MTFCA Forum

I have a 1925 Fordor. Once the engine is running it blows a mist of gas out the inlet to the carb.

I have done the following:

1) New timer (anderson flapper style)
2) Set timing....with the timing fully retarded, spark occurs at each cylinder at TDC. Good strong spark at each cylinder.
3) Fresh Valve Job, Cut seats & new valves
4) New Head Gasket
5) Compression test is ~45 psi, & each cylinder is within 3-5 psi of each other
6) Rebuilt carburetor: cleaning and seals

Once the engine starts, it also sounds like it it is not firing on all cylinders.

When I crank the engine over with the starter, the engine pulls a good vacuum at the intake manifold.

What should I try next?

Thanks!

Do you have the correct firing order? Or perhaps carbon track in coil box.

Does gas run out of the carb when it is not running?
RE: " spark occurs at each cylinder at TDC" needs to be AFTER not at TDC on full retard at startup.
What do you have your valve stem gaps set at?

The valves are set to ~.012" Inch

The carb doesn't leak any fuel when not running.

I haven't pulled the coil box yet. Is it common for carbon tracking to occur? Is there anything else to check with the coil box?

Thanks!

Forgot to mention, The firing order has been checked and is 1-2-4-3.

Pay attention to what Mark said about timing, for your starter's sake and your forearm's sake.

Mark is correct re the timing. With full retard at the lever, and the timing set at TDC, you stand the chance of the car firing up as normal, or Backfiring. I believe the figure is 15 degees past TDC. That way the car will always fire on the downstroke, eliminating backfiring, starter damage and possible broken cranking arms.

Allan from down under.

I can definitely retard a bit more. Once the engine is running, I do have to advance the timing. It doesn't try to "kick back" against the starter.

Thanks

Now that the spark timing issue is out of the way, you have defined exactly when spark occurs (correct or not). What you have not determined is if the cam itself is a tooth off. You can set the timer to be "perfect" to the cam, but if your valve events are off, as in the intake valve not closed at the point of beginning compression (cam retarded by a tooth), you will get blowing at the carb and a terrible running engine as the intake flow is going in and out as opposed to a relatively smooth flow toward the cylinders. All valve events will of course, be late, which will include a barking exhaust note and a very hot exhaust system.

Have you had the cam out, since the car last ran correctly?

Special ground cams have considerable overlap which mimic this situation to a degree, but carburetion, swept area of the piston, compression, and a need for a higher idle all go into the equation to minimize the downside of this condition.

I do not get that you are dealing with a high performance engine, but simply a mal-adjusted stock one.

Scott,

Thanks for the reply. The engine was running fine ~1 year ago. It began to start "hard" and then I started to dig into it and made the changes I mentioned. I first thought it was actually the cam gear, but after removing the timing cover, the fiber gear looked fine, and I left it as is. The timer that was installed was an anderson, and had quite a bit of wear on the flaps. I chose to replace with an anderson timer again.

Thanks

If in fact the valve events ARE occuring at the correct time, the timing gear is not damaged or misaligned, then you may really not have one or more valves sealing as well as you think. While even, your compression could be better, though not bad for a worn engine.

The only other likely way fuel is misting out the intake is there is a disruption of air flow or a seriously maladjusted carb which is doing things we cannot predict with certainty.

Guessing this is an NH carb, remember that this is a very primitive puddle-type carb and if the float level is seriously mal-adjusted, float valve is not closing off properly or more likely (based on symptoms, not because it is common), the main jet is missing a gasket and allowing volumes of fuel to puddle while running rather than being metered past the needle.

Easiest thing to do right now is to at least borrow a known good carb and see if you can pinpoint or eliminate that as the source.

Keith , Did you try an other model Timer ? Like an old style roller , or a New Day ??
Toon

Check for a restriction in the exhaust.

Keith, for gas vapor to go the wrong way out the back of the carb you have a valve or valve timing problem, for it to be an ignition timing problem it would be so far off the engine wouldnt run. Could be heavy carbon build up that is glowing hot enough to ignite the fuel vapor during the intake stroke, or some freak ignition problem that is causing a spark plug to fire more than once a cycle...a short, or carbon tracks in coil box could cause that.

"Is a puzzlement" as Yul Brenner famously said. I'm off the ignition business and on to leaking valve/blocked exhaust (Good guess Ed).

And finally, I would start the car, idle as best as it can for a few seconds and then shut off the fuel supply line (you do have a shut-off, right?). If after a very short while the car smoothes out and stops spitting gas (and then dies for lack of fuel), you have a bad carb. Anything else is valves/timing or as Ed suggested, and I concur, a restricted exhaust.

I think all the bases have been covered by the other posters, however one more thing which could be causing the problem. If the wires between the coil box and the timer are grounded anywhere on route, the coil will spark. If on battery the spark could be continuous. If on magneto it could still spark every time the AC wave peaks. Sometimes a wire of post can contact a bolt at the front of the crankcase. The bolt near the timer should be turned with the nut downward. Other places where it could ground would be against the spring holding the timer to the plate. So check carefully all those wires for one or more which might be grounded.
Norm

Sounds to me like you have a sticky intake valve. Take the plugs out, hand crank it over until each intake opens and spray some good carb cleaner down the inlet area under the valve. Let it set for a few minutes, do it again, put the plugs back in and go for a drive. Should take care of it.
Today's gas is very sticky

If it is ignition related, it would be a backfire, or for some reason igniting when the intake valve is open. If it’s not firing back out of the carb and just chuffing raw gas spray out, it has to be valve related. The only way gas can flow backward through the carb is through an open intake valve. Either an intake valve is not closing, or the valve timing has changed. An intake valve would have to be open on the piston upstroke after the intake stroke.

Another possibility is a bad cam lobe on an exhaust valve. If the exhaust valve doesn’t open enough, the pressure will release through the intake valve when it opens.
Usually runs fair till you get a load or open the throttle much.
And will show decent on a compression test.

Good luck

Dave

I once had to deal with a '16 with a broken-off exhaust lifter on #2 from a friend who bought a "great running car" off of eBay. The lifter piece was missing, and while too large to get out of the valve chamber...it wasn't there, so the valve cover had been off and the eBay lister/owner knew, and there was clearly no way this was a "great running car" when put on the transport. The explosive release through the intake valve/carb was horrendous and it had been run so long that way, the center main was beaten out of it. Pulling the pan, the center main cap was brand new and beaten to pieces. So it had been run long enough to wipe out 2 different center main caps.

Great running car, huh?

a new lifter and a carefully scraped new center main cap solved the problem until it was resold upon my friend's death. Fortunately for all, the block side of the center main survived unscathed, which I guess isn't all that big of a surprise when you do a failure analysis of the root cause of the situation.

That car nearly hopped off the ground while running in that condition. It had a starter, and when he first started it for me to listen, it sure made odd sounds while cranking and once fired up, I couldn't get to the key quickly enough to shut it down.