Carbs & accessories

airnutz · **Posted:** Wed Dec 22, 2004 12:07 am

BDK,
In a previous, but now "locked" thread, I stated that the cause of a
Buchon write-off was due to a poorly rebuilt float-carburettor. You stated
that "you had never seen a Buchon with a float-carb...and that only early
BoB Merlins had float-carbs." (close-enough BDK?)

I remembered incorrectly...they had not rebuilt the carb. BUT, I assure
you THIS Buchon had a float-carb!!!!

Jase, tag...yer it....how do ya like me now???

Jase · **Posted:** Wed Dec 22, 2004 7:53 pm

Chris: Actually, I count it as time well spent since I re-educated myself. If anyone else learned something, well dats gravy on da meat!!

Airnutz: Are you seriously saying that Buchon had *no* carb???????

airnutz · **Posted:** Wed Dec 22, 2004 9:18 pm

Jase, I Thought I was CLEAR in my previous post...the Buchon definitetly
had a *CARB*!!!!

Well, Jase you are timely..I was just coming on to alter my post, it
was a bit "tart" in its delivery.

I was surprised that it appeared to anyone that read this, would assume I meant that the written-off Buchon had no means of fuel delivery! Ya'll
musta' thought I had gone totally "around the bend"...well moreso than
usual!!!

Jase I was purposefully being vague because some things are better not discussed in public..but I left enough clues for the "old-timers" of this site.
Some of them, may know exactly what I'm talking about in reference to the Buchon.

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11324

airnutz wrote:

I remembered incorrectly...they had not rebuilt the carb. BUT, I assure you THIS Buchon had a float-carb!!!!

Ok, then- I'll take your word for it. I am not familiar with that circumstance, but who knows what someone might throw together given the opportunity!

Warbirdnerd · **Joined:** Fri Apr 30, 2004 7:34 pm **Posts:** 2923

Here is the NTSB report on the Buchon accident...

NTSB Identification: FTW88DRG04 .
The docket is stored on NTSB microfiche number 35613.
14 CFR Part 91: General Aviation
Accident occurred Saturday, December 19, 1987 in HARLINGEN, TX
Probable Cause Approval Date: 2/14/1989
Aircraft: MBB 109, registration: N8575
Injuries: 1 Fatal.
THE SET OF FLOATS WHICH ALLOWS A HIGH FUEL FLOW IN THIS CARBURETOR FOR HIGH POWER SETTINGS USED FOR TAKEOFF, CLIMB, ETC., HAD CRACKED AND SWOLLEN TO SUCH AN EXTENT THAT THEY WERE RUBBING AGAINST THE FLOAT CHAMBER WALLS AND FLOAT CHAMBER SHROUD TUBES. THIS INTERFERENCE PREVENTED ADEQUATE FUEL FLOW FOR HIGH POWER OPERATION OF THE ENGINE DURING THE TAKEOFF CLIMB WHICH TERMINATED IN THE ACCIDENT. THERE WERE NO ENTRIES IN THE MAINTENANCE LOGS WHICH INDICATED ANY MAINTENANCE OR INTERNAL EXAMINATION OF THE CARBURETOR SINCE THE AIRCRAFT WAS NEW (1959).

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

AIRSPEED(VS)..NOT MAINTAINED..PILOT IN COMMAND
FUEL SYSTEM,CARBURETOR FLOAT..DETERIORATED
FUEL SYSTEM,CARBURETOR FLOAT..MOVEMENT RESTRICTED

Index for Dec1987 | Index of months

Glenn Wegman · **Posted:** Thu Dec 23, 2004 8:33 pm

Yup......."airnutz" is correct, Merlin 500's, as used in the Buchon definitely have float type carburetors, and by the way, I keep seeing references to "Flow checking" float carburetors in previous posts. That's definitely incorrect, you flow check pressure carburetors, not float carburetors.

Glenn

Jase · **Posted:** Thu Dec 23, 2004 10:32 pm

Glenn: My references to flow checking came from my copy of the USAAC T.O. on aircraft carbs, number Idunno, that recommended flow checking all carbs O/H'd at the "depot level". They may have indeed been discussing pressure carbs, but it seems to me that the pic showed, and the caption referenced a float carb. I'll have to dig out the manual after the holidays and re-read it.

Say BDK, ever find anything about detachable superchargers? Not trying to stir you up, am just honestly interested if you can point me at an authoritative reference for ""Unless the supercharger section is detatchable from the power case. "

Regards and happy holidays to all.....

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11324

Jase wrote:

Say BDK, ever find anything about detachable superchargers? Not trying to stir you up, am just honestly interested if you can point me at an authoritative reference for ""Unless the supercharger section is detatchable from the power case. "

Glenn would know about the float carbs... I guess I blew it! My second mistake this week. :oops:

I do plan to check on the supercharger issue and will make a posting when I find out.

Jase · **Posted:** Fri Dec 24, 2004 1:13 am

BDK:

No worries. Don't feel redfaced, either. I could just as easily have been mistaken, and still may wind up so being. That's the cool thing about WIX when the trolls stay away, we can *all* learn schtuff.

HELLDIVERS · **Joined:** Sun Nov 07, 2004 3:38 pm **Posts:** 642

Hi : good posts!!hope this helps, if your experimental you can do such crazy things if you like but still not recommended,standard catagory and you better have some paper work to back it up!I can only hope our post are educational and helpful.Thanks for you efforts at typing up the regs.for all to read, sometimes a simple/common sense reply is not enough.I dont want to come off wrong but safety is the most important part of flight,with out it disaster is certain!Loss of life is all too common when rules and reg.s are not followed.Its not ment to scare anyone,but to educate and build safety standards we all must fallow.Thanks Mike

airnutz · **Posted:** Fri Dec 24, 2004 3:50 am

Warbirdnerd,
Thanx for digging up the NTSB report...I have been trying to get the FAA
report, but my computer skills are lacking. I sent you a PM, but I think
the "net" ate it. I was being "cryptic" with my reference because of who owned the aircraft...whenever someone mentions them in such a way..folks tend to get ballistic. In avoiding that, I think I made a mess.
Better to take me lumps, I guess!

Flow checking
I made a reference to the practice, because in the auto business, a shop
that I sent out my more difficult carbs to, offered that service
as part of the overhaul...I assumed the same went for aircraft as well.
When involved in trak/street, carbs I modified were sent out to be flow-
checked to see if our computations for jetting etc. were close to correct
after we had modified the engine. It cost me beer and pizza...and
saved my back from numerous jet changes etc. A Mikuni 4 bbl has
lotsa a little bits...and I really prefered to work with it on the bench. If
I made a mistake it was caught with the flow-bench. I didn't have them "flowed" every time...just initially, after I was "comfortable
with the "new model", it was adjustments for conditions/requirments.
Just my 2 cents worth...

Jase,
I hope you didn't mind my "editing mirth", if I did...apologies. I hope you
don't consider me a troll...consider me an amateur pain-in-the-arse..but
please, not a troll. I try to make intelligent moves here at WIX, but if I don't...please PM me and set me straight. I am here to learn.
I did read with interest, both your and BDK's detailed, in-depth offerings
with interest. Thanx...

Glenn Wegman · **Posted:** Fri Dec 24, 2004 7:19 am

Hello again,

OK, now I understand. What you are referring to in the auto industry is something completely different. In the auto industry, "flow chcking" is a reference to verifying the volume of air in CFM that the carburetor, cylinder head, intake manifold, air filter, etc. will allow to pass. There are carburetor dynamometers in the racing industry that allow you to take a carburetor that you know works very well and measure the fuel/air flow through each venturi exactly so you can duplicate the performance on as many carburetors as you like. This is common practice in NASCAR racing. Ten years ago they used to rework the cylinder head porting by hand and had to flow check and then grind some more, flow check it again, and grind a little more, until they had the results they wanted, and then then repeat the process for each head. When automated machines and software development progressed they went to mechanical porting on 5 axis CNC machines and can now port pallets of cylinder heads to essentilally exactly the same flow rate, hence the need for and development of carburetor dynamometers to achieve the same repeatability and results.

Anyway, back to the subject! The reference to "Flow Checking" in aviation terms is the practice of precisely measuring fuel delivery at certain throttle positions on pressure type carburetors under controlled circumstances. Float carburetors use air passing through the venturis to create low pressure which in turn draws the fuel through the jets. The more the volume of air through the venturis, the more fuel gets drawn in with it. These carburetors use fuel pressure strictly to maintain a predetermined level of fuel in the bowl so that it can be accurately drawn through the jets. Pressure carburetors, or injector carburetors, as they are sometimes referred to, on the other hand use fuel pressure to feed fuel through a delivery nozzle and then into the engine. In order to do this correctly a certain amout of fuel must be delivered to correspond to the throttle position. The process of coordinating this it referred to as "Flow Checking". The butterfly movement is divided into fifteen or so different positions, and at each position, a specific amount of fuel should be delivered through the nozzle. Adjustments are made until each point flows what it is supposed to so theoretically as you move the throttle you maintain the correct fuel air ratio throughout the entire range.

The one aspect of float carburetors that you would be correct in in reference to "flow checking" would be the fuel metering jets. At some point in their life the jets were flow checked to determine exactly how much fuel, measured in CC's, would flow through them and they were properly marked as such. Any nicks or scratches to the orifice of the jet would alter the flow so if you really wanted to get technical you coud flow check the jets to see if they still flowed the same as they are marked.

Ooop's, its time to go take my medication now!

Hope this clears things up a little.

Happy Holidays,

Glenn

Jase · **Posted:** Fri Dec 24, 2004 1:09 pm

Quote:

Jase,
I hope you didn't mind my "editing mirth", if I did...apologies. I hope you
don't consider me a troll...consider me an amateur pain-in-the-arse..but
please, not a troll. I try to make intelligent moves here at WIX, but if I don't...please PM me and set me straight. I am here to learn.
I did read with interest, both your and BDK's detailed, in-depth offerings
with interest. Thanx...

Oh heck no, the troll reference was to the anonymous types that stirred the pot recently, NOT you, or BDK, or anyone else. My apologies if I made you feel like that was directed at you. Ask Forgotten Field, he knows me and will attest that I'm NOT shy: If someone gets under my skin, they *will* know about it! :evil:

You're not there!

And I know bout the Buchon, and can understand the crypticness. BTW, I think you and I may have met at WOH in 01. I was with a C-46...ring any bells? And, for the record, I don't consider you or anyone else here a PITA (Pain in the ....)

Glenn: MANY thanks for that exceedly informative post. I imagine that was where my confusion came from, as like airnutz I started off as an auto mechanic before the Warbird Disease took hold. That, coupled with reading the USAAC tech order that talked about "flow checking" but gave no real details (that I remember, at least) is probly the source of my misstatement. To sum up: Float Carbs can get "air volume checked", and Pressure/Injection carbs can get "Fuel flow checked", right?

Helldiver: Concur completely!

HELLDIVERS · **Joined:** Sun Nov 07, 2004 3:38 pm **Posts:** 642

HI JUST TO ADD A LITTLE MORE CONFUSSION THERE ARE GRAVITY FED CARBS WHICH USES ONLY THE HEAD PRESURE FROM THE TANK,THUS GRAVITY FEED THESE ARE COMMON TO HIGH WING A/C.THEN A PRESURISED CARB IS ONE THAT IS FEED FROM A ENGINE DRIVEN FUEL PUMP THAT SUPPLIES 4 TO 5 P.S.I. AT THE CARB INLET THIS GIVES A CONSTANT FUEL FLOW TO THE CARB,WHICH ALLOWS FOR LIMITED INVERTED FLIGHT.THESE CARBS CAN LOOK EXACTLY THE SAME BUT YOU DONT WANT TO BE THE GUY THAT INSTALLS THE WRONG TYPE!!THEY ARE USUALLY MARKED EXTERNALLY BUT NOT IN ALL CASES.THE PRESURISED ARE USUALLY BACKED UP WITH A ELECTRICALLY OPERATED EMERGENCY BOOST PUMP AND MANY TIMES A SECONDARY BOOST PUMP THAT IS ON ALL THE TIME.THERE ARE LOTS OF THINGS TO THINK ABOUT WHEN INSTALLING NEW FUEL SYSTEMS OR REBUILDING A EXISTING SYSTEM BUT THATS A WHOLE NEW SUBJECT.I HOPE IM NOT THE TERRIBLE TROLL BUT IF SO LET ME KNOW !!THANKS MIKE

HarvardIV · **Joined:** Mon Oct 04, 2004 9:08 pm **Posts:** 1437

Hello Folks:

This is all a very good discussion. I talked to my IA, and he doesn't have the required carb. equipment, and so obviously we can't touch the carb.

However, I would be willing to do it, if the correct experience/infrastructure was in place.

At any rate, Merry Christmas!

Chris

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