To Mix Fuel and Air

I got my very own POSA FUEL carb today from, of all places, Greece.  More specifically the Isle of Crete.  This POSA was one of a group that was converted at the factory for use in light aircraft.  It has a fuel mixture valve and a rod operated air slide with no slide return spring.  It is a 32mm throat and has only had about 150 hours of run time total use.  I think I have the basis for a good fuel/air mixture device that is super simple.  With the bits of tuning information I have turned up from the light aircraft people this POSA should do everything I need.  It won’t be a quick fix and I will have a steep learning curve but the potential is there.  This should provide the means to make more precise tuning adjustments for varying conditions much quicker than with a conventional carb.

Just in case the term simple for a carburetor might seem to be overstated, here is the POSA Fuel completely disassembled.  Prior to having it in hand I had only read the patent and looked over the patent drawings.  It took all of five minutes to take it all apart.  There is one casket and two o-rings total for the whole carb.  Very pleased I was able to get one in such good condition and with mixture control.  This of course won’t be the last time I’ll be talking about the POSA, I can tell you!  Of course if this thing really drives me nuts I can always drop back and use the AMAL Mark II.  Nice to know I have a reserve.

The Works!

BROOKLANDS: Where the Magic Happened

                                         Brooklands sometime in the 1920s.

A.F. Locke-King, with his own money, built and opened Brooklands on June 17, 1907.  The intention of building the track was to provide the British motor industry a place to speed test.  Performance testing on a closed circuit would bypass the 1903 law relegating motor vehicles to a top speed of 20kph.

Brooklands was also envisioned as a profit making enterprise to capitalize on the growing interest in motor racing as a spectator event.  To satisfy both aims the track was built as a 100 foot wide 2.75 mile long banked oval.  The banking approached 30 feet high in places and the banked turns were of 30 degrees.  A later addition of a finishing straight increased the lap length to 3.25 miles.

In the early 1900s the technical ability to lay tar macadam on banking and the expense of laying asphalt lead to the choice of building with uncoated concrete.  This meant that all of the track sections had joints since by 1907 the technical ability to lay continuous sections of concrete had not been perfected.

Even with current suspension technology driving a long high speed distance on a modern interstate can be jarring.  The ability to smoothly joint concrete still seems to be in the future.  It can only be imagined what attempting a speed trial at Brooklands was like.  Some of us that still insist on riding hard tail girder fork cycles do have a perspective on what type of hard rider it would take to be an hour in the saddle at speeds of 100 mph or more.  I think young Fergus Anderson was one of those legendary hard riders.

I couldn’t find any Brooklands record photographs of Fergus Anderson.  This shot of Eric Fernihough on his Brough-Superior JAP 996 in 1937 gives a good approximation of what it would have been like at speed on the Brooklands banking for young Mr. Anderson.  Borrowed from Eric at Historic Engine Company.

MAGIC of the JAP Engine

Recently I was privy to a reasonable question ask regarding the fascination for JAP engines.  My immediate reaction was to think of the numerous speed records that JAP engine racers have made and broken over many years.  Of course it's also the look and the sound of them.  Thinking about the question of fascination and of course, in my case addiction, I reread what is probably the best example of the JAP magic.  It’s a story of record breaking as related by Jeff Clew in his history JAP: The End of An Era. 

By 1932 the JAP Speedway engine was well established as the engine to use if you wanted to win on the cinders or on a grass track.  The circle track racers loved it but the remainder of the racing community looked on it as a freak.  One young road racer didn’t have the same opinion of the engine.  As a result he determined to win a new trophy put up at Brooklands by H.J. Bacon for the first privateer to cover 100 miles in an hour.  Fergus Anderson was that young racer.

Mr. Fergus Anderson planned that if he could lap at around the 104 mph mark he could take one pit stop and carry off the hour record and the trophy.  To do so he went off to the Tottenham factory with cash in hand for an engine.  As his luck would have it the factory had five speedway engines ready for dispatch.  It has to be remembered that at this time the factory was building the engines mostly by hand and then dyno testing for output with a complete strip down and inspection before dispatch. 

As a result Fergus picked up an engine which was guaranteed by the factory to produce 37.8 bhp at 5,750 rpm.  Apparently he chose one of the five at random.  Fergus then installed the engine in a Grindlay-Peerless machine of Bill lacey’s.  His tuner for this escapade was Tommy Atkins who had about four hours with the engine before the attempt was made.  With a fresh engine and quick tuning Fergus took to the Brooklands banking, April 21^st of 1932, for his go at the record. 

In his first lap from a standing start Fergus brought the virgin engine across the line at 98 mph.  His second lap was a crazy fast 109.22 mph.  For the hour record with trophy Fergus averaged 100.52 mph.  All of this with a virgin engine, four hours tuning and an engine that was never designed for this type of racing. 

That's the JAP magic!

    This is close to what the engine, Fergus Anderson ran for his Brooklands speed fest, would have looked like.  His engine would have been a bit fresher looking as it was perhaps only 72 hours out of the factory dispatch room.

Bill Lacey was famous in his own right for his Grindlay-Peerless based Brooklands racers.  This is an example of one of his machines which is in the Brooklands Museum.  This is very close to what Fergus Anderson’s machine would have looked like for his Brooklands hour record.

ADDICTION and WAITING FOR PARTS

I have heard from people that have gotten skin illustrations that it can be addictive.  You get one and immediately start contemplating the next illustration.  That is what I have heard.  Speed drilling is addictive just as tattoos are.  I started with drilling and cutting the rear brake plate and I’m all ready contemplating what other bit and pieces could benefit from drilling.

I’m happy with the way this turned out.  The finish is not exactly what I envision for the end result.  There is a great deal of garage and mock up, tear down time before the wheel actually hits the road.  So if figure close is good enough for now.  I will touch up the finish when it’s time to bolt everything together in preparation for pronouncing it complete.

I will admit that waiting for parts is painful.  Even if that part may not be used for months and months.  It’s nice to know it’s on the shelf.  Still waiting for the POSA carb and word about my case rebuild. 

JAP at Auction

Today at the Motorclassica auction in Melbourne this went across the bloc.  A JAP Twin-Port Racing Engine: Engine no.1932 JORZ/D.  It sold for AU$3,360 inclusive of Buyer's Premium.  No details on the web site regarding condition but looks like it could be mostly there.  Somebody got a great engine for a project. 

Volatile bits and pieces

Later engines from the factory seemed to have had the intake sized so that they could use the new AMAL 932 carburetor.  This would have had a 32mm throat size.  Based on measuring up the heads I have available that works out.  However racers always try and get an edge so the AMAL Mark II I have is actually a 34mm on the intake manifold side and 43mm on the air side.  This may or may not present a tuning challenge. Since it's more normal, getting the engine to run well with the know quantity of the AMAL should prove to be simpler.

I got one!  I have luckily, for the ever curious part of me, been able to score a POSA Fuel carburetor of 32mm.  Even better yet it came off a light sport airplane and has had a fuel mixture control added.  Now I have a simple but reputedly enigmatic carburetor to eventually play with and either be successful or frustrate the hell out of myself.  No matter what happens it will be educational and there will be something learned.

Mechanics Warning

This is the JAP steel con rod that divorced the big end pin in an oil deprivation and heat induced marital disagreement.  The partnership strife was caused by inattention to the screws holding the Pilgrim oil pump to the timing case and oil stopped flowing when the screws backed out.  So the warning is, if you are assembling an engine and during your pre-flight checks be sure of the tightness of all those important pesky little nuts and bolts.  It will be worth the time it takes.

A Bit of Progress

Despite this fuel/air side track my time has been spent fairly productively.   The brake plate is almost finished.  What needs to be done is a bit more hand work on the finish and I need to source, drill and tap the screw holes for the screen frame.

The brake operating lever is also pretty much complete.  To correct the poor original quality of the factory arm has meant lots of time with files and aluminum oxide paper.  Luckily I’m not charging myself by the hour for the work.

The Problem with the POSA

One result of my curiosity regarding flat slide, rod metered carburetors is that I found several people in the light sport aircraft crowd who have cracked the mystery of the POSA.  For years the homebuilt crowd has used the POSA carburetor with decent results.  It seems that part of the reason it acts like a full throttle only race carburetor is the design of the throttle block and the taper of the fuel rod.  As one analysis stated it, the carburetor uses linear fuel metering with a non-linear air passage.  So the apparent fix was to reshape the rod to reflect a non-linear fuel metering which, by trial and error match the throttle block air passage at idle, mid and high speed operation.

Now that bit of information will have to wait until I actually can get one in my hand.  If anything all of this research has made me more curious than ever.  But for the future until that does happen I will plan on using the AMAL Mark II.  I still want a POSA!  At least to experiment with.

                                               A pair of chromed POSA carbs for a Harley.

More POSA Fuel

Just found an old motorcycle magazine article which confirmed what I was thinking was true.  James R. Birmingham inventor of record for Patent No. 3957930 was the principle of POSA Enterprises Inc.  POSA Enterprises seems to have actually started business making aftermarket parts for the early customizing scene.   

Besides motorcycles the POSA Fuel was used on a great many light airplanes using various engines to include modified VW engines.  From what I can tell most people hate the things or love them; doesn’t seem to be any in between.

I still want to find and try one on the JAP Privateer. 

Once More into the Depths of the US Patent Office

I have been trying to remind myself to take photographs of bits and pieces as I go along; more for my own records as for any other purpose.  I have been diligently sanding, filing and reworking the rear hub I will be using.  The brake plate is about ready to have the holes drilled and threaded to take the screws for the frame and screen for the hot air exhaust port.  I’m happy with how it has turned out.  So I turned my attention to the brake lever.  It was chromed from the factory but the quality of the metal work on the arm was atrocious.  This really surprised me, because Honda has always been lauded for the quality of their products.  There must be something besides motorcycles which has earned Honda the reputation for quality.

While not bending over the work bench with jewelers files in hand and aluminum oxide paper at my elbow I once more went into the breach.  Well not really just the patent archives. 

                                                       Inventor James R. Birmingham

What I found was a very keep it simple patent for several major improvements on the POSA carb.  Can’t decipher if this is a complete new design or just a major modification.  However what was interesting was that the description for the drawings and explanation of how the carb works was very easy to follow.  Unlike some patents I have attempted to read.  I do think I found one thing the inventor didn’t think of or include in the drawings.  There is a screw, labeled 30, which holds the fuel tube in place.  Fuel tube being 27 and the screw fits into groove 29.  The problem is that he neither describes nor shows how the throttle body 31 is supposed to move past screw 30.  In the drawing the throttle body is in the closed position.  In the open position 31 will move to the right in drawing FIG. 9.  The left hand extreme edge of the throttle body is defined by a line which abuts screw 49.

I may just be dense but I think that is a problem and I have read the patent several times.  I think there is a way to fix that over site but not really sure.  I would mill a slot in the face of throttle body 31 and relocate screw 30 closer to the throat of the carb.  Screw 30 would be part of a lying on it’s back L shaped lug which would support the fuel tube but also allow the throttle body to move past it.  The lug would fill what would otherwise be a vacuum leak in the throat of the carb if the slot for the screw 30 was left open.

But until I get my hands on a real POSA or build a copy of this carb I won’t know if I’m right or not.  So anybody got a POSA Fuel carb to lend me? 

Flat Slide History

                                          Ronald Albert Gardner Flat Slide Racing Carbs

It seems that William H. Edmonston is not the only inventor that has come up with a float less flat slide carb design for motorcycle engines.  A gentleman by the name of Ronald Albert Gardner around 1947 starting producing a flat slide carb for racing that is very interesting.  However I have only very thin information regarding his carb.  And he may have produced several versions of the design to include both float less and an internal float carb.  Still trying to find some information and at this point it’s more for curiosity than anything else.  As part of my research I stumbled across a reference to William “Bill” “Red” H. Edmonston having passed away in October of 2007.  I will try and  verify that.

Always Nice to Have a Basic Understanding of What you’re Trying to do

A carburetor is defined as a device for breaking up gasoline into a very finely divided state and mixing it with air in automatically varying proportions to meet the variable running conditions of a gas engine.  Ok now that sounds simple and it was when gasoline was available that was of a high test it was. 

So to actually get this all to work a few things are required for a carburetor.  A fuel supply is needed, air is needed to mix it with and the motive force of a vacuum to make it all flow and do its thing of producing homogeneity of mixture, which is the ideal objective for burning in a combustion chamber.   

One of the ways to make this all happen inside a carburetor is to use the Venturi Principal in the internal structure of the carburetor body.  All carburetors use this principle in some form or another.  Now it’s my understanding that using a venturi effect helps create a pressure differential which is lower than the atmospheric pressure the carburetor is operating in.  Of all the ways to get this effect one way is to machine a true venturi inside the throat of the carburetor body.  An example of this would be having an inlet of 32mm and in the area of the fuel supply valve the throat would taper to 30mm and then taper back out to 32mm on the combustion chamber inlet side.

Now obviously there are other considerations in design that I’m ignoring in my search for understanding.  My basic interest is in trying to find a simple carburetor that is fairly easy to tune for different operating conditions, altitude, fuel octane, and top end, mid range or low end performance.  But it remains pretty simple in design and construction.

All in all it seems that my best choice is still probably going to be a Lectron.  The current Lectron pretty much meets all of my requirements.  Plus it’s cheaper than all the alternatives and spares are very available since it’s still being produced.  But as always I could be dead wrong and your mileage may vary.  We shall see down the road when I get my engine built and try and feed it a homogeneous mixture of gasoline and air with a bit of spark added.

Gas/Air = Fuel Mixture and a bit of Interesting History

Along the way I have learned that most all designs for flat slide rod metering carbs produced in America, and there seem to be a few currently, come from a series of patents by one man.  The inventor is William H. Edmonston.  He has, by my count, 10 patents covering the flat slide, tapered rod design carb.  I’m not completely sure but from the patents it looks like the POSA and the Lake Injector came from his work.  Currently, as far as I can tell, the only carb being produced which cites one of his patents is the Lectron.

In researching the Lectron I ran across a few old references’ that suggested Mr. Edmonston had set up another company to try and produce a flat slide carb which would dramatically reduce emissions for two stroke snowmobile and water craft engines.  The firm was, or is named Atomized Fuel Technologies.   But I couldn’t locate any current information as to what type of carbs he is producing.  However I suspect it would be a variant of his existing patented flat slide, tapered rod carb.

                                                        Patent of William H. Edmonston

His first patent is Number 3,709,469 dated February 2, 1970.  The only patent ever assigned to a firm is patent number 3,985,839 and the firm is Lectron.  I am not an expert on how the U.S. Patent Office does things or what legal requirements they may have if the patent rights are sold or rights to production are granted.  So several of his patents could be currently in production and unless it's stated on the product or by the manufacture you may not know.  I suppose you could call around but at this point my curiosity regarding his designs is satisfied.  By the way if anybody is tempted to look in and wander about the patent archives; Warning, Don’t do it unless you have lots of time to spare.  It's endless and interesting, but easy to get lost in it like a maze.  I warned you!

Naked Alloy

Not a great photo but if you look in the bottom right hand corner at the outside of the brake plate;  well that is a fair representation of what alloy on the Overland will look like.  So looking at the photo I can see it.  But I did it so all others use your imagination.

The Tools of the Naked Alloy Brigade

At the top of the photo is a section of my new/old Boranni rim which I spent about 15 minutes on.  I know it’s hard to see.  This method won’t make all of the cinder nicks and small battle scars disappear.  But if that’s what I wanted I would have bought new.

The Look of Alloy

In my own grand tradition of having more time than money, in addition to being profoundly cheap, anything alloy on the Overlander will be naked.  And of course the racers reasoning is that paint weighs too much.  I agree! 

Never have liked chrome or mirror polish on anything I own, so I will be trying for something a bit different.  The look of alloy I do like is a satin, burnished silver look.   It is reflective and has a clean look but you can’t clearly see much reflected in the surface.

The method I use to do this, after experimentation I can tell you,  is too start the finish with 220 grit aluminum/oxide paper with either a bit of oil or WD-40 fish oil for a lubricant.  After I get the surface fairly uniform then it gets rubbed down with 0000 steel wool.  After all that the final is using a polish compound that comes soaked in a fine wool type material.  The brand name is The Original Never-Dull Magic Wading Polish.  I didn’t name it, but it works great. 

Best All Time Packing Material in the World

I got my Boranni today from my friend Dene in Tennessee.  Opened the box and found the packing material he used were old architectural drawings.  I’m telling you Dene has got class!!!!

Historical Reference Illustrated

                                         Two POSA flat slide carburetors’.   

                                          Magazine advertisement for the Lake Injector carburetor.

How to Feed Fuel to the Privateer

Back when my engine was new the factory supplied an AMAL 27 remote bowl carburetor with it.  As time went by, AMAL ended production of the 27 and the JAP factory started specing the AMAL 932; mostly because of availability and an increased intake size.  It seems, after a quick look at what is available, most carbs are a series of compromise choices that may or may not work.  So I decided to better define what I was looking for in a carb.

This maybe a dream but I wanted a simply design that was easy to tune for either street use or track use.  Will not really track but maybe some high speed work.  It would be reasonable in cost and had spares available and most importantly I wouldn’t have to buy it new.  Yes again I’m cheap.  In the years since my engine was new there has been lots of innovation and improvement in the area of carbs.  Or as they say, "Everything old is new again".

So I decided to do a bit of research to understand the process of taking fuel and mixing it with air to feed to the engine.  Research would hopefully give me some criteria for making a carb choice.  So to the library shelf I went.  When I need to understand the basics of mechanics I always go for my Father-in-laws, Charles ‘Chuck” Waltari’s copy of Audels New Automobile Guide, copyright 1949.  May seem strange to use an automotive book to understand a motorcycle but really the basic principles are the same. 

What I found was a step by step discussion of the principles of mixing air and fuel, with illustrations; I like illustrations.  What stopped me in my tracks was the part on efficiency and the venturi principle.  Sorry for the poor scan.  But the up side was that I learned something.  So I went to do some more research.  Oh the Audels guide says that a carb with a venturi throat shape at the fuel inlet jet is the most efficient design for obtaining, “Homogeneity of mixture “.  You have to like that!

So with this in mind I did more research into which carbs would provide that design; or something very similar.  It seems that modern carbs are built to a price point and with a design that is adequate for the job but not ideal.  Well except for one.  I reacquainted myself with a carb called the Lectron.

This carb is a third or fourth generation of the original flat slide carbs of the 60s called the POSA and the Lake Injector.  Besides being a flat slide carb it does have a true ventuir shaped throat for the fuel air mixture.  Well that’s what I believe the design provides.  Considering that on a 32mm air intake it tapers 2mm to 30mm at the fuel jet and then tapers back to 32mm on the head intake side.  Go here to read what Lectron says about their own carbs.  http://lectronfuelsystems.com/  Bottom line for me is that it should provided what I’m looking for.  We shall see.  I would appreciate any comments from the experts that may read this.

Saving Weight

In the Mountain Bike world somebody that is obsessive about paring weight off their bike is called a weight weenie.  In the motorcycle world somebody that obsessively removes, cuts, drills and pares weight of their cycle is called a RACER!  

More Bits to Massage

While waiting for the case to be repaired I have dug out some more of the bits I may use on the Privateer.  So going clock wise is the rear hub brake plate and the speed cutting as of now.  The bracket to hold the screen for the vents is close to being finished.  And the first bit, and not the last, of Birmabright to be used. 

Next up is the fuel filler I will be using.  It is from an aircraft and alloy.  The plan is that what ever shape the tank takes it will have a flat top and this filler will be frenched into the top so I can lay down on the tank for some aerodynamic speed effect.  Yeah right!  I do dream a bit.

Next two around are the remains of a Stromberg carb that was dead.  Forget the coffee cup, that’s not going on the Privateer.  The fuel bowl I’m going to morph into a tail light housing and the upper cover I’m thinking of turning that into the headlight.  Small and compact and maybe try a quick disconnect for both.

The final bit is a sealed on/off switch that will be used for the kill.  All of these bits are used, recycled and repurposed.  Before long I suppose I should be using the green buzz word someplace in here.  Nope don’t think so!  I’m not green, I'm just cheap.