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Ignition Troubleshooting

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mat in tn

Re: Ignition Troubleshooting

I wonder just how much the AutoZone supplied carbs will be "jetted differently, if at all? but it seemed to be a fairly reasonable price either way for a replacement.

Bullnose Gator

Re: Ignition Troubleshooting

yeah, it's a 460. What does jetted differently mean, and if it is, would that cause it to not work or just not work as well as the original?

Jeremy - Oviedo, FL
1986 F250 XLT Lariat Supercab 4x4 Manual 460

rcarlisle

Re: Ignition Troubleshooting

Do you have a vacuum gauge? I just got one and it seems pretty invaluable for figuring things out. It was like $15 at Harbor Freight, comes with a lot of stuff and it's own case. I'm really interested in knowing the final outcome on this one, since I've been having fueling issues lately. Turns out mine is a screw going missing I think.

Randy

Mt. Airy, NC 81 F-150 STYLESIDE regular cab 2wd. 302 Auto Zone crate. 5 spd M5od-R2

mat in tn

Re: Ignition Troubleshooting

trying to explain how a carb works can be awkward because you don't know the knowledge of the person(s) listening.
the fuel which the engine burns is actually fuel vapor. liquid does not burn. that fuel vapor is added to oxygen rich air. it's the oxygen which feeds the burn of the fuel. the carb holds liquid gasoline in a reservoir with a tiny "straw" type passage leading to the air venturi. the "barrel" which has a slight hourglass restriction causing a vacuum and drawing gas vapor through the straw into the air stream.
the jetting is a finer method of tuning the straw to make sure the carb gets the proper ratio of fuel to air in a range of run conditions. heavy load will require a little more fuel vs a lighter load needing less.
this is a basic explanation of the main circuit. the idle circuit is another finer set metering circuit which is semi-independent of the main venturi.
cubic inches of the engine play a big part of course but it is the air fuel mixture set for the expected demand that comes first. too much fuel is not only expensive and wasteful, but it is bad or worse than not enough for the engine
a good example of this might be the 300ci six with a 1 barrel of approx. 269 cfm while the 302 ci came with a 600 cfm 4barrel both works well for their respective demands.
I hope I gave the engineers a good laugh with my simplification.

Bullnose Gator

Re: Ignition Troubleshooting

In reply to this post by rcarlisle

Man, this has been quite the head scratcher from the start. I know it has been greatly complicated by how little I know, therefore, troubleshooting has been more like shots in the dark. But with the knowledge I have picked up coupled with regular logic, it still doesn't seem to be following the expected norms for these symptoms.

Which brings me to ANOTHER development this morning. I ordered the carb last night, but it won't be here for a week and I just can't help but keep tinkering in the mean time. So I circled back through the front and rear fuel bowls again to start. The rear bowl seemed to be the problem based on fuel coming out of the fuel bowl vent, but I had previously adjusted the rear needle and seat down pretty far and that didn't fix it.

So this morning I adjusted it up quite a bit and then back down to about as far down as it could go using the nut. I cranked it up and...that seems to have fixed the problem. I checked the sight plug and the fuel is right where it should be. I won't know for sure until I replace the front fuel bowl cover gasket because it is leaking too bad to let it run for more than a couple of minutes.

So my new questions are:
1) If that was the problem, does that mean the float was sticking since it didn't seem to respond to my first adjustments?
2) If so, should I expect it to stick again in the future and should I replace the float?

Jeremy - Oviedo, FL
1986 F250 XLT Lariat Supercab 4x4 Manual 460

Bullnose Gator

Re: Ignition Troubleshooting

In reply to this post by mat in tn

Valiant effort, Mat lol. Some of it was still not simple enough for this listener, but your description did explain the jetting mechanics in a way I could understand, thanks.

Jeremy - Oviedo, FL
1986 F250 XLT Lariat Supercab 4x4 Manual 460

rcarlisle

Re: Ignition Troubleshooting

In reply to this post by mat in tn

mat in tn wrote

trying to explain how a carb works can be awkward because you don't know the knowledge of the person(s) listening.
the fuel which the engine burns is actually fuel vapor. liquid does not burn. that fuel vapor is added to oxygen rich air. it's the oxygen which feeds the burn of the fuel. the carb holds liquid gasoline in a reservoir with a tiny "straw" type passage leading to the air venturi. the "barrel" which has a slight hourglass restriction causing a vacuum and drawing gas vapor through the straw into the air stream.
the jetting is a finer method of tuning the straw to make sure the carb gets the proper ratio of fuel to air in a range of run conditions. heavy load will require a little more fuel vs a lighter load needing less.
this is a basic explanation of the main circuit. the idle circuit is another finer set metering circuit which is semi-independent of the main venturi.
cubic inches of the engine play a big part of course but it is the air fuel mixture set for the expected demand that comes first. too much fuel is not only expensive and wasteful, but it is bad or worse than not enough for the engine
a good example of this might be the 300ci six with a 1 barrel of approx. 269 cfm while the 302 ci came with a 600 cfm 4barrel both works well for their respective demands.
I hope I gave the engineers a good laugh with my simplification.

EXCELLENT explanation! I'm in the middle and that made good sense. AND it helped the OP understand better. I have spent a lot of time reading, but also by studying a carb and passages by actually holding one in my grubby hands.

Randy

Mt. Airy, NC 81 F-150 STYLESIDE regular cab 2wd. 302 Auto Zone crate. 5 spd M5od-R2

mat in tn

Re: Ignition Troubleshooting

I guess the only real answer to whether it will stick again is maybe. I always have to ask "how long did this truck sit"? liquid gas can be a fair solvent for a while but then it can get gummy when talking about the fine passages in a carburetor. the inlet valve was disturbed by you going through the range of adjustment so it could be that simple. the rear bowl does not get the turnover in fuel which the front does for most people. I myself seem to flush out the old fuel more than most. Haha. The factory4 barrel runs on the front (primary). as if it were only a two barrel unless you stick your foot in it enough to allow the vacuum of the engine to open the secondary when it needs it. you give it permission and it regulates itself.

Bullnose Gator

Re: Ignition Troubleshooting

I replaced the front fuel bowl gasket tonight and took her for a spin. Sure enough, the rear bowl float level was the problem after all. There were a few hesitations as I got it up to 45mph+, but they didn't last and I assume it was her working out the cobwebs after sitting for over two months waiting on me to figure this out. All it took was for me to order a new carb in order to figure it out lol. So I'm quite happy, and a little embarrassed that it took 4 pages of me bothering yall for months, but thanks for all the help!

Jeremy - Oviedo, FL
1986 F250 XLT Lariat Supercab 4x4 Manual 460

mat in tn

Re: Ignition Troubleshooting

to the best of my knowledge, this is exactly why Gary started this. I found help and hopefully i have been helpful in return.

Bullnose Gator

Re: Ignition Troubleshooting

Indeed, and I hope to pay it forward one day myself.

Jeremy - Oviedo, FL
1986 F250 XLT Lariat Supercab 4x4 Manual 460

Gary Lewis

Re: Ignition Troubleshooting

Administrator

In reply to this post by Bullnose Gator

I'm glad you got it resolved! That's great.

One of the problems with the Holley carbs is that the secondary bowls are completely separate from the primaries. Most Holley's don't use the secondaries for idling, so unless you open them under power every once in a while the gas can get old. And ethanol-laced gas gets old FAST.

So I'd encourage "spirited driving" every once in a while.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

85lebaront2

Re: Ignition Troubleshooting

Administrator

Gary, many Holleys, particularly the older designs, have secondary idle circuits, mostly fixed. This is why there is an adjustment on the throttle body to set a small gap. This also keeps the throttle plates from sticking shut. Some emission models had sealed adjustment screws in the throttle body to set the mixture.

Even the Chrysler versions had secondary idle circuits and the heat warping of the metering body opened them to the main part of the float bowl causing rich idle and horrible hot start issues. You could pull the air cleaner off and watch the gas running across the secondary throttle plates.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

Gary Lewis

Re: Ignition Troubleshooting

Administrator

Bill - I wasn't aware that they actually had idle circuits. My bad.

But I was aware of the warping problem. Been there, had that done to me, big time.

Gary, AKA "Gary fellow": Profile

Bullnose Gator

Re: Ignition Troubleshooting

In reply to this post by Gary Lewis

Interesting you bring that up, Gary. I drove it again this morning and it still isn't running quite right. It is slightly struggling at the start of each gear, with a pronounced chugga-lugga sound, but gets better the more I gas it. It is also having some intermittent hesitation in 3rd and 4th gear. I assumed giving it more gas kicked in the rear bowl and other two barrels and that what's off must be something on the front end. I was thinking of replacing the fuel filter again. That's the thing that started all of my fuel system woes last year when it was choking at higher, prolonged speeds.

Jeremy - Oviedo, FL
1986 F250 XLT Lariat Supercab 4x4 Manual 460

Gary Lewis

Re: Ignition Troubleshooting

Administrator

Hopefully you've read that I was wrong about the secondaries. But the issue you describe could well be just with the primaries. Have you adjusted the idle air/fuel mix? It might be off.

Gary, AKA "Gary fellow": Profile

rcarlisle

Re: Ignition Troubleshooting

I'm agreeing that the fuel is off somewhere. This is where the vacuum gauge helps. Doesn't cure it, but can help diagnose. Mine was like $14.99 at harbor freight and is paying for itself with the education it is providing about adjustments.

Randy

Mt. Airy, NC 81 F-150 STYLESIDE regular cab 2wd. 302 Auto Zone crate. 5 spd M5od-R2

Gary Lewis

Re: Ignition Troubleshooting

Administrator

rcarlisle wrote

I'm agreeing that the fuel is off somewhere. This is where the vacuum gauge helps. Doesn't cure it, but can help diagnose. Mine was like $14.99 at harbor freight and is paying for itself with the education it is providing about adjustments.

Gary, AKA "Gary fellow": Profile

Bullnose Gator

Re: Ignition Troubleshooting

In reply to this post by rcarlisle

Yeah, getting a vacuum gauge sounds worthwhile. Are there other applications for it besides the fuel system?

Thankfully, this latest hiccup was another easy fix. I went out and checked the front fuel bowl level again and somehow it was lower than it was yesterday when I checked it. Not sure how, maybe driving it around for the first time in a while got things moving again. It's running good now, so hopefully everything stays like it is for a while!

Jeremy - Oviedo, FL
1986 F250 XLT Lariat Supercab 4x4 Manual 460

rcarlisle

Re: Ignition Troubleshooting

Besides the carb tuning, there are numerous things on Google about setting ignition timing with the vacuum gauge. See this: https://www.motor.com/magazine-summary/mastering-the-basics-reading-a-vacuum-gauge/

Right now I have mine plugged in to a manifold source and run up to the windshield. I have it hooked under the passenger wiper blade and can read what the vacuum is doing while I'm driving it around testing. Will show you what throttle application is sucking the most gas and where it is at various RPM.

If I were into adding extra gauges, a vacuum gauge would be near the top. I think the instructions also say it can be used to read fuel pressure, which doesn't seem to be a problem on my stock engine with 2 barrel.

Randy

Mt. Airy, NC 81 F-150 STYLESIDE regular cab 2wd. 302 Auto Zone crate. 5 spd M5od-R2

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