Tried leaning out the metering rod and it drives just the same, but idles rougher. Not quite sure what to do. Going to meet Harte3 and take his old carb and intake off his hands and see if it does the trick.

 

Did you ever get your manifold heat hooked up? If not, stop everything and hook that up before you beat your head against the wall any more.

 

That is something I'm still frustratedly working on. I cannot get it hooked up without it leaking everywhere. I've tried everything short of welding it on.
Hrmm....

I still don't think that would quite cause the problems I've been having though. I know it helps with fuel atomization, but I'm barely making it to work in the morning. If I push on the gas, it'll die without some SERIOUS feathering. If I push down on the gas anywhere under 2000 RPMs, it'll strain and struggle horribly to get moving. By the time I can finally get moving at a stop light, the car in front of me is already at least ten car lengths away and I have people behind me honking.
It'll finally smooth out above that and build fine, but it's still pretty gutless.

Thing is, it wasn't like this until I adjusted the metering rod. But I just can't see a slight adjustment to that screwing it up THIS bad! I'm not an incompetent mechanic by any means, but I simply cannot get the carb back to at least running the halfway decent way it was when I failed the emissions test. I've tried running it from the metering rod screw backed out so far it no longer adjusts, to all the way bottomed down. The only difference it makes is idle smoothness, but it still drives horribly. What gives? The best way I can describe the way its driving is if it had a clogged fuel filter (which I've replaced), and no matter what I do, the engine just can't enough fuel to run. (However, it tested super rich on the last emissions test.)

It'd be one thing if this was my weekend warrior, but I drive it to work every day.

I've gone through every vacuum line and tested for vacuum leaks, but I cannot find anything (the vacuum at the intake is a steady 18lbs). The intake manifold was also recently regasketed and installed. I've removed the carb and cleaned it piece by piece, checked for jet clogs, needle wear, float settings, you name it. I've ran the engine with JUST the carb and had all of the vacuum lines removed and capped off to see if I could even get the idle mixture screw to work, and it won't. I've replaced and properly gapped all the spark plugs and timed the engine. The engine still bucks at idle and runs like absolute garbage. It even hesitates to rev when I throttle the gas by hand in the engine bay.

What more is there? I've spent probably 20 - 40 hours on this thing over the last three weeks and I've gotten no where.

 

You said it's 20F out? I have no manifold heat in my truck, and it runs HORRIBLE in those kind of temps. Takes forever to be able to idle, and then another forever to get enough power to back out of the driveway, then a third forever to get enough power to climb the hill out of the subdivision. Once warmed and driven a few miles, it does OK though. Much, much better in say, 50F weather. Still can't get aggressive just off idle or romp on it, but it drives acceptably.

Did you machine/wire-wheel the mounting plate on the bottom of the intake? Tried RTV sealant? Just bolting the plate on is never going to seal up. The old setup used a gasket of some sort, I believe.

Ignoring the manifold heat:
The symptoms you're describing, with exception of idle, seem to fall under "combustion fails at low vacuum". You've been all over the carb, no adjustments make any difference, and you're not a mechanical moron. Sounds to me like it's not the carb anymore. My dad's old Honda had the same symptoms- wouldn't start, stalled, idled like crap, and had zero power until higher in the RPM band, when it would wake up again. It was fuel-injected, so no funny tuning problems. Turned out to be a carbon-arc'ed dizzy cap causing a really weak spark. Too weak to overcome significant quantities of fuel (low vacuum), and too weak to ignite the really sparse high-vacuum idle mixture. Would barely start on rainy days, and eventually it stopped running altogether until we figured it out and put a $13 cap on it, after which it ran like new. I know you replaced your plugs, but have you checked the rest of your ignition? Maybe something got bumped while you were changing the metering rod.

 

Thanks for the info. I know the heat spacer will definitely make a difference. The main reason I know that this isn't completely that is because it ran "ok" under 20 degree temps out. I drove it back and forth to work every day, grocery shopping, drove it 250 miles to visit my family for Christmas, and haven't necessarily been frustrated with it all winter until I started trying to tune it for emissions. I noticed a bog at idle that I attributed to no carb heat, but it wasn't anything serious and I wasn't overly concerned. Also, all of my diagnostics have been with a completely warmed up engine. I consider a cold engine out of the equasion in diagnostics. As it has been the last week or so, it has been dangerous to drive to work. It idled just fine though (a little popping) and starts like a dream. Just really fusses under low RPM accelleration.

Update though, after screwing with it tonight, I grabbed one of the metering jets out of one of my backup carbs and gave it a try. The one the guy at the carb shop the other day gave me appears to have been a 401 (not sure what the ratings mean except size) because it was running rich. I looked at the one previously in there was a 407, which he said was warped into an oval shape. I tried a 404 (out of a back up carb) tonight and it ran and drove much better.

I hadn't know of the jet size differences until I examined them tonight. I'll know how it runs under COLD weather tomorrow when I drive it to work (it was 40 this evening), but it ran a lot better than it has. No matter the tuning, maybe the jet was just too darn small?

I have machine wheeled all of the mounting surfaces and am using gaskets. No sealant though. I've never known anyone to use sealant on carb gaskets so I've never done it. What type should I use?

As for the distributor cap, the distributor itself, cap, and rotor are less than a year old.

One thing I am curious about though: the stock carb has three vacuum ports. At idle, one of them has 0 vacuum, one about 4, and one about 15. The EGR valve is currently hooked up to the 0, the distributor to the 4, and something with the air cleaner with the 15. I've heard the distributor should be 0 at idle and I can see the vacuum advance arm move when I plug in the vacuum line to the distributor. Is something wrong here too?

 

Glad to hear you're improved!

High-temp RTV sealant for your heater plate to manifold. Is your heater plate going between the carb & manifold, or does it bolt to the bottom of the intake manifold where the exhaust riser used to bolt? If it's the bottom, high-temp RTV. put on a bead, let it cure until dry but rubbery, then bolt 'er on and snug 'er down.

At least in the QJet world, jets are specified by diameter, but what you actually have to consider is the open area, pi*(radius^2). So that 404 opens 2% more than the 401, and the 407 another 1%. (that assumes that the diameters are directly proportional to the part number). If your "big" 407 was worn larger, you would have gone way rich. 401 might have been way too small, starving your motor for fuel when it needed it most- idle and the "power" mixture for acceleration. The 404 is back in the right direction, and maybe within the mixture tolerance of the engine. These older engines ran slightly rich to protect against pinging where they weren't assured of proper ignition timing, and were guaranteed mixture variation with temperature and altitude. High-vacuum, low-power "cruise" situations are very tolerant of lean mixtures, and I believe most carbs are tuned lean on cruise to take advantage of this and gain MPG. Which would explain why your truck still ran OK at higher RPMs and light throttle.

Off the top of my head, I'd put the ignition on direct manifold vacuum (15 at idle). Ignition should be advanced at high vacuum situations, and retarded at low. If it advances at idle and retards when you open the throttle, that's good. The dizzy should also have an internal mechanical advance to compensate for RPM. That's why you always set your initial (mechanical) advance with the vacuum advance disconnected. I think ported vacuum is the exact wrong type, too. Ported comes from the venturi of the carb. The harder the engine works (the more CFM through the carb), the greater the pressure drop at the venturi and the higher the vacuum will be- you'll be advancing your ignition at the exact time you want to retard it! I believe the ported vacuums are typically for emissions hardware.

 

Thanks for all of the information. This is the stuff I need to know. It's one thing to be able to look and see if something isn't quite right, it's another to understand why it isn't right.

Yeah, it's definitely running much better. The 407 must've been much too big, and the 401 too small. The 404 runs it a lot better, although it's still a little rough and the idle mixture still doesn't do anything. At least I'm back on the road for a while.

I took the entire heat plate apart last night and really covered all the threads with sealant, got some hardened bolts and washers, and cranked everything down as tight as I could possibly get it. I was beat after wards. It's still leaking from the threads of the pipe (at least not the plate base), but it's much slower than it was before. It's slow enough to where I'll probably just have to top it off once a week (instead of previously where it was spraying out) so I'm going to leave it hooked up and see how it performs. I just don't have it in me to go out and take it all apart again to hope I can get it a little tighter... Currently, it is a plate that bolts to the underside of the intake.

Still gotta pass emissions though!

 

Ok, did another test this evening to see how things were going.

First Test:

High Speed
CO: 1.75/1.20 Fail
HC: 125/220 Pass

Idle @ 860 RPM
CO: 1.20/10.77 FAIL
HC: 1241/220 FAIL


Fixed: New spark plugs, timing. Heet in gas.

Second Test:

High Speed
CO: 0.46/1.20 Pass
HC: 184/220 Pass

Idle @ 920
CO: 8.49/1.20 Pass
HC: 738/220 FAIL


Fixed: Hooked up heat to the carb. Removed worn larger metering jet and replaced. Still idles a little rough.



Today's Test: Third Test:

High Speed:
CO: 0.01/1.20 PASS
HC: 17/220 PASS

Idle @ 1060
CO: 1.41/1.20 Fail
HC: 539/220 Fail




So, I failed, but it's getting SOOOO much closer. It nailed the test at high speed, which is awesome, and almost passed the CO test at idle, but the HCs are still up there. Ideas? Diagnosis?

The options I have open to me are to hook up the smog pump and the EGR as none are hooked up. I can also tune the metering rod richer or leaner. I know the EGR doesn't even open up at idle, so does it even effect idle emissions? I know some oxygen in the cat would help, but are these symptoms of that, or something else?

I also have plans to go meet Harte3 tomorrow to take his old carb off his hands, but I certainly would love to save us both a trip if my emissions equipment (and not a new carb) or another tuning trick will make it pass. If this still looks like my carb is toast, then I'll forget any more work and go for a nice Saturday drive tomorrow.

Thoughts?

 

Smog pump ought to fix them HC numbers. Methinks. Don't hunt me down & kill me if I'm wrong....

 

Oh....you know I will.



Ok, so my smog pump goes into a valve with a vacuum line attached to it that regulates when the smog pump lets air into the exhaust. Does this open at idle or high speed? Anyone know?

How's it help with HC? Dilute it? Or help the cat burn better? Also, does that mean it's running rich or lean? I have the carb a little richer than "stock" setting right now.

 

HC = hydrocarbons = unburned fuel = too rich a mixture at some point in the process. The smog pump puts some air into the system so they burn in the manifolds. It may also help the cat burn them up too, but the cat isn't meant to deal with too much of this or it will overheat.

As for the specific regulation, don't know....

 

Just some off the wall thoughts... You get HC to be high at idle by either a rich mixture or by misfire leaving unburnt fuel in the exhaust gas. You can actually cause high HC by having a mixture that is too lean, leading to misfire. Do you remember how bad exhaust smelled when cars kept 'dieseling' when shut off? That was partially unburned fuel/air mix.

You note that the idle mixture doesn't have any effect, and that "the throttle wobbled a little bit". I think the two are related. You may be bleeding air past the throttle butterfly if there is slop. If you have enough, it can let the butterfly jam against the venturi wall.
Do you have the heater for intake air connected? Have you checked the 'wet' fuel level in the float bowl?
If the EGR is leaking, you can also get misfire. Work the EGR valve by hand, or with vacuum applied to the diaphragm, at idle. If you cannot stall the engine, or opening the EGR has no immediate effect, either the EGR is plugged or it is open partially all the time. Not applicable if the tube to the exhaust is still missing, but the inlet side of the EGR valve could be leaking extra air into the intake.
tom

 

PASSED!

Looks like the carb Harte3 gave me did it! The new test was:

HIGH SPEED
CO: 1.03 / 1.20
HC: 141/220

IDLE
CO: 0 / 1.20
HC: 40 / 220


I never did get around to hooking up any of the emissions equipment. EGR is completely blocked off, and the AIR pump doesn't have a belt. Looks like I don't need it.

Thank you again so much for everyone's help. I couldn't have done it without it.

 

Time to treat harte3 to an 'all you can eat and drink' at the local watering hole

Nice to hear you got that headache behind you

 

I was feeling his too. But now,