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I`m not getting the response off the line like I should, engine bogs or stumbles its hard to diagnois,spark plugs look light brown in center and black ring on outside.355 3:70 posi N50/15 tires in rear350 tranny w/ 2000 stall speed,700cfm holley double pump,edelbrock performer rpm manifold,msd6a,blaster2 coil,trickflow aluminium heads170cc,comp cams xe274 cam,msd electric distributor,9:5-1 compression.I`m thinking its nozzles and pump cams,I`ve got.31primary nozzle, and .28 in secondary,with stock pump cam,and stock jetting,what do you think?
 

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Your stall looks to small. I have a 272 cam for my 350 and a 2000 stall is on the bordline for my cam. Just a thought if all else seems to be alright.

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70 Camaro 307cid(350soon) /350th ex. dark purple (dark blue soon) in. black
74 Trans Am 400cid/th400 ex. red in. red power windows
 

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First things I'd do is to re-check idle mixture, make sure primary thottle plates are closed, if engine doesn't idle enough, turn up secondary adjustment on base plate on pass side to promote good idle. Then reset idle mixture, use vacuum gauge for best vacuum reading while tuning. Should be around 12-18 inches at idle, steady reading, +/-1 inch, meaning no short lobes, stuck valves, misfiring cylinders, etc. Probably set curb idle for 900-1100 rpm

Then, one should recheck initial timing, 10-14 deg, check mechancial advance is working and vacuum advance is working correctly if used. Check the books for total amount of advance @rpm, remember, rpm given for distributer is at dist rpm, not crankshaft, just X2 the amount. Ball park figure, I would suggest is 30 -34 degrees at 3000rpm with all three advances totaled up.

Now with the above done, try again. Might try more advance till it pings, then back off two degrees on initial.

If it still bogs, disconnect the secondary side all together, it may be the mech secondary is dumping too much too fast, then you might have to try a vacuum secondary carb to correct your problem.

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Everett 68/350/PG/11.90/115mph
 

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ooby <BLOCKQUOTE>quote:</font><HR>Originally posted by Everett#2390:
First things I'd do is to re-check idle mixture, make sure primary thottle plates are closed, if engine doesn't idle enough, turn up secondary adjustment on base plate on pass side to promote good idle. Then reset idle mixture, use vacuum gauge for best vacuum reading while tuning. Should be around 12-18 inches at idle, steady reading, +/-1 inch, meaning no short lobes, stuck valves, misfiring cylinders, etc. Probably set curb idle for 900-1100 rpm

Then, one should recheck initial timing, 10-14 deg, check mechancial advance is working and vacuum advance is working correctly if used. Check the books for total amount of advance @rpm, remember, rpm given for distributer is at dist rpm, not crankshaft, just X2 the amount. Ball park figure, I would suggest is 30 -34 degrees at 3000rpm with all three advances totaled up.

Now with the above done, try again. Might try more advance till it pings, then back off two degrees on initial.

If it still bogs, disconnect the secondary side all together, it may be the mech secondary is dumping too much too fast, then you might have to try a vacuum secondary carb to correct your problem.

<HR></BLOCKQUOTE>I have the intial timing at 20 degrees and total of36 all in by 3000rpm,I use 91 octane and engine still does not ping anymore advanced and its to hard to start,I dont get any black smoke out the exhaust,so I`m thinking I need to up the nozzle size?I have the vacuum hooked to manifold vacuum.vacuum is12hg at idle and about 7hg in gear,I have a 3.5 power valve in carb.
 

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One could try a larger squiter, I have installed a 37 on a truck I had.

But then, you get into the deal where the pump cam is too small, you step on throttle, engine picks up for a short amount, then dies due to not enough fuel delivered before the main system kicks in.

I'd still try disconnecting the secondary side just to see what would happened. Ideally, one wants the car to pick up and accel, but even if the Tq/conv is small, engine should still be loaded and not die out.

You said vacuum hooked up to manifold, I hope the vacuum diaphram on dist is hooked to a ported port, above the throttle plates, don't want vacuum at idle. I'd relocate vacuum source from full-time vacuum to ported. Try it.

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Everett 68/350/PG/11.90/115mph
 
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