Won't Idle, Carb, Possible Timing, and Definite Can of Worms Issues

[JeepGuy]

Sorry in advance for the long post. Seems my new gears and higher engine rpm's have highlighted some engine issues. I have not done anything to the engine, so as far as I know it is a stock 302, egr deleted stock manifold with stock motocraft 2100 2-barrel carb, points distributor vacuum advance.

Awhile ago when I was going through my brake issues I adjusted the stock points timing (coil and vacuum advance) to 15.5 degrees advanced for best vacuum at idle to help my brake booster. This was never an issue with idle or pinging prior to new gears. Got the new gears and noticed a substantial RPM difference while driving around. Went out for about a 30 minute drive and got a VERY LOUD backfire. Never had backfire issues before. Did a quick visual and nothing seemed out of place or disconnected under the hood. Kept driving and got a second backfire. Moments later the engine stumbled and shut off.

I let it sit for a bit and after some easy cranks it fired up. Got it almost home and it shut off again. I have two clear plastic Napa 3003 fuel filters and could see gas in both. Got it started and again and got it home and that is where I opened the can of worms.

I'd like to break this down into two different areas... Timing and Fuel.

Timing:
I re-set the timing to 12 degrees advanced, idle was at around 800ish (not stable) in neutral, 630-650ish in gear. That setting gave me right around 15lbs of manifold vacuum at idle. C-4 Auto trans. Without the vacuum advanced hooked up it flattens out around 37 degrees all-in advanced somewhere at close to 2800 rpm's. With vacuum advanced hooked up it reads just over 50 degrees of total advance at the same rpm's. I have no idea if it's a stock cam in there or if the balancer with the timing marks is correct. Are those numbers within spec? I can't find much about it for older timing.

Fuel/Carb:
That smoothed idle out a bit and I took it out for a couple test drives. No backfires, but it stumbled and shut off on my twice. Second time around I didn't immediately try to restart and popped the hood. Front filter was almost completely empty. Rear was full. Little engine cranking and it fired back up, but anything over just off idle I was running out of fuel and shutting off. Got it home and checked again and noticed a ton of bubbles in my fuel lines. Also noticed the rear filter was now only half full and trickling (thinking something in the old rusty tank is blocking the pick up) I replaced the fuel pump and all fuel filters. Needless to say, there was some nasty stuff in those filters. Brown stuff on the rag came out of the inline filter that screws into the pump.

Got all of those replaced and got a new fuel pump installed. I'm not convinced the fuel pump was bad, but after seeing what went through it, I didn't want to mess with a cracked or clogged baffles. I was also hoping this would solve the fuel delivery issue with half full filters. Prior to any of these problems those filters were always full with no bubbles. While at it, I pulled the top of the carb off and saw pretty much the same bronze colored fine dust in the float bowl of the carb. Pulled the carb off and used some brake cleaner to clean it out... I know, but I didn't have any carb cleaner sitting around.

Got it all back on and my fuel delivery issue is still not solved. I can tell while looking at the filters it's intermittent. Sometimes they are completely full, other times running out of gas, which take me back to something clogging the pick up inside the tank

I should add that I was trying to save a couple bucks and used a very old tank that sat outside for years. I cleaned it up inside as good as I could, but nowhere near sanitary as evident by those filters.

All of the above considered... Now I can't get it to idle, and starting it is nowhere near as easy going as it was. In an attempt to not just start throwing parts on random things I'm wondering what you guys think I'm dealing with here.

Plan going forward is to replace the old fuel tank regardless of everything else, which will also come with a new sending unit (greeeeeaaaaattttttttttttttt). I'm crossing my fingers those parts are good right out of the box.

Other than that, I'm kind of at a loss where to start.

Carb rebuild? (should note I've never had a working choke on this carb and it was never an issue before)
New Points?
Re-set timing to 15.5, set the carb to super rich and cross my fingers?

What say the experts?

 

[Bruners4]

Without fixing the fuel quality supply issue, you will be chasing this until it is corrected.
That said, you could install a sediment bowl to prefilter out the chunks coming out of the tank before the filters. But once full it will pass them along to your first filter.
A shop rag carb overhaul might pull the debris out of the fuel passageways in the carburetor and correct the fuel problem temporarily. This is performed by placing a cloth shop rag over the top of the carburetor with the engine running over 1500 RPM. Opening the throttle while blocking the air intake will draw fuel out of the fuel bowl from every opening trying to flood the engine. Remove the shop rag before the engine stalls keeping the throttle open until it cleans out. Sometimes this will help clean the carb passageways. But without a clean consistent fuel supply to the carburetor, this will continue to be a problem.
After the fuel supply is corrected, a proper carburetor cleaning/overhaul will be needed.

 

[gnpenning]

You need to go through the fuel delivery, from the tank to the pump and carb.

Do you have a switch over valve and auxiliary tank?

Why are you running 3 fuel filters? If you think your fuel system is that compromised you needed to fix it and not pump garbage through the system.

Yes you are going to need to remove the carb and clean it out.

Have you checked your plugs and wires?

 

[JeepGuy]

@Bruners4 @gnpenning All good points.

Fuel delivery will be addressed this week one way or the other. A new tank and rubber lines are already in the works. My plan has always been to swap out the old tank, but I wanted to get the axles squared away before I got into a new tank and EFI upgrade so I knew this day was coming, just hopping it was awhile down the road money wise.

I have the two inline prior to the carb because I figured I'd be pulling junk out of the old tank. Final plan will have one good inline filter. The one on the carb was always there but was new when I got this Bronco back on the road earlier this year.

I plan on pulling plugs this week to see what is going on with the mixture in the cylinders. I'll shoot some picks and post them up.

Any thoughts on one of the backfires possibly damaging the carb internals? The first on sounded like it came from up front, second I couldn't tell. But will say with no top or doors on I was very surprised at how loud of a bang it made.

 

[Bruners4]

The simple 2V Ford carbs don't have but two diaphragms that a intake backfire could affect. The first is the accelerator pump diaphragm and its highly unlikely that it would be affected. The second is the power valve that is on the bottom of the fuel bowl. if this diaphragm is damaged, it will leak fuel into the intake manifold until the fuel bowl is empty.
Here is another consideration to running dirty fuel. All of the containments that do pass through the carburetor are ingested by the engine. It can cause additional wear on the cylinders, rings, valves and valve seats.

 

[gnpenning]

Generally when vehicles run 2 filters there is a difference they microns they filter. Your first and second look to be the same. If they are and the second is catching debris the first let through you need to go to a different brand.

I just did a complete fuel system flush on one of my vehicles. Everything from the tank to the throttle body was flushed. Even the injector spent some time in the ultrasound and new O rings. Way easier to spend a little extra time up front to save a headache down the road.

Don't forget to ohm the wires.

 

[Broncobowsher]

Too add to the above...
Timing. Generally you don't run vacuum advance to manifold vacuum. Goes to ported vacuum. The high RPM light load is where the 50° of advance comes in. And that feels a little high to me, but not a major issue.
But back to timing. Has the timing chain jumped a tooth? or just crazy amounts of slop? You can get a feel for it by removing the distributer cap and rock the crank pulley back and forth. There will be backlash, that is normal for the chain and distributor drive gear. But how much?

 

[Sendero]

My vote is to switch over to electronic ignition to eliminate the variable of points. It is too cheap and easy in my opinion. Also, it may sound silly but how old is the fuel in it? I spent quite a bit of time troubleshooting a neighborhood cruisier japanese mini truck I had before I realized it had been a year and half since I had filled it up with fresh gas....

 

[JeepGuy]

Got a little time on it yesterday. Pulled the carb back off and gave it a good bath. Funny how you don't notice how dirty things are under the hood until you start pulling it apart. All that dirt on the intake is a couple decades old...

Point of interest here. Drivers side under the carb mounting plate had a gasket. The valley under that gasket was completely full of very old gas and I'm assuming oil. Nothing obvious on the underside of the carb that would indicate a leak, and given the underside of the mounting plate, I'm assuming it just internal sludge from years of use. When I rebuilt the carb early in 2025 I never removed the mounting plate, so that gasket also had a couple decades of work on it. The gasket was dry so I have no idea where or how it go there.

Which brings up a question. Is there any reason I can't just use some non-hardening RTV type gasket maker between the mounting plate and intake? Or is there a reason they use a fiber/paper gasket there for air flow directly under the carb? I'm assuming it's done with the paper gasket so it can be easily removed for carb changes.

Anyways... Carb isn't horrible, but there are definite signs of all that old gas tank flowing through there.

Gave everything a good bath in the Berrymans dip and a couple cans carb cleaner and got most of it back together last night on the bench. Still trying to figure out a couple gasket issues.

 

[JeepGuy]

As I was waiting for the Berryman's to do its thing I pulled the plugs. They look pretty normal to me but I'm far from an expert. These are OOOLLLDDDD and will be replaced just for fun since I already have them out. Looking at the passenger side front to back as they cylinders. (4,3,2,1). #4 cylinder does look a bit different in this picture, but this is after I had to use a little WD-40 to get them released from my spark plug socket so the moisture is more than likely from that. Came out of the hole looking like the others. I also checked the OHM on the plug wires. With the meter set at 20K, each wire (7mm) gave me a reading between .98 and 1.1.

Another look into the dirty fuel system. All this hose was replaced about a year ago when I did my first rebuild on the carb.

 

[JeepGuy]

Which brings us to gaskets. Something looks a bit off here to me.

The gaskets that came with this kit both times leave a bit of a hole on either side of that center tab. I had it sandwhiched between the insulator plate and the carb as you can see the impression left after some usage.

The insulator does cover the entire bottom of the carb.

I'm wondering if there was just enough of a gap difference there to create a little vacuum leak and contribute to my unstable higher idle. Sequence was carb to felt/paper gasket to insulator to mounting plate to felt/paper gasket to intake. I know felt/paper gaskets have a purpose, but they also seem to me to be a very possible source of vacuum leaks.

Is there any reason I can't use a little of the non-hardening RTV between the insulator and carb bottom when I put this back on? i'm talking a very thin layer around the outer edge only on the base of the carb.

 

[JeepGuy]

@Bruners4 Understood on the issues with running dirty fuel. For perspective here I think I have a total of about 300 - 500 miles on this thing total after getting it back on the road over this last year. It is generally a short local drive type deal. None the less, dirty fuel is dirty fuel.

@gnpenning The filters are just your run of the mill Napa 3003's. I intentionally put two clear ones on there so I can ensure I have fuel pulling from the tank and pushing past the pump. That was not only to try and filter everything, but due to a few different brand-new parts failing on me and trying to make it easy to check fuel delivery off my diagnosis lists. Finished system will hopefully only have one inline filter when I switch to EFI with an inline fuel pressure gauge. I know I know... I could do that now, but then I'd only be posting a fraction of the pictures I am now. and nobody is voting for that.

@Broncobowsher Timing vacuum is hooked to ported on the front passenger side of that carb. I'll pull the cap off and mess with the rotor a bit when I get some more garage time.

@Sendero I hear you. I'm too cheap to spend good money twice... or at least that is what I tell myself while I try cut corners and end up spending more money the third and forth time around. Been considering the Pertronix ignitor upgrade to keep it simple and not break the bank. My final plan is installing the ProFlo4 set up which will eliminate all those issues either way, but I'm trying my best to ensure everything else is working as it should before making that jump. This was actually pretty reliable all summer regarding firing up and cruising around (all kind of other unrelated issues), but I was not pushing the engine at all with stock 3:50 gears, 35" tall tires and a C4. Pretty low RPM cruising. Now with the 4:88's, cruising at 50-55 is much higher RPM and I'm assuming stressing old worn out systems a bit more.

That's just speculation on my part. This could all just be my short cuts with the fuel system catching up to me at this point. The actual fuel has cycled through a handful of full tanks over the last year. It's not old fuel that has been sitting around, but the tank it's going into is an old tank that sat outside unsealed for a long time. I did a few different clean ups on it with Acid and gas etc. just trying to band aid it for a bit. Should have just bought a replacement tank (It's already on order and shipping at the time of this post) and considered the few hundred bucks' peace of mind instead of trying to save it.

 

[gnpenning]

Check for play with the throttle shaft while you have it off.

Not a fan of using rtv around fuel. Is what you have even fuel rated?

 

[JeepGuy]

Check for play with the throttle shaft while you have it off.

Not a fan of using rtv around fuel. Is what you have even fuel rated?

Yeah, throttle seems fine. Permatex makes a fuel specific type for gaskets.

https://www.permatex.com/products/g...esistant-gasket-dressing-flange-sealant-2-oz/

 

[JeepGuy]

Little update:

Fuel system completely replaced (New tank, filters, lines, pump) with exception to the Carb. Finished the rebuild, pretty sure that carb is just old and worn out.
Plugs replaced, timing double checked and set at 12 degrees advanced.

Still having idle issues, meaning in park or neutral is bounces between about 900 - 1100 RPM's (based on timing light readings) and in gear between 850ish - 1000. I cannot adjust the idle set screw any lower on the linkage. Currently the idle mixture set screws on the front of the carb are 2 full turns out. A little squirt of carb or brake cleaner at the throttle linkage the idle shoots up....

Took it out for a test drive and I thought it was all good until just randomly shut off on me during acceleration. Pulled over, let it sit for about 1 minute, fired up and drove home. This happened one more time. No backfires, and fuel filters never emptied nor did all the other power shut off. There is the digital voltage gauge that showed consistent battery usually between 12.5 - 14.1 depending on what switches I have turned on.

Popped the hood once home and went to fire it back up with nothing. Just cranking... Noticed two things...

First was a little spark from my coil wire to a hose clamp on my heater hose. Yes, a little spark. The wire itself had backed out from the boot just enough to spark against the hose clamp. I pushed it back in and pretended I never saw it happen...

When hot, the engine would fire and then immediately die. I had to let it completely cool down before it would fire and idle again.

As of today, I have a new coil and wires on order. I'm not messing around with old wires randomly pulling apart and I figure the coil has been on there for at least a couple decades now so for peace of mind I'm swapping it out.

We shall see how this all goes.

 

[gnpenning]

In post 13 the question about play with the shaft linkage came up. You have now proven you have a issue there. It needs to be addressed. You can buy new bushings.

You also need to look down the throat of the carb at idle and look for fuel dumping in.

When it shuts off while it's hot you need to be checking for spark at that time. Checking ignition components while hot will help you narrow it down. Generally the only time you have fuel issues when hot will be from vapor lock.

 

[JeepGuy]

In post 13 the question about play with the shaft linkage came up. You have now proven you have a issue there. It needs to be addressed. You can buy new bushings.

You also need to look down the throat of the carb at idle and look for fuel dumping in.

When it shuts off while it's hot you need to be checking for spark at that time. Checking ignition components while hot will help you narrow it down. Generally the only time you have fuel issues when hot will be from vapor lock.

I was just watching a video on this. Seems pretty straight forward and I've had that shaft out each time I've rebuilt it (twice now). Does not seem that hard of a thing to do.

As far as fuel dumping in, do you mean from the bottom inlets that are controlled by the idle mixture screws, or from the two top inlets on the from the top cluster or booster assembly?

 

[Bruners4]

You can also have uncontrolled fuel getting into the intake past the power valve diaphragm into an intake vacuum port. This will also drain the fuel bowl of fuel overnight when leaking a lot. This causes the engine to have to crank until there is enough fuel pumped into the carb fuel bowl to allow it to start. This leaking fuel will also cause a hard hot start as the extra fuel leaked into the intake manifold causes a rich mixture.

 

[gnpenning]

I was just watching a video on this. Seems pretty straight forward and I've had that shaft out each time I've rebuilt it (twice now). Does not seem that hard of a thing to do.

As far as fuel dumping in, do you mean from the bottom inlets that are controlled by the idle mixture screws, or from the two top inlets on the from the top cluster or booster assembly?

Unmetered fuel will appear as droplets. You might see a fine mist, other than that you shouldn't see any fuel in the throat of the carb.

Don't forget to check for other vacuum leaks.

 

[Grey owl]

Sorry in advance for the long post. Seems my new gears and higher engine rpm's have highlighted some engine issues. I have not done anything to the engine, so as far as I know it is a stock 302, egr deleted stock manifold with stock motocraft 2100 2-barrel carb, points distributor vacuum advance.

Awhile ago when I was going through my brake issues I adjusted the stock points timing (coil and vacuum advance) to 15.5 degrees advanced for best vacuum at idle to help my brake booster. This was never an issue with idle or pinging prior to new gears. Got the new gears and noticed a substantial RPM difference while driving around. Went out for about a 30 minute drive and got a VERY LOUD backfire. Never had backfire issues before. Did a quick visual and nothing seemed out of place or disconnected under the hood. Kept driving and got a second backfire. Moments later the engine stumbled and shut off.

I let it sit for a bit and after some easy cranks it fired up. Got it almost home and it shut off again. I have two clear plastic Napa 3003 fuel filters and could see gas in both. Got it started and again and got it home and that is where I opened the can of worms.

I'd like to break this down into two different areas... Timing and Fuel.

Timing:
I re-set the timing to 12 degrees advanced, idle was at around 800ish (not stable) in neutral, 630-650ish in gear. That setting gave me right around 15lbs of manifold vacuum at idle. C-4 Auto trans. Without the vacuum advanced hooked up it flattens out around 37 degrees all-in advanced somewhere at close to 2800 rpm's. With vacuum advanced hooked up it reads just over 50 degrees of total advance at the same rpm's. I have no idea if it's a stock cam in there or if the balancer with the timing marks is correct. Are those numbers within spec? I can't find much about it for older timing.

Fuel/Carb:
That smoothed idle out a bit and I took it out for a couple test drives. No backfires, but it stumbled and shut off on my twice. Second time around I didn't immediately try to restart and popped the hood. Front filter was almost completely empty. Rear was full. Little engine cranking and it fired back up, but anything over just off idle I was running out of fuel and shutting off. Got it home and checked again and noticed a ton of bubbles in my fuel lines. Also noticed the rear filter was now only half full and trickling (thinking something in the old rusty tank is blocking the pick up) I replaced the fuel pump and all fuel filters. Needless to say, there was some nasty stuff in those filters. Brown stuff on the rag came out of the inline filter that screws into the pump.
View attachment 957556

Got all of those replaced and got a new fuel pump installed. I'm not convinced the fuel pump was bad, but after seeing what went through it, I didn't want to mess with a cracked or clogged baffles. I was also hoping this would solve the fuel delivery issue with half full filters. Prior to any of these problems those filters were always full with no bubbles. While at it, I pulled the top of the carb off and saw pretty much the same bronze colored fine dust in the float bowl of the carb. Pulled the carb off and used some brake cleaner to clean it out... I know, but I didn't have any carb cleaner sitting around.

Got it all back on and my fuel delivery issue is still not solved. I can tell while looking at the filters it's intermittent. Sometimes they are completely full, other times running out of gas, which take me back to something clogging the pick up inside the tank

I should add that I was trying to save a couple bucks and used a very old tank that sat outside for years. I cleaned it up inside as good as I could, but nowhere near sanitary as evident by those filters.

All of the above considered... Now I can't get it to idle, and starting it is nowhere near as easy going as it was. In an attempt to not just start throwing parts on random things I'm wondering what you guys think I'm dealing with here.

Plan going forward is to replace the old fuel tank regardless of everything else, which will also come with a new sending unit (greeeeeaaaaattttttttttttttt). I'm crossing my fingers those parts are good right out of the box.

Other than that, I'm kind of at a loss where to start.

Carb rebuild? (should note I've never had a working choke on this carb and it was never an issue before)
New Points?
Re-set timing to 15.5, set the carb to super rich and cross my fingers?

What say the experts?

Vacuum leaks can be hard to track down but they are notorious for for causing all sorts of issues.