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Trying to set the timing per everything I've read in just about every thread on the subject using the search. (Complete engine specs below). 

 

Vacuum wise it's hard to get anywhere past 7 or 8. I don't get anywhere near 15 or so unless I really rev the motor. I know the cam may have a lot to do with that. (This is vac capped at dizzy. Pulling from the tree from where the brake booster normally connects.) Should I see more, even with that cam? 

 

It seems like no matter what the timing is set at, the car feels best with a baseline idle of 900-1,000 over the published spec of 800. Could this just be my build also? This is timing from the gun. My gauge is apparently way off. Gun will say 800 when the gauge will say 500. 

 

If I drop the timing down to 12, she just straight wants to die. 

 

If I leave the timing at 16, keep the RPMs around 950 where it "feels" best, and then hook my vac back up, and give her some throttle, I'm well past 50 on the marks by the time I hit 2,000 rpm. No way I can find 32-36 @3,000rpm. 

 

Am I doing something wrong here, or with this type of build, is this what I should be seeing? 

 

Full Specs:

 

351C 4 bolt block, .030 over bore,TRW flat top pistons,stock rods, crank,file fit Federal Mogul rings,balanced rotating assembly, Pioneer SFI balancer, 

stock oil pump and pan. The cam is a comp 270 magnum cam 224 duration, 519 lift. 

Comp lifters, Cloyes double roller timing setup. Edelbrock aluminum water pump.The heads are 70 4v closed chamber heads, 

stainless one piece valves, cut for guides, screw in studs, Comp Cams springs, retainers, locks, hardened push rods, Crane gold roller rockers, non-ported, with factory Boss valve covers. The intake is an Offenhauser 360 dual plane, non-ported with a Holley 770 street avenger vacuum secondary. Holley mechanical fuel pump up front and Holley blue pump out back. Hooker competition headers.

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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General consensus is go with DuraSpark, Performance Distributors made to order by the looks of it. Cheaper too! https://performancedistributors.com/product-category/distributors/ford-distributors

Msd boxes were the cats meow, but recently they are all made in china.

10° should be easier to start with than 16°. At first I thought you might be having a carburetor heat soak/percolation problem, but now I'm think something else because it won't start. The b

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Plug off the vacuum advance and forget about it till you get it running good. I usually don’t even use it. Another problem is that carb. Sorry to say but I had the same one and it sucks. You must have a vacuum leak somewhere to be so low. When tuning or doing any diagnosis, the least amount of accessories hooked up the better to find out what is going on.

Was it running good before?

If so what was the vacuum reading?

Has your dizzy been recurved?

I am sure the experts on here will help you figure it out, which I am definitely not.

John - 72 Q Code

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Thanks guys.

 

So it's a new to me car. I have no prior vacuum readings to go by.

 

This is the way it ran before and after a carb rebuild by one of the best carb shops here in Phoenix(done last week).My biggest issue with it really is cold starts are terrible (carb has no choke. Was milled by previous owner after some sort of issue with it.). And also that no matter how it's adjusted it dumps so much fuel, your eyes burn just stopped at a traffic light. Wife won't even ride in it with my because you stink like gas after being in the car 10 minutes. I agree. I think the carb sucks. Would love to get recommendations on another one.

 

Vac was capped at the dizzy. The dizzy has also been re-curved by the previous owner.

 

When checking the advance, the vac was plugged back into the dizzy.

 

At a base timing of 16, it does run well when driving. No pinging or anything like that.

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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Well, you need a choke or cold starts will be an issue.

The carb was milled? Not sure what that means. The one thing that I can definitely tell you is that carb needs a hole drilled in each of the butterflies. Forget what size but Stanglover, who is a member on here can definitely help you out with trying to get your carb tuned. Your definitely not getting enough air.

John - 72 Q Code

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Big red mach 1,

Take the advice midlife and jpaz are offering.

You do not want any vacuum advance while trying to set the base timing or total advance.

most motorcraft distributors (especially duraspark ) have WAY too much vacuum advance built into them.

unless you have actually checked your harmonic balancer with true top dead center, your balancer could be misleading you.

how many degreed of mechanical advance does your distributor have? 10 degrees distributor = 20 at the damper.

you should be running no more than 10 degrees mechanical advance in your distributor.

To see how much mechanical advance your distributor has, leave the vacuum advance disconnected and plugged. and check timing at the lowest rpm that your engine is ok with, then slowly raise your rpm until you get your highest timing reading.

16 degrees at idle + 10 degrees mechanical advance will yield you your 36 total.

if your actual is over 36 degrees you have too much mechanical advance and you will probably spark knock and put yourself at risk of engine damage.

IF you are at or below 36 degrees total, I suggest you advance your base timing by 2 degrees and test drive, if no spark, try another 2 degrees if it spark knocks at any time back it down 2 degrees and keep it there.

Now go in there and adjust your idle mixture to achieve best (stable) vacuum at lowest rpm. if vacuum increases and rpm also increases, back the curb idle screw down (as to not go past the idle transfer slots)

If you still have really low vacuum at idle, I suspect cam timing or a vacuum leak at the carb base or at the intake manifold.

I am running 275/281 duration with 106/114 lobe centers @.575''.580'' lift with basically the same carb as you and pull 17.5'' vacuum at idle.

With that kind of vacuum at idle, your carbs power valve is most like open all the time, causing all the richness smell.

Boilermaster

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As others have mention check for any vacuum leaks or unplug ports. Your cam can be the cause of the low vacuum. Besides duration and lift the lobe separation has a lot to do with if a cam is mild or aggressive. If the cam is the cause then putting more timing in at idle will help bring the vacuum up some. See the attached article that might help you on the timing. https://www.fordmuscle.com/archives/2000/03/timing/.

 

If your vacuum is that low the power valves in your carb are probably the wrong size. Most holley's ship with 6.5. With such a low vacuum more than likely your current ones are open when the car is idling and that is why you are dumping fuel and running so rich at idle. The power valve size should be 1/2 of the vacuum. So if your vacuum is 7" then the power valve size should be 3.5. you could also have a blown power valve. The way to check that is to turn both idle mixture screws in all the way. If the engine stays running the your power valve is bad. If it dies then it's good.

 

Also, with such a low vacuum you need to open the secondary a little. You will have to have the carb off the intake to do this. There is an adjustment screw underneath the carb to do this. This will make a big difference on setting your idle mixture and the engine will idle much better. See link https://www.holley.com/blog/post/how_to_adjust_the_secondary_speed_screw_on_holley_carbs_/

 

Re-adjust your idle mixture and shoot for around 800 rpm. If you do the above I think your problems will go away.

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Kilgon

 

 

"The only dumb question is the one not asked"

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Klingon,

Suggest when opening the secondary to get the primary's to close and not get into the transfer slot, to slip feeler gauges between the stop and throttle blades to ( measure how much to go) then the beginning position will not be lost.

from there one can see if anything is to be gained.

I prefer to replace the stock slotted screw with a set serew with an allen head so the carb only has to be removed once.

Boilermaster

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I would verify the balancer is correct. FYI, if you are able to get over 20° mechanical advance on your dizzy, it needs limiter sleeves to reduce the total.

 

Some things I did not see or missed: Set your idle fuel levels to the center of the sight glass (IIRC, it should have that vs the sight plugs) After you do that, look down the throat of the carb. If you fuel dripping off the boosters, then you have to drop it down more, or you may have too much fuel pressure.

 

You may also have too much preload on the lifters, causing the low vacuum condition.

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Klingon,

Suggest when opening the secondary to get the primary's to close and not get into the transfer slot, to slip feeler gauges between the stop and throttle blades to ( measure how much to go) then the beginning position will not be lost.

from there one can see if anything is to be gained.

I prefer to replace the stock slotted screw with a set serew with an allen head so the carb only has to be removed once.

Boilermaster

  Thanks - I should have mentioned it but  it is explained in the video link.  I do like the idea of the allen head set screw.

Kilgon

 

 

"The only dumb question is the one not asked"

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Guys. Tons of great info here. Thank you very much. I will get to work. I'll post back any and all findings. It may be next weekend though before I get back to you, but I won't let the thread go dead until we have an answer/solution. Thanks so much!!!

 

We at least have to get her well enough to do a proper burnout. (Right now she won't). Scary huh?

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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So a quick visual inspection of the vacuum system at a couple of points has shown me that my functional Ram Air system should run to the tree on the back of the intake. Instead it runs to one of the 4 outlets on the firewall.

 

Also, this thing I believe is called a A/C Vacuum canister. It should have a hose on each fitting, right, and possibly a control valve on one of them??? This is how it currently sits. It seems like the vac diagrams I have seen don't show this canister.

 

 

20200315-113712.jpg

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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IMG_1812.thumb.JPG.c2412bbf5b090ef4d56e42a9325d712a.JPGIMG_1812.thumb.JPG.c2412bbf5b090ef4d56e42a9325d712a.JPGThis picture may help a little. Chuck
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Okay. So that's clearly wrong on mine. Thanks, Chuck. I think I've got stuff wrong all over the place. I also have one of the two vac lines under the main 4 on the firewall (the two coming from the dash area going to the carb). That doesn't seem right either.

 

 

20200315-113428.jpg

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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So Chuck, I see that the small hose is running to a hard plastic line, and then I assume it goes back to a soft hose, and then where is that bad boy headed and hooked up to??? Thanks!!

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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Most of the vacuum diagrams are for emissions. Try this one, it's for the '71 A.C., but should be similar to '73.

 

1971-Mustang-A-C-Vacuum-diagram.jpg

 

I also added a PDF of it to this thread

https://www.7173mustangs.com/thread-vacuum-hose-diagrams?pid=246021#pid246021

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“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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IIRC the vacuum routing is different between 72 and 73. My 72 doesn't have the vacuum tree mounted on the firewall. The thing that looks like a plastic piece is just a rubber hose splice, the PO had cut it for a reason unknown to me. The small hose goes through a large grommet (made onto the hose) in the firewall to the heater/AC control that sends vacuum to the proper vacuum motor. The large hose is coming from a vacuum tree on the intake manifold. Chuck

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Continuing to go over things....

 

Vacuum port on the back of the intake was very loose. Not screwed in tightly. I think that's easily issue #3 now with the vacuum side.

 

Also, How many of you chose to keep or delete your PVS Valve? The one that's in the water pump. I guess it's purpose was to speed up the idle to cool the engine if the coolant got to 220°. It sounds like it was popular to remove them under the mistaken belief they were "pollution equipment mandated by the government to rob the engine of power."

 

#1 on the diagram. Looks like the 73 was a 3 port version.

 

3-14-A-vacuum-diagram.jpg

 

20200315-165754.jpg

 

Screenshot-477.png

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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Also, closely look over the A/C vac canister they tend to rust out.

They get tiny pin holes by the edges or on bottom, depending on which way it is mounted

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Ohio Mustang Supply

440-949-2556

 

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Progress report.

 

I disconnected all vacuum lines and plugged literally everything at the tree coming out of the back of the intake. I also plugged all lines going to the carb. Nothing hooked up. That tree was loose, so that was re-tightened. Actually, the only thing hooked up was my vac gauge at the top of the tree. The large port on top that goes to the brake booster.

 

Car barely start, and would not stay running.

Reconnected the 2 lines to the carb back into the tree. The car would run. It took some effort, but it ran. According to my Innova timing light, at 1,000 rpm, I had 10hg of vacuum. I was certainly hoping for more.

 

I adjusted the idle mixture screws in, and yes they will kill the car of you run them in, so I believe the Power Valve to be good. Adjusting both of them up, I was able to get to 11Hg vacuum, but this was still at 1,000rpm.

 

When I adjusted the car back down to the optimal 800rpm, the car really didn't run well at all, and the max Hg I could get was 9Hg.

 

At this point my eyes are literally burning and I came back in to post these results.

 

Thoughts, comments, questions appreciated. Thanks!

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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I should also state that if I revved the car to 2,000 or 2,500 the vac gauge would jump up to 15Hg. I'm assuming this might mean that the car really isn't getting enough air at idle as jpaz stated.

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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Have you tried lowering the float bowls yet? Look down into the carb throat, if it;s dripping from the boosters, the floats are too high for certain.

 

 

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Yes, sorry, float levels are correct. No dripping. Thanks!!

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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They are set to just lower than the sight plugs. I have to bump the car just slightly to get fuel to come out of the sight plugs.

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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Another FYI. Just in case I can't make more vacuum than what I currently am at. I went ahead and ordered 4.5 and 5.5 Hg power valves taking into account vacuum number / 2.

I'd still like to see a higher vacuum number, but with that cam I'm not sure it's possible.

 

I don't know what size power valve is in there but the previous owner liked to drag race, so I'm sure it's a big one.

 

 

 

FB-IMG-1581996874622.jpg

Chris - BIG RED MACH 1

Born in '73 - Drive a '73

Former U.S. Army 63B10-H8

1st Infantry Division - The Big Red One

 

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