will not idle down
 

this new engine will not idle like my other model A's...they will idle to point you could almost count fan blade turning over...this new engine has high compression head, counterbalanced crank, and B grind cam...wonder if the non stock items can keep it from idling like other model A's...suggestions welcome...

Re: will not idle down
 

Timing!! is everything.

Re: will not idle down
 

Your engine should idle very nicely. It is largely the cam that affects idle, and a B cam should idle as good as an A. Look elsewhere.

Re: will not idle down
 

Hi Lopez,

Learned this over 57 years ago .... a high compression head like a Police Head with a B cam can never idle with low rpms like a stock A.

Re: will not idle down
 

What do you by not idling down ?
It won't idle as slow as you want ?
It idles rougher than you want at low speeds ?
The throttle adjustment screw won't allow it idle down ?
The idle mixture screw doesn't make any difference ?

Re: will not idle down
 

My Turlock Machine rebuild wouldn't really idle down until it had a bit over a thousand mies on it. Now, it will idle way down to the 200 rpm range if you really fiddle with it.

The can and the tightness of everything will affect your idle.

Re: will not idle down
 

Hi Lopez,

I think you are asking why is it that:

a. With your Model A Engine "A" properly timed with all original stock parts; and,

b. With your Model A Engine "B" properly timed which has the equivalent of a Model B cam with a high compression installed; and,

c. With spark all the way "up" on both, and with the idle setting on the carburetor as low as it can go prior to the engine stopping on both, is it normal that stock engine "A" can continue to run with less rpm's than engine "B"?

That is what I experienced in above reply no.4.

Re: will not idle down
 

Does this new engine have a lightened flywheel?

Re: will not idle down
 

Any new engine will be snug until broken in. I would not expect it to idle slowly just yet. My tudor engine has a Stipe cam, snyder head, and B carb, and with several thousand miles on it, I can idle it down to where it is almost silent.

Re: will not idle down
 

Hi Lopez,

This may or may not help one to visualize why one's performance engine, (even after 25,000 miles from now), will never idle at such low rpms as that of one's original stock Model A engine.

1. The pistons in both Model A engines will travel the same distances up and down.

2. The stock head has a larger combustion chamber that contains a larger volume of air than that of the high compression head which has a smaller combustion chamber; hence, one's performance engine contains a smaller volume of air before the piston begins to move downwards.

3. As the pistons in both engines travel the same distance downwards, the stock engine's combustion chamber has more air to begin with than the that of the high compression engine.

4. Because a vacuum can be translated into a container which has less air, the stock engine with more air will have less vacuum ........ and the high compression engine will have more vacuum because it had less air when it began descending.

5. More vacuum in a combustion chamber means more fuel drawn into the combustion chamber; and more fuel means more rpms ...... like opening the throttle.

6. Not trying to make one cough up their hot coffee; but if one drills small holes in one's intake manifold, and decreases the vacuum in one's performance engine's combustion chamber, by trial and error, one may be able make this performance engine idle at lower rpms to match that of the slow idling of one's stock engine.

7. Or for a final experience, one can drive to a race track where guys have very high performance engines, with terrific vacuums, with engineered matching racing cams.

8. Next, just crank up one's Model A and ask the race track driver if his car can idle this slowly to where he can see the individual fan blades rotating.

Hope this helps a little.

Re: will not idle down
 

There is your answer. I have found that worn stock engines idle he lowest.

Re: will not idle down
 

Can there be a point where the engine will run but the idle could is too slow? There is a spot at TDC and BDC that the connecting rod is going from one side to the other on the stroke and the piston is stopped. Is 200 rpm enough momentum for a smooth transition at those points?

Re: will not idle down
 

I was warned years ago not to lighten the Model A flywheel, as it would never idle properly, nor drive the same. Well, I did it anyway plus added a 5.5 HC head. It may not idle quite as low as an original Model A, but it is certainly a nice, very low idle. After 8 years, I've never regretted either choice.

Re: will not idle down
 

Idling a Model A engine at a very slow speed is a death sentence. Keep doing that and you will be back at some engine builders shop. Just because it will, doesn't mean you should.

Re: will not idle down
 

is the throttle plate inside the carb hanging up on the intake where the carb bolts on? easy to check, pull, carb and look for shine spot on manifold ports or on throttle plate, some times to fix it all you need is a thicker carb gasket

Re: will not idle down
 

I agree with James, and wouldn't want my engine to idle less than anything between 450 and 500 RPM.

Re: will not idle down
 

What is the harm to the engine with low idle ?

Marc

Re: will not idle down
 

If the idle is too low you won't get enough oil thrown onto the culinder walls and cam lobes.

The large old hit and miss engines with 5 foot flywheels run at about 275 to 400 RPM. My friend was playing with his large engine one day and got it to almost come to a dead stop when the piston reached TDC firing. When it fired you could watch the heavy crankshaft actually bend, or call it flex. Fun to watch, but couldn't be doing that crank much good.

Re: will not idle down
 

Speaking of idling, listen to this one.
https://www.youtube.com/watch?v=rKwZ...6aS9s&index=36