All Small Six Chasing vacuum leaks

[ActionYobbo]

I spent my whole weekend chasing vacuum leaks on a 1968 200 with c4 auto and a brake booster. It was what you could call running but it was not driveable. First leak was the rubber hose at the c4 modulator so that got replaced. Still not running better so I kept looking and found another leak at the brake booster where the hose was lose on the plastic plug. So I fixed that and it was running better but still could not get it to run under 1400 rpm. Then I find the pcv was stuck open so I replaced that. Now it won’t start. When it was running vacuum was between -15 and -18 when running and -7 when cranking. Now vacuum is 0 when cranking. When ot was running timing was fluctuating between 8 and 14 btdc.
The original carburetor was leaking fuel so I stuck on a rebuilt large bore 1100 with a 67 jet to get it running. Compression on all cylinders is close to 150. All tuning was done with the vacuum off the distributor.
So now it’s sitting in the driveway not running. It’s got fresh clean fuel, it’s got spark, timing was checked, all vacuum ports are now blocked. The motor spins but it’s got no vacuum.
Replaced the carburetor, fuel pump, fuel filter, fuel hose, hose at C4 modulator, distributor, coil, plugs, plug wires, engine oil, oil filter, water pump, belts, thermostat, and air filter
That’s my weekend roundup.

 

[DON]

troubleshooting!!!
Just some more details, you said you could not get it to run below 1400 rpm. Would it die turning the idle down below that rpm? Or you can’t get the idle to go down below that?
Have you checked the timing? Verify you have spark.
I might think about putting the old carb back on. What distributor did you put in? Where is your vacuum guage hooked up to?
A lot of problems with new fuel pumps- verify fuel pressure
If you have compression you should have vacuum.
Not many suggestions but details matter

 

[Frank]

troubleshooting!!!
Just some more details, you said you could not get it to run below 1400 rpm. Would it die turning the idle down below that rpm? Or you can’t get the idle to go down below that?
Have you checked the timing? Verify you have spark.
I might think about putting the old carb back on. What distributor did you put in? Where is your vacuum guage hooked up to?
A lot of problems with new fuel pumps- verify fuel pressure
If you have compression you should have vacuum.
Not many suggestions but details matter

Don- he's got no vacuum and no start.

 

[ActionYobbo]

It won’t stay running below 1400 rpm.
Vacuum gage is under the carburetor where the pcv should go. The distributor..it had a LOM and I swapped that for another LOM that was a good running unit I recently took out of another build. Made no difference. Then I swapped it to an electronic ignition unit I used in this build https://fordsix.com/threads/log-int...-started-and-running.87033/page-2#post-722585
I got totally defeated yesterday chasing a vacuum leak and after thinking on it I did not check the freeze plugs on the ends of the manifold. I was finding very small leaks on old hoses and a faulty pcv but the more I fixed little leaks the leak kept getting worse so I am now I have all vacuum ports blocked and coated the carburetor base area with spray can white lithium grease and have no vacuum.

 

[Frank]

I spent my whole weekend chasing vacuum leaks on a 1968 200 with c4 auto and a brake booster. It was what you could call running but it was not driveable. First leak was the rubber hose at the c4 modulator so that got replaced. Still not running better so I kept looking and found another leak at the brake booster where the hose was lose on the plastic plug. So I fixed that and it was running better but still could not get it to run under 1400 rpm. Then I find the pcv was stuck open so I replaced that. Now it won’t start. When it was running vacuum was between -15 and -18 when running and -7 when cranking. Now vacuum is 0 when cranking. When ot was running timing was fluctuating between 8 and 14 btdc.
The original carburetor was leaking fuel so I stuck on a rebuilt large bore 1100 with a 67 jet to get it running. Compression on all cylinders is close to 150. All tuning was done with the vacuum off the distributor.
So now it’s sitting in the driveway not running. It’s got fresh clean fuel, it’s got spark, timing was checked, all vacuum ports are now blocked. The motor spins but it’s got no vacuum.
Replaced the carburetor, fuel pump, fuel filter, fuel hose, hose at C4 modulator, distributor, coil, plugs, plug wires, engine oil, oil filter, water pump, belts, thermostat, and air filter
That’s my weekend roundup.

A starting place: pull distributor cap and verify it's turning. then verify the rotor is still positioned correctly with the crank (timing chain check)

 

[alwill923]

I spent my whole weekend chasing vacuum leaks on a 1968 200 with c4 auto and a brake booster. It was what you could call running but it was not driveable. First leak was the rubber hose at the c4 modulator so that got replaced. Still not running better so I kept looking and found another leak at the brake booster where the hose was lose on the plastic plug. So I fixed that and it was running better but still could not get it to run under 1400 rpm. Then I find the pcv was stuck open so I replaced that. Now it won’t start. When it was running vacuum was between -15 and -18 when running and -7 when cranking. Now vacuum is 0 when cranking. When ot was running timing was fluctuating between 8 and 14 btdc.

If it did not run after changing the PCV valve, remove pcv line from the intake manifold and plug opening on the intake manifold for testing. Appears pcv valve could be defective, letting in to much air. To go from 7" of vacuum when cranking to 0 means air is getting into the manifold at a significant amount.

The best way to check for vacuum leaks is to remove and plug all vacuum attachments to the carb and manifold. This would only leaves the carb, carb base or the manifold. Spray with Carb cleaner to find leak. Engine will speed up if leak.

Check the carbs. Are the butterflies centered in the openings and closed all the way around when the idle set screw is backed out all the way?

 

[Frank]

I've rarely seen measurable vacuum while cranking. . . Thinking on this situation, something came to mind: it is possible for an engine to get so flooded that the plugs have a "gas gap" and don't fire. Assuming it has not jumped time (likely has not) I'd pull the plugs and verify they're not choked with raw gas.
the replacement carb- was it running with that carb before, or did the issue begin with the swap?