Pillowthread

So, I was under the hood the other day, trying to figure out why my truck wouldn't start after sitting in a couple days of hard rain, when another potential issue made itself apparent...

It was about 9PM when I finally got the truck running after a jump--and this starting issue is interesting in itself because I have a brand new battery and a good alternator--and was staring at my now-running engine when I notice through the heat shield that my exhaust manifold is glowing orange. Not white-hot orange, just orange-red. At this point the truck had been running for about 10-15 minutes and had not been driven at all. It was just sitting there, idling the entire time.

I'm wondering if this is normal? I tend to think not, but I don't know much about these trucks. I've had my '79 for just a few months, coming from a WRX wagon. Now, I've seen downpipes on turbocharged engines glow orange like that, but only after being run quite hard.

Otherwise, the truck generally runs very well: carb is good, new hoses, new cap/rotor/filters/plugs/wires. Timing is good. The one thing I haven't touched is the exhaust, and it needs some attention...the muffler is intact, but filled with loose rust that I can hear when I shake it by hand. Fire will shoot out of my tailpipe and it will backfire like something nasty if I get on it hard, so I just drive it very well.

I get about 15 miles to the gallon on 31" tires, and it does run pig rich. Is this phenomenon I'm experiencing with the glowing orange manifold normal-ish?...is it related to my $h1tty, obviously-needs-replacing exhaust, or not?

creswellhick

thats not normal could be a bad fuel air mixture on the carb could be alot of things play with the carb recheck the timing its not normal

xxxtreme22r

A glowing manifold is either one of two things, raw fuel being burnt in the exhaust (due to either running rich, or timing way off) or it can also be caused by a clogged cat.

BoostedRNR

Timing could be your problem too

Team420

yup +1 to the above... timing is off, or cat is clogged

Pillowthread

Interesting...I don't have a cat on there, and the timing was re-set as of a month ago...I guess it could've jumped a tooth in the last 2000 miles of easy-going, exclusively on-road driving?

BoostedRNR

I don't remember exactly on if you're supposed to unhook a vacuum advance line going to the distributor or not on the 22r, when timing it. Did you adjust it following the FSM directions?

xxxtreme22r

Yes you have to remove and block off both vacuum lines on the distributor to set the timing on the carb.
Then set at 0 degrees. With idle no more then 700-750rpm.

Lycanistic

I would have to say its both, the rich fuel and a semi-clogged exhaust. Restriction to exhaust is terrible for an engine, although, a certain level of backpressure is needed to run smoothly, too much or too little can cook exhaust valves. The extra fuel is compounding a slight restiction....i.e. rust+carbon.....and superheating the metal. Just alot easier to see at night because of the lack of ambient lighting.

Pillowthread

I assume you mean 20R...and here's where my lack of knowledge is displayed: I don't have a copy of the FSM, and, due to a time crunch, took the truck in to have the timing checked...They said they adjusted it, and it was good to go and I took them at their word.

So, any links as to where I could read up on this stuff? If there is a blockage in the exhaust I don't know where it could be, as I'm running a straight pipe back to a rusted-out universal muffler. I know I need to learn a lot about carb tuning in general as well...

Just went out to look at it again, after being fully warmed up, and I can see the red-orange glow extending a good foot-and-a-half back from the reducer...backed the idle mixture screw about a half-turn out to see if it makes a difference...we'll see in about 10 minutes...

This is really weird, cause the truck runs like a champ! Solid 850 rpm at idle all day long...

xxxtreme22r

22r/20r not much different in operation. However, I wanna say the timing is different. 5 BTDC versus the 85+ model 22r 0 BTDC. Forgot we were talking 79 truck for a second.

I wouldn't mess with that idle mixture screw on the carb if I were you though. If the carb is dumping an excessive amount of fuel, it won't help anyway.

Are you getting any black smoke out of the exhaust?

You edited the original post, so I don't know what I missed from the original post. Backfiring through the exhaust is not a good thing. I wonder if the balancer shifted on you and what appears to be good timing really isn't. But I am unsure if the 20r balancer is a two piece one like the 22r's are.

Also bad baffles in a muffler can cause exhaust restrictions.

Also what was causing a hard start issue and how did you fix it?

Pillowthread

God-d@mn...my name should be Noobthread...so the manifold is not glowing as much now, after backing the mixture screw out a half-turn. Thinking about things a little bit more, I haven't adjusted the carb since I got back to Illinois, after purchasing/tuning the truck in Colorado at around 5000 ft...I'd bet a 5000-ft decrease in elevation might make it run rich?

Wait...lower elevation=higher density air="more" air per given unit of fuel=leaner mixture, yes? So if anything I should be running leaner...or is my logic off?

Pillowthread

Yup, black smoke on start-up, visible soot trail on snow...but no smoke when warmed up.

I edited my OP only for grammatical reasons...

xxxtreme22r

Your right a decrease in elevation will cause a leaner mixture. Which too lean will cause an engine to run really hot. Backing the mixture screw out will richen the fuel. Also it will mess with the timing on the engine as well.

SOrry forgot to ask, when you moved that mixture screw, did your idle change? It should have.

Pillowthread

Now we're getting somewhere...I figured that, if anything, a leaner mixture would have caused the glowing manifold I was seeing...which is gone now, by the way, after another 15 minutes or so of sitting at idle. I'm really perplexed by this now...

The idle did not perceptibly change when I moved the screw...which only serves to confirm that I need to re-build my carb...the engine was remarkably clean when I bought the truck, as was the inside of the carb, so I ran a can of sea-foam through the truck and called it a day, but I haven't taken it apart yet...when I did the tune-up in Colorado, my compatriot and myself both tried to make adjustments to the carb, but neither of us could affect any noticeable change, even making ridiculously coarse adjustments. The screw does turn with ease, and does move in and out, but my experience tells me I need to finagle with that screw some more...

I just figured that as long as it ran strong I didn't mind it running rich...I'd get bad gas mileage, but it wouldn't hurt the engine...I knew I'd have to deal with it at some point in time, and it appears that time might be at hand...

xxxtreme22r

If idle doesn't change with mixture screw movement, there is a vacuum leak somewhere. Which will also cause lean issues as well as timing issues. That's why I had asked if the idle changed.