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Timing frustrations
#1
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.

Born in '73 - Drive a '73
Former Mechanic U.S. Army
1st Infantry Division - The Big Red One
BIG RED MACH 1
(Learning a lesson (or three) on the Cleveland every day.)
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#2
When measuring advance at RPM, is your vacuum advance disabled?

Let me check your shorts!
http://midlifeharness.com

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#3
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.

run_horse Run Horse Run!
John 72 Q Code
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#4
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.

Born in '73 - Drive a '73
Former Mechanic U.S. Army
1st Infantry Division - The Big Red One
BIG RED MACH 1
(Learning a lesson (or three) on the Cleveland every day.)
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#5
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.

run_horse Run Horse Run!
John 72 Q Code
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#6
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
[+] 1 user Likes boilermaster's post
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#7
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_...ey_carbs_/

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

Kilgon


"The only dumb question is the one not asked"
[+] 1 user Likes Kilgon's post
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#8
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
[+] 1 user Likes boilermaster's post
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#9
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.


[+] 1 user Likes Hemikiller's post
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#10
(03-14-2020, 10:03 PM)boilermaster Wrote: 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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