air horn to take it out,, 3 wire plug,, the actual part, has a tip on each end and the spring that keeps it resting on the throttle shaft,,, to follow throttle postion and report back to the "Computer" I cant see that part doing anything mechanical by itself,,, but,, possibly it may have got jammed down in there too far some how,,, blocking it from full travel back to idle,,

Now facing the choke side,,, has whats left of electric choke,, the coil is missing,and everything works, and I did back the fast idle adjuster off so it should let the linkage to go full idle,,, simply out, its diasbled, but, not destroyed and will be put back together,,,,

Second plug is on top of the air horn,, towards the choke side,, according to the book, its called ECM connector and soleniod assembly,,, this is where it gets fuzzy cause al I have found is a break down on how its assembled and put back together,, but nothin on the wiring schematic for that plug. Id say this part just might do something mechanical,, Id say with its three wire plug,, one wire will open, one will close it, and one is ground,,, (thats a guess on how it might work) If anything,, this might be whats holding it,, but this is my first dive into early GM computers,,, before fuel injection.

Onthe Trans AM in late 84 early 85, the TA had this setup,, early,, like a test before it was found on bout all Chevy trucks, or Monte Carlos, and Camaros in the 85-87 years that still used carbs. More less, the computer, and its controls, took signals off the TPS as an input sensor,, and the second plug is and output and is controlled by the computer,, and does something,,, no description as to what the solinoid does in any book I found,,, whether it it speeds up the idle internally for the AC switch,, or fast idle,, but the choke does that,,, but not for the AC,, has no electrci swtich on the throttle linakge,,, has idle adjustment screws in the throttle plates,,, (down underneath) its the adjustable type carb,, take off the little cap up top and adjust something in there,,, that has not been done yet,, nor do I suspect it needs any adjusting,, I dont know at this time,,, On that series carb.. Secondarires are closed, the primaries, are being held open just ever so slightly,,, I can force it closed, and it will slow the idle speed down,, nothing on the outside I can see is holding anything,,, so could that ECM solinoid up in the air horn be a open/close or on off fast idle kicker upper for the AC that is built internally for when the AC is kicked on???

Ive ran so many Q jets,, I love em,, they sound great when the 4rs open up,, no holley sounds like that,,, I still have the 850 cfm carb I found off either a caddy or a 454 truck,, but they got some big butterflies!! Had that on a 350 chevy,,, WHEW would that thing go!! pass everything on the road!!!! but a gas station,,,,, , This is the first electric model Ive worked with,, and I think its possible to rig a switch with proper voltage and use a toggle switch to turn it on and turn it off,,, and not have to take it off and replace it with an,,, edlebrock,,, no,,, the thing runs real good!! starts good, even cold! if done right, q jet can give some decent gas milage and good performance. sorry for such a long post,,, just tryin to save a q jet. ChadS

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gab

03-21-2008 09:24:01




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 Re: Rochester 4 barrel carb questions in reply to ChadS, 03-21-2008 08:31:47  
That solonoid ahead of the choke is the mixture control solonoid. It's the electic version of the old vacum power piston. When it's working it rattles like a little machine gun. Jim



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Allan In NE

03-21-2008 08:57:33




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 Re: Rochester 4 barrel carb questions in reply to ChadS, 03-21-2008 08:31:47  
Yes Sir,

You have an honest to goodness CCC carb.

That connection up on the air horn feeds a rudimentary stepper motor that is continually "adjusting" the power valve when the system is in full loop via a computer feedback system.

Okay, you put it on an outfit without a computer control system. Now, what this amounts to is being in "limp mode" all the time, which translates to "dumping" all the fuel it will take just to get you to the hospital.

Being just as honest as I can here Chad, you need to get a different carb. One without the computer controls.

This one is nothing but an oversized paperweight without the dedicated computer system to run it.

Allan

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ChadS

03-21-2008 12:01:41




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 Re: Rochester 4 barrel carb questions in reply to Allan In NE, 03-21-2008 08:57:33  
Allen and all, I appreciate it!!! Wont throw it away,, but Ill save it,, maybe find the computer and distributor and add it someday. I got a huge tote full of rochester/carter Q jets. Probably 30 or so,,,,, Ill dig the best one out and rebuild it. Anybody needs a good carb like this one under discussion, ya know where to find it! Thanks again for the fast service!! Allen,,, I really like that M you got!! been followin that story since ya got it! ChadS

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Allan In NE

03-21-2008 12:07:54




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 Re: Rochester 4 barrel carb questions in reply to ChadS, 03-21-2008 12:01:41  
Thanks Pard,

She's just an ol' sweetie. Gonna make 'er happy by putting her back to work again. :>)

Allan

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ChadS

03-21-2008 14:47:47




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 Re: Rochester 4 barrel carb questions in reply to Allan In NE, 03-21-2008 12:07:54  
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Allen, this is one of my favorites in the shop. A 52 Super M. This one was found in a salvage yard,,, went thru a garage fire, it burned the tires off, but really never got hot,, enough to burn the paint off it,, engine wasnt stuck, so we got it fired up and it spit and sputtered for a second then smoothed right out,,, purred more like it. So we tore it down, fixed a few seals, a few gaskets, and some good primer and a light coat of paint, and there it is. this one has 14.9X 38 rubber on a 12 inch rim,, I think it sets pretty level with em,,, I have a 3 bottom IH pull type plow for it, and gonna turn some soil over with the SM soon as it dries up,,, I have a live hyd and resivior to add to it,, off a later SM,, but its a nice ol tractor. My Super H,, is my pride n joy,,, a 53 model, Ill be fixing up more and more soon on it,,, Did a 12 volt generator conversion on it,, and found the thin head lights,,, has fenders, belt pulley, tool box up on the light bar, few other goodies,,, but a tractor, I would work all day long and its never let me down. Chad

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Allan In NE

03-21-2008 17:46:36




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 Re: Rochester 4 barrel carb questions in reply to ChadS, 03-21-2008 14:47:47  
Whoooo Boy!

I like those rear tires! Where did you get the 12" center drops?

I'm with ya on the fire-babies. Don't hurt 'em a bit. If you're not afraid of a little soot, elbow grease and sweat, they'll come right out of it none the worse for wear.

Betcha bought 'er cheap too, didn't ya? :>)

Allan



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ChadS

03-21-2008 20:44:06




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 Re: Rochester 4 barrel carb questions in reply to Allan In NE, 03-21-2008 17:46:36  
Rims was on it when bought. Had 2 sets of rear wheel weights, and and old IH trip bucket loader. rims are the stepped style rims, Im not sure exactly when this rim came out,,, but some where in 51 or 52,, was thnking bout all the Super M ans Super H's had that style rear rim. Maybe even late production H's and M,,,, I have 560 rear centers on my 50 M, with John Deere 14 inch rims on 15.5X 38 tires. in that style, rims can be as cheap as a pair of 20 dollar duals sold at an auction. Bought the SM for 500, spent about 450 on it, already had the tires just alot of sanding. Need to wetsand it, and finish the hood off with paint,, put on the decal set, even have a set of duals for it. Would a SM handle a Super 68 New holland baler?? I got a #46 IH baler been greasing and try out. Chad

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jdemaris

03-21-2008 08:02:12




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 Re: Rochester 4 barrel carb questions in reply to Allan In NE, 03-21-2008 07:12:17  
The E4ME came out in late 1981. I've got a Rochester data book here showing me production dates. I suspect the first ones were for California use.



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Allan In NE

03-21-2008 08:06:25




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 Re: Rochester 4 barrel carb questions in reply to jdemaris, 03-21-2008 08:02:12  
Yes Sir,

That makes sense. There were a million variations on every model too. :>(

Allan



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