351C where to start?

[Cleveland Crush]

+1 on an AF gauge (wideband). Pull a couple spark plugs to get a read on them. Post some good quality photos of your spark plugs and we can offer some help.

 

[boilermaster]

351mach1,
never seen a cleveland need smaller than a .031 primary squirter, get a .033' and a .035''
you want just enough and no more.
Boilermaster

 

[Stanglover]

Now that I am a Holley tuning "expert" after 30 minutes of youtube this morning, I think my choice of carb is just fine for my stockish motor with auto trans. 600 CFM may be a bit small if I ever go with more power but for now its fine. the 4160 doesn't have a secondary metering block which is apparently beneficial for a stock engine with auto trans. If I ever drop the 5 speed in and rebuild the motor, I can add the secondary metering block via a kit but I personally would probably just be purchasing a larger carb (likely a 700 CFM 4150). Drilling holes in the throttle plates is generally for motors with very large cams that have issues idling. Probably not my case. My carb is currently sitting at 15" of vacuum.

I have an awful smell of gasoline inside of the car while driving. I thought it was a major exhaust leak but now I am thinking I am just running ridiculously rich. I think its time I purchase a timing light with tach so I can dial in the dizzy recurve myself and then really dig into the carb tuning. I don't really like paying mechanics for things I can figure out myself so I still have a lot more patience on this before giving up. I also very much enjoy becoming more knowledgeable on what I am running. If it gets to the point where I need to mess with the power valves I may enlist an expert but I think I should be able to get it pretty darn close with normal tuning and possibly swapping out the accelerator pump nozzles.

I am still learning if I actually need a smaller nozzle or a larger nozzle. I may purchase a .025 and a .035 and see how they each affect driveability. I could also play with a different accelerator pump cam but that will probably be the last thing I try to do.

Edit: maybe also worth investing in an air/fuel ratio meter

Messing around and learning as we go is a big part of the fun of owning one of these beasts. I knew practically nothing when I joined this forum and now I know almost nothing.......... and that's a big improvement.
As for the drilling of holes, my "guy" told me it was because Holley carbs tend to be too rich on the idle circuit and these big valve engine need that extra air. I do have AFR bungs welded into my exhausts and I did use an AFR which shows an almost perfect ratio. The plug read confirms that.
I also tried different pump cams but ended up with the original one, which seems to be the best option. I have tried differing choke settings, but again went back to a stock setup.
Have fun.

 

[73 SGM Mach]

Just a thought since your car has amnesia, it’s possible your symptoms point to a contamination fuel tank. I know you changed the carb, but did you trace back to the pump and the tank to verify clear fuel flow? Since the PO didn’t give you the straight story, what else did they fail to mention? Just to alleviate worry, I would check that out. Good luck.

I had a lot of issues with my car also that were similar. I threw alot of parts and money at it to fix it but it all boiled down to a gas tank full of crud. Fyi there is alot of good people in here that can help you out. Just keep plugging away at it!
Jeff

 

[351mach1]

I had a lot of issues with my car also that were similar. I threw alot of parts and money at it to fix it but it all boiled down to a gas tank full of crud. Fyi there is alot of good people in here that can help you out. Just keep plugging away at it!
Jeff

I have come to the conclusion that I would be foolish to not replace the fuel tank. It's on the list now!

 

[351mach1]

Installed a new fuel tank. The old one was way nastier than I had thought. I now have fresh clean fuel and fuel filters.

SO: I am still having a little off idle stumble that I can't seem to tune out. I am not sure what else to check. Anyone have any advice?

-I re-checked the timing. I am at 16* initial with 36* all in at 3000 RPM. Timing is steady at idle and at 3000 RPM
-I have 15 inches of vacuum at idle. Vacuum is steady
-I don't have a way to check the AF mix so I am just going by vacuum reading
-I am about a full turn out on the Fuel mixture screws. It doesn't seem to like going much more lean than there.
-I reset the transfer slots to the proper amount recommended. When I did this I was idling at 600 RPM and it was way too low. After a few adjustments I can get the engine to idle very nicely at 720 RPM. I have been mostly driving with the idle set at ~700 RPM but I thought maybe it wants a higher idle so turned the idle screw to ~820 RPM
-I tried a .035 accelerator pump nozzle but that seems to make the stumble worse. I haven't tried the .033 and I went back to the .031. I don't seem to be getting a super solid stream out of the nozzles.
-The accelerator pump is adjusted correctly.

Not sure where to go from here. The only thing I can think of is that some dirty fuel got in the carb but even with the dirty tank I was running 2 brand new fuel filters so I don't thank any major debris could have gotten in. I almost want to try swapping carbs but I know carbs are generally user era and that there is likely nothing wrong with my brand new carb.

 

[Cleveland Crush]

Installed a new fuel tank. The old one was way nastier than I had thought. I now have fresh clean fuel and fuel filters.

SO: I am still having a little off idle stumble that I can't seem to tune out. I am not sure what else to check. Anyone have any advice?

-I re-checked the timing. I am at 16* initial with 36* all in at 3000 RPM. Timing is steady at idle and at 3000 RPM
-I have 15 inches of vacuum at idle. Vacuum is steady
-I don't have a way to check the AF mix so I am just going by vacuum reading
-I am about a full turn out on the Fuel mixture screws. It doesn't seem to like going much more lean than there.
-I reset the transfer slots to the proper amount recommended. When I did this I was idling at 600 RPM and it was way too low. After a few adjustments I can get the engine to idle very nicely at 720 RPM. I have been mostly driving with the idle set at ~700 RPM but I thought maybe it wants a higher idle so turned the idle screw to ~820 RPM
-I tried a .035 accelerator pump nozzle but that seems to make the stumble worse. I haven't tried the .033 and I went back to the .031. I don't seem to be getting a super solid stream out of the nozzles.
-The accelerator pump is adjusted correctly.

Not sure where to go from here. The only thing I can think of is that some dirty fuel got in the carb but even with the dirty tank I was running 2 brand new fuel filters so I don't thank any major debris could have gotten in. I almost want to try swapping carbs but I know carbs are generally user era and that there is likely nothing wrong with my brand new carb.

Simple things first:
Back the idle screws out (counter clock) 1/4 turn. If that cleans your stumble either leave it alone or go back in 1/8th turn to see what your engine likes. Sounds like your close to nailing it!

 

[Q1SVT]

SO: I am still having a little off idle stumble that I can't seem to tune out. I am not sure what else to check. Anyone have any advice?

-I re-checked the timing. I am at 16* initial with 36* all in at 3000 RPM. Timing is steady at idle and at 3000 RPM

-I tried a .035 accelerator pump nozzle but that seems to make the stumble worse. I haven't tried the .033 and I went back to the .031. I don't seem to be getting a super solid stream out of the nozzles.
-The accelerator pump is adjusted correctly.

Not sure where to go from here.

I posted this youtube link before, but you might find the tuning part helpful...

Great tuning info.

If you change the fuel tank hopefully you changed out the fuel lines?

Open chamber heads seem to like a lot of tining... UT took 42*

UT showed the accelerator pump cam change helped a lot.

jm2c

 

[351mach1]

Great video!

I'll keep working on the accelerator pump and nozzle adjustments. I think I'll try to give it some more timing too. Most of the research I have done says to never go more than 38* on a Cleveland.

I did not replace the steel fuel line but did blow it out with compressed air.