Need I8MUD's Diagnostic Ears...

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C

cvan1971man

Joined
Nov 15, 2019
Threads
203
Messages
555
Location
Arlington, TX
I have attached a video recording as well as a voice recording. The Video does not do the sound that I am hearing justice. I was not able to upload the files so here is a Dropbox link for the video and audio - Dropbox - https://www.dropbox.com/scl/fi/k48igvak99fd1lvt8elzu/20260103_114346.mp4?rlkey=wrn30xqpvmi20g97z6tr303ei&st=s4vn5coe&dl=0

I need your expert ears to see if you can diagnose this problem over the interweb. Here are the details:

My son arrived home from college. A few days ago, the engine sounded normal and ran great. One morning, I get up and it is idling rough, sluggish under accelleration from 1-2 gears. Slighly less sluggish in 3rd - able to cruise at 70MPH in 4th.

1978 2F Engine
Holley Carb - (Not a Sniper)
Pertronix Electronic Ignition
Timing is set to 7 degrees. I have also set the timing up to 13 degrees, and it likes 7-9 degrees better.
Idle is set to 650 RPMs
I have tried installing new spark plugs and new wires, and no difference.
I have run Berrymans B-12 through the gas, and no noticeable difference

The sound makes me think that I have an exhaust leak, but I cannot find any black soot around the manifold. Given that this problem only arose a few days ago and I have not driven it a bunch, the soot may not have had a chance to show itself yet.

I have checked the exhaust gasket underneath, and I cannot feel any air leaking out when at idle.

I am fresh out of ideas, and I need someone on Mud who is smarter than I to figure this out.
 
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I would attach the video and voice recording here but when i click on "attach files", neither of the VLC files that are on my desktop are there to be saved within IH8Mud.
 
1st thing I'd do is pull that Holley and go thru it. Filters, fuel the inline and all the screens in the carb. Idle circuit check & clean, mixture screw, take out & check clean, by clean I mean verify passages are clear, they are small and its a PITA sometimes. Check the fuel bowl and the passage from bowl to venturis. Check the cross shaft for leaks, they get worn out and create a vac leak. The accel pump plunger, have a look. Are the butterflys returning to closed ? Are there any other potenial vac leaks ? You said it likes 7 - 9 better on timing, what do you mean by " likes " ? I ask because some find they run better close to 13 - 14. Next I'd check coil.
 
peesalot said:
1st thing I'd do is pull that Holley and go thru it. Filters, fuel the inline and all the screens in the carb. Idle circuit check & clean, mixture screw, take out & check clean, by clean I mean verify passages are clear, they are small and its a PITA sometimes. Check the fuel bowl and the passage from bowl to venturis. Check the cross shaft for leaks, they get worn out and create a vac leak. The accel pump plunger, have a look. Are the butterflys returning to closed ? Are there any other potenial vac leaks ? You said it likes 7 - 9 better on timing, what do you mean by " likes " ? I ask because some find they run better close to 13 - 14. Next I'd check coil.
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The only thing that I can answer right now is the coil was putting out 13.5+ Volts yesterday
 
I don't see much movement on the accelerator pump arm. Lag in throttle response could be because little or no accelerator pump fuel and the engine has to wait till vacuum begins pulling fuel. Does it respond better if you go straight to full throttle?
 
For me, running thru the carb is quick and easy, if coil good, sounds like you checked plugs & wires, how does dizzy look ? I never ran a Petronix but theres lots of threads about potential issues there.
 
peesalot said:
For me, running thru the carb is quick and easy, if coil good, sounds like you checked plugs & wires, how does dizzy look ? I never ran a Petronix but theres lots of threads about potential issues there.
Click to expand...
the key word is "For You". I have never torn a carb apart. That is the pickle!
 
Do you guys think that the poor performance / loud sputtering/backfiring, etc. could be due to a bad valve or cylinder issue? I am going to run a compression test and a leak-down test.
 
Imho Adjust your valves … one maybe miss adjusted and not fully seated

Compression test would tell you
 
I think you'll find it very straight forward and easy, there isnt anything to it. if you can do a comp test, you got it. the worst part is the bowl gasket, they tear. Sputtering, backfiring could be many things. a comp test is a good start to rule out mechanicals. pop valve cover while carbs off and check valves for lash & operation, pull coil wire, kick it over and watch each set of intake & exhaust go up & down, again the gasket can be the worst part. I ran video and it sounds it that like it runs, like no valve ticks or utter misfire. If comp #'s are good I might have a look at the Petronix
 
I’m pretty new to the 2F but maybe a few simple things to check?

How were the old plugs? Any black and sooty? All close to the same color? All burning clean?

Silly but possible, all the plug wires on the correct cylinders?

Fuel filter? Maybe some debris in there?

Is there an idle cylinoid on the carb? If so you can you unplug it and see if the symptom stays the same? Maybe it’s not closing the idle circuit when the accelerator is pressed?
 
peesalot said:
I think you'll find it very straight forward and easy, there isnt anything to it. if you can do a comp test, you got it. the worst part is the bowl gasket, they tear. Sputtering, backfiring could be many things. a comp test is a good start to rule out mechanicals. pop valve cover while carbs off and check valves for lash & operation, pull coil wire, kick it over and watch each set of intake & exhaust go up & down, again the gasket can be the worst part. I ran video and it sounds it that like it runs, like no valve ticks or utter misfire. If comp #'s are good I might have a look at the Petronix
Click to expand...
I am new to most of this. This was our very first tear down to the frame and build back up. The problem is that I don't do or see this stuff every day. The pertronix was the first Electronic Ignition that I have installed. It has run great for a long time. The search on the interweb essentially stated that the pertronix is either working or it isnt. Whether that is true or not... i have no idea.
 
try a search for Petronix on here. I had a very similar issue once and it turned out to be water in fuel and debris in bottom of fuel bowl on carb. Re Petronix that is my understanding, they work til they dont. how does the pick up/trigger for the elec ign look inside dizzy ?
 
Point of interest. I filled up yesterday and drove 65 miles trying to run some berrymans b12 through it. I used 9 gallons of gas. I typically get 14-15 MPG out of it. It is drinking gas like crazy. What in the carb could be stuck - i.e. float or crap in the needle. the choke isn't hooked up so that isn't it.
 
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