Starting Problem
- Thread starter Mercman53
- Start date
Will N
Well-known member
Backfiring out of the muffler, or out of the carburetor?
Backfiring out of the muffler indicates that unburned gas is getting into the exhaust, and then is being ignited. This coud be caused by several reasons. You could be running very rich, in which case the charge in the cylinder doesn't completely burn in the cylinder, and it continues burning in the muffler after the exhaust stroke. It could be that you have a valve sticking open, which is forcing unburned fuel into the exhaust, where it gets ignited by the exhaust from other cylinders. It could by you have a misfiring spark plug, in which case, like a sticking valve, the unburned fuel gets pushed out into the exhaust where it ignites.
I'd pull the plugs, and run a compression test to check for a sticking valve. I'd read the sparkplugs. If they are all fouled with black powdery residue, then you're running too rich. Close down that gas adjusting valve on the dashboard. If one plug is fouled but the rest are ok, that plug is misfiring. Could be a bad plug, could be a bad distributor body.
Backfiring out of the muffler indicates that unburned gas is getting into the exhaust, and then is being ignited. This coud be caused by several reasons. You could be running very rich, in which case the charge in the cylinder doesn't completely burn in the cylinder, and it continues burning in the muffler after the exhaust stroke. It could be that you have a valve sticking open, which is forcing unburned fuel into the exhaust, where it gets ignited by the exhaust from other cylinders. It could by you have a misfiring spark plug, in which case, like a sticking valve, the unburned fuel gets pushed out into the exhaust where it ignites.
I'd pull the plugs, and run a compression test to check for a sticking valve. I'd read the sparkplugs. If they are all fouled with black powdery residue, then you're running too rich. Close down that gas adjusting valve on the dashboard. If one plug is fouled but the rest are ok, that plug is misfiring. Could be a bad plug, could be a bad distributor body.
Steve Wastler
Well-known member
I'm missing something, is there a previous post regarding what you did and why you did it? If so, its best to post an update on your original thread.
Steve Wastler
Well-known member
Oh, and are you sure your timing is correct? Some get caught on the phrase opposite number one.....
Ok so heres an update. Originally I had what I thought might be a transmission problem but after getting input from you all, found that it was actually an axles key. I ordered a couple along with a few other things so thats a done deal. Next I had a problem keeping her running as she would start and then backfire and die. Originally I thought it was backfiring from the carb but I tried to start her again a few minutes ago and now Im pretty sure its backfiring out of the exhaust pipe. I pulled the plugs and cleaned them yesterday but noticed a oil/fuel residue when I stuck my finger inside each cylinder plug hole. If it aint one thing its another. If it is a stuck valve how do I fix that? and is it supposed to be like that inside the spark plug hole?
Patrick L.
Well-known member
Just start at the beginning.
Check compression
Check for proper spark
Check for correct timing
Check for good fuel flow
Check compression
Check for proper spark
Check for correct timing
Check for good fuel flow
Purdy Swoft
Well-known member
It could be the spark plugs. I had problems with Motorcraft TT10 plugs, they are too cold. you can sometimes clean them a time or two and get by, after that its replace them. I use Champion W-18 plugs, they are hotter than TT 10 plugs or Champiom W-16-Y spark plugs.
OK I've cleaned the spark plugs, they looked sooty black so I guess too rich so I only opened the gav 1/4 turn, Ive got good spark, and the timing is correct. Fuel Flow is good and gas is new and clean. As for the compression is there a way to check it without a tester hose and gage? Ive got a tester but its for the new engines and I dont have anything to fit the oversized plug holes.Anyway, still the backfire and won't stay on. Im working on this alone so at times I hear the backfire coming out of the tail pipe and at others I can see the spit out of the carb which was probably when I was trying to adjust the GAV. Also if anyone is near my area, Salinas Ca, I'd appreciate any help.
JESSE
JESSE
Tom Endy
Well-known member
Sounds to me that your timing is not set correctly. You probably also at this point have the engine flooded with fuel.
My suggestion:
Pull the plugs so as to make the engine easy to rotate. Take the top of the distributor off and rotate the engine until you see the rotor approaching the right head light. This should indicate you are coming up on the timing mark.
Take a flashlight and a small mirror and ease the engine around until you see that the timing mark on the cam gear is dead center in the hole on the timing cover. This will insure that you are on the timing mark. Set the timing. Rotate the distributor cam counter clockwise until you pass the point closure slightly. Come back clockwise until the points just crack open, lock it down. Make sure your spark handle is all the way up when you do this.
With the plugs still removed open the throttle full and crank the engine over with the starter for about 10-15 seconds to help clear the fuel out.
Put the plugs back in and try to start it, see what happens.
Tom Endy
My suggestion:
Pull the plugs so as to make the engine easy to rotate. Take the top of the distributor off and rotate the engine until you see the rotor approaching the right head light. This should indicate you are coming up on the timing mark.
Take a flashlight and a small mirror and ease the engine around until you see that the timing mark on the cam gear is dead center in the hole on the timing cover. This will insure that you are on the timing mark. Set the timing. Rotate the distributor cam counter clockwise until you pass the point closure slightly. Come back clockwise until the points just crack open, lock it down. Make sure your spark handle is all the way up when you do this.
With the plugs still removed open the throttle full and crank the engine over with the starter for about 10-15 seconds to help clear the fuel out.
Put the plugs back in and try to start it, see what happens.
Tom Endy
Have you timed it using the instructions from Marco's site??
http://www.abarnyard.com/workshop/timing.htm
Bob
http://www.abarnyard.com/workshop/timing.htm
Bob
Thank you Bob and Tom. I tried BOTH your ideas. The only thing I did find was that I was able to turn the rotor about 1/4 to 1/2 turn by hand. I dont think that I am supposed to be able to. So now Im thinking distributor problems. I also had a bit of Fire during the backfiring from my tail pipe. Your thoughts? Thanks for all your help and support.
Jesse
Jesse
Purdy Swoft
Well-known member
The 1/4 to 1/2 inch turn at the rotor is the backlash that i've mentioned about a thousand times here on the barn. On a new or rebuilt engine with new cam,new oil pump-distributor drive gear and new distributor intermediate shaft will have little or no backlash. Most if not all model A engines will have some backlash, 1/2 inch isn't uncommon. Backlash at the rotor tip will make no difference if the backlash is all in the counter clockwise direction. Its probably a waste of my time but I will try to explain the timing process again. Remove all of the spark plugs so that you don't have to fight compression when trying to locate the timing mark or dimple on the cam gear. When the timing pin drops in place. loosen adjust and tighten the distributor cam so that the trailing edge of the rotor tip aligns with the number one contact in the distributor cap with NO clockwise backlash. In other words when the cam is tightened the trailing edge of the rotor tip will align with the number one contact in the cap and will have No backlash or mnovement in the clockwise direction. There will still be backlash in the counter clockwise direction but it will make no difference with the timing. The distributor turns in the counter clockwise direction when the engine runs but rides on the clockwise side of the backlash. This will have the roitor tip at the sweet spot or timed where the spark should happen. If the points gap is adjusted anywhere from .018 to .022 it will run. The spark occurs when the points open. Fully retard the spark lever and the points should be just ready to open. You've got four thousants of adjustment to fine tune the points so that they are just ready to open when the rotor tip is adjusted as described above. Some of the things that can cause the points not to open at the correct time can be that the distributor cam is ill made as many are or you're not getting full retard and advance of the upper distributor breaker plate. Check to make sure that the lever on the breaker plate moves all the way to the right side of the window of the distributor cap when the spark is retarded and all the way to the left side of the window of the cap when the spark is fully advanced. The steering column tube can be loosened and rotated as needed to get the adjustment correct if you have the 30-31 two tooth style steering column.
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heneste
Senior Member
I would clean out the carburetor to make sure that you're not getting fuel restriction from one or more of the jets intermittently. It could be junk floating around in the carb that blocks the jets from time to time and causes the stalling.
You mentioned you have good fuel flow so I'm assuming it's good from the tank to the carb.
The other issue some people have with timing is if their timing cover has been replaced with a B cover. The timing hole on the A and B covers are not situated at the same spot relative to the timing gear.
You mentioned you have good fuel flow so I'm assuming it's good from the tank to the carb.
The other issue some people have with timing is if their timing cover has been replaced with a B cover. The timing hole on the A and B covers are not situated at the same spot relative to the timing gear.
Thank you Purdy for clearing up the backlash. I apologize if I "didnt get it" earlier. So I adjusted as you stated and still the same problem. Heneste, I removed the carb took it apart blew out every orfice on it and made sure it was clear and clean of any type debris. Afterward I re installed it and then tried to start. Now I am not only getting backfiring out of the tail pipe but an occassional back fire with FIRE out of the carb. Not to mention an occassional spit of fire through the little hole on the intake manifol right above the carb. What gives? I had to let it ride today as I was begining to want to look for a stick of Dynamite..
Im about to backfire myself if I cant figure this out...
Jesse
Im about to backfire myself if I cant figure this out...
Jesse
Purdy Swoft
Well-known member
This may not be the problem but is a possibility. I had a bad ammeter in my sept 29 that caused backfiring like you describe. I've had model A's since I was a kid but that one had me baffled for a while. I mostly use the repro ammeters and they are not the best. The juice has got to flow through the ammeter and if the flow is intermitant so will be the spark at the distriubutor. You can connect the wires and bypass the ammeter as a test. I've also seen bad spark plugs to cause constant back fire. If you've got a set of used spark plugs, it wouldn't hurt to try them. Good luck, I can only guess.
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heneste
Senior Member
I looked a bit on the www.modelabasics.com website under troubleshooting
They mention backfiring with no load could be caused by
- too lean on the GAV setting
- intake manifold leak
- low carburetor float
You also mentioned you got a little fire out of the hole above the carb (wiper motor connection). That hole should be completely plugged or connected to the vacuum wiper or you will have a small intake leak.
Maybe check the points also to make sure they aren't too badly pitted as that can wreak havoc on your timing settings.
They mention backfiring with no load could be caused by
- too lean on the GAV setting
- intake manifold leak
- low carburetor float
You also mentioned you got a little fire out of the hole above the carb (wiper motor connection). That hole should be completely plugged or connected to the vacuum wiper or you will have a small intake leak.
Maybe check the points also to make sure they aren't too badly pitted as that can wreak havoc on your timing settings.
markyb
Senior Member
if you have access to a known working carb, even to just borrow, try that. I fought an over rich fuel mixture all summer long and it turned out to be an improper GAV needle....I would clean the plugs, and within 5 or ten minutes of driving the car would be buckin' and spittin' and eventually stall from carbon on the plugs
eliminating the fuel delivery issue will get you real close to figuring out what's going wrong.
Definitely block off the hole in the manifold above the carb if you're not using it. Once you've eliminated the carb as an issue, you can use that hole for a vacuum test if you can get your hands on a vacuum gauge.
eliminating the fuel delivery issue will get you real close to figuring out what's going wrong.
Definitely block off the hole in the manifold above the carb if you're not using it. Once you've eliminated the carb as an issue, you can use that hole for a vacuum test if you can get your hands on a vacuum gauge.
Like markyb said if you don't have the vacuum hole on the intake manifold plugged
you will be running way to lean.
Bob