(Carb Mixt Modification) Off-topic project!

Posted: Sat Nov 06, 2010 4:10 am

Since there are so many technical minded pilots about, I thought I'd ask for ideas here.

Let me first provide the details of my project:

I waived the idea of EFI (Electronic Fuel Injection) on the 401 CID engine in my Cherokee in favor of a lower cost and reliable mechanical method.

I purchased a new Holley 4160 600CFM 4BBL carb, Percy's Adjust-A-Jet metering plate system and the Innovate LC-1 Air/Fuel gauge/datalogger kit from Summitracing.com

The goal is to be able to monitor and adjust the air/fuel mixture while driving...similar to how we used to do it in piston aircraft.
Now that I have received the items I have run into my first obstacle.....how to adjust the mixture screw on the carb from the driver's seat?
The requirement is to be able to make up to 14 turns which cover the entire mixture range of the carb from .060" to .140" jet sizes based upon the number of turns. The adjustment screw is made of brass and has a slot on the top for a screwdriver. There is very little room between the air filter housing and this screw (1/4" nominally) and the screw itself rises out of the metering plate as the mixture is enriched.
Here is a photo of the plate as mounted on the carb.

Our first idea was to use a speedometer cable that routed to the screw, but didn't realize it was in the vertical instead of horizontally mounted.

One idea is to add a short fluted or octagonal extension to the screw and place a driven gear next to it which is driven by a power transmission cable to a dash mounted knob. Another idea was to add a sealed tube that allowed a shaft to pass through the top of the air cleaner and connects to a hex head extension, but the limited hood clearance requires a sharp 90 degree turn immediately.

Any ideas for something that will make this work and is somewhat commonly available? My husband suggested a rod and u-joint affair similar to the venetian blind open/close rod and gears.

So HELP HELP HELP!

-Stregs[/img]

Hyper Postman Joined: Apr 21, 2008 Posts: 445

A simple rack and pinion would solve this that fits on top on the mixture screw, it can even be done using cable or pneumatic or even fluid pressure. The pinion/screw hybrid would have to be custom made so that the bottom is a screw and the top is a pinion although you can probably find one already existing.

If you want to be fancy you can try a servo motor to drive the rack and pinion to more accurate rotational translation.

The other solution is to still implement the rack and pinion idea but use a bicycle chain to ROTATE the pinion so that you now have a gear assembly instead and that would be easier to implement since you can move it off the carburator module.

You can also have a 'racker system', think of two rods (left and right) moving forward and back ROTATING the screw.

Another is a cog/wheel/gear and screw/helix solution with the cog/wheel/gear mounted horizontally to the mixture screw and driving a screw/helix which is what you use for the control.

There are so many solutions to this problem Smile

Just a matter of how much work and cost you want to put on it.

Posted: Sat Nov 06, 2010 7:23 am

How do you even know this stuff wright? lol Smile

Posted: Sat Nov 06, 2010 12:40 pm

Interesting ideas Wight Smile

I recall the equatorial mounts for cameras and telescopes that had semi-flexible cables with large knobs for azimuth and elevation controls that might work here. I assume they use a worm/helix drive at the cable which moves a flat gear etc. Somewhere in my travels I remember a cable leading to a small stamped steel cover that held the ran and pinion affair, but for the life of me cant remember where/what.
I admit this is a puzzle of some magnitude and finding an application and relevant parts is the tough part. We've been racking our brains for a solution found on the average US GM/Ford car in the form of either a stepper or servo motor or equivalent mechanical setup....but nothing comes to mind.

Hubby did have one idea tonight:
A vertical stepper motor fastened atop the purple plate, remove the threads and allow the needle to slide smoothly up and down with the motor....or a vernier drive push/pull cable assembly that does the same thing. I am not sure if we can achieve the tight tolerances needed to make things move smoothly OR how to get it to clear the air horn/air cleaner assembly.
A coarse/fine combo cable is fairly common and not too costly....but getting it to work is still a mystery.

Thanks for your input Hon.....you immediately keyed in on the function aspect!

=Stregs

Posted: Sat Nov 06, 2010 1:08 pm

No sooner did I post this last message than it hit me.....

The early 70s Ford and Chrysler Holley 4BBL carbs had some sort of funky bowl venting arrangement to allow vapor to be sucked into the charcoal cannister when the throttle was opened.

Now...if we can find this arrangement (Good possibility at the local pick n pull) and get it hooked up to the choke linkage (Passenger side) and simply have it control the mixture instead of closing the butterfly......we might be in like Flynn with a rotary vernier push/pull cable that is slow moving and precise. In the photo, you can see the linkage arm drops and pushes open a nylon button....that opens the vent passage when depressed.

So, I'm thinking of having a machine shop chuck the needle into a lathe and turn down the threads till a close fit is achieved between the threads in the metering block, but allows the needle to move up/down...then braze or solder a low lash/low slack eyelet to hook up the needle to the linkage arm.
This might be the solution Smile

What do ya think?

-Stregs

Posted: Sat Nov 06, 2010 1:21 pm

My head hurts ... Confused

Posted: Sat Nov 06, 2010 1:21 pm

How are you going to advance and retard the ignition without EFI/ECU to control knock and pinging.

Posted: Sat Nov 06, 2010 1:49 pm

If I keep the air fuel ration around 14.7:1 that wont be an issue since the timing, advance curve and vac advance are set and work great at all altitudes. If I lean out too much, a red LED will flash on the dash warning me of detonation. The LC-1 by Innovate is a great little unit that allows for three sensors as well as data logging and real time monitoring/recording via laptop.

Hyper Postman Joined: Apr 21, 2008 Posts: 445

That would certainly work Miss Smile

Sorry I was away.

@sgt.Johnston: I am a CAD/CAM designer and totally destroyed all my toys when I was little and put em all back together Smile

Posted: Mon Nov 08, 2010 5:48 am

Haha

that sounds like what i used to do Smile

Posted: Wed Dec 01, 2010 10:03 pm

UPDATE:
I got everything working and WOW WOW WOW!!!!!!!!!!!!!!

I found the proper cable through NAPA auto parts, and while spendy, was PERFECT for this project.

This is what the mixture needle looks like inside the metering plate.

I decided that rotation wasn't the answer, so I designed a vertical arrangement.
I had a family member turn the needle in his lathe to remove the threads which would allow the thing to move up and down easily, then fabricated linkage out of 1/8" brass rod.

This is the before shot after installing the Holley carb on the 401 and tuning it properly for 300 feet MSL operation with the metering plate installed.

The photo above shows the completed installation. This is a prototype and it needs some minor changes however. The red line shows where I will use a tubing sleeve to support the lateral rod to protect it from being bent. The yellow line shows the new path of the adjusting cable after I shorten the vertical arm. I found the length of this arm resulted in a too-fin adjustment ratio of 12:1. I will shorten it and end up with about 9:1 which will allow for better control of mixture.

As you can see, the linkage is crude, but it is in fact very effective!

With the Innovate Motorsports LC-1 installed, I can adjust the air fuel mixture in the same manner as an aircraft. I aim for 14.7:1 ratios but am happy with 14-15 average. Pulling 19" of manifold vacuum at 75MPH on flat ground, I was able to adjust the mix for proper ration AND gain 5MPH road speed without any other changes.

In the cold morning I do not need to use a choke. I simply pull FULL RICH and leave it there till engine temp rises, then slowly lean it out as the engine approaches operating temp. In town I am able to set the mixture after this warmup and forget about it.

I took the Jeep uo to a steep grade and turned around to head back to town. I pulled LEAN CUTOFF at 65MPH and let the engine brake the Jeep till I got to the bottom. All I had to do was pull the knob about 1/3 way out and the engine came back with no sputtering or backfiring. PERFECT!

I am taking a 400 mile drive tomorrow and will see how the mileage does on Interstate 5 on mostly level ground the whole way.

WEEEEEEEEEEEEEEEEEEEEEEEEEEE

Hyper Staff Joined: Oct 21, 2004 Posts: 100

so does the LC-1 give you real time monitoring of the exhaust gases then?

i ask because if your adjusting the mixture as you drive it can cause problems for you as the timing advances you can go too lean and that will burn a valve in short order an going in the other direction too rich and you'll fowl plugs in short order and it wont take much do do either
i have learned this over the years of tuning my bike

here's a pic for you strega

and a little theory on AFR

Air/Fuel Ratio (AFR)

Higher AFR values correspond to a leaner (less fuel) condition. The practical operating range for most engines using gasoline fuel is from approximately 11.5 to 14.7 AFR. Combustion of a stoichiometric mixture (exactly enough air to burn all the fuel) results in 14.7 AFR indication. Automotive engines with catalytic converters operate near 14.7 AFR during cruise and idle. Air-cooled motorcycle and automotive race engines require a richer mixture to limit cylinder head temperature and prevent detonation. The table below lists recommended AFR values for engines without emission controls.

Operating Mode

Recommended AFR

Cold Start (first 30 sec)
11.5-12.5

Idle
12.8-13.5

Part Throttle Cruise
13.0-14.0

Wide Open Throttle
12.5-12.8 (values down to 11.5 may be used to reduce detonation)

Where do these values come from and what is the effect of AFR on engine torque? The chart below provides some answers (ref: Automotive Handbook 2nd edition by Bosch GmbH, pp. 439). In the absence of other limiting factors, maximum engine torque occurs at about 13.5 AFR. Under wide open throttle (WOT) conditions, a richer mixture (12.5 to 12.8 AFR) is generally required to reduce cylinder head temperatures and avoid detonation. While the torque curve appears relatively flat from 12 to 14.7 AFR, the effect on cylinder head temperature is more pronounced. Please remember that the chart is based on lab experiments under carefully controlled conditions and with gasoline octane high enough to avoid limiting effects from detonation.

Engines with race camshafts exhibit large cyclical variations at idle - necessitating a relatively rich idle to prevent stalling.

so many have the idea the timing and AFR are two separate things but they do work together and if one or the other is out drastically then you can have a bad day in no time at all
in the way of poor performance and or engine damage due to too hot heads (burning valves) because of too lean a mixture or worse a holed piston
or excessive carbon build up from being too rich

you may already know all this or not
just thought i would pass on what i have learned over the years
one thing to remember is that air density changes on land are no where near as drastic as what you encounter while flying

going from sea level to 4300 ft cause me to richen my idle up 2 jet sizes (due to cams) and i had to lean the needle circuit out 1 notch on the needle and i had to drop 2 sizes on my main jets so the changes are minor by comparison as you can see

hope i helped you out and gave you some good info

Posted: Thu Dec 02, 2010 2:48 am

Thank you for the info Spyder Smile

Yes, most of what you shared I was already aware of, but it never hurts to read it again.
The main purpose of this mod was to avoid the side-of-the-road re-jetting once I got up to 7800 MSL where my property is. The poor Jeep ran like caca and the over-rich condition was killing my head. Re-jetting a Carter AFB is time consuming anyway, but with me having to lay across the radiator support while doing so HURT! My chest was black and blue after that so I wanted to do something.

For the most part, I set the mixture close to 14.7:1 as possible for the driving conditions and make a fine adjustment here and there as things change. Highway use will require minimal adjustment as well.
Yes, the LC-1 is a realtime wide-band AFR unit and seems to be accurate. I added an Edelbrock narrowband AFR meter and placed the sensor after the single muffler and it's reading close enough to teh LC-1 that I believe them both.

The AMC 401 will ping/detonate in a hurry if there is too lean and too much spark lead and to may amazement, have never heard it do so.
Much of this is due to good tune, clean fuel and well polished and de-burred combustion chambers. Typical AMC/Jeep cast iron production heads have a stupid edged ridge at the top part of the bore as well as fly-cut areas for the valves. My brother Ray ports and polished the heads and matched the chambers to the bores as well as knocked down all those sharp edges. The test was that he used a large blow-torch and moved it around the chambers till they were very hot. You could see the edges get bright red long before anything else heated up. He said this acts like a glow plug under lean conditions and without them, then engine would be less prone to detonation. I believe he was right.

Anyway, I am about to roll for a 400 mile round trip and can't wait to see how the Jeep does.

CIAO!

Hyper Staff Joined: Oct 21, 2004 Posts: 100

cool good luck on the trip

Hyper Postman Joined: Apr 21, 2008 Posts: 445

Wonderful solution Miss! Smile

Nicely done! I am glad that the solution is a much simplier one Smile