Technical backfire through carb question

I'm aware that a backfire through the carburetor means a cylinder fired while an intake valve was open. Also that a backfire through the tailpipe means a cylinder fired while an exhaust valve was open.

My question is whether I should retard or advance timing to eliminate carb backfires. This happens when trying to start the engine. If I could get the engine running I could time per factory specs, but right now that just aint happening.

The engine in question is a Ford 360 with the original 2bbl carb.

tia

 

Find the intake air leak. Does your carb have a choke and is it working properly?

 

It is not required to have an engine running to set ignition timing. A couple things you want to do maybe you know all this stuff already, maybe you don't. Don't want to sound insulting, I didn't know any of it when I started in on a Tune-Up.

Verify the spark plug wires are in proper firing order starting at the "1" on the distributor cap, and that the distributor itself has been stabbed in correctly. When #1 piston is at TDC compression stroke the distributor rotor will be in alignment with the #1 cap terminal's clock position. It is also possible with aging Ford crank dampers for the outer weight to slip, and the timing marks on it will of course move with it. All of these "previous owner" errors can make setting the ignition timing very confusing. Misrouted plug wires is common. Maybe you've checked all that.

Anyway the advice I find helpful for the folks that haven't, when the #1 piston is at exact TDC on compression (use a piston stop tool or equivalent) check everything else to see that it is at "mechanical zero", the timing pointer should also coincide with "0" on crank balancer, and rotor at #1 cap terminal alignment.

If you verify first that everything is straight and copacetic as Henry intended, then it's a simple matter to say, use a remote starter switch and set the initial timing by just cranking the starter over. But I bet it would start anyway.

Where people get confused, the engine or distributor doesn't really care how it is stabbed in, and the plug wires can be moved to compensate. Any cap terminal can be "#1" so long as the firing order is correct. Some previous owner might have found it easier to move the wires around than it was remove and re-install or "stab" the distributor itself.

 

In answer to the question.... retard the timing a couple of degrees at a time until it stops. If you get below factory setting, check compression.

 

Carb back fires are usually advanced timing
Or air leaks

as @Truck64 said mechanically confirm TDC (static timing)

confirm where the rotor is pointing and that the distributor is in correctly and all spark plug wires are in the correct order.

from there you can adjust if everything else is where it needs to be.

 

Consider a blown carb power valve replacement if it’s been backfiring through the carb

 

dont take anything for granted and check everything as outlined above.
if everything is ok and you dont have any leaks I support the idea your timing is too advanced
to retard, turn distributor counter clockwise as in picture

 

Is this a high mileage engine, or has it sat for an extended period with out running? Keep in mind that a valve sticking in the guide and/or weak valve springs could cause the problem you describe.

For that matter, if the oil wasn't changed regularly it may have a lifter varnished up that's not allowing the valve to close when it's supposed to.

 

Having the engine on TDC on number 1 and having the rotor point to number 1 on the cap with the points open. Or the electronic sensor lined up.

If you can see the piston top though the plug hole you can watch the piston to see if you have it at TDC or (I like to use a long plastic drinking straw) use something to check when you have it at TDC to make sure that your timing marks are right.
Firing order= you do have it wired in the correct Counter clockwise rotation and the wires going to the correct plugs? I'm not sure what you are used to working on but if you are used to Chevy V8 engines that have a clockwise firing rotation you may have automatically wired it for clockwise rather than counterclockwise.

Valves sticking? A compression test will give a yes or no on that one.

 

Thanx everyone for your help. The engine has sat for a while so maybe it does have a stuck lifter as has been mentioned.

Also this is the first Ford engine I've messed with since I pulled the flathead out of my panel truck in 1991.

I think that you guys have given me plenty to check on and I bet after using your advice I'll get it running just fine.

Thank you. Thank you. Thank you.

 

Also if you have never had the engine running consider a stretched timing chain that has jumped.

 

sometimes a lean mixture will do that