model a ford won't accelerate past 20

[Maggie05]

hello, My model a ford won't accelerate past 20 mph good flow of gas, timing set right, will accelerate while car is setting still, need some help with this one.

Thanks

[Brentwood Bob]

Try a different known good carburator.
Bob

[Terry, NJ]

Exactly what is your timing and how are you advancing it? And does the engine overheat?
Terry

[DJ S]

I had the same issue. The problem was timing.

[Marshall V. Daut]

After all the usual suspects have been eliminated (timing, carburetor, fuel flow, points, etc.), make sure the muffler isn't clogged. If it is, the engine will still idle nicely and accelerate smoothly up to about 15 mph, and then it will go no faster because the exhaust can't exit fast enough. Cheaper repo mufflers from the 1970's to the early 2000's (i.e., Midas mufflers, the only game in town at the time) tend to rust inside, so if the engine backfires or time takes its toll, the front baffle breaks loose from its spot welds and pushes toward the back. This effectively blocks most of the exhaust flow, which backs up inside the cylinders = low power. Try a known good muffler and see if that solves your problem.
Incidentally, I wrote an article about this very same condition in the printed version of "Model A Trader" in the late 1990's in the my column "What's Wrong With It Now?". Maybe it can be pulled up on-line, or I can scan it. The article describes what one Model A repair shop owner went through in tracking down the cause of the same problem you are experiencing. Yup - it turned out to be the cheap Midas muffler from the 1970's.
Marshall

[H. L. Chauvin]

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Hi Maggie,

Sounds extremely odd ..... but, one never knows what to expect on an 80+ year old Model A.

No. 2 above, if tried, will let us know about the internal condition of your carburetor.

No. 3 above will let us know a bit about your setting of engine timing.

No. 4 exhaust blockage?

You may also want to try removing your carburetor and notice the position of the side arm's position when the throttle is all the way "closed" and all the way "opened".

Then reinstall your carburetor and look at the side arm again to make sure your throttle is all the way "opened" when the accelerator is pressed all the way down to the floor board.

[pooch]

Maybe an easy first check is to make sure your carb butterfly is opening fully.

Have someone step on pedal and see if it goes to full open.

[ursus]

The situation described by Marshall V. Daut happened to me on a 100 mile drive. I was ascending a hill when the engine suddenly lost power and died. I tried everything to get it running but it would only run for a few seconds then crap out. I guy who stopped to help put his ear to the exhaust and immediately called it a plugged muffler, which it was. We cut off the pipe at the end of the muffler and extracted all kinds of rusted bits from the end and she started and ran well, but noisily, all the way home. Midas struck again.

[BILL WILLIAMSON]

Originally Posted by ursus

The situation described by Marshall V. Daut happened to me on a 100 mile drive. I was ascending a hill when the engine suddenly lost power and died. I tried everything to get it running but it would only run for a few seconds then crap out. I guy who stopped to help put his ear to the exhaust and immediately called it a plugged muffler, which it was. We cut off the pipe at the end of the muffler and extracted all kinds of rusted bits from the end and she started and ran well, but noisily, all the way home. Midas struck again.

A sure indicator of this: REV it up & listen for a HISS at the end of the tail pipe.
Bill Ssssst

[ol shakey]

A bad condenser kept my A from running over 20 mph, Heat from the manifold heater cooked the condenser, so I moved my new condenser and mounted it on the coil over 20 years ago I'm only into go go go mines not a show car.

[Mike V. Florida]

I know you checked it, but almost 100% of the time if the car won't go over 20 it's the timing and/or use of the lever on the steering wheel.

Let me edit this a little. If the engine is otherwise running well, no bucking, popping, belching, etc. It runs like it has a governor on it holding the speed back it's the timing.

[H. L. Chauvin]

Hi Maggie,

Not too many options left ....... don't get depressed.

Did you try driving in a 30 MPH Speed Zone?

[Tom Wesenberg]

Originally Posted by ol shakey

A bad condenser kept my A from running over 20 mph, Heat from the manifold heater cooked the condenser, so I moved my new condenser and mounted it on the coil over 20 years ago I'm only into go go go mines not a show car.

Yep. I've seen the same thing. It's very quick and easy to check the coil wire for a hot blue spark that will jump 1/4" from a head nut.

[H. L. Chauvin]

One reasonable question not answered would be:

What is the past history of this car?

One can have huge amounts of carbon build up around valves causing severe fuel starvation such that the engine is almost powerless ....... then add lots of carbon build up on plugs causing impaired ignition and engine malfunction causes begin to add up.

Also important is what kind of plugs ...... e.g., I have a 1947 Farmall Cub Tractor that without the heat range of D-21 plugs, it is almost powerless when under a severe load.

Few details always helps.

[juke joint johnny]

Could be the valve clearances adjusted too tight ,
,Does it have adjustable lifters? maybe they have unravelled

Has the car ever run right since you have had it?

[Fullraceflathead]

I would make sure the fuel line is not bottoming out in the carb fitting. It is possible to push the fuel line too deep past the ferrel and then the end restricts the fuel flow.
It will run but under a heavy load it will start to starve for fuel.

[KGBnut]

Can you describe how it behaves when you try to go faster than 20? Does it sputter and lurch like it is trying to go faster? Does it cough or backfire? It is perhaps nice and smooth, but seems to have topped out?

Ken

[tinman080]

Some of the cars built by the Big 3 during the '70's had a double-wall exhaust pipe. The inner wall would collapse and the car would do about 45mph tops. 472 cubic inches. Ha none of the owners thought it was funny. We automatically ordered new exhaust pipes for all our regular service customers.

[Jacksonlll]

At idle, put the spark lever all the way up. The engine should cackle. Pull the lever full down, the engine should change speed and lope. It it does not do this, retime it.

[Ed]

Intake leaking or carb mounting gasket not sealing correctly ?