Lean at idle, rich at WOT

[Brosky]

I did get the new Air/Fuel sensor installed today, which will be for another tutorial, but here is the issue of the evening.

I am showing (as on the Dyno), lean at idle and mid throttle and very rich at wide open throttle.

I average 15.50-16.00 at idle and on light acceleration up to about 2,500RPM, then it gets down to about 13.75 to 14.50 for a brief period and goes as low as 10.75 at WOT.

Here are some shots of the plugs after a few very hard runs. I have no smoke or burning smell (as in too lean) at idle.

Any thoughts on which way to go? Jeff Payla, who did the carbs is on a short hiatus and my main guy Erik is doing house work on his vacation, so I wanted to play a bit this weekend.

I'm open for suggestions as these ZS's are not my area of expertise.

 

[BryanC]

I'm confused. Are you doing this while on a dyno? If not, are you just in your garage? In the picture it seems the hood is up. If you are in your garage, how can you run the engine for more than just a second or so at WOT without the engine trying to go to 9000 rpm? I wouldn't think that you could hold WOT under no-load long enough for the carb pistons to rise much. In that case, you would just be seeing the rich condition caused by the damper delaying the piston's rise. It seems like you would need to be on a dyno or out on the road and under load to get a real idea of what the engine is doing. I guess I don't understand.

Bryan

 

[Brosky]

Bryan,

I had run this car on a Dyno several weeks ago and had another post all about that. That is what prompted me to buy the Air Fuel meter and install it in the car. I can see my idle condition as well as move the meter into the car and drive it hard on the highway for shorts bursts to check the WOT readings.

Tuning on a Dyno is $150-$200 per hour, whether it's running or sitting all apart, so I want to do as much as possible before I take it back for the final adjustments on the dyno.

 

[TR3driver]

Obviously your engine is rather modified for improved breathing ... makes me wonder if you are reaching the flow limits of the dual ZS carbs. When the piston hits the top, they do go rich because the venturi velocity goes up.

You might try a run with the springs removed, which is an easy way to lean out the top end (assuming it doesn't go lean enough to be dangerous or misfire). If they still go way rich, I'd say you need more carb. I believe several vendors will sell you the manifold for triple carbs.

Of course, I'm assuming you've already checked for anything that would limit the motion of the pistons.

 

[Brosky]

Randall,

I do have triple carbs and headers and a recurved ignition. Other than that, good compression and a stock 74 engine with 55,000 miles. https://www.74tr6.com/triplecarbinstall.htm

The carbs were just completely rebuilt and micropolished by Jeff Palya, so I think that they are OK, but may need some tweaking. And I did add the ZS oil to the dampers when we installed the carbs.

 

[TR3driver]

Sorry, Paul, I didn't realize. The springs & needles are the usual way to adjust the mixture curve, so I don't know what else to suggest.

 

[Brosky]

No problem. I appreciate your interest and advice. It gives me more options to try. I'm going to try to richen them a bit just to see what happens at idle and how much it will affect the top end. That's what is nice about having the meter in the car while you're driving it.

Since I know GM and Ford carbs inside and out, this isn't totally lost on me, but I've never really done anything with these ZS carbs except swap them when I had the originals rebuilt and swap the solid linkage for the folded original style on these.

I just found my ZS manual that I bought several years ago, so I'll have some late night reading to do.

 

[vettedog72]

Sounds like you need a needle (set of 3) with a little more mass (more diameter) at the point. BTW, did you have the o2 and bungs set up when you were at the dyno; if not, how was the ratio detected?

 

[Brosky]

Via his sensor in the tailpipe and the readings are nearly identical. Actually, mine are a little more forgiving, but it still is dead rich on full throttle and lean at idle.

Oddly, it runs cool all the time, no smoke, doesn't stink and the car actually runs great, IMHO. Maybe I could get a bit more on the high end at WOT, but that's why they call it tuning, not plug and play. And that's what I'm here to do.

Erik thought that the needles would be the best way to go too.

 

[RonMacPherson]

So, first step would be needles. If this were a Mikuni, or Keihin, like you find on bikes, first thing would be to raise the needles, make it richer at idle and cruise and go smaller on the fuel jets.

I would think that Jeff would be able to advise you on which needles, I believe that there are several( I know there used to be, so hopefully still are) different needles.

So thicker on the idle and cruise and thinner on the full throttle part of the needles.

 

[Harry_Ward]

Hey Paul,

Just talking about needles yetsrday and have to agree you probably need to play around with different needle diameters. Another question I would have is what your exhaust flow or reverse backflow pressure may be? I'm not sure what you're running for an exhaust system curently? If it's OEM exhaust mufflers even with headers it may be too restrictive for what you have going in and not enough coming out? Isn't this high performance stuff fun!

 

[BryanC]

Thanks for clearing that up for me. I was confused by the pictures. It sounds like a good plan. I haven't seen anyone selling ZS needles (other than stock). What is your source for ZS needles - Jeff Payla? I'll be very interested to follow this and see where you end up on needles and eventually how much it improves engine performance. This is fun!

Bryan

 

[Brosky]

Stick with us Bryan, it can get really interesting around here.

Harry, you may be onto something. I do have the stock exhaust from the headers back, so that will go on the list, but I'll make it last for now. I have no idea what the back pressure numbers are, but it's a good question. I really don't want the car any louder than it is.

Ron, it looks as though I'll be calling Jeff and talking about needle sizes.

I just was outside all morning playing golf and it is HOT here. It's in the mid-upper 90's and I'm soaked and tired. Yeah, old too! No tinkering in a hot garage today.

I do plant to play with the adjustments just to see what happens, but if the needle is allowing to little at idle and too much at full, then I may need to make some changes.

 

[AltaKnight]

This seems curious since aren't these carbs designed so that the fuel/air mixture is linear throughout the range? The clearance as the needle withdraws from the jet is matched to the amount of air blowing across the jet creating the venturi effect
I can only think that the needle/jet clearance is somehow not correct on WOT.
Do you think it's the same condition on all 3 carbs or could the problem be just one of them, not sure how you could check for that.

 

[DNK]

If you have the right tipe of headers you can hook the O2 sensor to the right down tubes and check then. On my set I have 6-3-2 so I will put 2 in to check each carb.

 

[swift6]

Paul, sorry it took so long for me to get in on this one...
I have had mixture issues since going to the triple as well. Spent some time talking to RG about it and decided most of my mixture issue was altitude related. Asked all sorts of people on the 6-pack list with triples if anyone else had experienced such problems and found I was pretty much alone. Mine was also discovered on a dyno.

Now I KNOW yours can't be altitude related since Rhode Island practically has no altitude.

This seems curious since aren't these carbs designed so that the fuel/air mixture is linear throughout the range?

Not necesarrily linear but 'constant depression'. There are different tapers for different applications and they do not taper in a linear fashion. Unfortunately there are not very many needle choices for ZS's anymore. Still lots with SU's though but less with ZS's. The old Haynes Zenith-Stromberg manual has a listing in the back of most of the applications and their needle numbers. In another section they list the actual diameter of the needle in 1/8" increments from the shoulder to the tip. I spent hours pouring over those figures comparing them to the B1AF (stock TR6 needle).

In the end, I called Joe Curto for help. His first suggestion was to move lower than cloud level (his wiley Brooklyn humor I guess), then he said he would look over his tables, see what he could find and asked me to call him the next day. When I did, he suggested I try B1CE needles. They were for Jag V12 Automatics or something like that and lo-n-behold were not included in the tables that were in my Haynes manual. With these different needles, I did notice an improvement in power and driveability but have not had the opprotunity to get it back on the dyno. I have toyed around with fitting some 'bungs' for O2 sensors and do it myself... but haven't gotten around to that either.

Another possibility of adjustment is in making sure that all the jets are the same height. Not an easy task on later ZS 175's.

Don't know if I helped any Paul, but that is about all I can offer right now.

 

[Brosky]

Shawn,

Thanks for your timely and valuable input, as always. I have Joe Curto on my list (if I can't get Jeff for a while. I guess that I will have to try the following first, to see what happens. I can do this easily because my tester is installed, so the changes will become obvious and recordable.

1. Jeff said that the carbs were all matched in settings and the fact that they only needed idle adjustments to run pretty well convinces me that they are at least close. So I will follow the procedure for adjustment to richen them where I'm lean and see what happens at WOT.

2. If that causes more top end issues I will remove the needles and mic them or try to find a number is there is such a thing and see what I have in there now. That will give me a starting reference point to work from.

Any other thoughts or ideas are greatly appreciated.

 

[LastDeadLast]

Paul,

I'm going to make an appointment to get my o2 sensor bungs welded in next week. I've got the same gizmo that Alan has (LM-1 from Innovative Motorsports) so hopefully I can get some good "on the road readings" with the unit. It also allows me to hook my laptop up to the sensors for data logging. I also got an add-on module that lets me run and log two sensors at one time (I believe this is called a LC-1). I did this because I run 6-3-2 headers and I wanted to log both banks at the same time.

If you like, we could exchange notes to maybe get my ride straight and when I'm done you can borrow my setup to work on yours. If you don't have a laptop I even have an old one that you could use for the logging. I don't know if you already have all the tools you need to get some solid readings, but nothing beats a loaded test with logging.

Lemmie know what you think.

 

[swift6]

I like Shannon's idea and need to do something like it myself as my header is also a 6-3-2 design.

Paul, there should be markings on the needles. If they are stock needles they should be B1AF's. You might need a magnifying glass and that is not a remark on your eyesight. /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

 

[Brosky]

Shawn, you must have known that I wear "helpers" for reading from the age of owner post! I can still see a golf ball 300 yards away, but I have trouble with the fine print.

Shannon, I have to call tech support at NGK to find out why the lights stay on in the unit after I shut the key off. I have it wired through the fuse panel on a circuit that has no power until the key is on, but the readout continues when I shut it off. That one has me confused a bit.

When I call, I'll ask about hooking this unit up to my laptop. I would like to work this out together if I can get my unit to work with something to collect and verify real time data.

In the mean time, I have emailed Shannon the Tuning manual that came with the unit. Let me know what you think about getting it to work with my laptop.