351C M-Code engine Timing issue!

[Meyer]

On my stock 351C 4V closed chamber M-code engine

4- speed manuel

21 in hg at idle

I run 95 unleaded fuel

Stock dual vacuum diagram distrubutor only hooked up to the advance to portet vacuum on  Carb metering plate/timed vacuum

Idle is 1000 cant go below since timing is so high initial

If i pull the vacuum hose and feel if it suck if i open trottle alittle it doesent do anything. The vacuum canister has been checked its not cracked if i install it at direct manifold vacuum it goes straight to 30’s deg at idle!

I have alot of pinging at WOt

The timing is set at 12 initial and 36 total here it drives great 

If i retard timing to 6 initial no pinging but the throttle response is terrible and it runs really bad, hesitates bogs ect.

Brand new 670 cfm quickfuel brawler carb vac sec stock jets ect

New stock fuelpump

New cap/rotor/plugwires/plugs/ignitor 2 pertronix and a new coil. 

New intake gaskets 

Can anyone help me im really lost here!  I can be the only one expericing this issue

 

[Don C]

Similar issues have been discussed several times in the forum. I would do a search, it's in the"More" tab at the top of the page.

Also, please go to the Introduction section, in the "Forums" tab and introduce yourself and your car.

 

[boilermaster]

On my stock 351C 4V closed chamber M-code engine

4- speed manuel

21 in hg at idle

I run 95 unleaded fuel

Stock dual vacuum diagram distrubutor only hooked up to the advance to portet vacuum on  Carb metering plate/timed vacuum

Idle is 1000 cant go below since timing is so high initial

If i pull the vacuum hose and feel if it suck if i open trottle alittle it doesent do anything. The vacuum canister has been checked its not cracked if i install it at direct manifold vacuum it goes straight to 30’s deg at idle!

I have alot of pinging at WOt

The timing is set at 12 initial and 36 total here it drives great 

If i retard timing to 6 initial no pinging but the throttle response is terrible and it runs really bad, hesitates bogs ect.

Brand new 670 cfm quickfuel brawler carb vac sec stock jets ect

New stock fuelpump

New cap/rotor/plugwires/plugs/ignitor 2 pertronix and a new coil. 

New intake gaskets 

Can anyone help me im really lost here!  I can be the only one expericing this issue

MEYER,

Couple of things here,

if your timing is correct, you should not have 21hg of vacuum at idle.

that engine in stock form with great idle quality should produce about 17-17.5 '' of vacuum.

It is possible that the harmonic balancer has slipped somewhat.

Also, your vacuum advance seems a little much.

when I first got my 71, I had that much vacuum at idle, and I knew it was not right.

I found that I had a 2v cam and 4v heads, probably NOT your problem.

how about disconnecting and plugging the vacuum advance for now and see how it runs.

I would see how much timing I could run before it spark knocks.

Also you need to see how much vacuum advance your vacuum canister is supposed to have.

Do you have the older style with the threaded nipple on the advance side ? if so they use washers to control the rare and amount of vacuum advance.

Everything you describe suggests you are getting too much advance.

Boilermaster

 

[Meyer]

Its a bone stock car checked the adavnce slot today its at the 13L position wich produce 26* Advanced timing initial 12 = 38 total

If i lower it to 10 initial it should produce total 36 wich should be perfect for a 351C but it still pings/knocks!!!

I have the factory double diagram vacuum advance on it no hex in it to adjust only shims/washers

 

[Jeff73Mach1]

you have the advance side hooked up to ported vacuum and the retard side unhooked?

Look at this diagram-do you have the thermostatic valve still. If so, you might try this set up.

http://1970mgr.org/302_2V_ImcoACalltrans.gif

If you don't want to try that, is the spare port open? It needs to be to allow the advance to work properly.

Fianlly, you can swap the advance canister for a single port one that is tuneable and may get closer to where you want to be. You\may want to check to see that you dampener hasn't slipped and that your timing numbers are indeed accurate.

 

[Stanglover]

Meyer, welcome to the forum and as Don C suggested, please tell us about yourself and car in the Welcome section. (if you have not already done so!)

I'm NO expert, don't pretend to be, there are far more knowledgeable members to give advice, but as I too have a 351C 4V 4 speed and had much the same issues getting it to run right, my configuration may help. As well, Boilermaster has good information in his reply above.

So here's what I have for timing, cam, compression, carb and distributor. Rebuilt 351C 4V, .030" over, 10:1 KB 148 dish top pistons, Melling MTF 2 cam, just a tad better lift than stock, Holley 670 Street Avenger carb, similar to yours, and a factory distributor WITH modifications and Pertronix Ignitor II module and matching Flamethorwer coil, (very important!!). My initial timing is 16 degrees with 20* set into the distributor, 10L slot or .410" width for a total mechanical of 36* plus about 6* of vacuum advance running off the timed port on the carb. The vacuum is 17-18 hg hot at idle. Carb jets are 65 primary 67 secondary with a 'heavy' spring in the secondary vacuum motor. The distributor springs are a Mr.Gasket 925D and a factory heavy spring set with just slight free-play. See picture below.

When the motor was first rebuilt, it had 11:1 flat top pistons and I could never get it to run on 91 Shell non ethanol fuel, best I can get here. A subsequent issue gave me an opportunity to drop the comp ratio to 10:1 with cylinder pressure between 195 and 205 psi.

I'll not go into more right now as it could get confusing, but in a nut shell, the results I now have give a strong pulling motor with no ping at all under heavy acceleration. It's all about balance to get it all working together. Your motor may need slightly different settings than mine, no two engines are identical, but you need a place to start.

Good luck with it, keep us informed.

Geoff.

Just read Jeff's post and he has a good point about the vacuum canister, change it to a single adjustable type. There will be a set-screw in the tube for adjustment.

 

[Meyer]

Only have advance side hooked up not the retard side

you have the advance side hooked up to ported vacuum and the retard side unhooked?

Look at this diagram-do you have the thermostatic valve still.  If so, you might try this set up.

http://1970mgr.org/302_2V_ImcoACalltrans.gif

If you don't want to try that, is the spare port open?  It needs to be to allow the advance to work properly.

Fianlly, you can swap the advance canister for a single port one that is tuneable and may get closer to where you want to be.  You\may want to check to see that you dampener hasn't slipped and that your timing numbers are indeed accurate.

 

[Don C]

If you keep the double vacuum advance, whether or not you are using the ported vacuum switch on the thermostat housing, you need to connect the port at rear of the advance to manifold vacuum, and make sure the front port is connected to the timed (ported) vacuum connection on the distributor.

High initial timing should not prevent your carburetor from idling down. Either something is keeping the primary throttle plates from closing or the secondary throttle plates are not adjusted correctly. Unless, someone drilled holes in the throttle plates, trying to adjust it and drilled too large. I would suspect a vacuum leak, except for your very (too) high vacuum reading. Are you sure your vacuum gauge is accurate?

 

[Jeff73Mach1]

If you keep the double vacuum advance, whether or not you are using the ported vacuum switch on the thermostat housing, you need to connect the port at rear of the advance to manifold vacuum, and make sure the front port is connected to the timed (ported) vacuum connection on the distributor.

High initial timing should not prevent your carburetor from idling down. Either something is keeping the primary throttle plates from closing or the secondary throttle plates are not adjusted correctly. Unless, someone drilled holes in the throttle plates, trying to adjust it and drilled too large. I would suspect a vacuum leak, except for your very (too) high vacuum reading. Are you sure your vacuum gauge is accurate?

Are you sure on that Don? It seems to me that if the retard function is getting full vacuum and the advance is getting ported vacuum that the effect of the combination would be to cancel one another out at any time other than idle or cruise. The thermostatic switch was to limit vacuum until the engine heat caused it to open and retard timing was it not?

 

[c9zx]

Denmark uses the RON method rating for octane. North America uses (RON+MON)/2, also referred to as AKI. 95 RON= 90 AKI, 99 RON=93AKI. I believe Shell sells 99 RON in Denmark. You might gibe that a try to see if it reduces or eliminates the pinging. How did it behave before the new carburetor? Chuck

 

[boilermaster]

Denmark uses the RON method rating for octane. North America uses (RON+MON)/2, also referred to as AKI. 95 RON= 90 AKI, 99 RON=93AKI. I believe Shell sells 99 RON in Denmark. You might gibe that a try to see if it reduces or eliminates the pinging. How did it behave before the new carburetor? Chuck

Meyer,

If C9ZX is correct (almost always correct) you Cannot get to where you need to be with the distributor configurations that you have unless you raise your octane rating at least 10 points from your current RON method.

OR

reconfigure your distributor to the 10 L slot and also reduce the amount of vacuum advance you are getting.

The 71 351 c with closed chambered heads required Premium fuel, in 1971, I believe our premium fuel in the states was 97-102 (RON+MON/2) that would mean that your (RON) requirement would have to be somewhere in the neighborhood of 102-107 (RON).

In the states here we can make our clevelands work on 91 octane, (96 to you.

That will require a complete recurve of your distributor.

10 L slot is a MUST, mechanical can be all in @3200 rpms or so and that also means a greatly reduced vacuum advance as well.

Most will shoot for around 16 degrees initial and a total of 36-38 maximum.

I am suggesting you move to the 10L slot .410'' and then see how much initial advance you can get away with until you just get a hint of spark knock and then back off an additional 2 degrees.

Do this with the vacuum advance disconnected and plugged.

Once you have accomplished this, you can begin to tailor the vacuum advance.

My best guess is that you will only be able to run 3-6 degrees of vacuum advance.

I am currently running zero vacuum advance.

my 351 4v closed chambered head with 4 speed is .030'' oversized with a .012'' deck height and (505) camshaft and flat pistons running 91 octane fuel (96 to you)

Boilermaster

 

[Meyer]

With the factory 4300 it was worse... ive been told they were problem from the beginning lean calibrated hesitations when new... so i switched to a 670 brawler from quick fuel.

and opened up the factory square bore intake to a rpm airgap opening, so there were room to the bigger throttle blades. 

There are no air leaks. I think the gauge is correct not sure havent tryed another one. 

Denmark uses the RON method rating for octane. North America uses (RON+MON)/2, also referred to as AKI. 95 RON= 90 AKI, 99 RON=93AKI. I believe Shell sells 99 RON in Denmark. You might gibe that a try to see if it reduces or eliminates the pinging. How did it behave before the new carburetor? Chuck

 

[Stanglover]

Boilermaster hits the nail on the head once again!

Just to be clear what I needed to do with my factory distributor, I had to dismantle it and weld up one of the slots (weight side, see picture) and recut it to give what I needed, a 10L slot. You may be lucky and have a distributor with this already there. I was not so lucky with the Cardone remanufactured one I foolishly traded the original for. If you have a 13L slot, there is a way you can cheat on this by slipping a small piece of 3mm Nylon tubing over the little post. This will get you close and may work while you figure things out. You can always make a solid job of it later.

Geoff.

 

[Meyer]

What springs should i get fir the distributor? Keep original!

I only have the 13L slot so i think i will weld and grind until i have 410”

 

[boilermaster]

What springs should i get fir the distributor? Keep original!

I only have the 13L slot so i think i will weld and grind until i have 410”

Meyer,

You need mr. gasket 925D spring kit, available from summit racing @ $6.46 USD.

Most will end up using a combination of one spring from the kit and the weaker of your 2 existing springs.

Or

Crane Cams99607-1 adjustable canister $ 45.26 USD. this kit also comes with springs.

you can tailor the AMOUNT of vacuum advance with this kit.

However you SHOULD be able to tailor the AMOUNT of vacuum advance with your early unit by

changing the length of the spacer and or adding or subtracting washers in the unit.

Most other aftermarket vacuum advance units only vary the amount of vacuum needed to move the breaker plate assembly.

Looks like you will be doing some test & tune in the near future.

you should be able to also measure how far your current canister pulls the breaker plate and how much that advances your timing and come up with some kind of data to determine how much your engine likes.

Please bear in mind that when you apply vacuum to your canister, you will raise engine rpm and then you will also be adding a small amount of mechanical advance alslo.

Boilermaster

 

[Stanglover]

What springs should i get fir the distributor? Keep original!

I only have the 13L slot so i think i will weld and grind until i have 410”

I used one heavy factory (Ford) spring with slight freeplay and one Mr.Gasket 925D set tight.

 If you do it right, you'll need to remove the gear and pull the shaft out. Make sure you mark it first so it goes back on the same way. There is a chance the roll pin hole is off center. Good luck and I/we hope you get to where you need to be with it. It looks like you have engine mods to deal with as well, so this may also affect your results. Also, just thought of this, if there is ANY side play in the shaft bushing, I suggest having it repaired or replace the distributor. DON"T buy cheap Chinese junk!!

Cardone Select has a reasonable copy of the Motorcraft but the threads are metric instead of SAE. Cardone may have a remanufactured Motorcraft in stock, worth checking, but it will likely have a 15L slot at minimum.

Geoff.

 

[boilermaster]

What springs should i get fir the distributor? Keep original!

I only have the 13L slot so i think i will weld and grind until i have 410”

I used one heavy factory (Ford) spring with slight freeplay and one Mr.Gasket 925D set tight.

 If you do it right, you'll need to remove the gear and pull the shaft out. Make sure you mark it first so it goes back on the same way. There is a chance the roll pin hole is off center. Good luck and I/we hope you get to where you need to be with it. It looks like you have engine mods to deal with as well, so this may also affect your results. Also, just thought of this, if there is ANY side play in the shaft bushing, I suggest having it repaired or replace the distributor. DON"T buy cheap Chinese junk!!

Cardone Select has a reasonable copy of the Motorcraft but the threads are metric instead of SAE. Cardone may have a remanufactured Motorcraft in stock, worth checking, but it will likely have a 15L slot at minimum.

Geoff.

Meyer,

The distributor does NOT necessarily even have to be removed from the engine to weld up the slot.

There should be a circular felt in the breaker cam mechanism, and under that there will be a circular clip that needs to be removed, (along with the advance springs) the brealer cam can then be wiggler off of the distributor shaft.

be sure to keep the orientation of the slot and what spring went where.

you will then want to put the weaker of the 2 stock springs were the stronger spring was, and the new weaker spring where the weaker oem spring was.

be sure to clean and lubricate well.

do Not try and take the weights off, (the plastic bushings WILL break, if you can possibly find replacement bushings, go for it.

Boilermaster

 

[Meyer]

Why is it nessesary to change the factory springs location? Its already in the 13l slot so the only thing i was planning to is to make it smaller to 10L and assemble it again

 

[boilermaster]

Why is it nessesary to change the factory springs location? Its already in the 13l slot so the only thing i was planning to is to make it smaller to 10L and assemble it again

Meyer,

if you look on the breaker plate , there should be a square hole,

this is where the (octane) is adjusted by lightly bending the tab that the heavier spring sits on.

All I would have you do is put the heavier of your 2 springs (now lighter than original) where the heavier of the 2 belongs.

this tang will often be tweaked by bending it thru the square slot.

Boilermaster