Almost ready for smog but...

[A guy named Rick]

My 720 is running great. Got the stock (not original though) carburetor on, all vacuum hoses hooked up.

timing good (3 btdc)

valves adjusted

Float level at dot

new O2 (bosch)

plugs (NGK bpr6es/bpr5es about .032 gap)

wires (ngk)

cap (brass contacts)

rotor (again brass)

air filter (wix)

 

To idle good I have the mixture screw out pretty far which is concerning me, and even then the RPM's are going up and down more than they should and a little bit rough. I'm not leaking at the base or bolts. I'm worried the egr may be open a hair. I did the PCV not long ago. Brake booster is plugged off because it leaks. Carb was fully rebuilt by me. Not my first rebuild either. Throttle switch set correct too. Help??

[datzenmike]

A vacuum leak will let in more air at idle and lean out the mixture requiring the mixture screw to be turned out to compensate.. Hunting up and down idle is another classic vacuum leak indicator.

 

While running, pinch all the vacuum hoses closed with needle nose pliers one at a time. Does the idle correct itself? on one of them??

 

Don't forget the vacuum hose to the power brake booster and if automatic there is a small line down to the transmission.

 

Could also be the carburetor base gaskets.

 

Check the intake bolts are snug.

[A guy named Rick]

6 minutes ago, datzenmike said:

A vacuum leak will let in more air at idle and lean out the mixture requiring the mixture screw to be turned out to compensate.. Hunting up and down idle is another classic vacuum leak indicator.

 

While running, pinch all the vacuum hoses closed with needle nose pliers one at a time. Does the idle correct itself? on one of them??

 

Don't forget the vacuum hose to the power brake booster and if automatic there is a small line down to the transmission.

 

Could also be the carburetor base gaskets.

 

Check the intake bolts are snug.

Brake booster capped off. Manual transmission. Sprayed around base to check for leaks. Definitely right it's classic vac leak signs. I was thinking about checking all the lines thoroughly. Maybe do a manifold vacuum test? What would it read at idle? Which port to test on?

 

Also, on a side note, I'm not entirely convinced secondary is opening, granted I know it's vacuum controlled. I get the rpms up on it too. But I would assume I wouldn't be able to do 90+ without the secondary opening right? 😏😉

[A guy named Rick]

Well I should be off to smog today or tomorrow. I'll let y'all know what happens.

 

I have a question. Previous owner sometime in the history of the truck had twisted one of the wires for the anti-dieseling solenoid together with one of the 2 black wires that are grounded near the throttle cable bracket. The jacket is stripped on both and twisted together. It's the yellow wire on the truck side of the 6-wire connector which would be the positive red wire on the carburetor side. Untwist, truck dies. 

 

I think I asked about this before. If it's not hurting anything I'll leave it but it would be nice to figure out how to fix it properly. Obviously I have a bad ground somewhere and this is the "solution" 

Edited May 4, 2023 by A guy named Rick

[A guy named Rick]

Alright I didn't pass smog. Here's the results.

 

 

Way too rich.

 

The mixture solenoid works.

I have a new O2 sensor

New plugs, cap, rotor, wires

15w-40 shell Rotella oil

Air filter good

Float level correct

Vacuum lines routed correctly

No vacuum leaks that may otherwise affect mixture causing lean making computer compensate (that I know how)

 

So I'm stumped.

Edited May 9, 2023 by A guy named Rick

[A guy named Rick]

Idk how much difference it would make but...

 

 

This was my view taking the lid off aftwe driving home. Apparently my choke butterfly linkage was a bit hung up. I pushed it and it opened all the way. How much difference at this angle vs all the way vertical could it make on enissions? Guess I need to lubricate it a bit. 

[datzenmike]

Choke fully off when warmed up?

 

 

Ah you noticed something. Yeah that might do it.

 

 

[A guy named Rick]

25 minutes ago, datzenmike said:

Choke fully off when warmed up?

 

 

Ah you noticed something. Yeah that might do it.

 

 

No, choke works, the linkage could use a little lube (giggity). Wasn't fully closed, but enough might make a difference.

 

However I found the problem... there's a little spring on the arm for the throttle position switch. The bottom that connects to the hole on the body of the switch came off. So I was driving around and took it to smog with the carburetor running as if it were at idle. 🙃 That'll richen things up a bit!!

 

Problem is it's in a real bitch of a spot. 

[A guy named Rick]

1 hour ago, datzenmike said:

Choke fully off when warmed up?

 

 

Ah you noticed something. Yeah that might do it.

 

 

OK you got me. Just checked and choke don't work. Spring is here in northern Cali, don't need the choke much so I'm taking the butterfly off.

 

Why would I have no power to choke??

[datzenmike]

Wire the choke (blue wire?) to the idle cut solenoid. (red wire) It's complicated but certain things are necessary for the choke relay to work and send power to the choke heater. Better to connect to the idle cut solenoid for power. It's only on with the ignition so it will work.

[A guy named Rick]

19 hours ago, datzenmike said:

Wire the choke (blue wire?) to the idle cut solenoid. (red wire) It's complicated but certain things are necessary for the choke relay to work and send power to the choke heater. Better to connect to the idle cut solenoid for power. It's only on with the ignition so it will work.

I'll figure that out later.

 

Will running Rotella 15W-40 raise my emissions at all? Just trying to cover everything before retesting. Should I switch to regular oil before testing again?

 

I also adjusted the idle switch a bit. I think it was off at 2000 rpm and I have it down to about 1400. It's annoying because you can feel the transition a bit depending how you drive it.

 

Also my idle mixture is pretty far out, about 6 turns, maybe 6.5. Still slight misfire, rpms fluctuate +/- 15-20 rpm so not terrible. Haven't chased down any vacuum leaks at all.

[A guy named Rick]

So I failed smog test again. This time I had high NO. I was also running on the lean side. Mixture solenoid definitely working this time. Do you think maybe over active EGR? It does work, I tested the diaphragm vacuum, but maybe I have something routed incorrectly. I have followed fastboatman's write up on nicoclub.

 

Here's the first smog: m/c solenoid wasn't active.

 

here is the second:

 

And here is from 2 years ago, granted different MC solenoid and overall different carburetor: 

 

 

i'm completely baffled. And I have until the end of this month.

Edited May 10, 2023 by A guy named Rick

[datzenmike]

EGR reduces the combustion chamber temperature thus NO is reduced. The is no (or should be no) EGR at idle.

 

Idle mixture setting... (timing set, valve lash set, engine completely warmed up)

Each idle mixture is unique so the number of turns out for you would not be the same for me. Set the idle at under 700. The lower the better because changes are easier to hear. Turn the mixture screw in till the idle falters and drops off. Now turn it out till it falters and drops off. There may be a plateau of maybe a full turn between these two where it idle faster and smoother. Just take a guess where half way is. Presumably the idle went up, so turn back down. Repeat as many times as needed to find the smoothest, strongest idle where you can't improve on it and the idle speed is 750-800. Mixture is set  

[A guy named Rick]

If EGR reduces combustion temp, then is it possible it's not funtioning how it should be?

[datzenmike]

Look at your first failed test.... it was working then. What ever changes you made to lower the CO has also altered the NO. Try dialing your changes back slightly.

[A guy named Rick]

17 minutes ago, datzenmike said:

Look at your first failed test.... it was working then. What ever changes you made to lower the CO has also altered the NO. Try dialing your changes back slightly.

 

I literally only reattached the spring for the idle switch, so now the MC solenoid works. That's all I did.

 

My float level is at the dot. Perhaps I need to go up a tiny bit more? Running it is at dot. Shut it off and it's a tad below.

Edited May 11, 2023 by A guy named Rick

[datzenmike]

Check your ignition timing, perhaps retard slightly. Says 3 degrees +- 2 degrees. Try taking 2 degrees off and down to 1 degree. 

 

Take the EGR off and wire brush any deposits off. Perhaps clogged and even though open not enough recirculation. (again it was working so...?)

[A guy named Rick]

12 minutes ago, datzenmike said:

Check your ignition timing, perhaps retard slightly. Says 3 degrees +- 2 degrees. Try taking 2 degrees off and down to 1 degree. 

 

Take the EGR off and wire brush any deposits off. Perhaps clogged and even though open not enough recirculation. (again it was working so...?)

I forgot to mention when I got home I looked everything over again and I noticed this plastic white vacuum valve was routed upside down. I'm not sure what difference it would make in emissions but it drives better now... in the pic it was upside down, so lines were routed wrong.

[A guy named Rick]

I also realized this is possibly a high altitude carburetor. It has 2 vacuum ports capped off on drivers side of carburetor. I don't need these ports as the oem card didn't have then (but had a faulty mc solenoid). Could this mc solenoid be different, maybe for a high altitude model? 

[A guy named Rick]

I also was playing around with vacuum lines potentially finding a leak of some sort, when I pinched the line that comes from the front passenger side of the carburetor and goes to the bottom of the TVV. Idle smoothed and raised. I concluded it was sending some vacuum signal to the vacuum Advance. But why at idle in the proper idle speed??

So took off the top 2 lines, had to plug both to achieve same result. At running temp, there should be no air entering from the air cleaner to the TVV, correct? 

[datzenmike]

I think the carburetors are the same for both. If high altitude then hoses go to the lines, if not they are simply capped.

 

That looks like the vacuum control valve. It lowers the vacuum advance vacuum signal under heavy load or high speed.

 

The top hose shown should connect (TEE) into the hose from the T V V bottom port to the distributor vacuum advance. Reducing vacuum advance under load also lowers combustion temperatures and NO. Was this connected wrong for the first test???? It passed NO so I doubt this is it.

 

[A guy named Rick]

31 minutes ago, datzenmike said:

I think the carburetors are the same for both. If high altitude then hoses go to the lines, if not they are simply capped.

 

That looks like the vacuum control valve. It lowers the vacuum advance vacuum signal under heavy load or high speed.

 

The top hose shown should connect (TEE) into the hose from the T V V bottom port to the distributor vacuum advance. Reducing vacuum advance under load also lowers combustion temperatures and NO. Was this connected wrong for the first test???? It passed NO so I doubt this is it.

 

Yes, the vacuum control valve was flipped upside down both tests. Strange that NO went up after fixing the idle switch. I'm thinking too lean, but why? Or maybe distributor is advancing too much? I'll have to check timing advance curve. 🤷‍♂️

[A guy named Rick]

@datzenmikeI tested the TVV just now in the sense I just got home from work and applied vacuum to the top port and, in theory, it should be closed and not allow any air through? The top port that goes to the air cleaner. Because on my vac gauge it reads nada. So air is passing through fully warmed up.

 

This would make the EGR not operate as it should, right? Thus, raising my NO? 

Edited May 11, 2023 by A guy named Rick

[datzenmike]

TVV is open when cold, so air filter air is allowed onto the EGR and the vacuum advance lines which destroys the vacuum signal. No vacuum no EGR/vacuum advance when engine is cold. As it warms up the air bleeds close at different temperatures and vacuum is sent to the EGR and the distributor vacuum, advance.

[A guy named Rick]

Alright time to find a new one then. Or maybe the line the air cleaner might "accidentally" plug up 😉.