Running rough

[JBohannon]

Well I have my A running again. But not very well. I had an issue with ignition I replaced plugs, coil, coil wire, rebuilt distributor etc and it started right up. Now it runs but not real well missing and sputtering some and a little backfire. I am going to recheck my timing again first. I also replaced carb with rebuilt one. My question today is this. When I cut off fuel valve to let it die the last few seconds the idle increases and engine smooths out just fine. Is that telling me my problem may be carb related or is that normal? Thanks Joe Bohannon

[P.S.]

Sounds like the carb is too rich.

As it runs out of fuel, it gets leaner and leaner.

[Wilbur]

Take a look a your plugs. If they are sooty black, she's running rich and it could be due to the float level being set too high or other carb adjustments. If the plugs are clean, she might be too lean, due to an intake leak either at the manifold or at the carb flange. A consistent small back-fire can point to either incorrect timing or a valve not fully seating.

[tbirdtbird]

P.S., agree. first try closing up your GAV a little, go from there

[H. L. Chauvin]

FWIW:

After new plugs, new coil, new coil wire, rebuilt ignition system, rebuilt carburetor, "everything" mentioned checks out "OK" and it starts right up .... but, "backfire".

Running "again" is mentioned ..... however ...... One Question: But, how long did it sit "NOT" running?

One Possibility:

Sometimes while sitting idle for a spell, oil and fuel can evaporate from Model A valve guides and valve stems and leave a sticky residue of sticky varnish ..... thus causing slightly sticky valves causing slightly rough running and backfire.

If so, "valve timing" is not properly coordinated and the atomized fuel mixture can arrive and exhaust later from in the combustion chamber where the spark plug ignites the fuel when the exhaust valve is in the open position.

Somewhat similar to an "open" exhaust valve is ....... you can hear a firecracker explode in a bathroom much better when the explosion sound travels through an open door in a bathroom ........ no end to what one can possibly find with 80 year old people.

One cup of Kerosene poured in each spark plug hole and allowed to sit for 24 hours was the vintage cure .... some today use transmission fluid, Marvel Mystery Oil, etc., to dissolve the stick varnish.

[H. L. Chauvin]

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Just opinions based on past experiences:

All of my A & B engines, even with different carburetors, plugs, distributors etc., have always speeded up for over 50 years during the last few seconds "after" closing shut-off valve.

A slow "idling" Model A engine runs a little richer than normal, as can be noticed by causing more carbon deposits when allowed to run as such for long periods; however, as RPM's increase, it runs leaner, burning off and leaving fewer carbon deposits.

After closing the shut-off valve, the atomized fuel mixture gets leaner and better balanced for a slow idling Model A engine, with more air and less fuel during the last few seconds.

[Tom Wesenberg]

Timing doesn't change on it's own. It changes after someone messes with it, so I (almost) never check timing for an engine problem.

The first thing is to determine if the problem is spark, or is it fuel related.

[BILL WILLIAMSON]

Generally speaking, cars that are driven OFTEN & with a little "GUSTO", rarely have performance issues. Idling for LOOOOONG periods usually crap up the plugs.
Bill W.

[JBohannon]

If I pour the fluid down the spark plug holes as H.L. suggested do I just start it normally after 24 hours ?

[Brentwood Bob]

Turn it over first With a teaspoon of motor oil added to each cylinder before startup.
Bob

[Farrell In Vancouver]

Check for a intake leak at the manifold port and carb to manifold gasket?

[H. L. Chauvin]

Per #9 (?), start normally.

Have no idea where you live, but with a cup of Kerosene in each spark plug hole, you can kill all of the mosquitoes in a large barn with Kerosene smoke ...... but ...... if sticky valves was the problem, it will afterwards run like a Swiss Watch.

Four (4) cups of Kerosene in a Model A crankcase usually warrants an oil change after the engine runs smoothly in usually about 90 seconds.

Many vintage farm tractor engines years ago had similar ailments after not running for maybe (2) years or more ......

[tbirdtbird]

" When I cut off fuel valve to let it die the last few seconds the idle increases and engine smooths out just fine"

So before you start to rip into everything the simplest test to make is to adjust the GAV valve (you are aware I am sure that your choke knob turns left and right to make mixture adjustments). This GAV (gas adjusting valve) was provided by Henry very deliberately so that people could play with the mixture from inside the car while driving to make the motor smooth as can be.

always go for the simplest test/fix first. If changing the mixture with the GAV doesn't make it better then you can go up the ladder to more complicated testing/fixing

It is possible that if you dump a cup of kerosene in each cylinder that you will hydrolock your motor and then you will truly have a problem

[H. L. Chauvin]

After several thin Kerosene valve freeing experiences, usually, after 24 hours, having open end gaps of Model A piston rings, and with some valves either already partially open, or immediately lifting and un-sealing upon minute engine rotation, one (1) cup of thin kerosene, after dripping 24 hours, usually enters the crankcase below faster than leaking through a leaking metal fuel tank shut-off valve.

[tbirdtbird]

well intentioned advice for sure
and
in the hands of the inexperienced you never know what can happen

? uses more than a cup ? cranks it too soon ?rings have a lot of deposits thus less draining etc. You never know

I've seen worse

[Tom Wesenberg]

Just to be sure, spin it over with the plugs out for a few turns.

[Chuck Sea/Tac]

So now you have 4 cups of kerosene in the oil? Seems like s good time to change it!

[H. L. Chauvin]

FWIW: This was an often used, simple and safe SOP sticky valve vintage treatment years ago .... even used safely for years in the military.

With added assumptions and instructions at this point, maybe worth a Newbie Model A Owner Clarification/Caution or two:

One could now possibly visualize a "Kerosene Model A Sticky Valve Treatment"
misinterpretation turning into a Laurel and Hardy Movie, such as:

1. Newbie reads this post after noticing after a complete tune-up, his engine
is missing and backfiring.

2. Newbie's Model A engine got hot while missing and backfiring -- manifold is also hot.

3. Newbie removes (4) plugs, and pours a cup of Kerosene in all four (4) spark plug holes and does not wait 24 hours.

4. Newbie leave plugs out to avoid possible hydrolock, and jumps in the car and hits the

starter to spin the engine a few turns.

5. Four (4) cups of wet Kerosene is sprayed all over the engine compartment including the hot manifold and the hot exhaust.

6. The hot manifold and hot exhaust ignites the wet Kerosene.

7. Newbie returns on Model A Forum with a photograph of his dog ..... in front of his new pup tent ...... where his house and garage once stood.

[H. L. Chauvin]

Forgot to mention in the #18 Post above, (described in the photograph), in front of the tent, next to the dog, one can see the Heat Resistant Pyrex measuring cup that was used to measure the very simple recommended four (4) cups of Kerosene that was supposed to soak Model A parts for 24 hours.

After the Model A engine compartment Kerosene fire heated up the Model A gas tank, and after the gas tank exploded, this Pyrex cup was the only part of this ever so simple proven method of the "Kerosene Model A Sticky Valve Treatment" remedy that survived.

Even More Important Caution:

When deviating from simple instructions, after all is said and done, make sure you use a Heat Resistant Pyrex Measuring Cup to measure your four (4) cups of Kerosene ...... it is a very safe measuring device for a Newbie to use later to fill his kerosene lamp in his tent after his house and garage burned down.

Then if your wife later returned from visiting your Mother-In-Law, the Pyrex cup can remind her of a happy marriage before your Model A valves were sticking.

Hope this helps.

[Mitch//pa]

Originally Posted by Chuck Sea/Tac

So now you have 4 cups of kerosene in the oil? Seems like s good time to change it!

Agree