Power Issue?

Rex Smith

Rex Smith

Member
Driving my '30 Model A coupe after a lengthy restoration. A complete engine rebuild with a Bumfield head was part of the project. I'm not sure I'm getting the power out of it I should expect, although I don't know what to expect. As it is, I'm not sure I could get up a steep hill without significant clutch slipping. I'm curious to know how to tell if my 'A' is performing up to snuff and some tips for maximizing power. FYI, the car has a '39 ****** in it.
 
The clutch should never slip. If it does it is time to fix it. I need to downshift on steep hills, after all it is a model A.
 
The clutch pedal should have 1 inch play before it starts to disengage. If you have that and it still slips, then there is something wrong with the clutch disk or pressure plate.

It will take a while to break in the new engine. The power should increase as it breaks in. If you get a chance, join a tour to compare your car with others.
 
I didn't mean to imply that I have a slipping clutch, I don't. I'm saying that if I were to climb a steep hill, even though in 1st gear, it seems like I would have to slip the clutch to keep the engine from stalling. At one intersection in our neighborhood, I have to go up a rise to make the turn. Had to do more revving than I thought normal to keep the engine going. I'm familiar with how to adjust the air mixture and spark advance, but not having driven a lot of miles in an 'a', I'm not sure what to expect or what to check.
 
Even a totally stock model A engine is no weakling in first gear or second. I'd suggest doing a compression test. Engine warmed to operating temp, throttle wide open, etc. I seem to recall seeing a chart up on the Ford Garage regarding various different numbers for different heads. Others might chime in here.

Our local club had a car come in with a new engine rebuild that wouldn't run much over 35mph. After a good bit of this n that etc. It was a leaking spark plug. None of the plugs were properly tight. 25 foot pounds on a torque wrench solved that one.

Good luck.
 
My dad bought a new lawn mower that he was having trouble starting, I tighten up the spark plug and it fired right up!
 
Crank the engine over with the hand crank. This will do two things. It will test your compression and test to see if the engine is tight. A normal engine will crank against compression for 1/2 of a turn and then be easy. At the top of the stroke the engine should turn easy.

Another thing to check is the carburetor response. If the idle circuit is not adjusted correctly or if clogged the car will not move away from idle very well and will hesitate, requiring you to rev the engine. The Model A should pull from idle without having to slip the clutch except initially.
 
Number 1, never slip the clutch. Number 2, do you have the spark lever set properly? Advance spark until you just start to hear some ping on a hard pull, then back it off a click. A steep hill is relative but yes, you may have to shift down sometimes. A lot of it depends on the gear ratio you have.
 
Your concern is one that needs the help of an experienced local Model "A" club member who can put hands-on your Coupe.
 
Tell us what you mean when you say complete engine rebuild and how much has the engine been run since the rebuild. After the rebuild how did you break in the engine?
 
By rebuild, I mean that the engine was completely disassembled, parts restored or replaced as needed. Boring, new rings, machining where needed, etc. The only mileage it has so far is driving around the neighborhood trying to get a feel for things.

Yes, I understand about not slipping the clutch. I've driven clutches all my life, beginning with delivering appliances in the 50's and 60's as a teen.

I will play around some more with the spark advance. The manual adjustments in the model a is where my experience is lacking. I did notice that the air mixture adjustment on the carb does nothing so I'm going to put my other carb on it.
 
Rex, after you do all of the stuff others have suggested, make sure you don't have a dragging brake (or two). Possible if the car has been sitting for a while
 
A model A is very zippy in first and second gear. As has been suggested find an experienced model A driver to check out and possibly sort it out for you.
 
At least we are 'consistent' with our advice!!
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462331
 
Make sure your muffler isn't clogged with mice nests or chestnuts stored for the winter. If the muffler sat in an unprotected environment - such in an outdoor carport - rodents can crawl inside and make themselves at home. They clog up the muffler so that it can't expel exhaust fast enough to allow the engine to develop its full power. The engine will idle nicely and run o.k. at lower speeds, but as soon as power demands are made of it, it lacks power because it can't "breathe". Sound familiar?
Alternately, if your car has an old Midas cheapie muffler (like we were obliged to buy for 40 years until the Aires muffler became available), I have seen the front baffle plate break loose from its spot welds and be pushed towards the back of the muffler by the extreme pressure caused by the exhaust. It becomes crumpled because it is bigger than the area around the back baffle, so it effectively blocks the exhaust from passing through the muffler. The results are the same as if the muffler were full of critter gunk.
Don't laugh! A clogged muffler will create the same symptoms you describe. It's happened to more than one Model A owner, who carelessly stored his muffler over a period of time or experienced a loud backfire that broke the front baffle loose inside the muffler. Check it out. Try a different known good muffler before panicking.
Marshall
 
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