I took my 79 F250 to the lake today for the first time with the boat in tow and I was upset with the lack of towing power this truck had. I've always heard that the big six was a good pulling/work truck engine that's why I bought it. on the way back home it developed an exhaust leak which i later found was a broken pipe coming from the egr? valve and leading to the smog/a.i.r pump ? exhaust was leaking all the time from this fitting I want to strip all the emissions stuff is it okay to just take everything off (egr,pump and hoses) and plug the ports and just run a straight carb. I know its against the emissions rules but performance wise will it hurt or run better with all this junk outta the way. the smog pump had no belt on it when I bought the truck.
the exhaust manifold also has some kinda butterfly valve that opens when the exhaust pressure increases and there is a small hole in the manifold directly across from the butterfly lever/return spring that is leaking exhaust I guess the hole is for the shaft for this valve but I can't tell if it had a threaded plug or was a pressed in cap.

I am also rebuilding the carb and doing a complete tune up on her while I got her down.

sorry for being so long winded but I was trying to be detailed i can also up load pics if it helps. any help would be greatly apprecciated

Thanks Lynn

 

If you simply remove the EGR equipment, the motor will run lean and the timing curve will be over-advanced. You'd have to run richer jets in the carburetor and install an adjustable vacuum advance. It's not worth the trouble; there are no gains to be seen by removing EGR in the first place.

I think the butterfly plate on the exhaust manifold you're talking about is the heat riser for the intake manifold. There should be a bimetallic spring underneath that opens and closes the plate based on temperature, kind of like a choke.

 

I'd Check for exaust restriction. Plugged Catalytic converter etc...

When mine plugged up a few years ago, it blew the Thermactor air intake manifold, and leaked exaust through the spark plugs.

 

so your saying i need to hook the pump back up as well ? what about the adjustable vac advance I thought this truck has vac advance at least there is a vac line going to the distributor.

I thing it might have an exhaust restriction too because it blew the fitting going from the egr to the pump apart. plus it just happened today I've driven the truck about 600 miles since I got it and it climbed hills fine but I wasn't towing, but this morning " it wouldn't pull a fart out of a pillow case!"

i am going to need some more help on this emission stuff because this truck has plugged and stray vac lines every where I was hoping i could get by on just doing a way with the emissions stuff because its been so butchered

 

The 300 will pull anything you put behind it. It might not be fast and it might not like it, but it will pull - or explode trying.
My advice is to go over all the emission stuff and correct everything you can. If I were you I would re-do the whole exhaust system too (a pain in the butt I know but it sounds like you need it). Would be a good time to upgrade to EFI manifolds or headers, a three way cat and a turbo muffler. I bet if you fix the emissions, exhaust and do a tune up you will see a big difference.

If I remember correctly, you have 3.55 gear ratio, right? What size tires do you have? Sounds like you might want to upgrade to a 4.10 gear. Yours revs will be around 3,000 at 70 mph though with that C6 tranny.

 

its a waste of time to remove that stuff and if the belt for the smog pump is gone replace it you will probably see some gains.

i say remove or replace the catalytic converter depending on the mileage its possible that caused the exhaust leak as well and back pressure that high will severely hurt the performance.

also if youre vac lines are plugged chances are they are leaking as well this is a problem that can cause poor performance

 

6cylbill, yeah it has 3.54 dana 44 front and dana 60 rear but it has np435 tranny with a 205 transfer case. to do a gear change would be about 400-500 bucks that is doing both diffs because they are around 200 bucks a set. I have found several 351 windsors's & clevland's for 200-300 bucks and I would probably do an engine swap before I would change the gears although most people said a 351 won't out pull a 300 I6 which I believe is true. I don't theing the gears are holding me back I think it is an exhaust/emissions problem. I mean my 01 nissan frontier with a v6 and automatic will out pull this truck right now, no joke. so somethings bad wrong somwhere

9.ford.5, I am gonna fix as much of the emissions stuff as I can today and cut the cat out of the exhaust run a piece of flex pipe to the muffler as temp test , the truck has fairly new exhaust from the cat back.

anyone know where i can find a emissions system diagram ?

 

the fitting that blew apart was the air pump check valve.

 

A 351 will outpull a 300 with ease. They have the same low end grunt, but the 351 keeps going where the 300 dies off. But you do pay for it in fuel.

You're on the right track. Fix the emissions and exhaust. I thought you said you had a hole in your manifold? If so, wouldn't it be imperitive you got that fixed? Do you have the EFI manifolds or the one single carb'd manifold log?

I pulled more than six thousand with my 300.. I didn't take it far, just around the block a few times to get some experience stopping / taking off, etc. My initial reaction was disapointment. It's kind of funny because I was complaining to the guys on here my truck had to rev to 2,000 to get the load moving. Mine is an automatic so that's normal. I think your problem is worse than just missperception though.

 

Ported vacuum runs from a ported vacuum source on the carburetor to a ported vacuum switch on the thermostat housing. The other side of the switch runs to the EGR valve.

The diverter valve for the smog pump runs to manifold vacuum.

Posting a picture of your engine could help, as it's hit-or-miss as to what emissions equipment would have been on the engine at that time.

 

thanks for all your help guys, I'm gonna make this ole girl run good again if nothing else just to spite my old man who thought I was crazy for buying that old of a truck
he told me the other day I ought to just get rid of it. but I like the ole truck its fun just driving it around and I love the simplicity of it except for the emissions ha!

6cyl, I have a log carb manifold and yes its leaking out a hole that is for a shaft that a butterfly type heat riser?????? is in. but the butterfly/heat riser is cast into the exhaust manifold not bolted on . it must have been a pressed cap kinda like a freeze plug in this hole for the shaft. the hole has to be there other wise there is no way to put the shaft through the manifold. I'll post a pic later.

fmc, thanks for the vac set up but its several more vac lines going to a canister that looks kinda like an old square lantern battery and some going to the air cleaner housing. it DOES NOT have the air injection manifold. I have it all tore apart right now but I'll make a mock assembly of it from smog pump back and post pics, might give you a better idea of what I got. thanks again for steering me in the right direction

I am ordering a complete 1979 Ford Truck shop manual set on cd-rom off of eBay today its only 30 bucks and I'll spend that much in alcohol trying figure some of this out Ha!

 

Good luck smoke!! Keep us updated please and be sure to post pictures!

By the way, when you get the time and money, I would suggest looking into a good set of headers or EFI manifolds. AbandondedBronco did this to his Carb'd 300. He had the log manifold too but switched to EFI manifolds. He runs a high flow cat and turbo muffler. The whole thing would be relatively cheap and grant you usable power. Plus it sounds good too.

 

You have a bit of a project ahead of you but nothing insurmountable. Your truck is 30 years old and like so many of them it was unfortunately neglected and abused. Get all the systems properly functioning and you are good to go. I pulled a 4 horse sometimes fully loaded with no problem...it wasn't particularly fast but it got down the road just fine. Brakes are a major concern pulling loads...make sure the trailer has them and they are working properly.

 

here are some pics of the system on my truck and the hole in the exhaust manifold

 

cut the converter off earlier and it was blown straight through I don't know if the guts went into the muffler or not but I'm gonna replace it anyway. I'm gonna run her straight piped for a road test when I get the emissions back together and the carb rebuilt