Hey guys! New to the forum here. I'm more familiar with Toyota's but am starting to get my 1985 F-250 up and running. It's been in the family for a long time and I was given it a few years back and am finally getting it ready for daily driver use - but first I need to fix these things.

Here's my main problem. It's got a 460 with a 4180 carburetor. Last weekend I rebuilt the carb because it was literally spewing gas out of every single gasket and all over the intake manifold - which is NOT good. So spent last weekend taking it apart and cleaning it out and carefully scraping off EVERY gasket. Installed a new power valve, gaskets, accelerator pump, choke pull off diaphragm, float valves & fuel filter. I pumped the gas a couple times to make sure that gas was getting to the carburetor (pulled the gas line to it and had it empty into a bag to make sure) and then I hooked it up and it fired right up. Idled a little high so I turned the idle down and it idled for about 15 minutes beautifully - not a single hiccup. Then I tried to take it for a drive down the street and it felt sluggish - almost like it was out of gas when I was at high RPM's.

Took it home and shut it off, went to get 5 gallons of gas since it was showing on E (temp gauge is a little finicky) and just to be sure it had gas. I filled it up and went to start it up and it started great but wouldn't idle anymore and was backfiring out of the carburetor. Thinking this to be a timing issue I did advance the timing a tad and the problem went away - but here's the weird thing.

The truck starts right up, but now it won't idle. Then randomly it'll start to idle really high (idle screw does nothing). If you give it gas manually for about 2 minutes it will then idle but will fluctuate and die eventually. Anybody have any ideas as to what could be causing this? I know that the 4180 has the tamper proof mixture screws in the base plate but would you think they'd have them set for the truck to be so lean? I did drive the truck after I got it to idle really well and it was driving fine but would start to die when I would stop it and wasn't accelerating. What would cause the truck to run so lean?

And I should probably mention that before I rebuilt the carburetor the thing would NOT run very well at all. So I guess the fact it ran for a little bit was a step in the right direction...but a really big tease too.

Thanks in advance for reading my long post and all the help/guidance you can bring!

 

A few random thoughts, in no particular order and possibly of no particular value:

1) I've "rebuilt" a few carburetors myself over the years, typically with some improvement, so I'd pat myself on the back for a job well done. In practice, though, all I'd really done was give 'em a good cleaning, new gaskets, and set the float level. Last year, while chasing down an off-idle stumble on my '84 351W, I finally bit the bullet and installed a professionally rebuilt carb. Oy veh! What a difference. I offer this to help avoid the mindset that since you've already tinkered with the carb, the problem must lay elsewhere. There may still be other issues than just the carb, but at least keep it in mind if nothing else seems to help.

2) Any idea how long the truck sat? Even though you've already added some fuel, I'd be tempted to drain it all and start with fresh stuff. Gasoline more than a few months old? The volatile, easily ignited portion evaporates. You're left with stuff that looks and smells like gasoline, but doesn't ignite reliably in the engine.

3) Why was the truck parked? If not for an engine issue, then it should still run again with fresh fuel and minimal adjustments. Be very wary of changing the timing, adjusting this, and tweaking that, at least until it runs again somewhat consistently. It's super easy to induce a new problem while trying to correct something else. Before you know, you've made things worse trying too many things at once. I do not care to discuss how I learned this.

4) Run some basic diagnostics before digging too deeply. For example, verify fuel pump pressure AND volume against factory specs. Make sure you've got a healthy blue spark at all cylinders. A weak spark could be caused by something as simple as carbon tracking at the distributor cap, etc. Give all vacuum lines a good visual inspection in case you've got some leaks.

FWIW. Keep us posted.

 

Hey @kr98664 thanks for the response! Here's some more info on the situation:

1) I have never rebuilt a 4 barrel carburetor before but did a TON of research on this carburetor before I did. I’ve done the 2 barrels on Toyotas and the simple dirt bike carburetors but this one was probably the worst I’d ever seen. I just cleaned it as thoroughly as I could, refreshed all the gaskets and vacuum diaphragms and put it back together. I’m not 100% positive that I didn’t do something wrong, but I’m having trouble figuring if I did make a mistake. If I can’t seem to figure it out I have another carburetor I can throw on and see if it makes any difference. I’m just trying to keep this truck as original as possible.

2) Yeah I do! So a little story on the truck. The truck has been in the family since 87. It was a secondary vehicle at my family’s cabin in Northern Arizona where it was driven sparingly. Maybe 1000 miles a year IF that. Mainly just used for going to town and back and small chores here and there. About 5 years ago my dad gave me the truck, and as a college kid I couldn’t really afford to keep it going. I would try to drive it as often as I could, but as a secondary vehicle for me too it just sat on the backburner waiting it’s turn. It was last driven more than around the block probably 7 or 8 months ago. My brother had been using it to pick up building supplies from Home Depot. It would always need a little bit of starting fluid to start or a jump. I finally drove it back to my house where it sat waiting it’s turn some more. Drove relatively well the whole way home.

3) Guess I included the answer for both questions up there. It just hasn’t been used very much but I have recently been working to get it to be reliable so it can be ready for daily driver duty. The timing has seemed to always be off on it, so I just figured it was time to fix that. Honestly with the carburetor rebuilt and the timing advanced it has never run/started as well as it has in the whole time I’ve owned it – but now it just won’t idle. And hey don’t worry, we all have stories like that!

4) I’m sure I’ve got some vacuum leaks which will need to be addressed as well. Do you know where I could get a vacuum diagram for this truck? I’ll probably just go ahead and start replacing all the lines. I did notice that the carbon box on the passenger side fender is cracked in half…are those necessary?

If I can’t get this figured out, I have a buddy who is a certified Ford mechanic and he said he can help me figure it out, but I’d like to save him a trip and figure this out myself, I’ve usually always been able to!

 

Also, here's a before and after picture of the carburetor. I know it's not perfect, but it sure came a long way!

 

i guess thats like a Holley?
I see the big screws for the float adjustment...does it have sight plugs you can remove to adjust the float levels?
(not saying thats your problem but it should be checked)

 

Yeah it's basically a Holley 4160 but it has vent tubes on the top of the float bowls and the mixture screws are in the baseplate and covered with lead plugs so they're tamper proof. It was manufactured by Holley for Ford in the 80's.

And yes I did do that adjustment on the primary float bowl. I can't seem to get my short arms across the motor when it's running to get to the secondaries however. When I rebuilt it I followed the instructions to get the float adjustment as close as I could and then planned on adjusting it when it was running. Haven't done that yet as I have just been struggling to keep it idling.

 

You should not be messing with the adjustment first. The first thing you should do is put a rag under the pass side of the carb and pull the site plugs. If gas pours out it's too high. If you do not see any gas press down on the fender and see if it sloshes out. If it does, that is about right. If the rear is too high, you will need to set it lower and then just wait till you run it hard some and then check it again. If you sit there in the driveway and let it idle, it will take a long time for the rear bowl to lower itself, the rear barrels use just a little fuel at idle.

And you should have cut the idle screws out of the baseplate. The carb rebuild kit instructions should have told you how to take a hacksaw and cut away the plugs so you can take the screws out and clean those passages. They get gunked up like everything else. Ford was trying to pass emissions testing when they came up with that idea. You really need to get to those screws so you can adjust them. It would be worth it to take the carb back off, take the baseplate off, and try to open them up. Hopefully since the gasket is new it will not stick and you can get it apart.

Some of these carbs had 4 corner idle adjustments with two in the rear also.

 

I did the adjustment on the primary side as it was running. Pulled the sight plug and adjusted the float needle so that you could just barely see it in the bowl underneath the sight plug. Was that incorrect?

Thanks for the info on the mixture screws! I'll turn them into flatheads and then pull them out and clean those too. I'll let you guys know what I can find.

 

Yes, that adjustment sounds excellent. You can do that to the rear also if it's low. Like I said if it's high, I would just arbitrarily turn the adjustment down about a turn to make it low, and then wait till you drive it some and then come back and pull the site plug, hopefully it's low. If it's low, do the same thing you did to the front and bring it slowly up to just below the hole.

 

I stopped reading here: “It was idling real high so I turned the idle down.”

My answer: That’s exactly what it’s supposed to do... until it warms up enough to come off of the fast idle cam.

The choke and the fast idle cam work together to warm the big block up. Mine idles up to 1700 off the bat and it might be about 15 minutes just idling (or a good trip around the block) before it will kick all the way down to 850.

So if you set the idle speed on a cold carb... well then it’s gonna go to zero as soon as it warms up.

 

Good information here. Agree instructions should have told how to remove the plugs but doubt they do.

Here’s what that looks like. A little Dremel tool with a cut-off wheel works nicely to cut a channel back far enough to get behind the plugs and drive them out with a flat tip scew driver.




Good question too about the secondary throttle stop settings. Since the primary idle mix screws are plugged I seriously doubt the secondaries have any adjustment screws. If this is the case I’d set the secondary throttle stop at zero while you have it back off and go from there with your fine tuning.

To make life even more difficult Ford used Allen headed bolts so you’ll need something like a 3/32” Allen wrench to turn the idle mixture screws after you finally manage to get the plugs out.

!!! But the first thing you want to do is count how many turns of the idle mixture screw it takes to gently seat them all the way IN... before you take them out. Then you’ll have a benchmark for putting it back together.

 

Don't mess with the Secondary screw stop unless you can't get the carb to idle down. The secondary's should not be fully closed but open just a hair so the fuel in the secondary bowl will get used and refresh and prevent it from going stale.... Exhaust all other options first before messing with the secondary throttle stop.

 

I agree. I have really messed things up before turning that screw. Sometimes you have to, but only as a last resort.

 

I don’t know why but i’m 2 for 2 on just setting the secondaries at zero. Today’s gas? Sloppy throttle shafts? Who knows. But since you have to take the carb off to even make an adjustment, Most late model 4180’s (not the ones with 4 corner idle) I’ve seen have had the stop lever on the throttle shaft bent so the secondary will close all the way. It’s the “I ain’t talking that thing off again” adjustment.

100% agree Matthew that it’s not perfect but I’ve got a lot of real world years and miles behind me and I’m happy with my tune. And 100% agree the gas in the secondary bowl will go stale so that’s why I heartily recommend exercising the secondaries from time to time to keep it limber and the gas fresh.

Yo Ho and long live the 460 and 4180!

 

Sometimes you just need to bite the bullet and close them up and worn throttles can certainly lead to having to close up the secondary's. But do exhaust all other options first before doing so, it should be the last resort. And really if you do not need to retain the 4180 for emissions it is best to just put it on the shelf and install a 4160.