SU Guru needed - Lean acceleration.

B-20 w. Hatachi SU's ( Japanese copy of the Euro SU's)
I've been through all of the tuning guides but am missing some link..
I have a WBO2 installed and am getting...

Idle @ 850 rpm 11.7:1 to 12.2:1 AFR
Cruise @ 40 mph 14.5:1 to 16:1 AFR
Hard acceleration 10:1 to 11.8:1 AFR

So far so good. But...
Slow acceleration or going up a hill, leans out and pegs the WBO2 above 17:1 AFR
and exhibits serious lean stumble.
I've tried several different weights of oil in the dash pots, everything from no oil at all, ATF, 20 wt, 30 wt and 20 wt mixed w. 90 wt gear oil. The heavier oil works better, but doesn't cure the problem.
I've also tried richer (HG) needles but still get the same result. Though the richer needles seem to give more power before it all goes to crap around 3500 to 4000 rpm.

I've checked for leaks (carb. shafts, manifold and everywhere else)
Confirmed the timing (12 degrees BTDC)
Adjusted the float levels
Good compression (165,165,160,165)
The carbs. are well balanced, clean & the needles drop as they should

The various information on tuning seems to say as long as your idle mixture is good, then the rest will just sort of fall into place.
Certainly not my experience.
So, where am I going so wrong?
Any and all suggestions welcome.

Thanks
-TR

Up date - With the cure...
I finally found the problem!
After trying everything I knew, guessed, read,and was told and the help from various sources.
I decided to, essentially, start over.
I removed the carburetors with the intention of going completely through them. There had to be something wrong with them!
The heat shield looked a bit shabby so I decided to pull it off and paint it.
There it was! No, there they were! The exhaust manifold had a 4" crack in the center and second crack in the #4 runner that wraps about 2/3's of the way around the casting.
The only clue I had to this was that the engine sounded rather loud and when I hooked up a vacuum gauge the needle shook violently. Vacuum gauge info says this indicates a sticky valve or a broken valve spring.
After finding the cracks, I Googled "exhaust manifold cracked lean carburetor" and found my experience was not an isolated case. I replaced the manifold (it is good to be a hoarder) and like a miracle things are as they should be.
It seems this is a "lost diagnosis" fuel injection will automatically richen the mixture because of the extra oxygen in the exhaust and just give horrible gas mileage. A carburetor can't make an adjustment, Thirty years ago, given the symptoms, a mechanic would have just said "ya prolly got an exhaust leak".

Thanks for your help,
-TR

I dropped the manifold on cement from about a foot onto cement and the #4 runner broke off!

Here is the manifold after a short (12") drop!

Tracy;

I'm happy you got this squared away, and thanks for follow up with pix!

Was there no suspicious and telltale engine compartment noise change that might have clued you in to a cracked manifold...?...or did you maybe just not take notice of it...?

In any case, I request permission to repost pix on SW-EM site.

Happy Easter!

Ron,
As far as obvious signs, I was looking at carbs, not exhaust for my problems. I didn't discover the cracks until after I removed the carbs and the heat shield.
There were some tell-tale signs that if I knew more I would have taken the hints earlier.
Yes there was noise, it was a ticking that sounded much like tappets. I adjusted them a couple of times but the clicking persisted.
The right side in the engine bay was getting dirty while the rest was staying clean.
The engine was running lean, which was my first complaint. Now that I understand that air pulses out and IN through the cracks, the lean state makes sense.
As noted earlier, when I hooked up a vacuum meter, it went so crazy at idle, I thought the needle was going to break off!

I love working on cars for the challenge, problem solving and learning. This is just another semester in my education.

-Tracy

Ron- you are welcome to use the photos in any way you wish.
I can email the files to you if you want.

Tracy;

I've thought about this some more and have to suggest that a lean mixture (associated with high exhaust temps) contributed to the cracked Manifold first...in other words, the lean stumble (associated with general lean operation) came first and was, in part, cause of the cracked Manifold.

Also, I have to question your assertion that: " air pulses out and IN through the cracks, the lean state makes sense."...in the first place, there is positive pressure in Exhaust Manifold at all times, so I don't believe and can't accept air ever flows IN there (crack was after all in Exh Man not Intake!...and the ticks one hears when that is the case are the exhaust pulses escaping)...second, you suggest lean stumble is caused by this opening...I have trouble accepting that also because even IF outside air was getting into Exhaust Manifold it wouldn't result in "lean stumble"...all the power-making and parameters which affect engine tractability are done at that point already...a crack in Intake Man, on the other hand, where there in negative pressure (and I would accept air flowing IN!) would allow False Air and a lean mixture, but this was clearly not the case.

I guess what I'm saying is, after replacing cracked Manifold, check to assure you don't still have a lean stumble due to a lean mixture...you wouldn't want to crack another one...!

Cheers

My original problem and its eventual solution has raised a really interesting discussion that goes way beyond my knowledge base. Thanks for sharing your knowledge, research and expertise.

I believe that the original problem was from running lean to begin with. I finally ended up re-shaping a pair of needles to conform to the W02 profile. These seem to work very well.
The best part is that I was able to drive the car to Davis and back (about 850 miles round trip) without incident.

Thanks
-Tracy

...in the first place, there is positive pressure in Exhaust Manifold at all times, so I don't believe and can't accept air ever flows IN there...

Not true, unless the exhaust is a hunk of junk. A good exhaust system is not only free flowing, but can also produce suction at various points of the rev range, that's the entire reason to fit headers, and the reason they used to be called extractors here in Australia.

A good intake produces pressure too.

Also, the old A, B & C cams are so slow off and on the seat, the amount of overlap is rediculous, that's one of the reasons B18B and B20B donkeys are so notorious at producing intake reversion.

Paul;

I (believe) I understand about extraction effects and scavenging of a Header, but these occur intentionally at elevated RPMs, and at the collector as a benefit of adjacent full-sized pipes. I really don't think it applies here much, firstly because I'm certain that the exhaust system is not tuned or optimized for anything at idle, and a small crack to the outside world, hardly works the same as a full cross-section passage, optimally designed to work at RPMs and in close proximity to the others at the collector.
Secondly..."suction" is a relative term...as long as pressure is lower at the collector than at the Exhaust port (because of the effects of adjacent cylinders at the collector at RPM), it might be called suction, and it will help with the extraction of gases of other cylinders, but I think the pressure is still above ambient such that any inadvertent small hole in the system (like a cracked manifold) will blow exhaust OUT, and not IN...that's what I think...!

Cheers

"I (believe) I understand about extraction effects and scavenging of a Header, but these occur intentionally at elevated RPMs...."

The only 4 stroke headers that are designed to work the best at high rpm in a narrow range are the zoomies you only see on Nitro burning TF and Funny Cars. They lose power in most of their rev range, but that doesn't matter because it is surplus.(Do you know how Top Fuel clutches and gearboxes work?)

Also note that they are tuned to the same rpm, but TF zoomies are very different in length than FC, TF would be 3rd harmonic, FC 2nd harmonic.

"extraction effects and scavenging of a Header, but these occur intentionally at elevated RPMs, and at the collector as a benefit of adjacent full-sized pipes"

Depends on the design. Old school Independent 4-1 headers on a race car have two tuning points, one where the primary enters the collector, and the 2nd point at where the collector enters the atmosphere. On a V8 with the typical 90° crossplane crank, the difference in area between the primaries and the collector is 300 to 400% and then the collector has an infinite jump. These are outdated since the 1990's

The alternate old school Interference design 4-2-1 headers seen on inline 4's and flat crank V8's fitted to a road car have the first tuning point where two primaries from opposite cylinders join the secondary, a jump of 20 to 50%, the 2nd tuning point is the distance between the opposite valves, the 3rd tuning point is where the secondaries enter the collector, a change in area of 30 to 50%, the 4th tuning point is were the collector enters a large chamber before a muffler or a proper straight through muffler like the original Volvo ones. If you add a step or two, you can add more tuning points.

"Secondly..."suction" is a relative term."

Headers produce actual suction at the valves at the various tuned points AND at their harmonics. The more modern NASCAR headers look like a combination of both designs PLUS they have a big step on the primaries PLUS they have merge collectors on the secondaries PLUS an X-pipe.

You have a very simplistic understanding.

Most headers are tuned to provide maximum suction just before peak HP at the 3rd Harmonic. They then produce suction again at the 4th harmonic, 5th harmonic, etc. A very average set of headers can produce 4psi of suction, easily. 4-2-1 will spread this over multiple locations.

Now to the camshaft, take your tappet cover off and see how many degrees of crank rotation both valves are off the seat as you turn it over by hand. WHEN YOU HAVE BOTH VALVES OPEN & THE THROTTLE IS LESS THAN FULL: The intake has vacuum in it and sucks exhaust from the exhaust system into the intake manifold, now you are getting more O2 mixed in to the intake charge, leaning it out, hence full throttle mixture can be fine, but part throttle artificially lean.

Mechanic School 101: If you think you are having carb or injection woes, check out the ignition, the exhaust, intake AND exhaust leaks, check your lash and look for missing cam lobes, NOW you can look at the carb condition, jetting OR injection woes.

You should read Philip H. Smiths book, it's 50+ years old, but the formulas in there are still valid and have been constantly fine tuned. I also highly recommend you get a copy of Pipemax. It is a program that gives good figures for header construction, intake length recommendations and port dimension requirements for X amout of power.

If you still doubt that suction is possible in the exhaust or pressure in the intake, explain how F1 engines can exceed 130% VE. Even a vintage Volvo aided with tuned length, one throat per cylinder 2x DCOE systems can give 113%. Now look at a dual plane manifold on a V8, beating 85% VE is hard, twin SU's on a inline 4 would be similar or worse due to firing order, and the dog leg 'log' style B20A and B30A intakes are much much worse. Compare B30A to B30F, same cam, compression, etc., basically just different intake manifolds, the differece in power and torque gives you the difference in VE. The extra output after you buy it comes for free.

Designing a performance and/or economy engine is a lot harder than you think even on are old dinosaur donkeys.

Paul;

Thanks for good info on engine flow...I'm no expert so I might have oversimplified, but it seems to me that your explanation: "WHEN YOU HAVE BOTH VALVES OPEN & THE THROTTLE IS LESS THAN FULL: The intake has vacuum in it and sucks exhaust from the exhaust system into the intake manifold, now you are getting more O2 mixed in to the intake charge, leaning it out, hence full throttle mixture can be fine, but part throttle artificially lean." ...does not factor in inertia of either exhaust or intake flows and their results...it would seem the dynamics should be added into the consideration. Thanks also for reference material suggestions!

Cheers

" ...does not factor in inertia of either exhaust or intake flows and their results...it would seem the dynamics should be added into the consideration. "

Where is the inertia coming from? There is none in the intake, because it has a partial vacuum in it, so no real airflow travelling inwards relative to the size of the port. There is very little in the exhaust, because not much air/fuel is going in to the cylinder and then the majority of the exhaust comes out when the exhaust valves opens.

Let's look at overlap, with a C cam there is about 60° degrees of overlap. If you look at the piston, it virtually moves nowhere for the middle 20° while both valves are off the seat and you are at part throttle, so you have the vacuum from the intake port sucking exhaust backwards from the exhaust manifold, leaning out the mixture with O2 from the exhaust + additional O2 from the cracks.

...and this occurred on the late factory 4 into 2 into 1 Exhaust Manifold which could hardly be called a "piece of junk"...

Well done, sir.
--
Barry '67 122S "Betty" (Rest in parts), '69 122S "Veronica"

Tracy;

Where did these carbs come from? Are they really SU clones? How are they configured...most importantly: What Metering Needles?, and are they correctly installed...what is jet position unchoked? Is FuPu able to keep up with demand at Revs/Load. Are Bowlvalves set correctly?

If your WBO2 meter is indicating very lean, can you enrichen to compensate by lowering Jets (pulling Choke)?

No oil would result in exacerbating lean stubble on fast Throttle opening...oil should be 20W or ATF.

"needles drop as they should" ...needles don't drop...Dashpots, into which MN are installed rise and fall...not to pick your info (on which I do compliment you for being as complete as you could be) apart, please use standardized terminology, so that everybody is talking about the same thing...

Have you seen these videos and you you understand them?:
SU Part 1. https://www.youtube.com/watch?v=7GRAcqDySog
SU Part 2. https://www.youtube.com/watch?v=60Bj_2cZQnc

Good Hunting?

My project continues...
As per the first reply regarding ignition, I spent the day upgrading my stock ignition to an electronic (Fireball XR700) unit. I didn't get it done in time for a test run. I'll test it out tomorrow. Then move on to the next suggestions.

Hatachi SU clones were made under license from SU.
Some differences (improvements) but the basics are the same.

What needles and spring do you have?

5W or ATF are the only 'correct' fluids. I've used WD40, others have used thicker oils, but both are band aids. Another tuning band aid is to add weight to the pistons such as lead sinkers.

If SU needles and springs fit, tell us the rest of your engines details, and we can tell you what needle and spring to use.

Do SU needles fit the Hitachis? Useful if they do. Needles can be selected with many variables but you may need to get the car on a dyno to get good mixture readings across the rev range.
Might be down to timing, carburation problems often turn out to be ignition ones. Check that the advance retard mechanism is free and working well. Again the dyno will be your friend there too.

I took the car out for a test drive today.
After changing out the entire ignition system (distributor, electronic instead of points, new coil, new ignition switch). It ran like a champ!
I'm confused here... If the ignition was crapping out, why was the engine running lean? Unburned fuel would show up as super rich wouldn't it?

I went with the ignition upgrade first since I had the parts lying around. I have a few needles to play with and can reshape them fairly accurately with a Dremel tool, wet/dry sandpaper and a micrometer. So that is where I'll go next.
I wonder if I can sneak a dyno into the garage without my wife noticing.

Thanks for the suggestions.

-TR

Tracy;

I'm happy you got this sorted out, but you still didn't answer the questions we posed...but now that ignition is (apparently) OK, how is WBO2 indicator indicating throughout operating range?

"Unburned fuel would show up as super rich wouldn't it?" ...I understand (and probably agree with) your thinking, but the question is: Would a normally rich mixture due to a "generous carb" result in the same hydrocarbons in the exhaust as when a misfire (non-ignition) occurs?, and what would the WBO2 indicate with that condition...Rich?...super Rich, out of Range? ...and you can answer and confirm this question for both of us by driving at some steady-state (Speed and Load), and monitoring the WBO2 indication...if in the linear region, and you pull the Choke (resulting in significant enrichment)...what does WBO2 indicator do?? I'd be interested in your observations.

Cheers

I’ve been working on the tune most of the weekend.
Here’s where I’m at.
Idle 12.5:1 AFR
Light accel 12 – 11:1 AFR
Hard accel 9.5 – 10:1 AFR
Cruise at 35 mph 15:1 AFR
Anything over 45mph starts going lean. 17+:1 AFR

Looking like fuel starvation at this point. I installed a new fuel filter today which seemed to help. Tomorrow I will test it with an electric fuel pump and see what happens. I hooked up a fuel pressure gauge today, but it is for fuel injection and didn’t even register, though I got a good stream of fuel when I pressed the pressure release

To answer your questions-
I don’t know the origin of the carbs, but this model was stock on early Datsun 240Z’s and some other Japanese domestic & import cars (early ‘70s).
I have watched those videos several times over the past few months, they’re good, but are based on a properly configured engine/fuel set-up.
The springs have no markings so I don’t know what they are.
I have installed a set of KD needles, the Hitachi and SU’s are interchangeable. But, just to complicate matters, have a different numbering system.

I spoke to Eric/Planetman, who recommended DX needles, I graphed out the KD’s and the DX’s and both are just about overlapping in the range where I am having problems.
Yes, pulling out the choke does richen the mixture, though I didn’t have time to try it at higher speeds.

Thanks for your input.
I will make run well, it’s my ride to Davis!

-Tracy

The SU/Hitachi gets the suction to raise the pistons via a hole on the outside flange, the one where you mount the filters. Not unknown for the holes the get obstructed by a gasket or the actual filter. This could mean that the pistons aren't rising enough, meaning the butterflies open and give you more air than the piston position wants, hence lean. How does the engine rev out in the lower gears? Does it have the same problem? Do the pistons rise fully if you give the engine a second or two's full throttle while looking down the carb throats? Loosen the dampers to check if the pistons rise smoothly and easily, using your finger.

Tracy;

That sounds like progress in...at least it sounds like your still data-gathering...but this data will help you understand what is not right, so you can correct it...and in the end, I expect, YOU will be an SU Guru!

My thoughts and questions...

I have not played with a WBO2 indicator so am not familiar with the correlation of AFR to drivability...drivability is really my/your goal (with a secondary goal of optimizing fuel consumption, or at least having it be reasonable, while the car runs well), and most tuners do not have an Exhaust analyzer, or maybe we have it briefly when we have the opportunity to put the car on a dyne...so we tune for drivability, and let the AFR be what it will...you have a different, and unusual situation (which most of us would love to have!)...with WBO2 indicator on board, you have CONTINUOUS Exhaust Gas analysis ...I guess what I'm trying to say it is: What comes First? Typically Drivability...and when we have it, we're happy, and when it goes away we wind up looking for what is wrong and out of the ordinary...in YOUR situation, you haven't had good drivability yet, so your still looking for it, and by having that WBO2 gauge, your already at an advantage in getting there...BUT...Drivability comes first...don't let that indication from that gauge make you crazy!...it's a carberated (not injected) engine situation (with instant electronic mixture correction happening thousands of times a second), so be careful you don't become a total slave to that WBO2 gauge, thinking it should indicate perfect all the time (I question if it ever can with a carberated engine), and always feeling you need to tinker with carbs (once they are set and running well)...

...and I presume you are confident that it is not Ignition System that is holding back engine...hows your Centrifugal Advance?

...so are you saying that for the first four conditions drivability is good and "over 45" it gets bad? How does Lean condition manifest itself? Engine feels like its being held back (even at steady speed) ...popping and spitting? ...poor throttle response?...

Question(s) you need to answer (also what happens when pulling Choke when it indicates lean!):...is it really Fuel Starvation (insufficient delivery to Bowls) or Lean due to Metering Needles...again pull choke when Lean condition happens, if it picks up and AFR indication comes back in range, I expect its the MN...but if this doesn't help, delivery may be insufficient for any number of reasons...blocked line or filter, FuPu problem, blocked Jet Delivery Tubes at carbs, etc.

A properly operating mechanical FuPu should be able to keep up with demand...(Low Pressure) Elec FuPus still will probably need a FP Regulator, and these are typically unreliable junk, so be careful installing an electric FuPu...their output pressure is typically way over the 2-3PSI max that the Bowlvalves can control and successfully hold back...a Manifold Vacuum/Pressure Gauge will have the low pressure range you need to monitor supply from FuPu....

OK on source of SUs, a functional indication of Springs being OK (configuring the carb to be within a usable/linear range under load, or when simply blipping the throttle) is that Dashpot is operating in the middle of travel (and not slammed up against the top or hardly opening)...(for B18/20 they are supposed to be Red).

The videos are theoretical and to help you understand what is SUPPOSED to happen...now it is up to you to correlate that with WHAT is happening...and come up with what is wrong so it can be corrected...

Finally, I always want to know what the engine response is UNDER LOAD...either on a Dyne (where they stick a probe in the tailpipe and tell you for instance "at this load, you're lean, so you could get a bit more out of it if you richened it up here"), or accelerating down the street, or better yet up a steep hill...that is where I use my "Seat-of-the-Pants" gauge...you have that plus a fancy WBO2 gauge to help you interpret what your SotP gauge is telling you...

Good Hunting!

Ron,

Thanks for hanging in there on this. I appreciate your insight and comments.

Today I installed the electric fuel pump. It made no difference, so I took it back off.
I spent some time setting up a small video camera in the engine compartment to see how the needle rises while driving. I got a usable video, but will work on it more tomorrow. I'll see if I can move the WBO2 gauge from the dash to the engine compartment to be shot in the same frame as the carb throat.
From what I did see in the video I shot, the dash pot seems low compared to your description (mid range). Perhaps I'll see if the springs I have in a set of Euro SU's will fit.

The experiment continues...

-Tracy

Tracy;

"Height"/length of relaxed springs will answer question if they are the correct ones...lay them down and measure, and compare to what they should be (unfortunately I don't have the reference info)...I just measured the one in my "training carb" to be 5 5/8"/140mm...use this dimension as a guide, not gospel! I can't guarantee it, and remember your carbs are the clones which MIGHT also have differences...you might at least compare the Hit to SU spring lengths...they shouldn't be too different... I expect too strong springs to cause lead stumble on fast accel only, not slow accel and after steady state is reached.

Remember also that unloaded, in the driveway, those Dashpots won't rise so much because demand is not there...under load driving they will...you're idea of watching them with camera along with WBO2 gauge is a good idea for data gathering...

another idea...but I suppose elec FuPu MAYBE already answered the starvation question already (BTW, did you supply it through pipe from tank? even elec FuPu can't supply fuel to carb that it's not able to get (clogged supply line or I've heard of in-tank line being corroded off)...you could supply it by hose into a fuel jug in the passenger seat floor to completely take stock arrangement out of the picture...): when it sputters, shut off engine immediately, pull over, and check levels in FuelBowls...if you catch them low, that again rather confirms starvation...so the suspicion would be off the carbs, because they can carburate what they are not getting supplied with...

Good Hunting!