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Flooding... Possible Carb Tuning Issue?
I have a 1976 F150 4x4 with the 360 engine (~130k miles). It pretty much always starts right up and idles great. If I only let it warm up for a minute or two, hop in and go, it wants to flood. I have to shift to neutral and rev the engine for a second, and then I can keep going. It'll do this multiple times until it's warmed up, and then it runs great. If I let it warm for 10+ minutes, it pretty much negates the issue. It seems to me like a fuel issue, but I guess it's also possible it's spark related. It's been suggested to me to check the needle & seat, or to check the float level. But I can't imagine those things would only affect the car for the first 10 minutes, until it's warm?
I did install a new carb when I first got it running. The old one was rusty and corroded, and I got a rebuilt one from O'Reilly's. I bolted it on and it fired right up first try, no problems there. Though it had a couple of extra metal tube-like extremities (vacuum connections?) with nothing on my truck to match up to them. I capped them, not sure if I should have or not. But this was almost two years ago, and I've put 500+ miles on it since then with no issue. (It only gets about 500 miles a year). Not sure if it's related, but if the car gets overly warm (for instance when I'm plowing snow, if I don't take a break for a while) it doesn't want to idle. If it sits for 5 minutes then it idles fine again. This may be a separate issue, I'm not sure. But my first and largest concern is the flooding. And let me follow up by saying that I know virtually nothing about carburetors. This is the first vehicle I've owned that had one, other than TBI on my Suburban which doesn't really count. I've had dirt bikes, ATV, lawn mowers, etc... But never really worked on their carburetors. Outside of that, I'm fairly mechanically inclined and can figure most things out pretty easily. Carbs are just new to me, and at first glance they're fairly complicated. |
A little back story, and what I've replaced:
My grandfather bought the truck in 1989 with 115,000 miles on it. He put only about 15,000 miles on it over 20 years, and then it sat for about 8 years. I always loved the truck, and I jumped at the chance to inherit it around the spring of 2017. The only things he had done to it (according to his records) were suspension and exhaust related replacements (OEM), otherwise it was all stock and original. It would turn over, but it wouldn't start. I flushed both gas tanks, oil, brake fluid, coolant, and got a new (re-manufactured) carburetor. After bolting that carb on, it fired right up. Over the next few months due to either necessity or for tuning up, I replaced the following things related to fuel or spark system: Mechanical fuel pump & fuel filter spark plugs & wires air filter distributor cap & rotor ignition coil ignition module and one of the gas tanks that was badly rusted. Since then it's been running great. I've put several hundred miles on it since doing all that. I've done a couple short highway trips (~30 miles), several trips to the dump, plowed my road several times (1 mile per pass), and it always runs well other than this flooding issue, and the occasional hesitation to idle when it's hot. It's flooded when turned off hot a few times, but that I suspect to be more of a vapor lock / heat soak issue. I've noticed a couple times that gas will run out under the carb, above the carb spacer, after I shut it off hot. But most of the time it's fine. |
Almost all the info I can find about carbs flooding is related to flooding when warmed up. I don't understand why mine would have the opposite issue. My best guess is issues with the choke. If it was lean, it would just stall out, right? But it bogs down, and when I shift to neutral to rev it I get a bunch of darker smoke and then regain power. And only for the first 10 minutes or so.
I have the style of choke where a metal tube goes from the carb down towards the exhaust. How carefully does this need to be positioned? I tried to leave it just above the exhaust area without touching anything. |
If a carburetor will bolt on the intake the engine will start and run, though not necessarily very well, as you've discovered. The spark plugs are a good indicator of fuel mixture. What do they look like? The first thing to check is fuel pump pressure output. A mechanic's vacuum gauge, which you should already have, will test this. Also check for adequate volume, by running the fuel line output into a clean container. Idle the engine for thirty seconds or so. At least a pint should flow. Excessive pressure is not a substitute for volume. After the carburetor is installed on the engine the "wet height" of the fuel inside the bowl must be checked, as either too high or too low an average height will cause trouble. There is a general float height spec when rebuilding a caburetor, this is not the same thing, and is commonly overlooked. The carburetor is calibrated from the factory to operate with a specific fuel height within 1/32" in. When this is satisfactory the idle and idle mixture screws are trimmed out. While it is called the idle mixture and the idle circuit much or most driving is done just off idle and even slower speed cruising is done mostly on the idle circuit, or should be anyway, so it's important to get them set right. Again, there is a pre-adjustment bench setting e.g. "1.5 turns out" but is only a rough approximation so that the engine will start and run, and final adjustment is made on the engine. Take the time to study the carburetor manuals, check the specs, measure, and set everything up in order 1, 2,3, to the specs along the way, starting all the way back at the fuel tank and working forward. If you take your time and are thorough you'll only have to do it once. Mike's Carburetors <------- Setup tips, parts, troubleshooting, and free carburetor manuals. |
Thanks for the reply. I haven't really done any tuning or adjustment on my carburetor as it seemed to run perfectly fine for the most part when I hooked it up. Sounds like there's a good chance that's what I need to do then. If I recall correctly, I didn't have the flooding issue at first; it seemed to run perfect when I first replaced it so I just never bothered to at the time. So a pint in 30 seconds or so, and I believe with the mechanical fuel pump it should be around 4-6 psi? If anything it could have excessive pressure, but I've not had any issues with lack of fuel. As for the spark plug, it looked fairly normal when I last pulled it but it's been a few months, so I'll have to check again. It only gets used about once a month unless I need to plow.
I just took it to work this morning so I could top off the gas. Warmed it up for 10 minutes or so, it tried to flood on me 2 or 3 times at first, and then it was good for the rest of the trip. Pulled into the gas station and it idled, started back up and drove fine. Couple of stoplights, parking lot, perfect idle and takeoff. Never an issue once it's warm, which is what keeps throwing me off. I will do some reading on these manuals, and I'll plan to try and go through everything this weekend. Hope it gets out of the single digit temperatures! |
Even though it starts and runs or "seems" to run OK, that doesn't really mean anything. A carburetor is just a calibrated fuel leak and the engine will run reasonably well even when everything is way, way off from spec. This is one reason carburetors went away and were replaced by fuel injection. A lot of times too, the carburetor is blamed when something else is causing the trouble. Ignition, or ignition timing for example. For the final pass carburetor adjustments like idle mixture to be precise, everything else has to be In tune. |
Has it only been doing this since it got colder? Do you have a warm air source for the air cleaner like from the exhaust manifold? Sounds to me like it is icing up in the venturis. I have had that problem and if the choke works properly it isn't an issue normally as by the time it kicks down off high idle the carb is warm enough. But if you can get some warm air from the manifold thats the best way to cure that should that turn out to be the case..
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Well I didn't get the chance to go through everything this weekend as planned... Ended up in bed with a fever all weekend instead. But I did have to get up for an hour to plow, and at one point the truck was bogging down worse than normal. I pulled the filter and there was water inside, and even some water drops sitting on top of the throttle valve. I'm guessing I was driving too fast while plowing the powder, and was sucking it into the intake, because there was water in several areas in the engine bay. But it was behaving just the same from the water as it normally does when it bogs down, which I just assume is "flooding". Dried everything up and it was running fine again. Hopefully I can find time this week to take a closer look.
wdfp: as far as I can tell it's all 100% stock / OEM. So it has the air filter with the intake over the valve cover, with a heat riser in it. I didn't use the truck much during warm weather, but I don't recall having this issue in the warm weather at all. As I stated earlier it ran great when I first got it running (summer) I just didn't use it very much at that time. It's mostly only been needed in the winter, and I didn't have it fully tuned up and reliable until last winter. I took it to the dump a few times over this last summer, and I don't recall having this issue then either, now that I think about it. I would not be surprised if the issue was directly correlated with the cold weather. I do have the heat riser, but I'm not sure if it's working properly. A sticking heat riser could explain the intake not warming up quick enough, and/or could explain the post-shutdown flooding. I should probably take a closer look at that side of things as well. |
From reading your symptoms it sounds much more like a malfunctioning choke than a flood. Why do you say it is flooding? Are you smelling or seeing raw gas? |
MBDiagMan: Thanks for the reply. I was just guessing it was flooding, because it smokes a lot after it bogs down. But I don't necessarily smell gas, and I definitely don't see unburnt gas; it was just a guess and I could definitely be way off. I am fairly new to carburetors and chokes. It bogs down, have to shift into neutral and floor it for a minute and feather the gas pedal around WOT to get the RPMs back up. And it blows a bunch of dark smoke while I'm doing that, which tells me it's rich at that moment? The choke seems to come on when I start it cold, and then goes off a few minutes later (smokes a lot at first, but lighter smoke, and down to mostly clear exhaust once warmed up). It always starts right up and idles great. Other than that, I don't know how to tell. Maybe it's coming back on, or not turning off fully. There's 3 types of choke for this engine that I know of: electric, climatic and hot air. I have the hot air choke.
It seems to bog down when I push it too hard (flooring it, going up a hill, pushing too much snow) but it's definitely more susceptible to this when the engine is less hot. It essentially goes away once the exhaust and everything is up to temp. Maybe my choke's hot air feed line is not lined up correctly, or has a leak or something, making it less sensitive than it should be? I have had so little free time to mess with it the last couple weeks, and it doesn't get used much other than when a foot of snow drops overnight. Going to try to pull some plugs over the next day or two and see if they're still clean. |
Is the heat riser tube for the choke supposed to connect to something on the exhaust side...? If so, I bet that's my issue. I just read something about that, where someone's is rusted off and their choke is staying on. Mine is not rusty at all, but it's just free floating down near the exhaust, I assumed it was just supposed to suck in air nearby the exhaust which would go from cold to hot over time. But if it's supposed to connect directly to and suck air from in/against the manifold, it's not doing that. Which would cause the choke to stay on much longer than normal, until there was a ton of heat radiating off the exhaust. I will have to look around down there when I get home, see if there's an obvious spot for it to connect. When I replaced my carb, I just took pictures from every angle, and put everything back where it was originally on the carb; IIRC the repair manual was not very informative.
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Pull a spark plug and post a pic. Black smoke is excess fuel, lots of excess fuel. |
Originally Posted by MWB323
(Post 18490444)
Is the heat riser tube for the choke supposed to connect to something on the exhaust side...? If so, I bet that's my issue. I just read something about that, where someone's is rusted off and their choke is staying on. Mine is not rusty at all, but it's just free floating down near the exhaust, I assumed it was just supposed to suck in air nearby the exhaust which would go from cold to hot over time. But if it's supposed to connect directly to and suck air from in/against the manifold, it's not doing that. Which would cause the choke to stay on much longer than normal, until there was a ton of heat radiating off the exhaust. I will have to look around down there when I get home, see if there's an obvious spot for it to connect. When I replaced my carb, I just took pictures from every angle, and put everything back where it was originally on the carb; IIRC the repair manual was not very informative.
https://www.ford-trucks.com/forums/1...ric-choke.html |
I believe I've found the issue. Now I just need to figure out how to fix it.
As you can see in the picture below, the "chimney" to the hot air choke tube is not connected, and never was. Both connections had some dirt caked in them, so I scraped the openings clean, sprayed some carb cleaner through it and then sprayed some compressed air through (as best I could anyway, very difficult to reach area, no room to work). I definitely felt air coming out of one side when blown into the other, so it's not blocked now. Looks like I can connect the chimney to one side with no issue, but I believe there's supposed to be a vacuum hose of some kind connected to the other side that travels up to the air cleaner? Otherwise it will still work, but it can probably suck dust and crap into the carb? I need to figure out how to replace the other line then. This would definitely explain my issues. Essentially the choke never fully turned off so the car was always starved for air. If it idled long enough and got warm enough, it may turn off part or most of the way, but it never functioned as it should have. And it's been much worse in cooler weather. https://cimg3.ibsrv.net/gimg/www.for...134c7f7279.jpg |
tedster9: I was going out to pull a plug yesterday, but as soon as I found that issue I got distracted trying to clean out that area and further inspect it, forgot all about the plugs. I'll probably try to pull a plug still, but I'm pretty sure it's running rich due to the choke not operating correctly.
hooler1: I don't believe I have an electric assist choke. I don't have any wires or electronics around the carb or choke that I know of, just a couple vacuum lines. I have this carb with hot air choke: Tomco Ford Carburetor #2-708 It appears that this thread will tell me most of what I need to know now: https://www.ford-trucks.com/forums/8...-answered.html It has the same choke/carb as mine, with pictures of how things should be routed. I probably could have found that much faster if I had known it was the choke that was the issue. Now I'm anxious to get home from work and get this figured out! I do have something plugged into that spot on the carb, but either it's routed wrong or it's the wrong line altogether. I will have to go through all those connections this evening. |
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