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I know Victoria's secret....
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Discussion Starter #1
Early spring I swapped out a Weiand intake with Edelbrock carb for the same Weiand intake with a spreadbore pattern so I could upgrade to a JET performance Qjet on my 305. I lost the timing during the intake swap, and reset by watching the #1 rockers and damper to set the distributor. Got it started, but with a constant backfire through the exhaust. Not a slight pop, but enough that it sounds like a shotgun and I can feel it in the seat. It's not a consistant/rythymatic backfire. The car has NO torque, too. I have to rev it to almost 3k to make it up our driveway incline without it stalling out, and about 2500 rpm just to get moving. Under light load it's constant popping and bucking.

Since all of this started, I've:

Replaced cap and rotor
Replaced Plugs
Replaced Plug wires
Replaced Ignition coil
Replaced Distributor
Replaced intake gaskets
Replaced Carb Gaskets

Due to the firewall and intake, and factory spec, the connectors on the HEI have always pointed at the driver side fender, and #1 should have rotor pointed at the driver side headlight. I have tried this multiple times with no luck, as well as going clockwise one or more teeth from OE spec with the rotor. It's gotten better but not enough.

What else should I be checking? I've been told I wiped my cam, but that seems suspect with no warning signs prior. It was like I hit a backfire switch with the intake/carb swap. My time to work on the car is limited and spaced out. Maybe 6 times since spring, including tonight.
 

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Remove #1 spark plug, put finger over plug hole, now crank eng over by hand until it starts pushing air past your finger. Slowly continue until dampener line is at 0. Now set distributor rotor to line up with #1 on cap.
Now put spark plug back in and start it up then adjust timing with timing light.

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You have the distributor in 180 out.
 

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You need to check not only the #1 rockers but the rockers of the 5th cylinder in the firing order, they will be in overlap if you are truly on #1 compression.
 

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I know Victoria's secret....
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Discussion Starter #5
Remove #1 spark plug, put finger over plug hole, now crank eng over by hand until it starts pushing air past your finger. Slowly continue until dampener line is at 0. Now set distributor rotor to line up with #1 on cap.
Now put spark plug back in and start it up then adjust timing with timing light.

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I have tried that multiple times as well.

You have the distributor in 180 out.
Would it even idle if that was the case? It starts and idles as would be expected, but has the addition of no torque and constant exhaust popping/backfiring.

You need to check not only the #1 rockers but the rockers of the 5th cylinder in the firing order, they will be in overlap if you are truly on #1 compression.
I'll sanity check that the next go around.
 

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I don't know what timing cover timing pointer you have along with what balancer you have but one thing is chevy used three different timing locations over the years and sometimes you can have the wrong timing pointer with the wrong balancer and you can be off on your timing no matter what you try to set it at.

It sounds like your timing is just way off with what your describing and I would do a TDC location check just to make sure yours is right on. The chevy used the 12 o'clock position and the 2 o'clock position and also the 2:30 clock position and I think most aftermarket balancers for the small block chevy is that is what you have, use the 2'oclock position I think as on a 6 3/4 size balancer the TDC mark will be an estimated 10 to 12 degrees to the left of the middle area of the crankshaft keyway groove. The 2:30 position would have about 2 degrees left of the keyway groove.

The 2:30 position is usually on 69 and earlier balancers and the 2'clock was used up till around 1986 and then after that they used the 12 noon position on there balancers factory wise.

If our unsure you can always get a piston stop and take your number one plug out then put the piston stop in and slowly turn your engine by hand clockwise, then once it stops mark the balancer where it shows TDC then rotate the engine the reverse till it stops again, mark the TDC location again where it shows up on your balancer.

Then measure the halfway point between the two lines and that would be your true TDC and if it lines up then your good if not that would be your correct TDC location and make a new mark if needed. Also make sure you use a timing light as one time I had my engine all tuned well and I had to replace a distributor cap and I just made a mark where I left my distributor at and loosened it up and replaced everything as I am cramped at the firewall and its hard to get a screwdriver down in the rear screws if I leave it alone where it is at the correct position that I need so I loosened it up to make it easier.

I also at the time swapped out carburetors as well and I put my new cap on and put my distributor and tried my best to align it with the mark I made on the intake and distributor and it was really close. I installed my new carburetor and adjust the thing and kept getting a backfire when hitting the throttle and it puzzled me as to why when I set up my new holley the same as my old.

To save my time the hassle I should have used a timing light to check and verify I was back to where my timing was previously even though my mark looked liked it was right back, it was not and I was almost ten degrees off initial timing and could not believe I was off that much and I loosened it up and just had to turn it about 3/16 of an inch or a hair more and it was then where it should be.

After I did that I was able to no longer have any backfires and ripping my hair out for three days trying to change this and that on my new carb and could not get rid of it. Verifying timing is critical even if you think your close its always to make sure and verify things to eliminate problems like this.
 

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I know Victoria's secret....
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Discussion Starter #7
Balancer is a CAT performance fluid damper. Pointer is from speedway and timing cover is either summit or speedway. Built the engine 15 years ago so a bit foggy on details. Turned very by hand until compression on #1, and moved it to 0* on balancer at 230. Trying to stab it currently and get the rotor pointed between 1 and 8. I think the incline on the drive is working against me with the oil pump driveshaft.
IMG_20201222_102243.jpg
 

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Remove #1 spark plug, put a finger over plug hole, now crank eng over by hand until it starts pushing air past your finger. Slowly continue until the dampener line is at 0. Now set distributor rotor to line up with #1 on the cap.
Now put the spark plug back in and start it up then adjust timing with a timing light.

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This explanation was the best as far as timing an engine that has been disturbed during disassembly allow me to clarify:
Compression pushing your finger at the number 1 spark plug hole is an indication that the number 1 cylinder is about to fire. when you stop at this point, the balancer timing mark should be near 0 Top Dead Center. Bear in mind! if you move the balancer backward you will take any slack out of the timing chain before your camshaft moves hopefully what we are trying to do here is catch the timing mark so you don't have to move the damper BACKWARDS to put it on 0 TDC. Hopefully, the damper has not spun on the rubber insulator sometime in the past.
With the timing mark on 0 TOP DEAD CENTER, your distributor should be inserted so that the rotor is pointing at the number 1 terminal on the distributor cap. This is rough or static timing. The wires in a clockwise position starting at the number 1 terminal is 1-8-4-3-6-5-7-2. It's not hard to get messed up doing this so check and double-check.
So Assuming this is what you have done time and time again lets address backfiring :
Constant backfiring thru the exhaust sometimes is an indication of the spark occurring while the exhaust valve is still open
or not seating. one possibility is a crossed wire! (double check and triple check ) One sure way is to follow the wire by hand from the cap all the way to the appropriate spark plug. Another grim reality is there is a broken exhaust valve spring not allowing the valve to seat completely.
Finding the backfire: place the wires loosely on the distributor cap and one by one remove the wire from the cap.
the backfire will stop when you have removed the wire depriving that cylinder of spark. I am assuming that you are aware of the spark that can be created by HEI and insulated pliers are recommended. Hopefully, now we have found the backfiring cylinder and next is to Quadruple check the firing order and if the wiring is correct its time to pull that plug and try a compression test in that cylinder. you can also check the valve springs in that cylinder for broken springs.
I'm imagining at this stage of the game you had to have found something so keep us posted and good luck!
 

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I know Victoria's secret....
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Discussion Starter #9
I'll have to check out for certain which position my balancer is. Appreciate the info for ID!
 

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A common problem is intake gasket leaks, hence it is important to use a vacuum gauge to get a reference before starting such projects but even now it’s a good idea. These are a valuable diagnostic tool. While perhaps not giving a specific answer in terms of off timing versus a vacuum leak it is a tool that identifies problems and narrows the bandwidth of possible places to look rather than just heaving parts at it and hoping something sticks as that gets expensive and doesn’t usually solve the problem.

A good vacuum gauge is part of my instrument panel as well as a couple test models in my roll around, that’s how important a tool I consider these. Price is not an indicator of quality, I have a Stuart Warner that against a manometer reads high by 5 inches where I, also, have two cheap Harbor Freight units that are balls on.

Bogie
 

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I know Victoria's secret....
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Discussion Starter #11
Got her running, again. I need to get a new timing light since my pickup just melted on the #1 primary. Explains the electrical odor and why the light wasn't firing. I am planning on using the rear port (brake booster) to read vacuum for idle. Still have the popping under throttle. Seemed to get worse as it warmed up. Would extended needlenose pliers be insulated enough to safely remove plug wires?

Interesting things of note-
1. My fans weren't coming on (unrelated), but were drawing power from the HEI 12v power source. When I disco'd the wire, the engine died and it somehow shorted the coil. I tested primary and secondary per the manual, and it failed secondary test. Replaced coil with known working coil. Wiggling the wire caused it to die again, but not short the coil.

2. While it was idling, I thought maybe it's jetted too rich for a .30 over 305 with a cam (214/224). I opened the secondary butterflies with no audible change in engine RPM.

I took a couple videos so you can hear it below. First video was with newer coil that shorted, 2nd with the old coil.


 

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Have you done a cylinder leakage test or even compression ?
That sounds like exhaust gasses igniting in the intake to me.

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I know Victoria's secret....
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Discussion Starter #13
This explanation was the best as far as timing an engine that has been disturbed during disassembly allow me to clarify:
Compression pushing your finger at the number 1 spark plug hole is an indication that the number 1 cylinder is about to fire. when you stop at this point, the balancer timing mark should be near 0 Top Dead Center. Bear in mind! if you move the balancer backward you will take any slack out of the timing chain before your camshaft moves hopefully what we are trying to do here is catch the timing mark so you don't have to move the damper BACKWARDS to put it on 0 TDC. Hopefully, the damper has not spun on the rubber insulator sometime in the past.
With the timing mark on 0 TOP DEAD CENTER, your distributor should be inserted so that the rotor is pointing at the number 1 terminal on the distributor cap. This is rough or static timing. The wires in a clockwise position starting at the number 1 terminal is 1-8-4-3-6-5-7-2. It's not hard to get messed up doing this so check and double-check.
So Assuming this is what you have done time and time again lets address backfiring :
Constant backfiring thru the exhaust sometimes is an indication of the spark occurring while the exhaust valve is still open
or not seating. one possibility is a crossed wire! (double check and triple check ) One sure way is to follow the wire by hand from the cap all the way to the appropriate spark plug. Another grim reality is there is a broken exhaust valve spring not allowing the valve to seat completely.
Finding the backfire: place the wires loosely on the distributor cap and one by one remove the wire from the cap.
the backfire will stop when you have removed the wire depriving that cylinder of spark. I am assuming that you are aware of the spark that can be created by HEI and insulated pliers are recommended. Hopefully, now we have found the backfiring cylinder and next is to Quadruple check the firing order and if the wiring is correct its time to pull that plug and try a compression test in that cylinder. you can also check the valve springs in that cylinder for broken springs.
I'm imagining at this stage of the game you had to have found something so keep us posted and good luck!
I've done the checking of wires multiple times. Ran it in the dark, ran a screw driver across them looking for an arc. Did it all over again, multiple times, after replacing the cap and rotor, coil, distributor, and wires. I think I ran compression and it all came out good. I don't recall. The odd thing is it's not at idle, only fast idle, and when revving. I'll check valve springs. The motor has maybe 7k on it, but wouldn't be the first time new parts have failed.

A common problem is intake gasket leaks, hence it is important to use a vacuum gauge to get a reference before starting such projects but even now it’s a good idea. These are a valuable diagnostic tool. While perhaps not giving a specific answer in terms of off timing versus a vacuum leak it is a tool that identifies problems and narrows the bandwidth of possible places to look rather than just heaving parts at it and hoping something sticks as that gets expensive and doesn’t usually solve the problem.

A good vacuum gauge is part of my instrument panel as well as a couple test models in my roll around, that’s how important a tool I consider these. Price is not an indicator of quality, I have a Stuart Warner that against a manometer reads high by 5 inches where I, also, have two cheap Harbor Freight units that are balls on.

Bogie
I have replaced intake gaskets 2x now. The first time it showed slight evidence of a leak between 3/5 IIRC, the 2nd time didn't show any evidence of leakage when sprayed with carb or brake cleaner but I went with a thicker gasket IIRC. I agree on the vacuum gauge. I don't know how accurate mine is, but it's good enough for government work in finding high/low vacuum, and just reading it in general. Need to replace my timing light but running out of time before the 3 days of family Christmas start.

Have you done a cylinder leakage test or even compression ?
That sounds like exhaust gasses igniting in the intake to me.

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I believe I did run compression on a couple cylinders where the primaries were cool relative to the others. Ended up being fouled out plugs that I was sanity checking on the cylinders. I haven't ran leakdown. I am 95% certain it's in the exhaust because you can hear/feel it in the seat, and it's 150% louder behind the firewall. The car hasn't been ran much more than 5-10 minutes at a time since the swap.

I really appreciate all your guys' help, ideas, and time!
 

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Possible loose valve seat ?
Would be more intermittent like it sounds. I think it would have to be visually found after teardown though as a last resort. I'd be interested in leakdown test results though.

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Many things to speculate, need answered to some testing and or inspecting to go farther I would say. Go back over all these notes and get back to us I'm dying to know whats going on now.

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It was my understanding that the engine ran fine before the intake swap. Timing, a poor sealing intake, or damage to valve train could cause the issue. If this is true then something during the change caused it. A stab in the dark would be an intake bolt being too long and contacting a push rod. I don't know if that is possible on a sbc, but a thought that would cause a backfire.
 

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It was my understanding that the engine ran fine before the intake swap. Timing, a poor sealing intake, or damage to valve train could cause the issue. If this is true then something during the change caused it. A stab in the dark would be an intake bolt being too long and contacting a push rod. I don't know if that is possible on a sbc, but a thought that would cause a backfire.
You are correct! small block Chevys have bolts that line up with pushrods too long a bolt can come into contact with certain pushrods. one should be careful of switching bolts around and putting a bolt that is too long in the wrong manifold
bolt hole.
 

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Idle is fine, Fast idle is not, WOT is unknown...Correct?
Dirt and debri in the carb air bleeds right at the transition of idle to main circuit.
 

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I know Victoria's secret....
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Discussion Starter #19
Sorry for the delay guys. Finally got another timing light. Hoping this weekend or next I'll get to finally time it.

Last day I toyed with it, I turned the APT screw all the way out (richer), and it revved MUCH easier, and made the popping better. May be a carb tuning issue. A few day or so prior to that I smoked an ignition coil messing with distributor wires while it was running. Spent most of that allotted time pulling coil, testing, checking wiring and cap.

Many things to speculate, need answered to some testing and or inspecting to go farther I would say. Go back over all these notes and get back to us I'm dying to know whats going on now.

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Hoping to get some more time/weather to dig deeper into all recommendations. I'll bet you I'm dying more :) It's been too long since I've drove the car!!

It was my understanding that the engine ran fine before the intake swap. Timing, a poor sealing intake, or damage to valve train could cause the issue. If this is true then something during the change caused it. A stab in the dark would be an intake bolt being too long and contacting a push rod. I don't know if that is possible on a sbc, but a thought that would cause a backfire.
Correct- ran fine before intake AND carb swap. Carb is brand new Jet performance. Will check valve train after timing is set.

I should be able to visually "go/no go" the pushrods and bolt interference, correct?

You are correct! small block Chevys have bolts that line up with pushrods too long a bolt can come into contact with certain pushrods. one should be careful of switching bolts around and putting a bolt that is too long in the wrong manifold
bolt hole.
Going off of memory, the only ones I likely kept in the same holes were the front due to alt bracket, etc. I do recall swapping a couple bolts with 'new' since there was either an issue with getting access with the allen wrench or box end. Been long enough ago I don't recall.

Idle is fine, Fast idle is not, WOT is unknown...Correct?
Dirt and debri in the carb air bleeds right at the transition of idle to main circuit.
Correct on idles and WOT. It seems fine cold until the choke opens. Richening the APT helped out some. Leads me to believe it's a lean condition at this point. I shouldn't have to tear down a brand new carb, but stranger things have happened. I'll check into that and the other mechanical possibilities above once I get it timed.

Here's a couple videos from just before messing with APT. Didn't think to get any after. We're looking at a new truck tonight since mine was totalled Christmas day. If I have time after we get back I'll see about getting a comparison vid.

Cold

Warmed up
 
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