I have a rebuilt 272 and I am checking the vacuum pressure. I have only the specs for a 292 which are 18 in/Hg. Are they lower for a 272? I am worried because I measured 15-16 inHg. at 500 rpm curb idle. I noticed when I increased the idle the vacuum increased but starts to wiggle. Could that mean a vacuum leak somewhere? Appreciate any help.

 

Not sure on the specifics of the 272, 15-16 isn't horrible, just not right for a stock engine. What's not stock? Was a bigger cam used? How big is the 'wiggle'? Google 'vacuum gauge test' - there are some very good reads on the subject. Here is a list of readings:

* a lower reading indicates possible incorrect timing, incorrect valve timing or adjustment, incorrect setting of idle mixture, worn piston rings, or leak in intake manifold.
* readings that change slowly indicate incorrect setting of idle mixture screw.
* readings that change quickly indicate sticky valve guides, burned valve sets, or leak in head gasket.

testing at 2000 rpm
* a lower reading indicates possible restriction in exhaust.
* oscillating reading indicates possible weak valve springs.

------------------------------------

* gauge reading steady 17-22 in Hg indicates normal engine in good condition.
* gauge reading low (15-20 in Hg) but steady indicates late ignition or valve timing, low compression, stuck throttle valve, leaking carburetor or manifold gasket.
* gauge reading steady but dropping regularly indicates burnt valve or improper valve clearance.
* gauge reading dropping gradually at idle indicates choked muffler or obstruction in exhaust.
* gauge reading slowly dropping to zero as engine speeds up indicates choked muffler.
* gauge reading fluctuating between 15 and 20 in Hg at idle indicates stuck valve or ignition miss.
* gauge reading drifting indicates improper carburetor adjustment or minor intake leak at carburetor or manifold.
* gauge reading fluctuating as engine speed increases indicates weak valve springs, worn valve stem guides.
* gauge reading vibrating excessively at idle but steady as engine speeds up indicates worn valve guides.
* gauge reading vibrating excessively at all speeds indicates leaky cylinder head gasket.

 

It is a stock 272, the heards are from a 62 292 truck and it has a ford rebuilt 2100 carb off of a 63 292 truck. It has a stock rebuilt distributor, new wires. The engine rebuilder put in a stock 272 camshaft. I thought since it was low on the test, I would pull the plugs and do a compression test and see if it could be a problem with the rings or a valve sticking. It runs good at idle but when you stomp on it or try to take a hill it loses power and bogs down. Thanks for the information.

 

Regarding the stock rebuilt distributor, is it a 56 and earlier or 57 and later. The earlier only had vacuum advance. The later had vacuum and centrifugal advance. An earlier distributor on the 2100 will not work right.

 

I purchased a rebuilt distributor for a 59-60 292.

 

I misspoke in my previous post. 15-16 may be OK on a stock 272. I don't know. If you have 62 292 headsand a '63 carb, it isn't really stock anymore. The compression ratio probably changed a bit because I think the chamber size is different (again I think), but I doubt that would affect your vacuum much. Try adjusting your timing a little while watching the vacuum gauge to see if you can get the vacuum a little higher. Peak vacuum is the best setting as long as your not over 12-14 degrees and it doesn't ping.

The bog on acceleration sounds like either bad vac advance or the carb isn't tuned to the motor - wrong size power valve or accelerator pump needs adjusting. You may need to adjust the vacuum advance on the distributor.

What is the timing read at idle with and without the advance hooked up?

Just some thoughts - I'm just a hack at this myself.

 

I checked the vacuum advance on the distributor and it seems to be working. I added vacuum to the diaphragm and the plate advanced. My mechanic who built the engine changed jet size from 48 to 54 to see if it was a fuel problem and the advanced the timing to 10 degrees. It seems to accelerate better but not like it should. I can only get it up to 40 mph on a hill due to it bogging down. Could I have a vacuum leak in the intake? I was thinking of spraying some ether around the legs of the intake to see if it picks up this weekend. Any ideas appreciated.

 

Regarding the rebuilt carb. When was it done and how long ago. Was there an amount of time the carb sat unused? You definitely have a problem and my first guess is it is the carb. Sure try spraying some volatiles to look for a vacuum leak. But with this days poor gas, and all its additives, precipitates occur which jamb up the 2100s, requiring some service every 2-3 years.
The vacuum sounds reasonable, though I dont know the actual spec. The recommendation on the carb assumes that the tune up specs of valve lash, points, condensor, and timing are in order. Maybe you should do a compression check before diggin into the carb.

Oh, on the carb jets, they should be no more than 2 sizes high or low of standard. 54s are too high. 48s should be just right.

 

I just bought the carburetor from Holly and put it on. I had a previous 2100 that I rebuilt but had the same problem so I purchased one. I am going to do a compression check this weekend. I will let you know what I find. Thanks.

 

I don't think a leak causing that slight of a drop in vacuum would cause that poor of performance. You seem to have no power.

How many miles since the rebuild on the motor?
How big is the 'wiggle' on the vac gauge?

 

I agree with Sam's point on the leak. I thought of another poss. If your area is one that mandates E10 gas, the ethyl alcohol can and does dislodge deposits in the gas tank and lines, clogging up filters.

 

The engine has about 2000 miles since rebuild. I had a couple problems from the start though. It was overheating. Recored the radiator with 4 row. Heating fixed. Then power problem surfaces. I changed the oil at 1000 miles and found to my disgust that there was only about 3-4 quarts of oil in it. The dipstick was marked wrong. I refilled with 6 quarts. It does not knock or burn oil. I had the gas tank boiled out at a radiator shop and sealed. New lines from tank to carburetor. New fuel pump and rebuilt carburetor. All gas around here has 10% ethanol. I thought at looking again at the tank, filter and checking the volume and pressure test but haven't had a chance.

Funny thing though when stomping on it, it starts losing power, not jerking or anything like that. But when I ease up from accelerating it catches up about half way up and takes off again. Almost like it reaches a threshold of air, fuel, vacuum, or something and loses power then when there is less demand it takes off again. The power loss is more pronounced on a hill.


Appreciate any ideas.

 

I'd start with the filter and volume test. Might be improper float level?

Note on vacuum: When you first stomp on it, vacuum drops to near zero, then will increase as the motor speed catches up (increasing air intake) to the throttle opening.

 

I,m also running a holly 94 and also have a 272 with later C1TE heads.
I made a 2" spacer added 65 jets and accelarater pump is attached at the middle possition. It runs very good, respons is also verry good and up hill or not full trottle = more speed.

 

When I tested vacuum on acceleration it did respond correctly by dropping low quickly then increasing. I thought I would check the fuel volume, pressure then go from there. I will probably check it this weekend. No light in evening and I hate to mess with gasoline in the garage. I will let you know what I find. We will get this figured out yet!! Thanks for all of the advice.