Cured: Smell of Gas and Stumble at tip-in

[KevinCowTown]

First post...

I recently bought a 1985 Sierra Classic K2500, 5.7L. I drove this same truck brand new, back in the day, and wanted to recapture my youth. Sort of. The truck I drove back then was a freaking beast with a flat deck that was set up for seismic work in the bush. This one has power windows and velour seats.

Anyway, it had a bit of a stumble tipping in off idle and I could smell that it was burning really rich. Since I'd moved it from Cambridge (Ontario, elevation 1,000') to Calgary (Alberta, elevation 3,500') I assumed the Rochester needed it's idle mixture adjusted.

The idle mixture "screws", however, are goofy shaped things that defied my attempts to put a tool on them - bit of a road block - but while screwing around with that I busted one of the vacuum hoses that goes from EGR to Air Cleaner assembly so I bought some 5/32" line to fix that.

Well, every vacuum line you pull on a 30-year old vehicle reveals another vacuum line or fitting that's cracked or swollen so... long story short - there's nearly 25' of vacuum lines under the hood of that thing and I replaced all of them (except three from the fuel vapor canister).

Them oldy-day peoples sure were ingenious! They used vacuum like we use computers. Vacuum lines everywhere.

Good news is: truck runs great now. Throttle response is crisp and smooth. No flat spot at all. And that was a lot easier than rebuilding the carb.

Couple issues, two tips and some questions:

The first issue was that there are two temperature-vacuum switches, one screwed into the intake manifold one into the thermostat housing. Each of those has a... I believe it's called a "vacuum switch harness connector"

It's a "manifold" that connects the 3 or 4 vacuum outlets on the temperature switch to vacuum fittings on the carb and stuff. Seems like you can't buy those harnesses. Since both of these were swollen and cracked and since it looked like each of the vacuum ports went straight through (none of them were interconnected), I just connected each of the vacuum ports on the switch directly to the vacuum lines (bypassed the "harness connector").


And that seems to work so tip #1 is: you can bypass that goofy bit of rubber hosery (tho I'm a tiny bit bummed because I was hoping to make this truck look factory original, anybody got NOS on those harnesses? - email me) Tip 2 is: replace one vacuum line at a time... that sh*t is confusing!

The second issue was that the bracket which mounts the vacuum actuator to the EFE (Early Fuel Evaporator) on the passenger side exhaust manifold was busted. Both EFE valve and Actuator still work but the bracket is busted. LMC truck sells that thing but it's $300 so I think a trip to the junk yard is warranted. But before somebody tells me "you don't need that emissions junk, just cut it off"... hey, that may be true, maybe especially in California or Texas but up here it gets brass-monkey cold. Alaska cold, colder than that sometimes, like... Siberia cold and I think this EFE thing helps warm the engine up.

So that made me wonder... as I understand it, the EFE forces exhaust gas through a channel in the intake manifold under the carburetor to warm it up, is there a way to make that work with headers? Also, the heat riser on the air cleaner assembly draws warm air from around the exhaust manifold and pulls it into the air cleaner. Has anybody made a shroud to do the same thing around their headers?

How do you people with headers deal with the cold? Just idle her up for 10 or 15 minutes? Maybe I should rephrase that... how do you people who live East of Salt Lake, West of Chicago and North of Minneapolis deal with the cold? (Sorry Tennessee and others, no disrespect intended, I know it snows there - sometimes - but it ain't "cold")

[geezer#99]

Here's an 83 vac diagram. 84 and 85 are similiar.
http://67-72chevytrucks.com/vboard/s...d.php?t=215546
With headers kinda hard to divert heat from the exhaust under the intake. You can make a heat stove off the pipes to get heat to the air cleaner or just use the method I describe in this other thread. I lived in Alberta for 55 years so know all about cold weather and trying to run modified motors.
http://67-72chevytrucks.com/vboard/s...d.php?t=606901

And they make a tool to adjust your carb with.
http://quadrajetparts.com/rochester-...ool-p-371.html

[motornut]

Hi Welcome aboard
yup those vac lines can sure make or break a car running well
I remove the heat valve on the manifold,stove pipe
bypass other stuff I can,lots do and still run all winter

[KevinCowTown]

Yeah? I lived in Kanata a couple years. Saw some weather there too.

Come to think of it, I put headers on my '74 Olds and she ran OK in the winter.

Thanks.

[motornut]

Originally Posted by KevinCowTown

Yeah? I lived in Kanata a couple years. Saw some weather there too.

Come to think of it, I put headers on my '74 Olds and she ran OK in the winter.

Thanks.

born and raised here,Hows your weather now? hear its dropping again....
we hit +8 thursday....-10 sun. lol +1 monday.

[KevinCowTown]

It's been bouncing between cold and... bitterly cold

Tomorrow's warmer (-5) and it might be 0 on Thursday. Might can wash my car again!