What the heck is this?

Plumbed new fuel line to the carb, got the old girl started, then noticed what’s in the picture.  What the heck is that supposed to be?  I know the EGR is right near it but it’s jagged like it broke off and it has threads on one side.  It almost has to be part of the smog setup, which was already gone when I got the truck. It’s an 81 F100 with the 4.9.  

that is what is left of the screw in check valve for the air coming from the air pump/thermactor system.

That makes sense. I have a replacement carb spacer coming and that was blocked off on the replacement.  Oh, what fun. The previous owner had jammed a freakin piece of string in there to seal it so he could drive it to where it was parked in the field I guess. Ran pretty good until I took the string out

oh yeah. that is a major vacuum leak. a 3/4" npt pipe plug will suffice till the proper parts get sourced (until) haha

I actually found a direct replacement on eBay for 50 bucks. Should be here Wednesday.  I’m honestly stunned that ran so well with that rope stuck in it. I’m glad it didn’t get sucked in.

think of it as an impromptu filter. it should run much better with the new part installed.
there is one point of caution. the fact that it has rusted away says that corrosion is a real issue on your truck. the egr/air carb spacer is aluminum while the broken part is steel. these are known for corroding at the threads and when removing the broken part use plenty of penetrating oil and re spray as soon as it moves then again at 90 degrees. work it back and forth a bit to keep from stripping the aluminum threads.

yeah its pretty rusty.  Im going to have to do a lot of rust repair on the panels.  The frame looks pretty good though, with surface rust being the main thing on that.  I scored this thing for 400 bucks, though, and the engine runs so I consider that a win.  Ill be taking the bed off to get at pretty much everything so I can get the rust off and use a ton of POR 15.  Gonna change out the gas tank, fuel lines, brake lines, service the rear end and change the gearing (has 2.47 gears), new bearings for the axles, new shocks, brake lines..... well, everything really.  This is really my project to learn on so I can teach my son when he gets old enough.

FYI, my experience on POR15 is that the first coat goes on great, but the 2nd coat of base is hard to do because you can't tell the shiny wet stuff you are putting on from the shiny 1st coat.  So just do your best to slather everything with POR15.

However, I don't use the POR15 top coat.  You do need a top coat to keep the UV from turning the base coat white, but while the POR15 base coat is sticky any top coat will stick to it.  So I bathe the thing in POR15 and while it is sticky spray it with whatever top coat I want.  So much easier than trying to brush on their top coat, and so much faster.  Otherwise the base coat starts to set up, you leave brush marks, etc.

don't be in too much of a hurry to replace the 2.47 gear. look into the gear ratios of the transmission first. I imagine that the door tag says that you should have 195 or 205 sized tires also. all of these together are a system. if you change one thing then the whole is affected. if you plan to install larger tires then compensating with the gear is a good consideration. but if you consider the overdrive of fourth try to keep the rpm at 70 no more than 2k rpm.

Thanks for the tip Gary.  I’ll be doing that for sure. And Mat, I might be doing a ZF5 swap since the top loader that’s in there is bad. Got that info from the last owner as I was buying it but at 400 bucks, hey, what are you gonna do? I figure I’d be better off going ahead and changing it out with a better one.  I’ve located one at a local pick and pull out of a brick nose that’s on a 4.9 2wd like mine. Plan on yanking the clutch master and slave cylinder, trans crossmember, trans, and flywheel.  I have a bead on an 84 clutch and brake pedal assembly to switch over to the hydraulic clutch and I plan on buying the firewall reinforcement panel from bronco graveyard.  After that, I’ll reevaluate the gearing in the rear end.  Might do a posi diff too unless you guys on here have a better option?

As Mat said drive the truck with the 2.47 rear gear to see how it goes even with the ZF5.
My 81 F100 parts truck came with a SOD 3sp OD and a 2.47 rear gear.
I never drove it, no motor and was rolled over, but my 81 F100 flare side has a NP435 granny 4sp, Advance over drive and a 2.75 rear gear and on the high way at 70 MPH is 1800 RPM.
1800 is the sweet spot for power on the 300 motors.
Oh tire size is 235 / 75 / 15 and is a 4x2 truck.
Dave ----

Oh yeah I might do that then. I just looked up the ratios for the ZF5 and with the tires I have, at 80 mph and 2.47 gears, I’d be sitting at 1800 RPM. I like that combo. See? That’s why I’m here. So much helpful information and people. Thank you.

I also have a 2.47 on the shelf from a conversion that I did. it is an 8.8 size. otherwise, I would put it in my f100. but it is a 9" and has a 2.75. my next best adjustment for it will possibly be 235/75 size tires. however the tires are nearly new, and I will probably put this one up for sale before too long. I'm wanting to build a 4wd and this one is almost completed as a driver. I'm driving it daily and almost have 3k miles on the new engine.