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Old 08-01-2003, 06:42 AM
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350 running rough

I just bought a 84 chevy 3/4 ton at work mostly to haul my horses. It has a freshly rebuilt engine. Judging by it's appearance and compression and vaccume readings. The q jet was worn out beyond repair and yesterday I installed a new edelbrock 1406 600 cfm elec choke carb with a mister gasket 1 in thick adapter plate onto the old intake. It was an aluminum spreadbore intake marked gmc on the back. I doubt if it was original. I still have some cooling system issues to deal with like a worn out fan clutch and a 1 row radiator. I have no idea how that got there. It has a goose neck and 5th wheel plate in the back and i know he didn't do any hauling like that around here. Anyway. I tried setting the timing to factory specs and boy does it sound like it has a big cam in it. Specs called for 6. I had a lot of trouble with it having to idle too high just to stay running and I ended up moving the vac advance to the timed port on the carb and I bumped the timing up to 10. It idles ok there but still feels like a big cam. Timing doesn't feel quite right yet also. Assuming this engine does have a bigger than stock cam what is the best way to get it timed. I have been working on fuel injection systems and big diesels way too long and have forgotten most of this fun stuff so please forgive if this is a stupid question. I have the idle set at 850 in neutral and it dropps to 600-650 in gear right now. If I put the advance hose back to the other port on the carb and reset the idle to 850 then it will drop rpm down to the point of stalling when I put it in gear. I didn't think it was sopposed to go on the timed port but maybe I was wrong. It wasn't hooked up to anything when I got it. I looked at the total advance it was getting but can't remember what it was. Do ya'll think I should just go by that instead of base timing and learn to live with a rough idle. Just let me know the best way and I'll give it a try.

Oh I forgot to introduce myself. Sorry you know how new guys are. Any way My name is dan and I recently retired from the military. I haven't had time for hot rodding in a few years but we do got a nice one that my wife drives every day. Although not the normal car for hot rodding it can beat anything around here that I have seen. It is a 73 electra 4 door in shoroom condition , Light crystal blue, with a 455 stage 1 that I overhauled about 3 years ago. It is mostly stock but has a edelbrock performer intake and a holley 750 cfm carb. It dynoed last year at 400 horse. My wife sure likes driving around in her duece and a quarter. I call it the professor mobile. She is a professor at texas tech. I just wish people would quit asking if it was for sale. We also have a 91 ford 150 4x4 , This chevy truck that I just got and a 50 year old farmall super c that is my favorite hot rod. You should see the wheelies it can do. Unintentional usualy. My son and I restored it a couple years ago. I hope I can help someone here out some day. See ya.

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Old 08-01-2003, 02:18 PM
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was the adapter a open adapter? if so this is half the problem, the open adapter kills low end power in favor of upper RPM power, and causes the vacuum signal to be out of whack. you can go to advance auto parts and get a edelbrock 4 hole adapter that will take care of that. you should bump your spark timing up to 12 degree`s before top dead center,and 38 degree`s before top dead center all in before 3000 RPM, and leave your vacuum advance connected to a timed port. it idles rough likely due to the open adapter, one cylinder is drawing off 2 barrells instead of one so it`s likely very rich at idle.
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Old 08-01-2003, 02:42 PM
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DV hit it before I could, good going.
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Old 08-01-2003, 05:43 PM
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Ya know I think you did hit the nail right on the head. I was thinking about this all day at work and it dawned on me that is about the only thing it could be. I don't know where my brain was yesterday. I actualy asked for the edelbrock adapter by part number even from advance and they sent me the mister gasket open one. It runs just like that old scorpion intake I got sitting in the garage. Big open plenum. I didn't say anything since they were also delivering a pizza from pizza hut for free. Between my truck and my bosses and one car from the lot I spent over a thousand bucks there yesterday. That's why they brought pizza. Car quest does the same thing for us. Cool huh? That open adapter would also explain to some extent at least the long crank time when the engine is hot wouldn't it? It ain't that bad but 5 seconds or so. I got spoiled with my wifes hot rod 455 always starting right off unless it is raining bad out. It still has points. Oh well thanks for the help.
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Old 08-02-2003, 11:58 PM
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Cool

I am a new user also so I hope I can help you out here.
First the vacuum advance goes to the venturii vacuum(timed) port. The other port is the manifold vacuum. Connect a vacuum gauge to that port and it should read between 18-20 inches of vacuum. I think you will find you have about 10-12 inches of vacuum. I think this because I think you have a vacuum leak around the base plate. There are two gaskets on this one inch plate and I think the one next to the manifold has slipped aor just doesn't fit causing the rough idle. Once you get the engine up to speed it runs fine. To check if I am correct just hold your hand over the top of the carb while the engine idles, if the RPM goes up you have a vacuum leak. If the engine trys to die out then you don't have a leak and I am red faced, but I am certain this is the problem.
Once you have the leak figured out to set the timing just leave the vacuum gauge connected and turn the distributor with the vacuum line disconnected and plugged until your vacuum is 18-20 and you are good to go.

Now a little about me.
My name is Dave and I have been an Industrial Arts Instructor for 29 years. At this time of my life I am looking to retire into something I love and that happens to be hotroding or should I say building the fast vehicals. I have taught everything from photography to woodshop. I have a Vocational Credential in Automotive but for the past few years I have been teaching Manufacturing Technology(metal shop).
I hope I don't make to big a fool of myself as I use this new form of communication. I can talk but when it comes to writing I stink but I try.

Later
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Old 08-03-2003, 06:33 AM
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I got the gaskets on good the first time. I did think about that though and checked a couple times with carb cleaner around all the places a leak could happen. It is just that open adapter. and last night as I was checking the valve lash I found all kinds of goodies under the valve cover. a nice set of comp cams alum roller rockers. I went a little further and got out the dial indicator to check all the lobe lift heights and I got a sneaking suspician it is a comp 280 in there. Just a suspician though since I hav no way to be sure without pulling it. I had that same cam in a 69 chevy truck about 10 years ago and I had a 305 dur one in a 68 nova about 5 years ago . The idle quality is about the same as a 280. Lobe lift about matched it too if I remember right. Oh well. I only got it about a week ago . A teenager traded it in on a newer z71 after he got done butchering it. I got most of the problems fixed now but still need to get the proper radiator. It only has a one row in it. I got the air fixed up and charged and the carb replaced. Engine is adjusted properly and it actualy runs pretty good for a kid built motor. I just hope it holds together. I did a few runs on a backroad the other night playing with the timing and carb and now it will really take off hard and light the tires up pretty good. It should pull a trailer pretty good.
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Old 08-03-2003, 09:09 AM
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At this time of my life I am looking to retire into something I love and that happens to be hotroding or should I say building the fast vehicals.


I think thats great, Im sure whatever you plan on building, consult the many experts on here and youll get it right the first time..
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Old 08-04-2003, 06:15 AM
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Glad to hear that you have it running, stay in touch if you change the spacer and the outcome.
To scholman if you have a different question PLEASE make a new post on the forum as stated in the guideline' to stop all confusion.
Thank's George
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Old 08-04-2003, 06:37 AM
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I will stay in touch. I plan to put on an eldebrock performer manifold instead of the spacer though. Right now I got another list of priorities though and it will have to wait a while. At least it runs good and will pass inspection now. Thanks for the help.
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