Spark advance lever & backfire

[Randini509]

I recently put a new timing gear on, dropped the pan and cleaned it out. replaced all the gaskets put it all back together. And re-did the timing. My 1929 Backfires at the top of each gear, at what feels like top speed at each gear. And the other day it backfired shortly after shutting it down. I havent owned it long, and i have been driving around with the spark advance all the way down after startup. But i was recently told i should be driving with it 1/2 way down just normal driving, and 3/4 the way down at faster longer driving. But could this backfire be from carb settings? Or maybe my timing isnt spot on? Or could driving with the spark advance lever all the way down do it? Im new to the Model A seen, dont know all that much yet. Im sure there is already a thread on this but i couldnt find it through the search. sorry if so.

[Purdy Swoft]

You've got an exhaust leak, either where the exhaust pipe connects to the manifold or where the manifold meets the block. The exhaust manifold may also be warped. Exhaust leaks contribute to back fire or pop at gear changes or when decelerating. Driving with the spark advanced will not cause backfire. I have cranked with the spark fully retarded and drove with the spark fully advanced for 53 years with no problems. I never lug the engine. Some retard is needed when creeping over trails with hills and sand beds. I usually drive with the gas adjusting valve (knob on the choke rod) , about 1/4 turn open to the left after warm up and up to a full turn to the left if real cold, untill warm up. Driving with the spark lever half way up the quadrant will cause overheating and loss of power.

[marc hildebrant]

Randini509,

The Ford Owners Manual for your car (available at Model A parts stores) has a nice section regarding the spark advance and how to use it.

My method, which is out of the book, is to start on full retard (up).
Once running, down about one inch. Then as you drive , it's down about half way for low speeds and down all the way for highway driving.

Your motor will "tell you" what the best position is as it varies for the conditions.
Full up for start and full down for run isn't wise as you need to adjust it some for the conditions.

Using the spark advance, for me, is part of the fun of driving the Model A. It makes you much more connected to the driving experience.

Marc

[Larry Seemann]

If you're in the Spokane area get in touch. [email protected]
We have a group that gets together every Wednesday night.

[Randini509]

Originally Posted by Larry Seemann

If you're in the Spokane area get in touch. [email protected]
We have a group that gets together every Wednesday night.

Im actually just outside spokane, about 15 minutes away. Also could timing cause the backfire at higher speed? its not a real loud backfire, more like a little pop-pop. I did just replace the timing gear, and dropped the pan and put on a new gasket. I also put a new gasket on the carb where it meets the manifold too, dunno if that would cause anything. The exhaust manifold bolts were barely hand tight though, dunno if that will fix it, bad weather today and didnt feel like taking it out. Didnt do this until i changed that timing gear though.

[newtoAs]

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i was told by some of the guys in my local model a club to push the spark lever all the way up (retard) before turning the key off to prevent backfiring. as for backfireing when you are shifting gears, try resetting your timing, that might be the cause.

[marc hildebrant]

newtoAs,

The reason to put the spark lever up (retard) when you turn off the key (ignition) is to aid in having the spark ALWAYS at full retard when you START the car.

Hence, leave it up when you turn off, then its ready when you start.

Retard when starting helps to avoid a kick-back during starting.

Marc

[whirnot]

Mine was backfiring through the muffler once in a while on deceleration. Not sure the mechanics of the theory that an exhaust leak causes that, but I just turned the GAV a little richer and it stopped immediatly. Mine does not have an exhaust leak. I agree that having to adjust the spark control, and GAV sometimes to get the best runnning is part of what makes a Model A fun to drive.

[Don S]

A similar problem with a popping noise either from the carb or exhaust,hard to tell while driving,although it will do the same thing while in the driveway with the throttle advanced. Both manifolds are new from Brattons,and machined locally cause they were not flat to each other. No leak from the manifolds ,if I close off the breather hole at the back of the cars she stalls out. Timing appears to be good,nice low pluk a pluk idle. Has Nue Rex ignition set to their specs. I changed carb float to even level from just less (down) level,changed carbs no different. So must be a leak somewhere.The only joint Not fully checked yet is the exhaust manifold to muffler . The new exhaust manifold flange area is machined not to a point like the original but with a 1/8" or so flat bottom edge. Even though I am using an adapter pipe to help keep a good seal at the clamp, the original clamp was meant for a more tapered end to the manifold. I use lots of muffler cement at the joint and with the clamp,but still get a popping noise and some backfire going down hill on compression Next step is to re-do the exhaust connection. Anthing here I may have missed ?

[Don S]

Sorry,previous thread should have read Carb, not cars

[Randini509]

Originally Posted by whirnot

Mine was backfiring through the muffler once in a while on deceleration. Not sure the mechanics of the theory that an exhaust leak causes that, but I just turned the GAV a little richer and it stopped immediatly. Mine does not have an exhaust leak. I agree that having to adjust the spark control, and GAV sometimes to get the best runnning is part of what makes a Model A fun to drive.

I did find my GAV was completly unscrewed inside the carb, and i was probaly running it that way, i do remeber twisting it counter-clockwise thining it may be the issue with the back fire, and also remeber thinking "god d!@# does this thing ever stop turning". The weather is so crappy here though i havent wanted to go out and see how it drives now

[Purdy Swoft]

Turning the gav knob on the choke counter clockwise opens the valve. The more the gav is opened, the richer the mix. Running too rich causes the engine to lope at idle and emit black smoke but doesn't cause backfire in any case. Running with the GAV knob closed ( all the way clockwise) causes a lean condition that will cause the engine to run hotter and backfire. This applies to the model A carb. The B carb was suppose to run with the GAV closed after warm up.

[Randini509]

I really dont think its an exhaust leak causing the problem, im going to double check the timing, and pay much closer attention to the positon of my GAV, it never back fired at all until i put in my new timing gear.

[Purdy Swoft]

If the initial timing is slightly retarded or if you are driving with the spark slightly retarded this will also contribute to popping between gear shifts and when dcelerating. You might try increasing idle speed on the carb, sometimes this helps. Here is a quick way to set the timing without the confusing tests.When the timing pin drops in place, set the rotor tip so that the trailing edge aligns with the number one contact in the distributor cap body. in many cases there will be 1/2 inch of backlash in the distributor shaft. When you tighten the cam screw, All of the backlash needs to remain in the counter clockwise direction. In other words the trailing edge of the rotor tip needs to be locked in place pointing at the number one contact in the cap with NO clockwise movement.

[Randini509]

ok soooo maybe i was wrong about the exhaust leak lol. After trying to start it today i got a big backfire. Pulled the exhaust manifold off just for the hell of it and found this.... (what is in the picture) Looks like the number one cylinder exhaust port was blowing by bigtime.

[Tom Wesenberg]

That's pretty thin on the front port from years of water rusting it from a leaking water pump. I'd probably just buy a new manifold.

[Randini509]

Originally Posted by Tom Wesenberg

That's pretty thin on the front port from years of water rusting it from a leaking water pump. I'd probably just buy a new manifold.

don'y really have the cash for that at the moment.... sucks.

[Purdy Swoft]

I think that a lot of the warped manifold problems are caused by over tightening, regardless , most are found to be warped when removed. I use to have manifold assemblies planed for around 35-40 dollars. The local machine shop closed and I now have to either find a better manifold or level it out with a large file. If you lay a metal straight edge across the ports of the manifold, you will probably find that the rear edge of the front port is kicked in where the manifold stud meets the manifold. I have had pretty good luck hand filing but its a slow process . I use the 31 style manifold gaskets, they are wider and give a better chance of a good seal. Good luck.

[Randini509]

Originally Posted by Purdy Swoft

I think that a lot of the warped manifold problems are caused by over tightening, regardless , most are found to be warped when removed. I use to have manifold assemblies planed for around 35-40 dollars. The local machine shop closed and I now have to either find a better manifold or level it out with a large file. If you lay a metal straight edge across the ports of the manifold, you will probably find that the rear edge of the front port is kicked in where the manifold stud meets the manifold. I have had pretty good luck hand filing but its a slow process . I use the 31 style manifold gaskets, they are wider and give a better chance of a good seal. Good luck.

This thing is so pitted out, im probably going to the shop near by that sells all model A and T parts and get a new one. Looks like it may have pin holes all in it. Dont want the neighbors to come runnig over again asking if im ok after it backfires and makes all them go def.

[Randini509]

Would that leaking by that bad cause it to backfire extremly loud through the muffler when i try and start it? Cause thats not only embarassing as hell but scares the $%it out of the neighbors lol.