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Old 06-09-2022, 09:58 PM   #1
Daves55Sedan
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Default misfire update

I got the '55 Ford 292 Y-block running today on all 8-cyls for the first time since I abandoned it in the garage last December.
Still, I am not satisfied with it. The engine idle speed seems to have slowed and sometimes, the engine surges between 500RPM and around 400RPM repeatedly. I increased the idle speed at the carb a little bit. I checked for a vacuum leak and sure enough, the rubber vacuum cap I had on my test port in the manifold vacuum tubing had cracked.
I got out my vacuum tester and connected it to the manifold tubing. The vacuum was still very low, so I fiddled with the carburator idle/fuel mixture screws on the carb and got it up to 19 inches, but there is still that surge in idle. I disconnected the vacuum advance from the carb and plugged the tubing from the carb and connected my timing light and adjusted the timing to about 8 degrees BTDC then reconnected the vacuum advance tubing.
BTW, here is everything that was replaced since January 2022.
New points, condenser, rotor, distributor cap, spark plugs and spark plug cables. I swapped the cast epoxy ignition coil for a used oil filled coil that is more than 30 years old, but tested out okay. The carburator was taken apart, cleaned out with spray gumout, the inlet needle operation checked and a new power valve and gasket were installed and some new gaskets. A new fuel filter was installed.
Anybody have any ideas about the idle surge???
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Old 06-09-2022, 11:54 PM   #2
KULTULZ
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Post Re: misfire update

Quote:
I got out my vacuum tester and connected it to the manifold tubing. The vacuum was still very low, so I fiddled with the carburator idle/fuel mixture screws on the carb and got it up to 19 inches, but there is still that surge in idle.

I disconnected the vacuum advance from the carb and plugged the tubing from the carb and connected my timing light and adjusted the timing to about 8 degrees BTDC then reconnected the vacuum advance tubing.
When you removed the DIST signal, did you monitor the vacuum reading? Did it remain steady? You need to monitor the vacuum reading at correct curb idle and initial timing and then remove any vacuum signals one by one (DIST-WIPERS-BOOSTER) and watch the gauge for a while. Write the reading(s) down for reference.

What engine/carb/trans setup do you have?
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Old 06-10-2022, 02:08 PM   #3
Daves55Sedan
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Default Re: misfire update

This is a 292 Y-block with all original '55 272 intake, carb and distributor (load-o-matic). It has Ford-o-matic trans. The carb is a Ford EBU (similar to the 51-53 Flathead carbs, but was used on all '54 Ford 239 Y-blocks). The fuel pump has vacuum booster. There is one tubing connection from fuel pump to intake manifold, off of which there is a compression "tee" and short piece of tubing with a vacuum cap (for use with vacuum testing guage). The vacuum cap was cracked, but now replaced. After I discovered the bad cap, I hooked the vacuum test guage to the tubing and was able to achieve a steady vacuum reading of 19. The only other vacuum line (coming off the third leg of the tee) is the line to the vacuum windshield wipers.
Typically, when timing an engine, I always pull the rubber hose (this is a new hose) off the tubing from the distributor vacuum advance and plug that hose with a pencil so that there is no signal from carburator to vacuum advance. I then proceed to run engine at idle and view the timing light at the pointer and adjust distributor as needed to get around 6-8 degrees BTDC.
The only vacuum circuit I have not checked is the line to the windshield wipers. I will need to go buy some more vacuum caps to do that.
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Old 06-11-2022, 02:35 AM   #4
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Arrow Re: misfire update

Quote:
I got out my vacuum tester and connected it to the manifold tubing. The vacuum was still very low, so I fiddled with the carburator idle/fuel mixture screws on the carb and got it up to 19 inches, but there is still that surge in idle.

I disconnected the vacuum advance from the carb and plugged the tubing from the carb and connected my timing light and adjusted the timing to about 8 degrees BTDC then reconnected the vacuum advance tubing.
Sorry Dave, I didn't explain that very well. She is reading #19 steady. That's good. You need to watch the gauge while she is idling especially when she starts to roll. That reading should indicate whether it is a vacuum leak(s) or a carb problem.

Here is a partial reading chart that may help. Just post what the needle is doing at idle and beginning of roll.

- https://www.onallcylinders.com/2016/...auge-readings/
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Old 06-11-2022, 07:05 PM   #5
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Default Re: misfire update

According to the guage reading chart, I shouldn't be unhappy about my vacuum reading (steady at 19 in, engine idling). No valve, ring or oil problems present. Timing seems to be right on the money too according to this.
I have just begun to wonder if a drop of gas every few seconds is falling off that new power valve down the throat and causing the on and off cycling surge of the idle. That would be a dissapointment as I worked like crazy to get a good gasket that fits right and used a brand new power valve.
However, as I mentioned in the original post; I did test to see if the power valve or gasket leaked overnight prior4 to assembling the valve body to the main body. I did notice that the gasket (some type of red asbestos cement style gasket) was totally soaked with gas, but it hadn't dripped a drop overnight in the tuna can below unless that evaporated (I doubt it).
But something like that might cause a surge like I am seeing here.
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Old 06-11-2022, 08:14 PM   #6
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Default Re: misfire update

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Holley power valves that were original to the old carbs are not available and the modern replacement don't seat quite right in the late flathead carbs. I wonder if the early Y-block carbs have the same problem? CharlieNY has a fix for this. It might be worth a PM to him to find out.
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Old 06-12-2022, 07:46 AM   #7
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Post Re: misfire update

Quote:
According to the guage reading chart, I shouldn't be unhappy about my vacuum reading (steady at 19 in, engine idling).
You need to continuously monitor the gauge, just not a snap-shot.

What does the gauge do when she begins to roll?
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Old 06-12-2022, 08:57 PM   #8
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Default Re: misfire update

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Originally Posted by rotorwrench View Post
CharlieNY has a fix for this. It might be worth a PM to him to find out.
I just sent Charlie a message asking if he had any PV's for for Ford EBU, Holley 2100 or Holley 2110 bugsprayer style carbs.
I have noticed that the modern PV's have a radius chamfer at the gasket surface, but they should be perfectly flat, but if you can get a good gasket, they might work, but always need to be tested for leaks first.
I also asked Charlie if he had any ignition condensers for '54/55/56 Y-blocks. Told him I wanted to buy four of each (PV's and condensers). That should last me till I'm six feet under.
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Old 06-12-2022, 09:14 PM   #9
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Default Re: misfire update

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Originally Posted by KULTULZ View Post
You need to continuously monitor the gauge, just not a snap-shot. What does the gauge do when she begins to roll?
I left the guage on the tubing for several minutes and watched it. The needle remained steady even through the idle surges. As best I can describe it, from the set idle speed (which is about 600rpm right now), it stays that way for about 3 seconds, then the idle speed drops down (sometimes so slow that the engine almost dies), but then it cycles back up to normal idle speed. repeat, repeat. However during all this cycling, the vacuum needle is steady as she goes at 19.
Right now, I have a spare carb sitting on a tuna can with gas in the float bowl to sit overnight and see if the power valve leaked into the tuna can in the morning.
There is no whistling noise anywhere, but when the idle surges down, sometimes you can hear a sound like compressed air rushing out at high pressure from cylinder #8 somewhere. I pulled the spark plug boot and tried to tighten #8 spark plug but it is already super tight. But when the idle is up, there is no air rushing sound. It is a minimal spurt, like it may be coming out of #8 intake valve guide, but thats a wild guess. All cylinders are firing great and engine starts up like brand new.
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Old 06-14-2022, 01:21 AM   #10
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Question Re: misfire update

Quote:
... it stays that way for about 3 seconds, then the idle speed drops down (sometimes so slow that the engine almost dies), but then it cycles back up to normal idle speed. repeat, repeat. However during all this cycling, the vacuum needle is steady as she goes at 19.
If the needle stays steady, I don't know what to tell you.

Sorry ...
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Old 06-20-2022, 01:37 AM   #11
Daves55Sedan
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Default Re: misfire update

After swapping the carburator with my spare rebuilt one, there is no more idle surging at all and the engine runs and drives like new. Checked vacuum after carb swap and it is still reading steady at 19. Didn't even need to turn idle/fuel mixture screws. The new rubber vacuum cap should hold up till after I'm dead based upon how long the other one lasted.
She's back on the road again.
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Old 06-20-2022, 08:23 AM   #12
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Thumbs up Re: misfire update

Glad you found the cause Dave ...
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Old 06-21-2022, 05:00 PM   #13
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Default Re: misfire update

Apparently, my suspicion about the leaky power valve was correct, even though I had done an overnight check to see if it was leaking gas, but there wasn't a drop in the tuna can. However, when I looked at the bottom of the main body of the carb, the red gasket for the power valve was soaked.
Now that I have been driving the car with the spare rebuilt carb on it, I have noticed that all it takes for the float bowl to leak dry is to let it sit for over 24 hours. Just enough gas left in the float to start the engine, then it immediately dries.
I am back to getting out, taking the oil-bath air-cleaner off, dumping a half a tuna can of gas down the air-bleed tubing in the carb throat (which fills the float bowl). Get back in and it fires right up and ready to go down the road.
At this point, I don't drive everyday, so it is likely I will always be taking the air-cleaner off and dumping gas in the carb just to get going.
BTW, I tried to get hold of Charley NY about getting some power valves and mating gaskets weeks ago, but he apparently doesn't visit this site very often.
Anyway, here is my theory of the idle surge that was happening; there may be a small drip between PV and gasket which would rev the idle up a little bit till that drip is burned, then the idle settles back down. The drips occur at around 3 second intervals so it seems like the idle is surging every 3 seconds.
I have also checked the accelerator pump ball check, but it is properly seated by the spring-clip (both carbs). This carb that is on the manifold now is primo!
The carb I just took off of it was rebuilt, but I noticed some damage to valve-body to main body gasket and the power valve gasket not fitting well (perhaps not even the right power valve for the mating surface of this carb. I fixed all that (I think) and placed it back in the spare box. I will wait until it is time to swap again before I test for leaks on the bench.
Nevertheless, there is no more idle surge and the engine sails down the road at any speed or acceleration I want.
Thanx to everyone for your input
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