Acceleration problems

[History]

I rebuilt the carburetor and believe I did that correctly as it ran well then. I did have to clean the plugs as they were covered in black soot and it ran awesome. That was a year or so ago and it’s sat since then. I’ve never driven it any distance on the road, just around my shop area. I just redid the brakes and brake/clutch shaft and jumped on the road and it will not accelerate smoothly. It acts as though it’s starving for fuel (backfiring during acceleration)but I don’t believe that’s the problem as I borrowed a known (good) carburetor and it ran the same. My fuel flow looks great to me so let’s assume it’s adequate. I checked the timing and it seems correct, cleaned plugs again, set points 20 thousandth. What would you guys recommend to look at and what order? I appreciate any help you can give.

[lrf]

You said the car sat for awhile, there's a good possibility that the points are oxidized so clean the points by pulling a clean strip of paper between the closed points. You don't need to use sandpaper, the old timers use to use a match book cover drawn through the closed points. Hope this helps. Keep driving your "A".

[Synchro909]

"That was a year or so ago and it’s sat since then."
Did you replace the fuel? 12 month old fuel doesn't run as well as fresh stuff does. The engine loses its sparkle.

[Bob Bidonde]

I suspect 2 things: 1) Poor grounding of the ignition to the battery; 2) Try replacing the condenser.

[History]

New fuel with no corn it before or after. Will check ground and make sure points are cleaned. Thanks guys

[bruceincam]

Sponsored Links (Register now to hide all advertisements)

I'm just passing on my experience with an identical problem. My problem ended up at the coil. Once I replaced the coil, no more backfiring on acceleration.

[Gary WA]

Check for manifold leaks..

[Rob Doe]

X2 on #7, at carb to manifold, intake manifold to block, at the vacuum wiper line, and at the throttle plate shaft. Check the thru bolt holding the carb together is snug.

Where is your GAV set? 1/4 turn ccw from fully closed? Did you try opening it a small amount multiple times?

Are you driving the car when this happens or are you manually manipulating the throttle in the drive and it misses and backfires at higher rpms?

[old ugly]

i know you said you tried a different carb, to one you know is good. and you said the fuel flow is good.
to really check the fuel flow to the carb run a line from the carb line into a bucket, then turn the gas on and let it run for a while. sometime the initial flow will look good but then it will slow down. if it slows then there is a partial plug in the line or the tank is not vented. if it runs continues then move on to from the carb.

[Patrick L.]

One thing not mentioned is the fuel line ferrule. Make sure the line doesn't protrude past the ferrule too far which can restrict the flow.


Where is the spark lever set when this happens ? Once started the lever should be down 1/2 to 2/3.

[jack backer]

‘If you think it’s a fuel problem then it’s an electrical issue, if you think it’s electrical it’s fuel’


old mechanic proverb

[History]

I just got a chance to look at it again and here are the findings,,,,cleaned points but they looked good, changed coil wire, exhaust manifold gasket is blown on front cylinder (maybe from backfiring) and when I hold the choke closed at a certain point it seems to run much better (sitting in garage with me inside car). Where/ what is recommended intake/exhaust gasket and to buy??

I will check the flow again as suggested and let it run enough to see how long a gallon takes to run out.

Spark lever half way down

[Rob Doe]

I'd fix the manifold gasket. If the exhaust is leaking the intake may be also. Do one thing at a time so you know what fixed it. I torque the intake and exhaust manifolds on my car at 25 foot pounds and come back after a few miles to make sure it is still tight. After a couple checks I go every 500 or so before checking again.

[nkaminar]

I have had the best luck with the original gasket, see https://www.snydersantiqueauto.com/p...htm?pid=979402

Torque the nuts to 55 ft-lbs and use the conical washers. Make sure the manifold is flat by setting the exhaust and intake manifolds bolted together on a flat surface. If they are not flat you can sand them using 80 grit sand paper that is glued to a flat surface. Check the torque after one drive and then again after a few hundred miles.

Check the fuel flow by removing the smaller bolt under the carburetor. Use a bucket to catch the fuel. Do this outdoors with a fire extinguisher handy. By checking the fuel flow there you take into account all the fittings, lines, filters, and float valve. If you get low flow at that location you can isolate each component one at a time to find the fault.

You can use the clear distributor cap to view the sparks while the engine is running. They should all be blue and uniform.

[Patrick L.]

If it runs better with the choke partially closed then its probably running too lean. So there is an intake/carb gasket leak somewhere or an improper low speed idle mixture adjustment.

The suggestion of opening the GAV in increments is a good one. Not all carburetors are created equal. They all tend to have their own preferred setting from closed to a turn open.

[jetmek]

Check your float level

[ronn]

you can also shoot some carb cleaner in the carb, while its running.......

[History]

I believe my flow to the carb is adequate, I tested it by using a quart measuring cup. Had my son to turn it on and I watched and timed it. To run one quart it took 1 minute and 10 seconds, so a gallon would be over 4 1/2 minutes. I believe that is more than adequate so we can rule out a restriction in fuel supply to carb. The line just sticks past the Ferrell into the carb so I think it’s ok as well.I’ve ordered new manifold gaskets and will replace them soon. There could be leaks there now on intake but it’s hard to tell. I think the float level is good because of the other carb doing basically the same thing.

[ronn]

wasnt speaking on fuel restriction- more on cleaning out jets, float etc.


taking any gum out of carb and free flow

[History]

Took 3 minutes 20 seconds to run a quart through the carburetor. I don’t know what rate should be but it seemed more than sufficient to me. Carb doesn’t appear to be gummed to me as the known good carb runs the same.

[nkaminar]

16 miles per gallon and 45 mph = 3/16 quart per minute or 5/8 quart in 3 minutes and 20 seconds. If you are accelerating or going up a grade the car will require more fuel. The fuel flow seems a little slow to me. Or maybe not.

On to the ignition.

Did someone stick a potato in your exhaust pipe?

[Rob Doe]

Originally Posted by History

when I hold the choke closed at a certain point it seems to run much better (sitting in garage with me inside car).

If this is repeatable, as stated above, this is an indication of a lean condition. Since you tried a known good carb, FROM A CAR THAT IS CURRENTLY RUNNING GOOD, and got the same lean symptoms:

Perhaps remove the fuel line at the carb again and attach a 1/4 " fuel hose and blow back through the line with the fuel valve open to temporarily clear the line??? Do you have a pencil filter in the top of the fuel valve?

[Rob Doe]

Originally Posted by History

I’ve ordered new manifold gaskets and will replace them soon. There could be leaks there now on intake but it’s hard to tell.

While waiting on the manifold gaskets, you could try to verify that there is an intake leak using a can of WD40 with the red straw, or an unlit propane torch. Take proper precautions.

[Charlie Stephens]

Check to be sure the throttle is opening completely against the stop. Be sure to post what you eventually find.

Charlie Stephens

[Marshall V. Daut]

Aha! Charlie finally hit a point that I have been waiting for someone to mention. Often when owners discuss lack of power from their Model A's, they don't realize that although their carburetors have been cleaned and rebuilt and the fuel flow checked, there is still a good reason the engine doesn't seem to reach high speeds. When guys swap from a Zenith to a Tillotson (or Marvel), they don't notice that the travel of the throttle arm is the not the same. It's impossible to sit inside the passenger's compartment with your foot on the accelerator and check whether the carb's throttle is pegged against its stop. And you can't check that from inside the engine compartment by pulling on the arm. That will give a false result because of the leverage your hand imparts that is lacking with your foot to the floor. This needs to be checked by two people: one holding the accelerator button to the floor inside the car and the other one checking whether the butterfly arm pegs wide open. Often times when a Zenith is at full throttle when the foot feed is floored, a Tillotson that replaced it might only open to 3/4 throttle, and visa-versa. I have yet to see many accelerator linkages (where the rod connects to the carb) that haven't been "adjusted" in their 90+ year lifetimes. Most of the arms have bends in them from past owners tweaking their throttle linkages to achieve full throttle.
On Model A's I have bought and repaired over the years, or for customers/friends, more often than not a different carb had been installed by the new owner or a past one, but the throttle linkage arm had not been commensurately adjusted (bent) to accommodate for full throttle. The first thing I check when someone complains about his lack of top end is the butterfly arm travel. I almost always end up bending it to achieve full travel. The owners are shocked by how much faster and peppier their engine is once full throttle has been attained. Well, Duh!!! ANY engine will feel underpowered with only 3/4 throttle! The Model A engine is more than capable of reaching 55mph, but unless it can also reach full throttle, it won't get there and owners will be disappointed in their car's performance. I suspect owners who complain that they can't get their Model A to go faster than 40-45mph may have a misadjusted accelerator linkage, assuming the speedometer error is within acceptable tolerances.
Check out the throttle arm travel with a friend and see if that helps you attain higher speeds with more power. Also check that the upper floorboard isn't prohibiting the accelerator linkage from full travel. Oftentimes poorly-made floorboards or ones with too much sound-proofing will stop the accelerator linkage from going down all the way. Make sure the arm beneath the accelerator button is not chafing against the hole in the upper floorboard. If so, bend the arm beneath the button to clear any interference around the hole.
Marshall

[History]

Sponsored Links (Register now to hide all advertisements)

I checked float level again and it is right at 5/8” from the bottom of the top half of carb. (Pictured). I decided to check things out in the bottom while I had it off and there was some crud on the gav needle tip so I cleaned all again AND it runs correctly now. I did blow back through the fuel line as I do have a pencil filter on it, it didn’t push fuel back toward me so cap is venting. I don’t understand why the good carb didn’t run well. Maybe I’ll put it back on now and see if it runs well also. I’ve had waaaayy to much going on so I’m a little scatter brained on top of being born scatter brained. I had already blown through the fuel line so I don’t believe it was that. I really appreciate all of your responses and they all could have been the culprit but I’m thinking at this point it was the crud.

[shew01]

Wow. I’m glad you found the issue.


Sent from my iPhone using Tapatalk

[nkaminar]

Progress. Good work. The spray carburetor cleaner can sometimes work wonders.