She's running - but rich

[JPSmit]

rich enough that she is leaving soot on the snow.

First off, could it be something as simple as the rings not fully seated? I've run the car for maybe an hour total and likely put 2 miles on it.

And/Or, is there something I can do?

To recap, it is a Zenith Stromberg. Water choke has been removed and replaced with a manual choke - which is not currently hooked up and which I have not actually needed to start the engine. As well, I am not running the original air cleaner as it did not come with the car. Instead I have a longflo air cleaner (https://www.victoriabritish.com/ICATALOG/SM/full.aspx?Page=30)Also, all the pollution stuff is disconnected.

thanks all

 

[bthompson]

You answered yer own question: it's a Zenith Stromberg. Find me one that <span style="font-style: italic">doesn't </span>run rich. Seriously, though, I know that aftermarket air cleaners will cause a rich condition; they flow too freely. You might try restricting the air cleaner a little and see if it works.

 

[jvandyke]

Maybe just put some duct tape over part of the cleaner, covering 50% of it and see? Reminds me of that guy (can't find the site back at the moment) who couldn't get rid of a stumble until he taped up his K&N filter (later going back to stock housings).
I've got that same Longflo on my Weber. I don't think I'm running rich though. On my to-do list is try to dial that Weber in, then try the SU's and decide which works best for me (I'm hoping it's the SUs).

Found the site

scroll to the bottom and read the final solution

 

[Morris]

Unless you are billowing great clouds of smoke or the car seems undrivable, I would not worry about it too much for now. I think the best procedure is to get the car on the road, do some light and easy driving, tune and adjust. Then do some more light and easy driving, tune and adjust. Then try some slightly more aggressive driving, tune and adjust etc. until the car is fully broken in.

The ZS carb does tend to run a bit rich at idle. You may be able to tune the richness out, but it will could require playing with a few different needles.

The best thing you can do right now is make sure your spark timing is correct.

 

[Hairyone]

Yes running it in for a bit sounds like a good plan to me. Then adjust.
Check tappits (when cold) as well as timing.
Not sure how that restricting the air flow (blocking up half of the air cleaner) will make a rich mixture leaner???? less air in, the richer surely.
If you've got excess fuel sounds like a supercharger will sort it out. he he.

 

[JPSmit]

If you've got excess fuel sounds like a supercharger will sort it out. he he.

Mmmmm supercharger

 

[jvandyke]

Not sure how that restricting the air flow (blocking up half of the air cleaner) will make a rich mixture leaner???? less air in, the richer surely.

I think the guy linked above concluded that since the SU's rely on vacuum to move the piston, too little restriction on the air intake side allowed the piston to move too freely resulting in too high a piston drawing the needle up too fast, making it too rich on initial acceleration at least, maybe he needed heavier oil in his damper? I don't know, just remembered the site and passed it along. Like tuning without any air filter attached, putting them on then changes things a bit, but hey, I don't know squat, I haven't even tried to run SUs yet.

 

[PeterC]

Or.... just old gas. More than a month old will not burn completely. The soot is unburned, and mostly unburnABLE, gas. I have seen this countless times. The assumption we all make is that the stuff that isn't burning is flammable.

Put in fresh, very fressh, gas before you go to too much adjusting.

Peter C

 

[tweety]

My 1500 with the ZS carb with a foam filter and no choke was running crazy rich... It was considered a "Gross Polluter" by the state of California.

Luckily, my regular mechanic was authorized by the state to repair and retest gross polluters. I had bought another complete ZS carb on E-Bay to use as a parts to build a frankencarb.

He spent about two hours putting reinstalling the water choke and making the adjustments. It passed smog with flying colors after that.

I do plan on replacing the water choke with a manual eventually so that it's easier to start.

 

[bthompson]

Right idea, jvandyke, but you have the mechanics backwards. SUs and ZSs work by using the piston height to adjust the size of the venturi across the jet, to keep the vacuum constant regardless of engine speed. (CD=constant depression) Slower engine draws less air=lower piston=smaller venturi increases vacuum. Faster engine draws more air=higher piston=larger venturi decreases vacuum. Having a less restrictive air cleaner decreases the vacuum across the piston, fooling the carb, and causing it to sit LOW. A low piston increases the venturi, and it sucks more gas. This is the way the accel pump works, BTW: when you stomp on the go pedal, the increased air draw will try to pop the piston up. The damper retards this action, and the smaller venturi will suck more gas. It's really a beautifully elegant system. When it works. :laugh:

 

[JPSmit]

I'll certainly try what has been suggested. BTW, the gas is new. I'm leaning to run and adjust as I hope to have my mechanic looking at it soon.

one question - somewhere, someone mentioned that the screw on the front (rad side) of the carb as a mixture adjustment screw, but, if I recall, it was counter intuitive to adjust - does anyone remember?

 

[jvandyke]

Cool, thanks! I'll get it someday.

 

[bthompson]

The frontside screw closest to the engine is the overrun valve. That's the one that screws out to close. If the engine stumbles when the throttle snaps shut, you can open that one a bit (by screwing it in!). The screw-within-a-screw behind that is for finetuning the mixture, to set the emissions CO. It's supposed to be such a fine adjustment that it won't really affect rich running.

 

[JPSmit]

thanks Bill, but, therefore, neither really is of help to me.

 

[DrEntropy]

A couple random thoughts: was the jet body replaced? I've seen some of them worn to "ovality". i.e. needle 'floats' and is in contact with the intake side of the bore and over time can wear the jet and itself, causing a rich run.

In another thread someone posted a diagram of the dreaded device. In that thread I suggested blanking off the little compensator device with a DIY gasket with only the three attachment screw holes in it. Did you try that?

ISTR you have 2~4 PSI fuel pressure. Anything above that can cause issues.

Tie the choke lever closed with a tie-wrap or wire tie to be SURE it's closed.

Worn piston damper.

Air cleaner is FINE... rerstricting it enrichens not leans mix.

 

[JPSmit]

Doc, I rebuilt it - including a new needle. I've also had an MG mechanic look at it twice. (off the car) he pronounced it fine

I'm not familiar with the DIY gasket.

fuel pressure is original pump.

at this point I can tie the choke closed but it is not connected to the cable - so the spring is holding it shut anyway.

BTW how can I tell it is leaner since it smokes anyway because of the cold? (other than pulling the plugs)

 

[bthompson]

Air cleaner is FINE... restricting it enrichens not leans mix.

:confuse: Wait...are you <span style="font-style: italic">sure </span>about that, Doc? Don't rain on my parade just when I think I have the dang things figgered out!
...A restricted intake on a reg'lar carb with a <span style="font-style: italic">fixed </span>venturi would run richer, cause it would add more fuel relative to the air...a <span style="font-style: italic">variable </span>venturi would open up with the increased vacuum, slowing the airflow across the jet and pulling <span style="font-style: italic">less </span>fuel...right? If I'm off base on this, I'd appreciate any re-edumacation.

 

[DrEntropy]

a variable venturi would open up with the increased vacuum, slowing the airflow across the jet and pulling less fuel...right?

umm... I can't dispute the physics, Bill. I just don't think the Longflo air cleaner is that restrictive.

 

[Roger]

Air cleaner is FINE... restricting it enrichens not leans mix.

:confuse: Wait...are you <span style="font-style: italic">sure </span>about that, Doc? Don't rain on my parade just when I think I have the dang things figgered out!
...A restricted intake on a reg'lar carb with a <span style="font-style: italic">fixed </span>venturi would run richer, cause it would add more fuel relative to the air...a <span style="font-style: italic">variable </span>venturi would open up with the increased vacuum, slowing the airflow across the jet and pulling <span style="font-style: italic">less </span>fuel...right? If I'm off base on this, I'd appreciate any re-edumacation.

'Cept it don't work like that. The increased depression means the engine's sucking from somewhere, and if it can't get air, it'll suck fuel.
In my youth I raced with twin SUs and deleted the mixture richening mechanism. To start I stuffed rags on a bit of string into the intake to richen the mixture, and pulled 'em out once I got going.

The early Keihin carbs, like on the Honda S600, are CD very much like the SU, and have a strangler plate upstream of the choke.