[Kfir Kedar]

Hello everyone,

New-ish poster here. Replaced the timing set on my 1974 Pontiac 350 and while i was at it, i replaced my points system with a new HEI distributor, spark plugs,and spark plug wires.
Took me a long while to get it to even start, but now it seems to take forever to start, if at all. Every other time i try to start it, a loud earbursting pop comes out of the exhaust. The type that makes people from half a mile away come check if i'm still alive. But the rest of the time it takes 10-15 seconds of starting and eventually manages to start and even idle nicely. I'm fairly certain it's the ignition timing, as i've double and triple checked the chain set itself and the firing order, and because i'm pretty sure if i was 180 out it wouldnt even start.
Any help would be more than appreciated!

 

[BogiesAnnex1]

Whew, this is either out of time, has a vacuum leak, or the mixture settings are off.

Bogie

 

[Kfir Kedar]

Whew, this is either out of time, has a vacuum leak, or the mixture settings are off.

Bogie

Thank you! Mixture settings have been reset, vacuum leaks checked, and i have no idea whether to retard or advance the timing. Issue still persists.

 

[RWENUTS]

Did you use a 12v dedicated power source for the hei? It needs it.

 

[Kfir Kedar]

Did you use a 12v dedicated power source for the hei? It needs it.

It's wired to the IGN plug on the fuse box with a new wire.

 

[RWENUTS]

That’s good.
Start from the beginning.
Re-time your motor.
#1 on tdc compression, align timing tab at zero, point rotor at #1 on the cap, advance distributor a little and fire it up.

 

[Kfir Kedar]

That’s good.
Start from the beginning.
Re-time your motor.
#1 on tdc compression, align timing tab at zero, point rotor at #1 on the cap, advance distributor a little and fire it up.

Just got done doing as you suggested mate. Seems to take a little less time starting up, but still backfires ridiculously. i'm starting to get worried about causing valve damage with all these attempts. Absolutely no clue if the timing's too advanced or too retarded, or maybe the vacuum advance is messing me up.

 

[RWENUTS]

Pull the valve covers off and check all the rockers and valves are moving equally.
Could be a stuck valve.

 

[Kfir Kedar]

Pull the valve covers off and check all the rockers and valves are moving equally.
Could be a stuck valve.

Done and done. all of them move freely up and down. Backfire still persists.

 

[RWENUTS]

Back to the start.
Pull it apart and check your timing gear installation.
Could be off a tooth or two.

 

[LATECH]

Sounds like no power while cranking. Did you check to see if the distributor has power while cranking. Remember a points system has a bypass wire ( usually) to power the ignition while the starter is engaged . without it the only way it will start is fi there is enough momentum in the engine when you turn the ignition switch from start to run.

Try hotwiring it. see if it starts right up.
Or check for 12 v power at the distributor while cranking with a test light.

 

[BogiesAnnex1]

I missed the part about the HEI, this requires 12 volts all the time. The points use 12 volts to start which when the starter is grinding drops the B+ down to about 10 volts on a good battery. After starting a points system switches to about 9 volts to run either through an external resistor located in the engine compartment or on the engine, or through a resistive wire between the ignition switch and the coil. You will need to rewire this so it has B+ voltage all the time.

You keep saying you haven’t checked to see if the ignition timing is retarded or advanced,,,well finding out where the ignition timing is would be the first, easiest, and cheapest thing to have done.

it was offered that you check for TDC firing on number one cylinder by observing valve motion. This being pretty simple with the rocker cover off over the side with the number 1 cylinder; you wrench the motor around watching the valve motion. Once you see the intake open then close observing the location of the crankshaft timing marks being aligning with the pointer will tell you that number 1 is ready to fire. At that point the distributor rotor needs to be pointing at the terminal for the number one spark plug. Fine adjustment from here is done with a timing light.

It is unlikely that backfires will harm the valves, the exhausts in particular run red hot and the constant banging onto their seats is tolerated for thousands of miles. The valves intake included are plenty strong enough to survive back fires.

Checking the crank to cam timing takes disassembling the front of the engine again to get into the timing case in order to see whether the gear alignment marks match where they should.

Another PIA is the damper as often old dampers loose the rubber bond between the hub and the damper ring which allows the ring to fall out of position taking the timing marks with it. There are ways of testing for this with a piston stop in the spark plug hole where you use the valve cover off watch the number one intake as it closes stop turning the crank and screw in the positive stop until it hits the piston, you might have to move upward till the piston finally is stopped by the tool. Mark this location on the damper. Now rotate the crankshaft backward till the piston hits the stop again, mark this location. TDC is absolutely the point that is half way between these marks. Now pull the positive stop tool out and rotate back to see if the damper zero mark and your chalk line’s midpoint match up.

Report back, Bogie

 

[LATECH]

Probably not timing related.It runs OK when it does start, at least what the OP says

It's wired to the IGN plug on the fuse box with a new wire.

Be sure it is hot while crsanking.

 

[khanta77]

Kfir, hope all is well, great advice from all our resident experts, you definitely came to the right spot.

The ignition issue you already have figured out I take it, the BAT wire on the HEI must have key on power. Make sure your battery is supplying a good 12.7ish volts at startup, you can check with a voltmeter before starting. Then test at the BAT wire to make sure you're getting a good voltage supply. As for HEI's in general I personally recommend an MSD unit for any muscle car ignition, the added sparking power makes a huge different in startup and overall performance.

The backfire issue and probably the hard starting is due to an over advanced distributor, while you were working on the ignition its possible you moved the distributor timing forward to the point that its firing too soon. The first thing you should do is loosen the dist bolt under the distributor (not too loose) start the car and then slowly turn the distributor to a point where the car is neither backfiring nor pinging, go a fraction advance from there and tighten down the bolt.

The right way to set this is with a timing light, you can buy one on ebay for about 40 bucks, find out the recommended timing setting for your engine and then use the timing light shining on your balancer to check how far advance/behind you are.

A good balancer is always best, if you're running the original balancer from 1974 then the elastomer band is probably worn out and the balancer is useless anyway. Buy yourself a good summit fluid balancer for about $75 dollars and it has the marks already written on the side. Your engine will love having a good balancer to smooth things out.

I hope this is helpful brother, let us know what happens,

 

[Kfir Kedar]

Sounds like no power while cranking. Did you check to see if the distributor has power while cranking. Remember a points system has a bypass wire ( usually) to power the ignition while the starter is engaged . without it the only way it will start is fi there is enough momentum in the engine when you turn the ignition switch from start to run.

Try hotwiring it. see if it starts right up.
Or check for 12 v power at the distributor while cranking with a test light.

Sorry for the late reply! I have tried starting with the HEI wire going directly to B+ with the same result!

 

[Kfir Kedar]

Probably not timing related.It runs OK when it does start, at least what the OP says

Be sure it is hot while crsanking.

True, it does. no backfire, builds and drops RPM quickly with no lag

 

[Kfir Kedar]

Back to the start.
Pull it apart and check your timing gear installation.
Could be off a tooth or two.

Double checked. No misalignment!

 

[Kfir Kedar]

I missed the part about the HEI, this requires 12 volts all the time. The points use 12 volts to start which when the starter is grinding drops the B+ down to about 10 volts on a good battery. After starting a points system switches to about 9 volts to run either through an external resistor located in the engine compartment or on the engine, or through a resistive wire between the ignition switch and the coil. You will need to rewire this so it has B+ voltage all the time.

You keep saying you haven’t checked to see if the ignition timing is retarded or advanced,,,well finding out where the ignition timing is would be the first, easiest, and cheapest thing to have done.

it was offered that you check for TDC firing on number one cylinder by observing valve motion. This being pretty simple with the rocker cover off over the side with the number 1 cylinder; you wrench the motor around watching the valve motion. Once you see the intake open then close observing the location of the crankshaft timing marks being aligning with the pointer will tell you that number 1 is ready to fire. At that point the distributor rotor needs to be pointing at the terminal for the number one spark plug. Fine adjustment from here is done with a timing light.

It is unlikely that backfires will harm the valves, the exhausts in particular run red hot and the constant banging onto their seats is tolerated for thousands of miles. The valves intake included are plenty strong enough to survive back fires.

Checking the crank to cam timing takes disassembling the front of the engine again to get into the timing case in order to see whether the gear alignment marks match where they should.

Another PIA is the damper as often old dampers loose the rubber bond between the hub and the damper ring which allows the ring to fall out of position taking the timing marks with it. There are ways of testing for this with a piston stop in the spark plug hole where you use the valve cover off watch the number one intake as it closes stop turning the crank and screw in the positive stop until it hits the piston, you might have to move upward till the piston finally is stopped by the tool. Mark this location on the damper. Now rotate the crankshaft backward till the piston hits the stop again, mark this location. TDC is absolutely the point that is half way between these marks. Now pull the positive stop tool out and rotate back to see if the damper zero mark and your chalk line’s midpoint match up.

Report back, Bogie

Hey Bogie, thanks for the detailed advice! I have double and triple checked both the ignition and cam timing and they seem to be properly adjusted. Once the car does get going, it has absolutely no backfires and no trouble idling at low RPM even when cold.

 

[Kfir Kedar]

Kfir, hope all is well, great advice from all our resident experts, you definitely came to the right spot.

The ignition issue you already have figured out I take it, the BAT wire on the HEI must have key on power. Make sure your battery is supplying a good 12.7ish volts at startup, you can check with a voltmeter before starting. Then test at the BAT wire to make sure you're getting a good voltage supply. As for HEI's in general I personally recommend an MSD unit for any muscle car ignition, the added sparking power makes a huge different in startup and overall performance.

The backfire issue and probably the hard starting is due to an over advanced distributor, while you were working on the ignition its possible you moved the distributor timing forward to the point that its firing too soon. The first thing you should do is loosen the dist bolt under the distributor (not too loose) start the car and then slowly turn the distributor to a point where the car is neither backfiring nor pinging, go a fraction advance from there and tighten down the bolt.

The right way to set this is with a timing light, you can buy one on ebay for about 40 bucks, find out the recommended timing setting for your engine and then use the timing light shining on your balancer to check how far advance/behind you are.

A good balancer is always best, if you're running the original balancer from 1974 then the elastomer band is probably worn out and the balancer is useless anyway. Buy yourself a good summit fluid balancer for about $75 dollars and it has the marks already written on the side. Your engine will love having a good balancer to smooth things out.

I hope this is helpful brother, let us know what happens,

Hello! Thanks for the info!
Regarding the balancer, it is actually almost brand new so no issue there, and regarding the timing, that's the weird thing, theres only one loud vaccuum-ish backfire if i let go of the starter before the car actually starts, but if i do get it going, there are no more backfires or pinging, as if timing is set perfectly. only the startup is both very long and has the huge backfire thing.

 

[RWENUTS]

What carb you using?
Do you have a functioning choke?

And what’s your starting procedure?
Do you tap the throttle once to give it a shot of fuel and set the choke and then crank it over?
Or are you the guy that can’t leave the pedal alone and keep pumping it until it finally starts.