So the lower the sea level the better, correct?

I wonder how much power sea level can rob. I'd like to see numbers!

Thanks AB.

 

Sea level, 55*, high humidity...it doesn't get much better than that. Loveland Pass in CO, just shy of 12,000 feet elevation, 0* mol, low humidity...doesn't get much worse. I get short of breath just thinking about it.

 

After all these years, I guess I don't understand how hi altitude really affects performance. The downstroke of the piston(s) will pull in "air". Isn't that air oxygen? If it's light on oxygen, what's the rest of the "air" composed of?? The pistons still pull in the same quantity of vapor no matter what elevation. Thx

 

Think of it like this:

When you're under the water in a swimming pool, and you're up near the surface, everything's fine. But if you dive down to 8 - 10 ft, you're already starting to feel pressure in your ears. Now, if you dive down to 2,000 ft under the water, the pressure is going to be insane. This is because the water you're now in has water on top of it, which compresses it. If you go down to 10,000 feet or lower, the water is going to be so "squished" from having 10,000 feet of water on top of it, that it's going to be as thick as syrup. The weight of all that water on top of it is A LOT.

The same goes for the air. Since there's oxygen molecules and stuff in it, it actually has weight. When you're down at sea level, the air probably has around 50,000 feet of oxygen sitting on top of it. Like the water in the bottom of the ocean, the oxygen starts to "squish" under it's own weight. That compresses it, and forces more oxygen molecules into the same amount of space. So basically what all this means is that when you're at sea level, there's more oxygen in one square inch of air then there is at 10,000 feet.

So even though an engine at sea level pulls in the exact same volume of air an identical engine at 10,000 feet does, that air at sea level has a lot more oxygen in it, gets a much better mixture, and a bigger explosion in the combustion chamber.


As for what the rest of the air is composed of, nothing. When you go higher up, the air has less weight on top of it and doesn't compress as much. The molecules aren't pushed as close together and just plain old have more room to move around. So what the rest of the air is composed of is just empty space.

 

A picture is worth a thousand words. =P

If each dot in the picture represents an oxygen molecule, you can see how the weight of them sitting on top of each other really starts to compress the ones on the bottom. More oxygen in the same amount of space.

 

Ok, ran another emissions test. Since then, I put in new spark plugs and re-timed the engine. I also added a can of heet to the gas tank and ran it on premium.

New failed report:

2500 RPM Test:

CO% Require: 1.20 Me: 0.46 PASS
HC(PPM) Require: 220 Me: 184 PASS
RPM: 2496

Idle test:

CO% Require: 1.20 Me: 8.49 Fail
HC(PPM) Require: 220 Me: 738
RPM: 775 (+/- 425)




From this:

2500 RPM Test:


CO% Require: 1.20 Me: 1.75 Fail
HC(PPM) Require: 220 Me: 125 PASS


Idle test:

CO% Require: 1.20 Me: 10.77 Fail
HC(PPM) Require: 220 Me: 1241 Fail





So, I was able to now pass on both of the high speed tests, but still failed at idle. The results were definitely better, but still not good enough.



The timing and new plugs definitely helped. The old plugs looked very healthy, but just a bit aged. I think it had been a few years since I had replaced them.
Got to get it to pass though. So, would adding more heet possibly help? What about advancing the timing even more? I haven't heard any ping yet (not really sure what it would sound like if I did though.) Another idea I had was, since 2500 RPMs pass, and I have 425 RPMs of forgiveness at idle, maybe hold it at around 1000 or so instead of 750?

As stated in other posts, my idle mixture screw doesn't seem to want to do anything, so I can't really just lean it out or have it run richer. I took a vacuum gauge to my engine and went through about every vacuum line but couldn't find a single leak. Also, the vacuum at the intake was about 18 and didn't fluctuate around. Everything seems tight, but things still point to a vac leak. Not sure what more to check.

Since the last test, I opened up the carb, cleaned it and checked the gaskets (they were fine), and checked all the gaskets that mated the carb to the manifold. There was a little residue on the manifolds so I smoothed them to shiny and reinstalled the gaskets. Still no idle screw response. Sprayed carb cleaner all around the manifolds and carb and nothing happened, which implies no leaks. Just to see what the effect would be, I sprayed some directly into the carb and it just about killed the engine.
I can also still hear the exhaust bucking (even though the engine doesn't physically move.) I also tried advancing the timing to 8* instead of 6*.
Going to test it again, but I'm pretty sure it'll most likely just fail again. If it ran super well, I'd just say it was a symptom of some EGR equipment not working, but it still doesn't have a snappy throttle, and idle mixture screw not working says something. I've also known people with 300s with no emissions that have passed with better numbers than I have.

Ideas?

 

Sounds like the idle air bleeds in the carb are off. That controls the fuel mixture for idle operation.
The idle mixture screws just adjust the amount of that mixture to a very limited degree.

 

There isn't a whole lot inside these carbs. How do you fix this?

 

Pull the idle screw all the way out, blast the hole with carb cleaner. If you can do this with the carb off and taken apart, you can blast both ways. The results certainly point to something fubar with the idle circuts. Also, have you checked your float level? And is the needle holding? With the low demand for fuel at idle, a leaking needle and too high a float level will cause problems.

 

I've pulled the screw all the way out and all that happens is the RPMs rise a little bit. I haven't sprayed carb cleaner into it while it's running though. Are you meaning to clean it? Or test for leaks? If cleaning, then, yeah, the whole carb has been thoroughly disassembled, cleaned, and rebuilt. If there's a problem with it, it's a part that is not included in rebuild kits that has gone out. I just don't the full dynamics of how the carb actually works to be able to tell what may be out of alignment (with all the intricacies of little tiny vacuum/fuel holes that run through it.)

The two things I can think of is that the throttle wobbled a little bit, so maybe there's a vacuum leak at the base? I've sprayed carb cleaner around there thoroughly with no ill effects. The other is what a carb tech mentioned over the phone and that the metering rod has worn down the sides of the metering jet, throwing everything off. I took it apart and it didn't look bad. I may have an untrained eye though.

 

IF the metering rod controls idle, then replace it. A worn metering rod is going to cause a rich condition, which is what you are fighting.

A vacuum leak would result in a lean condition.

 

Where does one get replacement metering rods and metering jets? I've been scouring the internet and have come up empty handed.

Secondly, would a worm metering jet cause me to bog on takeoff? That's another issue I'm facing... It was "ok" yesterday, but last night I tried adjusting the metering rod according to spec (as per instructions in my rebuild kit and my '81 Ford Engine manual), and today if I did more than feather the gas below 1500 RPMs (no matter the speed), the engine would bog so bad it would almost die. Above those RPMs and it started to pull like normal.

 

Anything that meters fuel can cause a bog. A worn rod or nozzle will allow more fuel in than "planned".

At this point, keep your adjustments "one at a time".

Was your last adjustment aimed at reducing fuel at idle?

Do you get a black cloud when it catches and cleans out?

 

I know all of the needles and stuff are only a year or so old, because it's been rebuilt recently. I also replaced the metering jet yesterday (the guy at the carb shop I got it from told me the metering rod looked fine.)

I'll have to look on the way home to see if it blows black smoke after it bogs. Right now, since it's 20 degrees out, all exhaust looks white. :P It doesn't really "catch and clean out" (I know what you mean though). It moreso just seems to really struggle, and then finally when it can get the RPMs high enough, it smooths out and regains it's ability to build power. Kinda different.

My last adjustment was actually aimed at increasing fuel at idle, since I was seeing if maybe it was being starved for fuel. It really smoothed the idle out, and had a much snappier throttle response (when the vehicle wasn't moving). It was pretty rough before that. Didn't make any difference when driving though.
Maybe it's too much though, so I'll try leaning it out tonight when I get home.

 

Only if you were so lean at idle that you had a pretty good miss fire going would you pump out enough unburned fuel to get the HC numbers you have.... But if the idle is rough, that might be what you are doing.