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Old 11-02-2002, 03:57 PM
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Post popping thru carb.on accelerration

Still having the problem of poor acceleration & popping up thru carb. on accel.only this is on a new rebuild,cam,dart heads,wires,dist.pistons,q-jet carb. Stops the popping once you reach any RPM. Also when you remove vaccum hose from dist. there is no change in engine or timing and for engine to run timing is not even close to where it should be. Could this be a vaccum leak somewhere? This is a 77 350 with all emmissions removed.

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Old 11-02-2002, 04:07 PM
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sounds like vacuum leak, but a retarded ign will also give similar problems, so will a junk q-jet.
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Old 11-02-2002, 04:22 PM
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Q-jet was fine 6 weeks ago when i pulled engine for rebuild,and if i retard more than 8BTDC it won't even run.
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Old 11-02-2002, 04:30 PM
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how about a bad advance unit in the distrib.i mean mechanical not vac.or maybe a crossed ign wire?

[ November 02, 2002: Message edited by: BOBCRMAN@aol.com ]</p>
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Old 11-02-2002, 04:39 PM
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No crossed wires and i do get advance when I accellerate useing timing light. Timimg is now set at [guess 20 btdc]. But as I said when I remove vaccum hose from dist. nothing changes in engine speed or timing. Checked all wires with timing light and all seem to be fireing by the strobe the same.
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Old 11-02-2002, 06:54 PM
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You say the timing and idle doesn't change when you disconnect the vacuum line to the distributor. Well that would be normal if you have ported vacuum going to the distributor. Are you using ported or non-ported vacuum to the distributor?
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Old 11-03-2002, 12:57 AM
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Whats ported or not ported mean?
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Old 11-03-2002, 08:03 AM
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Carbs supply ported and non-ported vacuum signals. Non-ported receive their signal from below the throttle plate and supply vacuum all the time. Ported vacuum fittings receive their signal from above the throttle plates. When the throttle plates are closed (idle) there is no vacuum signal but when the throttle opens it creates a vacuum signal above the throttle plate and you now have a vacuum signal. The only problem is I don't have any chevy books telling me whether or not the distributor is supposed to be connected to ported or non-ported vacuum. My Ford is connected to ported. If you hook up a vacuum gauge to the hose going to the vacuum advance or just stick your finger over the end of it, check to see if you feel vacuum while she's idling. Then rev her up to about 2,000 rpm, do you have vacuum at the hose now. If you have nothing at idle but vacuum at higher rpm it is a ported signal. If you have vacuum at it all the time it is non-ported. If it's non-ported and has a vacum signal continuously but it doesn't change anything when you hook it up to the distributors advance can then you may have a frozen advance mechanism. If it doesn't have vacuum at idle (ported) then you need either a hand pump or a vacuum line from a non-ported signal to hook up to the distributor to check the advance mechanism. If your system is supposed to be on a ported signal and there's nothing wrong with your advance mechanism after you've checked it then your problem is probably somewhere else.
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Old 11-03-2002, 08:06 AM
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Does anyone know if his '77 should have a ported or non-ported signal to the distributor?? Where are you 4-jaw???
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Old 11-03-2002, 08:13 AM
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It is my understanding that all distributors should use ported vacuum. You don't want vacuum at idle. If your vacuum advance in the dist. is sticking it will cause your timing to be off. Your base timing should be around 8 - 12 btdc, if your engine won't run there is definitely something wrong. I would check the distributor, the carb like already stated, vacuum leaks as stated, cam timing. Hope this helps.
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Old 11-03-2002, 08:31 AM
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Yes the underhood decal say to remove the hose from dist. and plug and I do have vaccum at all RPMs. I have plugged all ports and really don't find any leaks. I'am going to get a new vaccum advance for the dis. right now will let you know if that works. Its the only thing on dist. I haven't changed. Thanks for all your help. jw
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Old 11-03-2002, 09:22 AM
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If the advance isn't doing anything even with good vacuum source conected to it it's probably bad. All cars say to disconnect vacuum line prior to setting timing to eliminate possible residual vacuum in the line, also on cars with a high idle the throttle plates are open enough to allow a partial signal at the ported line. I would stil double check to make sure you are geting the right signal to the distributor after fixing the advance mechanism. Good luck!
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Old 11-03-2002, 10:40 AM
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i no what the poping is in yr carb but if u hav any nolage on how a crb works u could give it a go but if u dont i would leave it 2 sum1 who does. what has happened is the is ur valves is ur crb is clogged up with **** take ur carb apart give um a good clean and c what it is like then

let ms no if u fun in2 ne trouble
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Old 11-03-2002, 11:49 AM
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Huh?
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Old 11-03-2002, 01:47 PM
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how new is this engine is it possible that the timing gears are off maybe a compression test is in order cam lobes can wear off very quickly if not broke in right for one reason or another
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