Ignition Troubleshooting

[Bullnose Gator]

Well, the plot thickens...as I said, it will turn over, but runs rough and I have to keep my foot on the pedal or it will stall.  For no good reason I decided to flip the switch to the rear tank (that tank doesn't work, or works poorly, haven't figured out the problem yet) and it settled into what seemed to me to be a pretty normal idle and I didn't have to keep my foot on the pedal.  This only lasted a couple minutes because, like I said, the rear tank doesn't send properly.  I am also getting fuel coming out of the center of the carb when I give it gas, but the front fuel bowl level looked good last time I checked the sight plug.  I just haven't been able to check it again because I can't keep it running long enough.  So now I'm even more stumped lol

[Gary Lewis]

Well, I think the plot just took a significant turn - away from ignition to fuel.  So you probably have a carb issue.

And I'll guess it is a float level or needle and seat issue.  I say that because with the rear tank not supplying fuel the float level would drop as the engine uses fuel.  So a too-high fuel level, which could be caused by either a too-high setting or bad needle/seat combo, would go away pretty quickly.

Another issue I thought of was the power valve, but it wouldn't change with the removal of fuel pressure when you flipped the switch.  So I'd rule that out, although if you are into the carb you might want to replace it anyway.

[Bullnose Gator]

that's good to hear, i think.  I've only messed with the front fuel bowl so far on the carb, so I'll start with adjusting the float level again first and then read up on how to test the needle and seat operation and the pressure valve.  When it's on the front tank and I'm giving it some gas, the engine runs with a chugga-chugga kind of wobble, at a consistent rhythm, does that also sound consistent with how fuel is flowing through the carb?

[Gary Lewis]

I suspect it is the float level, and since that's the easiest thing to adjust I'd start there.  It won't hurt anything to have it low.  All a little low will do is to cause it to run out of fuel on hard acceleration as you wind it out in a couple of gears.

Your description sounds like it is rich, and that is consistent.

[Bullnose Gator]

I adjusted the float level up and down, no position seems to make a difference in the "chugga chugga" rough idle and it still stalls without giving it gas.  I took the front fuel bowl off again and the float and needle seem to be doing what they're supposed to.  It seems to run with a regular idle until the fuel bowl fills up and then it kicks into the chugga chugga stall routine, which is consistent with what happens when I switch it to the rear tank until it stalls.

Any more carb troubleshooting things I can try or should I look into carb rebuild/replace options?

[Gary Lewis]

If I understand what you are saying, that it does the same thing on the front tank as on the rear tank, then that is not what I understood before.  And that suggests to me that you have a blown power valve or accelerator pump.

If either of those things are bad you'll dump fuel right into the intake, and the higher the fuel level the more fuel since there is more gravitational pressure.  Not "fuel pressure" as in pressure from the pump, but gravitational pressure caused by the weight of the ever-higher fuel.

[mat in tn]

im assuming that this is a Holley carb based on the front fuel bowl reference. is it a replacement or a factory? more just for specific understanding really.  mostly this sounds to me to be that the carb should be rebuilt thoroughly. first thought is that the needle cannot seal off the incoming fuel.  if the carb has had the privilege of sitting for any length of time and ever had the chance to dry out then all rubber items are potentially dry rotted from the ethanol evaporation.

[Bullnose Gator]

What I mean by it doing the same thing on the front tank is that if I let it sit for a few days and then start it, it starts with a normal idle and then after a few seconds kicks into the rough idle and stalls.  It seems as though it runs fine until the fuel bowl fills up, which would make sense that it would run fine when I switch to the rear tank because it is probably just running on the fuel that was in the bowl.  Just thinking through it logically, what you're saying about the pressure makes sense though.

[Bullnose Gator]

It's a motorcraft, made by holley.  I believe it is original, except for the front fuel bowl, which I replaced several months ago after I accidentally stripped the fuel filter intake threads.

[Gary Lewis]

Your latest description brought something else to mind - the choke.  If the choke is set too rich the engine will start running rough and potentially die.

What I'd do is start the engine, cold, with the air cleaner off and watch the choke.  If it is still on a bunch when the engine starts running rough I'd manually open the choke a bit to see if that helps.  If so, we are onto something.

[Bullnose Gator]

Thanks. I've never messed with the choke before, are all Holley's the same?  I'll youtube how to adjust it, but wanted to make sure I don't screw anything up by following whatever videos I find.  

[FuzzFace2]

Bullnose Gator wrote

Thanks. I've never messed with the choke before, are all Holley's the same?  I'll youtube how to adjust it, but wanted to make sure I don't screw anything up by following whatever videos I find.

Holley chokes have been known to be a little finaky and need some playing with at least most of mine did.
Dave  ----

[Gary Lewis]

You never know what you are going to find with Youtubes since literally anyone can make them.  Personally I prefer to read what the factory had to say about a subject since their techs used their documentation.  There are two such documents here: Documentation/Fuel & Air Systems/Carburetors, Chokes, & EFI/Holley 4180C.

[Bullnose Gator]

I've messed with the choke and both fuel bowls as far as I can (too far, the front fuel bowl gasket that I recently replaced now needs to be replaced again).  Still can't get it to run right, so I've decided to go ahead and replace the carb with the one below.  Should this be a straight forward swap out, or is there anything about my engine (e.g. all the emissions stuff) that I'll need to give special consideration?  

Also, just curious, why do carbs specify automatic vs manual transmissions?  I wouldn't have expected the type of transmission to impact the carb, but that's how little I know.  


https://www.autozone.com/fuel-delivery/carburetor/p/national-remanufactured-carburetor-nd4851m/577135_0_0

[Gary Lewis]

Jeremy - I can't answer your question about the carb as I get "Access Denied" when I click on the link so I don't know what carb it is.

As for manual vs automatic, an auto has to have the kickdown or TV linkage and a manual doesn't.

[Bullnose Gator]

That's unfortunate.  I'll try it again, but no worries if it still doesn't work.  It looks just like my current carb, so I'll give it a go.  Thanks, again, for all your help.

https://www.autozone.com/fuel-delivery/carburetor/p/national-remanufactured-carburetor-nd4851m/577135_0_0

[Gary Lewis]

Sorry.  I still get:

Access Denied
You don't have permission to access "http://www.autozone.com/fuel-delivery/carburetor/p/national-remanufactured-carburetor-nd4851m/577135_0_0" on this server.
Reference #18.9736d517.1643058738.e2736e2

[Bullnose Gator]

Weird.  Just to see what it does I tried the "Link" button.  Other than that you'd probably have to go to autozone.com and search part #nd4851m directly.  Don't worry about it though, thanks for trying.

http://www.autozone.com/fuel-delivery/carburetor/p/national-remanufactured-carburetor-nd4851m/577135_0_0

[mat in tn]

i got right to the autozone page. that looks exactly to be a replacement for the 351/5.8 H.O.
is that the engine you have?  im not certain of what issues you are having

[Gary Lewis]

His signature says 460.  And the 351HO and 460 both used the 4180C, although jetted differently.

Strange that I can't get in.