351C where to start?

[351mach1]

I bought just about everything possible to solve this issue, just haven't had time to install it all. I still need to install:
-Stainless fuel lines
-Fuel Pump
-AFR gauge
-8.5 power valve (and carb rebuild kit)

The good news is that I think I found what was fighting me and I have the engine tuned really, really close. So turns out the "brand new" cardone dizzy I bought had a leaking vacuum advance can. With a non leaking vacuum advance, it runs much better. After much reading of forums, I also decided to switch to manifold vacuum for the vacuum advance.

I still have the very slightest of small stumbles but I will install the AFR gauge to help dial in the carb tuning and hopefully get it 100% solved.

I ended up using the blue pump cam and .035 nozzle for now. The pink cam is actually significantly less aggressive than the orange and the orange and red appear to be identical.

I am not exactly sure what detonation/pinging sounds/feels like but I definitely did something that my engine was NOT happy with. With the defective vacuum advance can installed, I had 2-3 instances where at WOT I would have a severe hesitation, with some smoke from the engine, and I immediately let off the gas and everything went back to normal. After looking around the engine bay it appears that it was some kind of backfire as the intake gaskets got pushed out which also is causing a very very minor leak at the engine block as well. Ill add reinstalling the intake manifold on the list of things to do. With the new vacuum can on, the engine is running great and this issue does not happen at WOT anymore.

I did a compression test and the engine seems to be in good working order. Cylinder one is actually closer to 140. I checked it a second time and got a higher number.

I think after reinstalling the intake, replacing the steel lines and fuel pump, installing the AFR gauge and fine tuning the carb, I am happy to report that this engine appears to be healthy and will be I'll be confident in saying that it's in good working condition. Oh, and the engine is pulling close to 18" of vacuum so I will try swapping out the 8.5 power valve and reclean the carb when I install the fuel lines and fuel pump.

 

[Q1SVT]

 

[basstrix]

Sounds like you're almost there with getting the tune dialed in. Great work!

Were you able to find a definitive cause to your stalling problem? The filter on the suction side of fuel pump was suspicious IMO. In general, fuel filters on the suction side of a pump will have a negative impact on fuel flow and will promote vapor lock...although that's much more of a concern with a filter back at the tank. If you're going to put a filter on the suction side, close to the pump is the best option.

Q1SVT beat me to posting up the pump cam chart. I'll go ahead and post a color version that might help discern each curve.


With regard to the pink cam, I encourage you to try it. The pink cam spreads the pumps shot over a much broader range of throttle application. It might help, it might not, but you already have it, so why not take an hour and test it. I suggest testing in both screw positions.

Like the pink cam, I encourage you to try the 8.5 power valve if you're still experiencing a stumble.

Glad you found the defective vacuum canister. Proper base timing and the addition of vacuum advance can certainly alleviate or reduce a stumble. You can adjust the contribution of advance from the canister using an allen wrench accessed from the hose nipple on the canister. Below is a chart I created by measuring advance vs vacuum at different adjustment positions.

You described a concerning engine behavior under full throttle. I suggest you prioritize knowing the AFR and the ignition timing advance curve to understand why this happened. Ideally, you let the engine tell you what AFR it wants using a dyno or making timed runs at the drag strip. I use a device called Dragy in lieu of a drag strip. As a safe starting point, I suggest you shoot for a range of 12 to 13:1. My engine likes 12.8:1, but you should be safe in the above range. DO NOT shoot for 14.7:1 under wide open throttle! That is too lean. 14-15:1 is good for cruise speed at light throttle, but richer is ok too...just won't be as fuel efficient.

Where is your PCV connected? It should be at the base of carb or some port common to the intake manifold plenum. Also, make sure your brake vacuum booster is not leaking. That will lean out the runner the line connects to....your #8 looks like it could be lean.....#4 looks like it's been cooked.

The advance curve consists of the sum of base timing, mechanical advance, and vacuum advance. 34-36 degrees total under WOT is a fairly typical number that a cleveland likes. Here's a quick rundown of determining the advance curve: Disconnect vacuum advance, and set the base timing with engine idling. Then rev the engine and hold stead at various RPM and measure/record timing at each RPM. You shouldn't need to go beyond 3000-3500 RPM...and if you're like me, it's unnerving to rev to those levels without any load on the engine. Subtract the base timing from the values at each RPM step to determine contribution from mechanical advance. Next, you want to measure the RPM and manifold vacuum aka Manifold Absolute Pressure (MAP) at idle, cruise speed in high gear, and WOT. This must be done while driving, so you'll need a vacuum gauge and long hose. Use the chart I posted to add in the contribution from vacuum advance. Vacuum should not be more that 2-3 in-hg at WOT, so it usually has no contribution under that condition. Be sure you're in the 34-36 degree total advance under WOT. Even 36 might detonate....so this is important step.

I suspect the engine condition you described was detonation. The pressure inside the crankcase must have been pretty high to push the end seals out from under the intake. Was the dip stick pushed up or PVC blown out? Your distributor's advance plate has 2 positions. You need to determine which position it is in. A "10L" advance plate is a good one to have. It will let you set base timing at 14 deg and add 20 more via mechanical for a total of 34. BTW, 10L stands for 10 degrees of distributor advance (equals 20 degrees at crankshaft) and a left hand rotation distributor. You have to pull the reluctor and advance plate to check what you have. Set it to use the 10L if your distributor has that. Not a bad idea to install the Mr Gasket advance springs at the same time.

Again, great progress and please let us know what was causing the stalling and blown out intake end seals.

 

[Q1SVT]

As a safe starting point, I suggest you shoot for a range of 12 to 13:1. My engine likes 12.8:1, but you should be safe in the above range. DO NOT shoot for 14.7:1 under wide open throttle! That is too lean. 14-15:1 is good for cruise speed at light throttle, but richer is ok too...just won't be as fuel efficient.

351mach1 ​

... the numbers are good, but you need to be running Pure Gasoline...
14.7 under Pure Gasoline equals 14.08 with just 10% Oxygenated

 

[Stanglover]

A couple of awesome information post guys, thank you.
I need to save this thread.

For my own engine, I'm pretty close to the settings given, but could be improved slightly.......... in spring.
One thing I will mention is my engine, 351C M code CC heads and 13cc dished pistons running at 17in/hg, did not like an 8.5 power valve at all. I went back to the 6.5 the Holley 670 came with.

 

[boilermaster]

351mach1,
You are getting some priceless tips from some of our top of the line contributors.
T would like to add, if you change out fuel pump, spend the time to re check and adjust float levels
and idle mixture, as any change in fuel pressure will have an effect on float levels and therefore air /fuel ratio.
Please be advised that all intake manifolds (especially dual planes) will have cylinders that are either richer or leaner than others, that is why they don't lock down a specific air fuel ratio and suggest a range instead.
Lastly, I am not a fan of the print o seal intake gaskets for our 4V cylinder heads, you will never find a perfect match with that Edelbrock manifold.
I might get some flack here, but I have been making my own for quite some time and have had better results by doing that.
I end up glueing them to the intake manifold and not the cylinder head.
Boilermaster