2F Intermittent Lean Condition (1 Viewer)

[Stexag]

Good evening mud. The 2F in my 1978 40 (desmogged) has developed a nasty habit out of the blue. The truck has run fine in the past, I completed a major re-fit of the truck in 2022 and since then drive with less frequency (shoot for a drive a month but sometimes don't accomplish that - so it does sit a bit). Things that relate to fuel/vacuum that were replaced in '22: carb rebuild (including ICS), new fuel pump, new fuel filter (and all hoses related to those), new manifold gaskets (factory), new brake booster, new PCV valve. I live at sea level and have driven it over Imogene without touching a thing - it ran fine there and it's been rock solid here - until now.

The Problem: Truck starts and drives normally. I will refer to that as the "Good" condition; all systems completely normal. Usually within a mile or two of going down the road it will *die* unexpectedly and almost instantly. I used the * because it doesn't actually die. It leans out to the point the I can't touch the throttle, but it WILL idle, and idle smoothly. When in this condition, which I will call the 'Bad' condition, I can pull the choke all the way out and the engine will spit and sputter but go back pulling hard enough to get me home (very similar to when the ICS is bad). With the choke pushed back in the engine will idle, but NO MORE than that.

So the problem is binary; it's either in Good condition, running fine, or Bad condition where it will idle normally (choke pushed in) but requires the choke pulled out to achieve anything more than than idle. 90% of the time the switch from Good to Bad is instant (chip your tooth on the steering wheel type instant) with the other 10% of occurrences being a gradual slowdown before finally going completely to sh*t. It will switch from Good to Bad regardless of time/temp, as in, it will do it on the first drive of the day or the 15th drive of the day. (I've replicated this more times than I care to count)

Once the truck is stopped and the engine is off - sometimes for a few minutes, sometime a little longer, but without fail... it will revert to the Good condition on its own and run like nothing was ever wrong. Then it's off to the races for a few miles before it happens again.

MY ORIGINAL DIAGNOSIS: This seems pretty easy - lean condition caused by fuel starvation/bad fuel pump/clogged lines/something in the tank. However - the fuel level is NEVER out of the center of the window. NEVER. In both conditions, with the engine running the fuel is steady, dead center the widow. That said - I have taken a 12v aux pump and plumbed it in the fuel system around the filter and pumped through the mechanical pump, but it made no difference. The fuel level stayed steady but the problem persisted with no difference.

Other things I've done:

• verified ICS works good and clicks. Wired it direct to the battery to circumvent ignition circuit. No change. (I should note the problem doesn't lend itself to bad ICS since idle is the one thing it will do correctly in Bad condition AND unplugging it will kill the engine from idle in both conditions)
• checked vacuum - 20Hg vac rock solid at idle in Good condition, 19 in Bad condition.
• not brake booster - I've driven it with the vac gauge connected where the brake booster normally connects. No change.
• pulled plug wires on each cylinder while idling to look for dead cylinders - all fine, in BOTH conditions.
• pulled air horn off carb, drained and cleaned bowl, pulled/cleaned primary jet and first main nozzle. All clean.
• verified accelerator pump squirts fuel. Check.
• checked pcv valve - seems to be working fine, putting my thumb over it made no difference when in Bad condition.
• in the shop idling in Bad (lean) condition I used darn near a whole can of starting fluid looking for a vac leak, around carb base, around manifold gasket (above and below). Nothing.
• I did the paper clip test on the secondaries and they are not opening past the mechanical crack provided by the linkage. I am a flatlander, so it's hard to find an incline long enough to truly put that to the test - and the nearest overpass is beyond the range this gremlin will let me travel. However, I don't think the secondary butterfly NOT opening is causing the engine to lean out.
• it persists with the smog 'computer' plugged in or unplugged, if that makes any difference.
• the fuel in the tank was low when this started (last filled sep/oct) added fresh fuel today. No change.

Something is causing the engine to lean out predictably, and almost instantly, after short time running. Then, the problem fixes itself after sitting a while (time can range from 4-5 minutes to half hour), but repeats without fail. I feel like I have proven to myself the problem is not fuel delivery to the carb since I have visual proof (via window) that fuel level is good in both conditions. Air is not the problem, it does this with and without the air cleaner on, and I've had it off more than not while diagnosing. I don't have any reason to suspect ignition is the cause, nor can I picture how that would result in a condition where the engine would respond to the choke.

Before I pull the carb off for a rebuild (because I at my wits end) - do the good people of mud know of another smoking gun or something else I should check? I only have one carb so once I pull it I can only dream of sunset drives until I get it back. At the current rate: if it gets as cold as predicted next week I might burn the truck to stay warm - so help is appreciated before I do something rash. Thanks.

 

[45Dougal]

I had a similar problem with an old mini years ago, which was caused by the vacuum advance pipe being loose.
Idle was fine but zero power to drive.

Check your points are in good shape, free to move and whatever advance you have is working correctly..

 

[Grayscale]

The spark plugs are likely not clean after running bad. Pull them, photos, clean and replace.

Do you use fuel-stabilizer? Infrequent driving is tough on fuel systems.

 

[Stexag]

I'll pull the plugs, look at them, and check the vac advance for leaks - I do know the hose is secured well to the carb.

I should have mentioned, I have an HEI (DUI) distributor. I did have and issue when I first bought the truck with the ignition module. In that instance the truck would not have spark when hot and after replacing the module I've had zero problems. The truck does have spark and will start at all times now - whether it's in good or bad condition.

I do keep SeaFoam in the tank, yes. Religiously.

 

[B y r o n]

Could be something got into the carb and is blocking one of the circuits. You might try grabbing a gasket kit and going through it making sure to blow through all the circuits.

 

[Stexag]

Could be something got into the carb and is blocking one of the circuits. You might try grabbing a gasket kit and going through it making sure to blow through all the circuits.

This kind of where I'm at and why I was about to pull the carb off - I just wanted to make sure I wasn't overlooking something simple first. The come/go nature of the problem screams of something loose and floating somewhere in the fuel system or a massive vac leak I can't find (that comes and goes). I used the search function and couldn't find the exact thing discussed so I thought I'd ask.

 

[cbmontgo]

Ignition and grounds can do weird things.

 

[pb4ugo]

Is the ING system points, electronic, or something aftermarket like petronics?

You might try rebuilding the carb yourself tocsave time snd $. I hear there's good videos by Pinhead.

 

[Engineer8000]

Something is heating up and growing possibly. When it is running cold, carefully take a heat gun around the various electrical connections associated with the ICS and ignition system. Possibly a bad wire connection. I've seen poorly crimped electrical connectors do this. More than likely junk in the carb tho.

 

[pb4ugo]

Something is heating up and growing possibly. When it is running cold, carefully take a heat gun around the various electrical connections associated with the ICS and ignition system. Possibly a bad wire connection. I've seen poorly crimped electrical connectors do this. More than likely junk in the carb tho.

I was thinking the same thing. Yrs ago, we had a boat acting like a fuel delivery problem and it ended up being the pickup coil failing when it got hot.

 

[Stexag]

@pb4ugo , yes, it is an aftermarket HEI all-in-one. Toyota Landcruiser DUI Distributor

@Engineer8000 , don't laugh, about things growing - yesterday I convinced myself I had a crack in the intake manifold that was growing to a gaping chasm at times... but I couldn't find it with the starting fluid.

I can order another ignition module and swap it out - but if it is the ignition - do we think that pulling the choke would be the 'remedy' to keep it running?

thank you all for the replies. I will try to get out the shop this evening to verify/troubleshoot what we've discussed.

 

[Stexag]

I want to follow back up with the resolution of this problem in case it ever helps anyone down the road.

On the advice of posters here I did pull spark plugs for clues. What I found were plugs that appeared to be in good shape without soot - which stood to reason since the problem appeared to be the truck leaning out. Plugs:

Geez, is the picture that big? Anyway, the spark seemed to be consistent when the truck was acting right and when it was acting up. Since the problem manifested itself and all the while the fuel level was just right in the fuel bowl - I went with the problem being somewhere in the carb and ordered a full kit.

When that arrived I disassembled the carb, soaked it in carb cleaner, rinsed it in the ultrasonic cleaner, and reassembled it per the FSM and tips from a friend. During disassembly, I found the ball under the accelerator pump, the one under the coiled keeper, was stuck and *gunked* shut. I got the keeper out easily and with a pick genlty dug some gunk from around that BB until it came out. I am thinking that despite my best effort with the seafoam, this was a result of sitting parked. That was the only thing I obsereved really bad. I genly blew through all passageways with compressed air and reassembled.

With the carb back in place the truck fired right up and ran like a top. I drove it 60 trouble-free miles that day. I have since driven it that much or more in subsequent cruises - all trouble-free. I have renewed confidence in my Ol' Buddy. I should add that since the rebuild it starts much better and seems to require less half-choke warm-up. But I live in south Texas, so that might just a result of warmer temps; either way, it has yet to do this nasty trick since the rebuild.

Thank you all for your suggestions and advice. This forum is an inavulable resource for us and in my research I love finding threads that contine all the way through resoutions. I want to help keep that tradition up.

 

[charliemeyer007]

If its going to be parked for a long time, put a pair of hemostats on the gas line and let it run out of fuel - no shellac build up that way . Not a seafoam fan but I do like PRI-G.

 

[Stexag]

If its going to be parked for a long time, put a pair of hemostats on the gas line and let it run out of fuel - no shellac build up that way . Not a seafoam fan but I do like PRI-G.

Thanks for the tip. I certainly don't own any stock in Seafoam... so off to get some PRI-G.

You know, I don't INTEND for it set long stretches... but it happens. I'm probably not alone.

 

[Grayscale]

Techron High Mileage, and Lucas Fuel Injector Cleaner. That, and regular use should be not too different from a rebuild using the Berryman Carb Dip. I've heard that the price reflected in higher octane fuel is because of the quality fuel additives, not so much the octane. There was what appeared to be quite a bit of rust and aluminum corrosion in my original carb. I think more Cruisers died from lack of maintenance and sitting, than regular wear and tear. I don't store a carb, unless I pull the air horn, drain the bowl, maybe compressed air to dry it. It is like the fuel tank, it absorbed water, especially with the ethanol, dry it completely or keep it topped-off regularly.

I'd be on the lookout for a vacuum leak, excessive timing advance, engine temp. (too hot). The spark plugs should look tan on the insulator. (Haynes)

 

[pb4ugo]

Your plugs look fine and the timing appears close enuff.

 

[Land Shark]

Techron High Mileage, and Lucas Fuel Injector Cleaner. That, and regular use should be not too different from a rebuild using the Berryman Carb Dip. I've heard that the price reflected in higher octane fuel is because of the quality fuel additives, not so much the octane. There was what appeared to be quite a bit of rust and aluminum corrosion in my original carb. I think more Cruisers died from lack of maintenance and sitting, than regular wear and tear. I don't store a carb, unless I pull the air horn, drain the bowl, maybe compressed air to dry it. It is like the fuel tank, it absorbed water, especially with the ethanol, dry it completely or keep it topped-off regularly.

I'd be on the lookout for a vacuum leak, excessive timing advance, engine temp. (too hot). The spark plugs should look tan on the insulator. (Haynes)

View attachment 3835808

You mention Fuel injector cleaner. I have been running Gumout Carb/fuel injector cleaner every so often. How often are you running that?

 

[Grayscale]

I use the Lucas every other fill-up. Lucas, then Techron. The Lucas is supposed to be an upper cylinder lubricant, and I know that I have worn thru the cylinder hone (oil distribution) in places, so it seems logical to use it. Less is more, but, I think that commercial gas probably lacks enough of fuel additive for an older, or high-mileage motor.

The image you posted of your plugs suggests something else. There are ash deposits, so maybe it is enough SeaFoam or whatever additives? Gasoline is a straight hydrocarbon, but the oil and fuel additives are mineral or metals (like calcium or magnesium) somewhere placed in a hydrocarbon chain. So, the minerals and metals don't burn, and you are left with a bit of ash deposit.