351 running rough

yes,
wires are new as of 20 hours ago and I double checked them by switching them with the strong sparking cylinder.

What do you mean by my plugs should tell me if its a fuel/air problem? is that why I have weak spark in the middle four cylinders?

gun-driver wrote: Your plugs tips will be black/carbon if rich, white/gray if lean. If only one or some of the plugs are fouled/black and others are burning properly then it’s probably a ignition problem.

Ok thats good advice. It is definitely running rich, I can tell from the exhaust smell and the plugs are black. Some worse that others. The four outside corner cylinders (the ones that show good spark)are clean. So the good news is, I can say with good certainty the issue is carb or dizzy. The bad news is both those parts are expensive. Bummer.

I will have time to fiddle again tonight, I plan to try and rule out the dizzy and re-adjust the mix screws. I am going to first check weak spark plugs outside the engine by holding to the block with the inline light tester to see if it is stronger, this will rule out rich mix choking spark. If that is still showing weak, I will then check the points gap on every lobe to check for wear there and inspect closer for any dizzy cam play or wear. If at any point these check out, I will then turn my attention to adjusting the carb.

Thanks for all your help and advice. I am better armed to tackle this issue with your shared experiences and comments!

8122pbrainard wrote: Jllogan wrote: Bri892001 wrote: There's a piece inside the bowl that's replaceable, right? The needle and seat I think. You are right, I didnt replace that on the rebuild either. Justin, I have to ask why you didn't do a full rebuild on the carb. The needle and seat are key componemts. What else did you leave out? Did you soak the carb in a carb cleaner or just try to use one of the aerosol carb cleaners? Did you blow all the passages out with compressed air?

I replaced everything that my rebuild kit came with. I didnt realize until later that those needed to be purchased separate from the kit. I didnt replace the floats (I have the black plastic ones) or the idle mix screws because these not included in my kit either. Everything in the kit went it. I did just use the aerosol cleaner and compressed air . If I rebuild again, I will soak over night. I was worried I would lose track of where things went if I completely dissassembled so I tried to work on it one side at a time and then put it back together right away.

Also when I rebuilt the carb it was due to a fuel leak and not because it wasnt running right, so I decided if it wasnt broke and it didnt come in the kit I wasnt going to worry about it.

TRBenj wrote: Did you get a genuine Holley rebuild kit? Ive never seen rebuild kit that didnt include a needle/seat. I would think thats the #1 most important part to replace during a rebuild.

Ya, it was a holley renew kit. It was at the beginning of the summer so maybe I just forgot or lost it somehow. I am pretty sure I didnt replace and didnt get one. Well jury is still out on carb, seems to be better now. If I can get it tuned Ill leave it. If not I feel more comfortable with where stuff goes as I have had it apart before. This time I will soak it overnight and replace everything!!! Someone also told me to add a little water remover to that carb cleaner, not sure if thats necessary.

89Martinique wrote: try a new distributor cap my dads friends' boat ran like crap and had a loud knock turned out to be a hair line crack in the new distributor cap causing cylinder #7 to fire with every other cylinder we put the old one on it ran great

Ya, if signs point to the dizzy it could be the cap, even though its new I suppose anything can happen. I bought a genuine PCM cap from skidim but I feel like the gasket is cheap and I have a hard time getting it to lay right. Its like the gasket is almost too small or something.

if the gas is not spraying (atomizing) and its streamimg, this will cause a rich condition. the venturi effect should atomize the fuel, just like a paint spray can, when atomized the flashpoint is lowered, you should get a nice atomized spray down the throat

LOL, my eyes always read your name that way.

Did that the new spring and button fix your dist cap issue from before?

Brian, yes, the erratic timing problem went away with the new spring, later that same cap had moisture issues and put and old one back on with the "improved" spring and it's been working flawesly since.

There shouldn't be any fuel spraying into the body at idle. You said that when it started it was idling at 200. You had to crank up the idle screw to get it to 600. I'm no Dolley expert but this tells me that your idle circuit is blocked and you are having to use your primary circuit to get it to run. Fix your known issue, your carb, then move on to other potential issues like your spark. More than likely there rated by having rich mixture. I dealt with this issue and had my car rebuilt two times in a row then ended up buying new and never looked back. By the way red flags are flying with a kit not having a replacement float bowl needle valve.