I am currently running a two barrel carb, have a 660 Holly and four barrel intake waiting in the wings. Trying to keep it mild.
I want to make sure that the 351W is in proper order before installing the four barrel, but can't get the vacumm to read normal. It reads around 6 in-Hg. , intake bolts were loose retightened and retorqued. Still read 6 in-Hg. Checked timing no go . Will be replacing all vacumm lines next, since they can be still put on the four barrel later. If that don't go then it may be the carb thats the problem.

Should I just install the new setup then work the bugs out?

This is all because of an intermitence overheating problem that points to the vacumm. It will show up at times then disappear when you hunt for it.

It has a 351W with FMX tranmission. Just finished painting the inside of the hood.

Thanks, Dale
Ford52F2

 

I did a really stupid thing when I put my engine together. I put the carb on and the vacuum read low. So, I went through all the steps to get the idle mixture correct and th emechanical idle screw way up to the correct position.

But I had this weird whistle! Mileage was horrible.

Come to find out that there was a vacuum opening in the body of the carb (Edelbrock 750) in the back for something to hook up to that was WIDE OPEN! I plugged it with a 1/4 inch plug and then had to turn the idle screw way down.

You might want to check to make sure you don't have any openings any place (check the tranny too)- just a thought.

 

Yep my holley has one but its on the side ofthe base plate its manifold vacuum (sucks all the time) its for your PCV to plumb into.

The car I am going to be working on has a ford motorcraft 2V (not orignal) but there was alot of probems with the engine and while inspecting the car I noticed about four vacuum ports on the carb with no caps on them. Family says they could have rotted but the other caps are still there.

So its a good idea to check all vacuum ports.

Another thing are you sure you are hooked up to manifold vacuum port and not a portedvacuum port? Hook the gauge up to the same port and open the throttle if vacuum goes up then thats ported vacuum you have to plumb into a vacuum port below the butterfly valves to get manifold vacuum.

I have a 351 with the orignal 1978 motorcraft carb. I adjusted the timing using a vacuum gauge and at idle (950 rpm in park) the gauge is steady at 22 in Hg.

 

Even if you follow the lines and they are plugged into something, there is a possibility that there's a diaphragm that's broken somewhere, making a leak- things like the modulator on your tranny or the vacuum advance on the dizzy. If you unplug the hose at each of those places and plug them, you'll know if they are leaking or not.

 

Correct another way is to just unplug the line, if the engine changes as far as sound or idleing goethen theres no leak. If there is no change then your not getting vacuum there or you have aleak already in the line.

Yet another way is to take a small propane bottle (the kind you get with those torches) and open it up slightly and go around vacuum lines if your engine speeds up or slows down you got a leak in one of the lines there and its pulling the gas in through the leak.

Same is done on sparkplugs while engine is running pull one at a time will tell you if you have a dead cylinder causing a bad idle.

 

Replaced hoses and checked for extra ports. I did get an improvement it is now between 14 to 15 in-HG. It moves between them in a steady slow breathing movement. I forgot to check the modulator , I did replace it about a year ago. Maybe its loose or something. Check it out on Monday, Sunday kinda busy.

I did find something in the Haynes Ford Engine manual. It reads engines with high performance camshafts will have a lower and somewhat erratic reading at idle. Emission controlled vehicles from the mid-1970s tend to have slightly lower vacumm due to modified valve timing and retarded ignition timing.

My engine has 1980 shortblock with 1969 heads and a 1977 carb. Don't think that applies to it. If it did then my engine is reading normal per-say. Still will try to get a 20 in-HG consider as a normal range.

Thanks, Dale
Ford52F2

 

Here's one other thought. I learned this the hard way also.

Seems when I went to set the timing on my newlt rebuilt 390PI, all the timing values in the books said "6 degrees BTDC is the correct timing." These were the Chiltons manuals etc. I really didn' think I was getting the preformance out of that engine that I should at that setting - pretty sluggish.

So one day I picked up a copy of the original 1966 Ford Shop Manual and turned to the tune up section and guess what? Sure 6 DBTDC was correct - for a newer year engine with the "Thermactor" and all the other pollution control devices installed.

BUT!!!!!!! with no thermactor or pollution control devices installed (as in the earlier engines) the correct timing setting bumped up dramatically to 12 DBTDC and the book recommended another 3 to 5 degrees for performance cams. I have a Melling RV cam in mine.

So, I put the timing light on it and bumped the timing up to 12 degrees before and there was no chance in the idle. Then I took the vacuum gauge and slowly advanced the timing until I got the maximum vacuum, then backed the timing off one inch of vacuum (all at 1200rpm - the recommended setting) The difference on the road was phenominal!
My vacuum at 1200 rpm was almost 22 inches. (but I have a compression ratio of 10.5 to 1 as well)

If you have a cam, and no pollution control on the engine, I might suggest you hook up your vacuum gauge, set the rpm (and the rest of the engine ie vacuum advance etc) for checking the timing, then slowly start to rotate the distributor to advance the timing - while maintaining rpm (which yo may have to increase or decrease, until you get that maximum vacuum, then back the distrubutor to drop the vacuum one in hg. Then set your idle mixture and check the vacuum timing again. Bet it improves and you find you engine timed at about 12 -15 DBTDC.

Try it then drive it. If it pings bring it back and back it off another inch hg! Let us know what you end up with.

 

My stock 78 351w calls for 16* BTDC and its a bone stock emission engine but at that timing with 0.050" plug gap and 9mm ford racing wires the thing just surges at idle and the vacuum waves between 15 - 17 in HG. I hooked it up and advanced the dist and got 22 in HG but now the engine is alittle harder to start. Might be advanced too much but the engine idles very smooth and my economy shot back up to 15 - 17 mpg city where at the factory timing spec I was getting 9 - 12 mpg city. She also has the power to smoke the tires now and does it randomly but before only way was i you were half waysinto a turn and floor it to get the tires to break loose.

But I would recomend using vacuum gauge on all engines just to be safe. Lots of these harmonic dampners (the Yblocks have it for sure) have rubber and over time the rubber falls apart and the TDC mark can move.

 

That could be what my problem is all along? When I originally set the timing was when building the engine. I did it with the timing cover off an then put the distributer in. I have since had the distributer out, but was going by the manual to set the timing. I have Chilton's also. I'll do it an check it Monday.

Thanks, Dale
Ford52F2

 

Honestly your engine could have a rubber ring harmonic dampner and the TDC mark could have shifted. If that is the case I can provide the link to a guy that is supposed to be very good and supplies new dampners which has higher quaility rubber ring than replacements.

 

Well I checked all lines for vacumm, the dist. advance works, plugged lines, then put everything back. Then started messing with timing. I can barely get to 17 in.Hg when dist. advance hits the thermostat housing. Could I have had that distributer one tooth off, all this time .

In 2000 I toasted the torque converter going down hill at about a hundred with the original stock rear end. Blew head gasket at that time also . Thats the last time I tore down the engine, rebuilt trans also. Nothing else seem wrong with the engine, so started rebuild. I do remember that I had to find the TDC after the intake was on. May have to find TDC again and check alignment.

It ran great until 2004, but since I go on travel a lot. I just parked it mostly, then it started to have an intermitant overheating problem that keeps pointing to vacumm.

I be checking the TDC Thursday.

Thanks for any imput, Dale
Ford52F2

 

Ford52F2


Ive messed with lots of different years 351w, and I have ran into a mix of parts, there are
different timing (POINTERS), and diff damper with different markings! As stated in other posts, the out side ring on the dampers
do move some times, when I get a'' good one'' I scribe a mark from outer ring to the center!
So you can keep an eye on it.


P.S. did you use the cork gaskets at the front and rear of your intake, they do push out and cause a leak, Ive used RTV it works great and never leaks!


Wally Womack

 

Have 302 with Holley 4v. might I ask where you connected the vac line to get the 6" reading.

Also, just got back from visiting a bud who had a hell of a time locating a vac. leak on his vehicle only to find he purchased a new carb gasket that's layered with a brass eyelet at each corner which holds it together. Well, couple days of trouble shooting he came to realize the brass eyelets were preventing the gasket from seating fully and the layers were beginning to separate and the brass eyelets prevented him from torqing to required spec's. In other words the gasket was suckin wind. Fortuately, salvaged the orginal to get on the road until the none layered replacement arrives.