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Old 03-08-2004, 04:41 PM
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black Smoke and Stalling

Ok, with all of you help, I finally have gotten my truck running half decent (at least compared to what it was like when I first got it). Pretty much the last major piece of tuning left is minor stuff with the carb. Heres the scenario:

On quick acceleration, the engine stalls. This happens no matter what speed I am going, off of start, or at 30, or at 50. The engine just dies. If I press the accelerator peddle slowly and evenly, the truck will accelerate as it should, with out hesitation.

At WOT, I experience black smoke out of my tail pipe. Letting off WOT and re-accelerating at a normal rate, i experience carb backfire at all points of accelerations. If i wait for about 20sec or so, this stops, or won't even happen at all. This only happens immediately following WOT. I'm puzzled.

I have tried my idle mixer screwed at about 1 1/2 turns, 2 1/4 turns, and even 1/2 turn. seems to be the same symptoms at all points. Could my floats be off and I am possibly flooding the carb?


Sorry for being so wordy.

Steve

******************************
1979 Chevy Pickup K10 4x4
Stock 350ci w/ exception of
Holley double pumper 4bbl 650cfm
224,000mi on Truck w/ about
150,000mi on Engine

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Old 03-08-2004, 04:44 PM
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Black smoke usually means you are running too rich.......

The stalling sounds like a bad accelerator pump, or a vacuum leak......

What carb is it?
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Old 03-08-2004, 04:51 PM
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its a Holley 4bbl double Pumper with a single feed line. Below is one similar to what I purchased.

http://cgi.ebay.com/ebaymotors/ws/eB...tem=2465040653
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Old 03-08-2004, 04:57 PM
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Thats a Holley 650 spread bore.....Possibly too much carb for a stock 350.

You would be better off with a Holley 600 Vacuum secondary, but then you should also get a square bore manifold.
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Old 03-08-2004, 06:00 PM
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yup, that sounds like exactly what I did on my first 350. Figured "more is better" and slapped a 750 cfm dp on there... thing would die everytime i'd try and beat a rice-rocket off the line. got pretty frustrated with it. then i bought a 600 cfm edelbrock. suddenly my car was alive again!

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Old 03-08-2004, 06:15 PM
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That is a terrible carb for your application. Sounds like a badly adjusted acc pump or restricted squirter started the problem but now it sounds like maybe you toasted a power valve from all the backfiring from bringing that large secondary in too fast. DOUBLE PUMPERS DON"T BELONG ON THE STREET with a mild engine and automatic trans drive train combo. Go to a properly adjusted vac secondary carb and your troubles will vanish.
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Old 03-08-2004, 07:48 PM
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Well,I think you have a bad,or wrong sized,or both,power valve myself. I personally like a double pumper,yea,they use a little more gas,but if they are set up right they have zero lag between the primaries and secondaries. 650 might be a little bit big,but not to bad. I would also make sure your timing weights are working properly and your vacuum advance line is hooked to the port on the carb that has minimal or no vacuum at an idle and more at a rev. Just my opinion.

Then set your timing,timing problems can do the same thing,and blow your power valve.
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Old 03-08-2004, 10:14 PM
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for my timing, I am using an advance cure kit with the silver springs. I have my timing set at 10deg at about 700rpm
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Old 03-09-2004, 06:37 PM
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How about that advance hose location? Has it always run like that with that carb?
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Old 03-09-2004, 08:48 PM
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The carb hos only been on this engine for about a month or two. It hasn't been driven too much due to the poor conditions of the engine.
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Old 03-09-2004, 09:18 PM
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Keep in mind,if your vacuum advance hose is hooked to constant vacuum,that portion of advance will be maxed out at an idle. When you give it throttle under any load,your manifold vacuum will drop,as will your timing,and can cause major acceleration issues at the least. Check that first. An easy way to check it is while its idling low,pull the hose off the distributer and see if the idle changes.If it does,its on the wrong port. If its wrong and you switch it to the right port,you will need to retime it because it will be retarded at an idle. I still think you have a bad power valve as well.
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Old 03-10-2004, 12:41 AM
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I replaced the power valve tonight, re torqued my intake manifold, as well as my carb. Same thing. After letting off the throttle, then re-accelerating, my carb pops slightly, and then sometimes stalls....if i just lean on the accelerator at any point, ie. off of a stop, or at any speed, it will also stall. my accelerator pump seems to be working as it should.

I did check the vacuum port where my vacuum advance is connected too and that is fine. I timed the engine with this advance disconnecter. Could me vacuum advance canister be bad and causing this problem? Or is there an other adjustment that I am missing. Could my engine be starving for gas, my stock fuel pump not putting enough out, or is my carb flooding. Keep in mind that this is a double pumper. Thanks for taking the time to try and help me, I do appreciate it greatly.

Steve
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