DCRC Club Meeting DCRC Third Friday of each Month 7:30...

DCRC Club Meeting

Third Friday of each

Month

7:30 PM

Montgomery County

Council building

100 Maryland Ave

Rockville, MD

PROGRAM: Tom Pfarr

RAFFLE: David Garri-

son

Don’t forget the model

shop.

Volume 59, Issue 2

DCRC

NEWSLETTER

DCRC Club Meeting

March, 15 2013

District of Columbia Radio Control Club Montgomery County Maryland AMA Chartered Club 329 Established 1951

Bealeton IMAA 2003

Jim and Joseph McDaniel getting their Cub ready

Volume 59, Issue 2

DISTRICT OF COLUMBIA RADIO CONTROL CLUB

Xipp Engine Tuning Method

by: Xipp, Flying Giants

Gas Engine Tuning

Carbs aren't too difficult to

tune up if you know what you're doing.

First of all, you need to know how the

carb works and how the settings inter-

act with each other. About 95% of all the

gas airplanes I've seen at the field are

somewhat out of tune. How can I tell

this? Simple, at some point the engines

"four cycle" in flight. Two Cycle engines

are not supposed to "four cycle" PE-

RIOD. This is caused by a rich mixture

that is forcing the sparkplug to inter-

mittently miss making it sound like a

four stroke. This is not good. HOW-

EVER the good news is; gasoline two

stroke engines are very tolerant of rich

settings (most of the time) and will run

fine. You'll just consume a little more

gasoline than necessary, and create a

little more oil mess on your plane. You

may eventually foul your spark plug as

well. So why do so many people leave

their engines tuned like this? Simple

answer, the engine will start much eas-

ier when it's cold AND there's little or

no warm up time needed prior to flying.

Those are pretty good reasons! But the

fact is... the engine is not running like

it's supposed to.

(1) The low end needle on a Walbro carb

is ALWAYS the one closest to the en-

gine, the high end needle is the closest

one to the intake/choke.

(2) There is no fuel adjustment for idle

fuel, only air feed set by the idle stop or

servo.

(3) Both low end AND high end needles

feed the top end fuel supply.

Let's tune up a Walbro!

Set the low end & high end needles to

about 1 to 1 1/2 turns each. Choke the

carb or prime it, until the carb is wet.

Fire up the engine and let it warm up.

Let's set the top end first since it's the

easier of the two. Go to full throttle.

Adjust the top end needle for peak RPM.

Leave it wide open for about a minute to

see if it changes any. Should the engine

go lean, open the low end needle

slightly, if this doesn't work... you will

have to adjust the needle valve inside

PRESIDENT: Jim McDaniel

V.P. Walt Gallaugher

County Liaison: Jim McDaniel

BOARD OF DIRECTORS

Andy Finizio

Jim Fisher

Walt Gallaugher

David Garrison

Allan Hoffman

Andy Kane

Jim McDaniel

Jose Sanchez

Thomas Pfarr

TREASURER:

Doug Harper

MEMBERSHIP SECRETARY:

Jose Sanchez

20017 Haller Ave

Poolesville, MD 20837

RECORDING SECRETARY:

Doug Harper

SHOW TEAM MANAGER:

Jim McDaniel & Allan Hoffman

NEWSLETTER EDITOR:

Andy Kane

[email protected]

MEETING PROGRAM COORDINATOR:

Walt Gallaugher

OFFICIAL CLUB PHOTOGRAPHER:

Thomas Pfarr

The DC/RC Newsletter is published monthly

by the District of Columbia Radio Control Inc.

Deadline for submitting materials for publica-

tion is the last Friday of each month. Any part

of the newsletter may be reproduced for non-

profit purposes unless otherwise noted. Please

credit the Newsletter and Author if named.

Articles may not reflect the opinion of the club,

but that of the author.

www.dc-rc.org Did you know that any airplane brought in to the

model shop will receive 3 free raffle tickets. Bring in

your models each month for your free tickets, and to

share ideas.

Some reminiscing from Bealeton 2003

Photo by Mike Dooley

GAS ENGINE HOW TO SET YOUR

CARB

PG 2

BOARD MEETING MINUTES PG 3

BUILD YOUR OUR TANK (CONT) PG 4

CLUB MEETING MINUTES PG 5

CLUB MEETING MINUTES PG 6

CALENDAR OF EVENTS PG 7

the carb.( I will explain this later) If the

top end runs OK, then slowly pull the

throttle down until the engine begins to

"four cycle" hold the throttle there. Ad-

just the low end needle until the "four

cycling" stops. Now lower the throttle

more until it "four cycles" again, and

adjust the low end again. Keep doing

this until you reach full idle. Now, from

full idle begin to throttle up until the

engine starts to bog or hesitate. Open up

the top end needle just enough to elimi-

nate the bog or hesitation.

When this is done right, you will be able

to set the throttle in any position and it

won't four cycle, plus you will be able to

transition from idle to full power with-

out any hesitation at all. -Xipp, Flying-

cirkus.com Member

Understanding a Walbro Carb

Ok this is for people who need a little

insight into how a carburetor works in

this case I will be using a Walbro for

example.

Starting from the gas tank, the fuel is

pumped from the fuel tank and enters

the carb through the inlet. The fuel

works its way through the fuel pump

through a little diaphragm pump that's

controlled by 2 one way valves (little

flaps). The fuel then passes through a

needle & seat that is controlled by the

"float" diaphragm. This "float" dia-

phragm manages how much fuel is

available for the idle, low-speed, and

high-speed throttle positions. The "float"

diaphragm opens & closes the needle

through a small lever attached to the

needle. The fuel is then "standing by"

waiting in the float area for a vacuum

signal at the various jets. The lever set-

ting is very critical since it controls the

available fuel to the jets. If the lever is

too low, the engine will run lean, if the

lever is too high, the engine will run

very rich and will likely flood out at idle

The fuel starts its journey through the

pump assembly first...

Then the fuel is regulated by the float

diaphragm that controls the needle &

seat.

All of these parts reside in the float cav-

ity area as well as the fuel ready to be

(Continued on page 3)


Volume 59, Issue 2

January Board

Meeting Minutes BY DOUG HARPER

The meeting, held at the

home of Andy Finizio, was called to

order by President Jim McDaniel at

6:10 PM. In attendance were Andy

Kane, Allan Hoffman, Jim McDaniel,

Walt Gallaugher, Doug Harper, Jim

Fisher, Dave Garrison, Andy Finizio

and Jose Sanchez.

Committee Reports:

Public Relations & County Liaison:

Jim McDaniel reported that the

County Office Building meeting room

has been retained for another year for

our use. Jim also reported that the

AMA Leader Club Status is in effect

for another year.

Sound & Safety: The Board asked

Walt Gallaugher to come up with a

procedure to create an annual pilot

proficiency assessment for all mem-

bers who use the field. Walt will re-

port back next month with his sug-

gestions on how to do this.

Field Maintenance: Allan Hoffman

reported that the repairs to our signs

have been done.

Flight Instruction/Awards: Jim

Fisher is contemplating a "user fee"

to help offset some of the training

costs in the coming year. He will

work out the details as we get closer

to the training season.

Jim asked for help constructing new

trainers for the coming year. The

Board will help Jim and welcomes

other members who would like to help

as well. Jim also reviewed the list of

IPP instructors for the coming year.

Events: Jim reported that we have

the Soccerplex for indoor flying every

Wednesday from 11:45 to 3:45 from

now to 3/6/13. In addition, we can

use the facility in the month of Febru-

ary up to 6:30PM on Wednesday as

well as on Friday from 9AM to 4PM.

Treasurer: Doug Harper reported

that he wrote five checks over $100 in

the last month. He presented a YTD

Budget report to the Board for their

consideration.

Membership: Jose reported that we

have 102 paid members to date.

Newsletter: Andy Kane. No report.

Web Master: Tom Pfarr. No report.

Old Business: The Board conducted a

lengthy discussion about any prospec-

tive change in our fiscal strategy for

the coming year in lieu of no increase

in dues. After much back and forth,

they decided to stay on the course al-

ready set. Namely, a budget was

passed in late 2012 for the 2013 year

and that budget is still in effect and

will be used to fund Club activities for

the coming year. The Board commit-

ted to try to spend funds prudently

where possible but, in effect, there

will be no change to our budget. Also,

the Board, as well as Club Members,

should look for ways to raise addi-

tional funds where feasible to aug-

ment our dues income. Andy Kane

made a motion to continue with the

current budget for the 2013 year. The

motion was carried unanimously.

New Business: None.

The meeting was adjourned at 9 PM

fed through the jets as needed. The

amount of fuel available in the cavity is

regulated by the lever and its relation-

ship to the float diaphragm. So it's criti-

(Continued from page 2)

cal that the lever be set properly. Within

the cavity, there are distribution holes

that are managed by the low end and

high end needles. Plus the idle circuit,

which is a fixed size.

(Note) All Walbro carbs will run in any

position, but they tune "best" as a side

draft carb. The down draft position

tends to run a little rich at idle, and the

updraft tends to run a little lean at idle.

No big deal though, it's easily tuned

none the less.

This photo depicts one of Walbro's pre-

mier carbs, having a large bore and

equipped with a high speed check valve

and external fuel pump pulse inlet.

Now let's talk about the pulse signal for

the fuel pump.

Your ENGINE will determine which

pulse inlet type you need! If the engine

"carb base" has a hole drilled into the

crankcase you will use the STANDARD

pulse port and the optional (if you have

it) port must be closed off. If there's no

hole drilled, you will find a fitting lo-

cated somewhere on your crankcase.

Use a piece of fuel line to connect the

crankcase fitting to the fitting on the


Volume 59, Issue 2


How to Build Your

Own Fuel or Smoke

Tank By Andy Herold

Continued from last month

In the first phase we made

the plug for a custom tank.

Now we will make the

mold. The first thing we

will do is to make a parting board to

hold the plug while making the actual

mold. This board will be where we

create the top and bottom to your

mold and will be where the glue joint

in your tank will be.

You will need two 1/4 inch pieces of

luan plywood about 6 inches larger

than the plug’s dimensions. One will

create a flat edge all the way around

the plug. The other will just act as a

flat base to work on making them one

unit. You will need a piece of Formica

( countertop material ) some Home

Depots have 2 ft X 4 ft pre-cut pieces.

The Formica is not glass smooth and

may have a sandy texture to it. Using

3M spray adhesive or contact cement,

laminate it to one of the pieces of luan

plywood. Next you will cut an opening

in the luan/Formica for the plug. You

want this to be a very close fit, 1/8

inch max. When laying out the cut-

line use masking tape to mark the

lines on. This will prevent the For-

mica from chipping.

Using a hand jig saw and a sharp

fine-toothed blade, cut on the marked

lines. Go slowly to prevent chipping.

You may need to sand the rounded

corners for a perfect fit. You will need

to support the plug firmly in the part-

ing board so that it does not shift dur-

ing the lay-up process. You can use

white foam or blocks of wood like I

have. (See photo #12.) Once you have

the parting board and the plug fitted

to each other, you will need to seal

any gaps between the plug and part-

ing board.

To do this, modeling clay is pushed

into the small gap with a popsicle

stick. Sand one end of the stick square

and a taper to cut the clay after push-

ing it into the gap all the way around

the plug (See photos #13 & #14.) If the

tank is symmetrical and you need to

be able to tell front from back, use a

few small blobs of clay on the flat

mold surface to create humps in the

surface. Now that we have the plug

fitted to the parting board and all the

gaps filled, carefully apply 6 coats of

mold release wax to the plug and

parting board being careful not to

move the plug while applying or re-

moving the wax. Make sure to get wax

on all surfaces including the clay.

While applying the wax and while it

is drying, I cut the fiberglass mat in

preparation for the lay-up process. We

will need 4 layers of fiberglass mat for

each side. Cut the fiberglass mat

making 4 pieces. Two for the flat area

of the parting board one for the plug

the sides the parting board, and one

for the bottom of the plug. Cut each of

the pieces about 1 1/2 inches oversized

for overlap and waste. We will be fray-

ing the edges of the mat so that they

will lay-up into the 90 degree corners

better. The pieces that will be used

on the parting board will only be

frayed on one side. The pieces that

will be making the ends, sides and

bottom or top will be frayed on all

sides.

Now that the fiberglass mat is cut,

using pliers or your fingers pull the

edges of the mat creating the frayed

edge. (See photos #15 & #16.)

Once all the wax has been applied and

buffed off, we can apply 4 very thin

coats of PVA with a normal automo-

tive paint spray gun creating a me-

chanical barrier between the gelcoat

and the plug. These coats of PVA

must be very thin, Use 100 psi air

pressure and adjust the flow rate

down, you should barely be able to see

any of the PVA material coming out of

the spray gun. Allow the PVA to dry

between each coat. Coat the entire

area that was waxed following the

instructions on the can of release

Photo #11

Photo #12

Photo #16

Photo #15

Photo #17


Volume 59, Issue 2

CLUB MEETING

MINUTES FEBRUARY

2013 BY DOUG HARPER

agent.

We are now ready to apply the orange

polyester tooling gel-coat with the

dump gun. Mix the gelcoat with the

hardener using the correct amount for

the ambient temperature you will be

working in. (Hot temp use less hard-

ener- cool temp more, follow the mfg.

recommendations.) This is a messy

process and should be done outside

due to overspray. Spray the entire

plug and parting board surface mak-

ing sure that you get all corners of the

plug to parting board well coated. You

want to put it on heavy but not to the

point of running. It does not have to

be pretty just well covered. If you get

it too heavy the air pressure will blow

the gel-coat around and cause it to

ripple. Try to avoid this but don’t

panic if it does. (See photo # 17.)

After the gel-coat has cured for about

4-6 hours, it should be hard but still

tacky to the touch. We will be apply-

ing the first two of four layers total.

We are doing this in two steps to

avoid building up heat and pulling the

gel-coat away from the plug. Now

measure out a cup of polyester resin,

(I started with 3oz for this mold ) then

a separate cup of hardener of the

proper amount for the resin and set it

aside. Mix a small amount of the gel-

coat (about 2 oz) with hardener then

add phlox into it to make a peanut

butter consistency. Now spread this

mixture into the corners on the part-

ing board with a tongue depressor,

creating a filet in the corners. Make

sure there are NO AIR POCKETS.

(See photo #18.)

Once that is done, mix your first cup

of polyester resin. Using a 1 inch dis-

posable paintbrush lay the first piece

of mat around the parting board, al-

lowing the frayed edge to overlap up

into the filet you just created. Don’t

worry if the mat overhangs the part-

ing board. Wet this glass completely

out all the way around. Now do the

sides of the plug in the same way al-

lowing the sides to wrap down over

the glass mat that you just wet out

and to wrap up over to the bottom of

the plug. Wet this glass mat out. Then

add the bottom to finish covering all

the gel-coated surface. Once you have

that done, immediately add the sec-

ond layer. You can reverse the order

of lay-up working down to the parting

board. The second layer will soak up

some of the polyester resin from the

first layer. These layers should be

completely wetted but not soaking

wet, (See Photos #19 & #20.)

Let these layers cure overnight.

To be continued next month.~

Photo # 18

Photo #19

Photo # 20 The meeting, held at the

County Office Building, was called to

order by President Jim McDaniel at 7:36

PM. Jim asked for the

introduction of any new

members or guests. Jer-

emy Nelson was present

and intends to join the

Club. He is just getting

into RC. Martin Green is

a new member who in-

tends to fly fixed wing planes. Bruce

Drury is a full scale RV8 pilot. He is

looking at RC as a possible hobby.

Jim again indicated his intention of

minimizing the business content of the

meeting.

Public Relations: Jim announced that

DCRC has qualified as an AMA Gold

Leader Club again this year. We also

have rented the County meeting room

for the coming year.

Events: Jim announced that the indoor

flying has been extended to 5:00 PM for

the remaining Wednesdays of February.

We also have Friday till 4 PM thru the

end of February. The Soccerplex does

withhold the right to take the field back

if a paying customer shows up.

Heritage Day is set for June 29, 2013,

from Noon to 4PM. Opening Day will be

in April, date to be determined.

Training/Community Outreach : Our

first STEM night is April 11 at Orchard

Grove Elementary School followed by

Rockville Science Day on

April 28 at Montgomery

C o m m u n i t y C o l l e g e

(Rockville Campus). Jim

Fisher plans to contact

AMA and Model Airplane

News to get copies of

magazines that we can

distribute to various locations.

Field Maintenance: Allan Hoffman. No

report.

Membership: Jose Sanchez. Member-

ship is open and he solicited all mem-


Volume 59, Issue 2


bers to send their renewal. Cards are

on the way.

Safety Coordinator: Walt announced

that AMA has published guidelines for

field sound. He encouraged Club Mem-

bers to read this in the AMA magazine.

Walt plans to have an annual Club

safety review. His checklist included

c h e c k i n g b a t t e r i e s

(including cycling), going

over the fuel system in-

cluding the tank and

clunk, making sure control

services and linkages are

solid, inspecting the prop

and nut, tightening motor

mounts, making sure servo

mounts and connectors are tight, and

finally doing a range check. Frank Ne-

her suggested that the wing attachment

be checked so the wing stays on in

flight. Jim Fisher suggested that those

flying 2.4GHz make sure the transmit-

ter is bound to the correct plane. Andy

Finizio recommended that a thorough

inspection be conducted on the inside of

the fuse to make sure everything is

solid.

Raffle: Jim Fisher and Dave Garrison

presented a BNF Edge 540 QQ indoor

flyer for tonight's raffle. Gus Crosetto

pulled the winning ticket that was held

by Walt Gallaugher. Walt, a member of

the Board, thanked the group for their

resounding approval.

Treasure’s Report: Doug wrote one

check in excess of $100 this month. He

had a copy of the YTD Budget Report for

anyone who cares to see it.

Web Site: Tom Pfarr. All is good.

Newsletter: Andy Kane. No report.

Awards: Award night will be held dur-

ing the April Club Meeting. Jim asked

members to submit names to him of

people who should receive awards.

Flight Training: Jim Fisher announced

that the first day of Training is April 20.

Jim plans to run 20 people through

training this year so that everyone gets

a longer time on the sticks. He also

plans to have separate dates for mem-

bers and IPP folks. There should be as

many as 19 training days this year.

(Continued from page 5) Jim announced that new training mod-

els have been ordered and will be built

by Jose Sanchez. We should also have

some spare parts in case they are

needed. (Modified) Giant Big Stiks will

be used this year and hopefully will

stand up to the use. Jim asked if any

Club members could do vinyl logos and

lettering.

New/Old Business: Hank Jacob sug-

gested last month that DCRC consider

placing an AMA magazine with a note

about DCRC at various places of busi-

ness around the County. Andy Kane

printed label sheets that can be applied

to magazines that members can leave in

various public locations (like Doctor's

offices).

Model Shop: Gus Crosetto presented his

pusher delta Force One kit from Balsa USA.

He received this kit from member Ron Bozi-

netti when he moved to Florida. It weighs

around 4 pounds by using a lighter battery.

He finished it in stars and stripes with a very

attractive scheme. He is using a modified

12X6 prop. He had to work on getting the CG

correct but feels he has achieved that. He

plans to fly it at the next opportunity.

David Harris presented his miniature rubber

powered sea plane based on an Aronca K

design from a kit supplied by Comet. It has a

24" wingspan and Dave built it with both

floats and wheels. He covered it with pre-

colored tissue and produced a very attractive

result. He is working on getting it to fly

longer.

Andy Kane presented his B17 Bomber ARF

from Hobby Lobby. It is very attractively

finished in olive drab with an 63" wingspan

and four electric motors that are all linked

together electrically. It also features operat-

ing flaps and retracts. The left and right

motors counter rotate. It made quite an in-

teresting noise as the four engines revved up.

Andy also talked about his new Quique

Somenzini version of the DX18 radio from

Spektrum. It features some additional pro-

gramming options and comes in a very attrac-

tive black case.

Program: Tonight's program is presented by

Don Gray on the subject of

"weight and balance". Don

referenced Dave Garrison's

very interesting talk last

month on the F106 and de-

cided to present some of the

planes he worked on when he

was in the Air Guard in the

late '60s. These included the F-100 Super

Saber as well as the F-86 Saber, the T-33

Trainer and the F-105 Thunderchief. The

Thunderchief was very high maintenance.

Don feels this is a good time of the year to

think about weight and balance since we are

finishing our winter building projects and

getting ready for the coming flying season.

He listed the effects of weight and balance

which include longer takeoff run, lower rate

and angle of climb, higher cruise speeds( in

sailplanes), increased sink rate and reduced

wind effects ( heavier is better).

Don indicated that wing loading (weight over

area) is much more important than weight

alone in predicting performance. This affects

stall speed as well as other flight perform-

ance parameters. Don then presented data

he has developed on 13 different full-scale

aircraft where he compared actual versus

predicted stall speeds. He found that he

could come quite close to predicting this pa-

rameter.

Don then discussed vertical CG location

(versus longitudinal CG) on roll stability. A

CG above the centerline is a destabilizing

factor and, conversely, a CG below the center-

line stabilizes an airplane. He showed a cou-

ple of examples of each of these.

Don then presented a balance equation which

is used to calculate the CG of a plane by sum-

ming the weights and moments of various

components around a common point (like the

wing leading edge).

Don then moved to the technique he uses to

balance a model airplane. He starts by level-

ing the plane in roll and pitch. He then de-

termines the weight under each landing gear

wheel. He also showed how to determine the

Mean Aerodynamic Chord for a tapered wing.

He uses 25% of MAC as a rule of thumb for

determining CG to start. He also talked

about how to do this for a delta wing.

Don then presented the See-Saw Equation

that he uses to fine tune weight around the

CG. This comes down to making sure a given

weight a certain distance from the CG is bal-

anced by an equal weight times distance on

the other side of the CG. This can be an it-

erative process.

Finally, the CG can be fine tuned by flying

the aircraft and making final adjustments to

the CG. That is a subject for another day.

Don received a resounding round of applause

for his informative talk.

Jim announced that next month's meeting is

March 15. The raffle for next month is a

brand new 120 ABC glow engine.

The meeting adjourned at 9:00 PM.

Volume 59, Issue 2


Indoor flying at Soccerplex

every Wednesday 11:45 till 3:45 pm through Feb 27

March

15 DCRC Club Meeting Tom Pfarr

17 PGRC Sprinf Auction, Falls Church VA

20 DCRC Board Meeting Tom Pfarr

April

19 DCRC Club Meeting Jim Fisher

24 DCRC Board Meeting Jim Fisher

May

1-5 Top Gun Scale Competition, Lake-land, FL

11-18 Joe Nall Fly IN, Woodruff, SC

17 DCRC Club Meeting David Garri-son

22 DCRC Board Meeting David Garri-son

25-30 First in flight Jet Rally, Wilson NC

June

21 DCRC Club Meeting Allan Hoffman

26 DCRC Board Meeting Allen Hoff-man

July

19 DCRC Club Meeting Allan and Andy K

24 DCRC Board Meeting Allan and Andy K

August

1-4 Summer Afterburner Jet Meet Hamburg, PA

16 DCRC Club Meeting Walt

Gallaugher

16-18 Giant Scale IMAA Hamburg, PA

20 DCRC Board Meeting Walt

Gallaugher

September

6-9 DCRC Bealeton IMAA Flying Cir-cus, VA

20 DCRC Club Meeting Andy Kane Nominations

Calendar of Events 2013

optional pulse inlet. There's no need to

block off the standard port, as it's al-

ready blocked off by the engine mount-

ing.

The carb must get a pulse signal from

the engine! This signal "pushes and

pulls" on the pump diaphragm which

feeds the carb fuel.

Now let's check out the "float needle &

seat" setting.

This is the single most critical setting on

a Walbro carb! Walbro offers a "setting

gauge" to properly set the height of the

lever for your particular carb. If you

don't have one, the setting will be a trial

& error adjustment and a real pain in

the butt since you have to open up the

carb to make the adjustment. For gen-

eral purposes, the lever will be almost

perfectly parallel to the carb base. This

will get you close. If the lever is too high,

your engine will tend to run a little er-

ratic at idle. If the lever is too low, your

idle will be OK but it will tend to run

lean on midrange and high end. It may

also run the float cavity "dry" at full

throttle and die, regardless of your high

speed /low speed needle settings.

The needle valve seat is pressed into the

carb base, and you should not remove

this without having the correct tools and

setting gauges. Do not remove it!

Typical PROBLEMS The engine stalls

when accelerated: POSSIBLE solution:

High end needle way too lean, or low

end needle slightly lean Engine goes

rich in flight : Low end needle too rich,

(Continued from page 3) float diaphragm needle lever slightly too

high

Engine goes lean in flight : High end

needle slightly lean AND low end needle

is rich, float needle lever may be set too

low

Engine runs good, but no idle at all :

There's crap in the idle jets, the carb

will have to be removed and cleaned.

You may also have an air leak at the

base of the carb. The throttle butterfly

could be damaged or worn out carb

leaks fuel when not running : float nee-

dle is bad or has crap stuck in it, or the

float lever setting may be too high, or

the float diaphragm is bad.

My engine four cycles momentarily

when I back off the throttle, then runs

normal : This is perfectly normal for

carbs NOT equipped with a "check

valve" high speed jet. If you do have the

check valve, then your float needle set-

ting is slightly too high, or your float

needle is leaking a little the fuel leaks

back into the gas tank when it isn't run-

ning : Bad fuel pump membrane, or an

air leak in the fuel line at the carb

NOTE 1:

A very common problem with cowled in en-

gines is, the air pressure in flight changes

the "natural" pressure on the float dia-

phragm. This causes the engine to run rich in

flight. There are several possible fixes avail-

able. Most of the time you can simply tune

your engine for flight by trial & error. How-

ever, the easiest fix is to open up the cowling

around the carb area to lower the air pres-

sure. You may also rotate the cover to differ-

ent positions to see if that works. The "BEST"

fix is to solder a piece of brass tubing where

the vent is, and route the vent line to a better

location. I normally route it into the fuse

going through the firewall. It works perfectly

every time! Plus, your ground tune doesn't

change in flight!

NOTE 2

Carbs equipped with the high speed check

valve are greatly superior for flying aerobat-

ics, or flying whereby the throttle will be

used extensively. The check valve prevents

jet dripping when you back off the throttle.

That's all it does...

Straight through (non-check valved) jets

always drip a little fuel while the throttle is

being backed off, and causes a momentary

four stroking of the engine until the jet stabi-

lizes to the new air flow rate. This is com-

pletely normal.~

First Class Mail

March 2013

Andy Kane/Newsletter Editor

305 Natick Court

Silver Spring, MD 20905

E-mail: [email protected]

One of the oldest and largest RC

clubs in the US.

And now an AMA Gold Leader Club

District of Columbia

Radio Control Club

www.dc-rc.org

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