The mixture adjustment needle valves primarily have an effect on idle and low speed while the main jets and power valve have most effects on midrange and high speed. I've never seen a need to adjust mixture screws seasonally. Once in a great while due to deposits in the passages possibly.

 

I've always done it seasonally.......but that's just me. There is quite a difference in air density when it's 100+ degrees outside in the summer and when we drop down in the 20-30 degree range in winter.

 

I can't see why you can't put a 4160 on and pass emissions
if cfm size is the same it should be as clean or cleaner than a 4180
I can't imagine an inspctor or very few mechanics that can visually tell the difference between the two

 

Thanks to Jim for providing this information. Just wanted to share it with ya'll.

On a side note, I rebuilt my 4180 with a kit from NAPA. Unfortunatly, the problems continue. It's still dumping fuel and causing visible backfires out the exhaust. I've been out of work for a few months now so I've run out of finances to play around with. Looks like I may have to sell ol' blue due to a faulty carb

 

Have you checked your timing? It might be the fact that your vacuum advance isn't advancing at all. If you rebuilt your carb and it's still acting up, then it's not the carb.

 

It could be. I've put a new thermal vaccum switch in. The one that runs from the distributor to the intake manifold but it didn't make any difference. I'm going to recheck the timing but with a balancer that's 20+ years old it's hard to tell how accurate it really is.

 

Don't do it, I'd hate to see you sell your truck!
But maybe you're not in love w/ yours like I am.

It must be something really simple that we've overlooked.
Would you try posting a thread link to the fuel delivery board?
Maybe someone else will chime in w/ some constructive ideas.

Are you sure the floats are ok and the heights are set correctly? (not to doubt)
That the fuel pressure regulator is working?
Perhaps the return line from the pump to the tank is restricted, pinched or something. (but you'd likely see evidence of this when checking float height above idle) You might try connecting another hose from the return at the pump to a jug and seeing what happens. Either it clears up while you're testing it =bad return, or the carb overflows= bad regulator, or....dunno.

The damper could have spun, but I doubt it. Pull the #1 plug and check TDC against what's indicated on the timing marks.

This is my second carb dumbfoundness this week, at least you're providing real information.
Hate to hear you've spent the $ and time on a rebuild w/ no joy.
Work is real sketchy for me too, (I'm in the building trades) so I know just how you feel.... That's why I'm spending/wasting so much time online.

As I said to the guy from Indiana, I'm running out of ideas.

 

I do love both my trucks but I don't have much more cash to just throw at ol' blue. A friend of mine, who is really familiar with Holley carbs, assisted me with the rebuild and as we were working on it we couldn't believe how clean it was inside. I contacted the previous owner's mechanic (who sold me the truck) and he said that he had personally rebuilt that carb 4 times and that it would work okay for about a week and it would act up again. I'm guessing that there is just some internal problem that is allowing way too much fuel to pass through. I did verify that the floats were in good condition and that they seemed to be adjusted properly. I haven't done any testing on the regulator or return.........I'll have to look into that. I do have some credit at the local pick-n-pull that I could use but I just went out there and there was only one truck equipped with a 4 barrel that still had the carb on it and it didn't look the same as mine. It was a small block though so that could explain why it wasn't the same.

Thanks for the help so far Jim, you've given plenty of good ideas. Unless the local trucking market picks up I may end up having to sell it regardless of the carb situation.

 

Did you ever check the power valve for a blown diaphram? To check it, remove the main metering block and suck on the end of the power valve not screwed into the metering block. If it passes air through it then the diaphram is ruptured and the power valve must be replaced. Also, the 4180 power valve uses a gasket with 3 prongs pointing inward. Power valve gaskets for other model carburetors use plain circular gaskets which will not seal in a 4180. You'll have to remove the power valve from the metering block to see if the correct gasket is installed. Click this link: http://www.autozone.com/az/cds/en_us...rInfoPages.htm and then click on Fig. 31 to see an exploded view of a 4180.

 

You wouldn't by chance have another carb to stick on there just to try to make sure it's the problem? The old mechanic said it would run good for a about a week, did it run good after your rebuild and then return to rich? Piffery is right about those power valves, they are quite particluar, I always get worried when I replace em b/c it seems like everytime I do one, it's some new "updated" style. Anyways I had a guy come into the shop with his truck just barely running, belching smoke on which I had rebuilt the carb about a half a year ago (390 w/ factory 4-barrel) somehow the screw that adjusted the accelerator pump had worked it's way down and was basically holding it 3/4 the way open. But I'm sure you had adjusted that during the rebuild or toyed with it while trying to get it to run right.

On a side note, I don't know if this is true since I'm in NE, but somebody had told me if you went in for an emissions test with an older vehicle and it "flunked" all you had to do was make a certain % of improvement. If that were true I'd trade up for the 4160 u wanted. Plus I'll never understand the gov. but why would it matter what carb you had on if you pass ur emissions? If it's up to par whatta they care?

 

OK,
If the return line were restricted to where it couldn't handle the volume from the pump I'd think that would cause a problem. If you have access to a low pressure fuel gauge I'd be interested to see what it reads through the RPM range (between the pump and the carb). Thinking it should always be less than 10 psig, or it's likely to overwhelm the floats.
Do you have any raw fuel in the bowl vent hoses?
*Idea*
Is there vacuum @ the vent hoses, and how much? Could fuel be getting sucked past the float valve. That wouldn't occur when the sight plug was out. I don't know squat about how the charcoal canisters purge, but try disconnecting the bowl vents from them and see what happens.

Seems like this has been a recurring problem w/ this truck. I had no idea it was the subject of multiple rebuilds. But if it would clear up for a week and then go bad, there's got to be another problem causing the carb to screw up. (and has the PO's mechanic stumped too)


@ 5.6 mpg there's something causing it to get too much fuel.....obviously. I thought my 7 city/ 11 Hwy sucked, but it's always been this way since new. I assume you checked the EGR and plate for function when the carb was off. I'm still trying to think of things other than timing that could affect the fuel delivery.
Man, this is frustrating........

 

Well fellas, just wanted to update my thread here. I wound up selling ol' blue.......but the guy that bought her has lots of experience maintaining Ford trucks so I'm sure she'll treat him well. I just wanted to say thank you to you guys. As always ya'll have been very helpful.

 

Thanks for the update Breech!
Good luck with finding some steady work.

 

Thanks Jim. I'm sure I'll find one thing or another. It's hard times for a lot of folks right now.