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i just love using old tilly alky karbs.
BUT they are a pain to get right.

so far i've learned to sand out every flat surface.
to clean them to death and clear all tiny holes.
to remove the adjustment needles a lightly buff them with 000 steel wool.
check all functions and moving parts.

and still i get issues.
so i'm starting a thread for everyone.
eventually all the guys "in the Know" will pipe in and we'll have a good thread for rebuild.
later today i'll post pix of four project tillies and post as i go on rebuilding them.

for now here's an ec birt utube video on pop off pressure
http://www.youtube.com/watch?v=OaFvtlGzCB8

AND

Tillotson carb tuning - 2 cycle.
This comes from an early, genuine Tillotson factory service brochure.  It still applies today as a great starting point.
                                      ( Go to  .. here ..  if you want a methanol or petrol double pump conversion setup )

Setting up your 2-cycle Tillotson Carburetor.
W
ith today's state of the art motors and stinger type exhaust systems, the following information will help you achieve the desired results that you need from these motors.  Before mounting your Tillotson carburetor check the pulse track from the carb mounting surface and make sure that this track through the carb adapter , gaskets and etc is clear and in line with each other.  
Set the low speed needle at 1+1/2 turns out and the high speed needle at 1+1/8 turns out.   Adjust the throttle stop screw on the carburetor so that it just cushions the butterfly when the throttle valve goes closed.  Do not set the carburetor so that the engine will idle as this will cause the engine to lean out in the corners and anytime you are off the throttle.

Track tuning your Tillotson Carburetor.
I
f the carburetor settings are too rich ( too much fuel ) the engine will falter at that section of the track corresponding to that particular range of the carburetor settings.  A spluttering or irregular firing sound will be heard.   This sound is also called  4 stroking.  If this sound occurs at low speed while at full throttle, such as coming out of a tight turn, it is usually due to the Low Speed adjusting needle being turned out too far.  If the sound occurs at high speed while at full throttle, such as on a straightaway section of the track, it is due to the High Speed adjusting needle being out too far.  In either case, needle adjustments must be made inwards gradually, in approximately 1/8 turn increments.  It is best to adjust the Low Speed needle first for best overall low speed performance and then follow with the final high speed adjustment.
If the engine does not 4 stroke or give the too rich firing sound, any place on the track, it could be because the engine is running too lean ( not enough fuel ).  This is easily checked by opening the needles out in 1/8 turn increments until the engine  4 strokes.    In general, the optimum performance and engine reliability will occur at carburetor settings just slightly leaner than the point where the engine will begin to 4 stroke.   

If you find that the engine will not chop off clean or is slow to come back from high rpm's when you lift the throttle, this is a sign that the pop-off pressure in the carb is too high.   The cure for this is to lower the pop-off pressure.   If you experience loading-up problems, this is a sign that the pop-off pressure may be too low.  The cure for this is to raise the pop-off pressure.  As a general rule of thumb, the pop-off pressure will be from 8 to 12 lbs,   and is a tuning factor that you can adjust for  the altitude of your racetrack and the type of racing that you do. 

                               [Image: parts2-2.gif]


dave[Image: cool.gif]
Tillotson carb -- double fuel pump conversion
The Tillotson HL or HR series carburetor can be converted to high volume double pump setup to allow the use
of methanol ( alcohol ) fuel,  or just to feed more petrol to thirstier engines.

The parts required to do the conversion are ...
    1 only    #91A-351    Fuel strainer cover
    1 only    #198-305    Fuel pump body
    1 only    #91A-303    Diaphragm cover
    1 only    #67-38         Inlet valve body
    1 only    #DG-4HL    Double pump gasket and diaphragm kit
    6 only    #15B-343    Long body screws   
this is "borrowed from the ec birt site.
good info here plus i left the kit numbers in case you want to order e.c birt needle kits.
these needles are exactly what i'll be trying first myself.
dave


first read this whole little service manual.
it tells you about everything to do with a tilly rebuild.

https://eccarburetors.com/store/tillotso...e-kit.html
Here is the direct email to Carroll ec birts tech guy
carroll@ecbirt.com
he can answer many of your questions though it would be awesome if you asked here too and posted his answer.
Almost everything you ever wanted to know
About Carburetor Rebuild Kits
To rebuild your carburetor in a professional manner there are a few simple and precision tools that you need to have in your toolbox.
  1. A pop-off gauge is a must
  2. A small machinist brass and stainless steel brush
  3. an old tooth brush,
  4. a small tip screwdriver that will fit the screws that hold your carburetor together
  5. a couple of old cake pans (one to hold some cleaning solvent in for washing and one for parts), a small can of WD-40 or Marvel Mystery Oil
  6. a bottle of good castor based oil
  7. a dial caliper and a precision machined fulcrum arm gauge to fit your carburetor
  8. If it's a Tillotson carburetor an inlet seat gasket line up fixture
  9. a box of Q-tips
  10. a roll of lint free paper towels (an old t-shirt will substitute for the paper towels).
  11. An air compressor is nice to have but if you don't have one go down to the local auto parts house and get a couple of cans of pressurized brake cleaner
  12.  a pair of tweezers
  13.  a small pair of side cutters.
  14. Last, but not least, a handful of pop-off springs.
 For those that don't have the special tools needed to rebuild your carburetor with we have made them available in kit form to fit your needs and you can get them from us or any EC Distributing/Carroll LTD distributor.

In the complete carburetor kits (RK for Tillotson, check carburetor page for your carburetor to see what kit fits) there is no fuel strainer screen in the kit. Cleaning the fuel strainer screen is where the toothbrush comes into play or take the easy way out and replace it.

We will do the Tillotson kits first because these carburetors are used for 85% of small engine racing worldwide.
Tillotson carburetors fall into two different groups or types. There are double pump carburetors or three plate stack and single pump which is a two-plate stack.

 For the most part it is thought that the three-plate stack,which is referred to as a double pumper, is for alky only and a single pump or two stack plate carburetor for gas only.
This is not true.
 A double pump carburetor does not have a double fuel pump built into it. The extra plate that you have is what is referred to as a double pumper Tillotson carburetor and its purpose is to double up the volume of fuel that is in the carburetor.
This extra amount of fuel in the carburetor is preferred for alky burning engines or the HR series of gas carburetors because of the size of the carburetor.

Now if you have a two-plate carburetor and you think that you have a fuel problem because of volume and it's legal for the class that you run you can put the three-plate stack on your carburetor. These plate stacks are designed to fit any HL or HR series carburetor.

Needle and seats in all diaphragm carburetors fall into two groups or types. These are captured or un-captured types.

As a general rule of thumb, a captured needle and seat assembly is preferred for carburetors that are used on the asphalt. For dirt racing an un-captured needle and seat assembly is the most preferred.

A captured needle and fulcrum arm, which makes up the assembly, means that the fulcrum arm has a fork on the end of it and this fork hooks into a machined slot on the end of the needle.
 The advantage of this type of needle and seat assembly is that as soon as there is a depression on the wet side of the carburetor and the metering diaphragm comes down, it over runs the pressure of the inlet needle spring (pop off pressure) and the needle is pulled off the seat. Now fuel is allowed to fill the wet side of the carburetor.

In an un-captured assembly the fulcrum arm is not hooked to the inlet needle and when the main metering diaphragm starts its travel down and starts to over ride the inlet spring tension the needle comes off the seat by what little pressure is supplied by the pump pressure of the carburetor and a fuel pump if the engine has one on it.

 Now that we have opened up this can of worms we have to go a little further.
Let's look at the needle in the needle and seat assembly as a door.
Now this door is only allowed to open as far as you want it to or let it open.
Now staying with the thought that the needle is the door part of the needle and seat assembly then the seat must be the size of the door.
 In short the Fat Lady can't sing her song if she can't get through the door opening and your engine won't be a happy camper if it can't get enough fuel to the wet side of the carburetor.

This action has nothing to do with where the inlet seat pressure is (pop of pressure) but the adjustment of the fulcrum arm itself.
This would be the distance off the carburetor body or the topside of the metering diaphragm gasket to what we call the foot part of the fulcrum arm (end of the fulcrum arm where the striker pin of the main metering diaphragm comes in contact with the fulcrum arm) that will affect how far the door is able to open.

The following information on heights relate to the distance off of the carburetor body with original equipment replacement main metering diaphragm gaskets.

As a sample let's use a Tillotson carburetor for the rest of this information. With gasoline for the fuel of the day, we like to have this measurement from the carb body to the fulcrum arm in the range of .085 to .075 thousands of an inch. This is all that is needed for gasoline as fuel.
 With an Alky burning engine we want to have .075 to .065. In short, as you can see, if the arm measurement from the carb body to the fulcrum arm foot is .065 verses .085 then the door is able to open further and this will let more fuel come into the wet side of the carburetor.

Most of these needle and seat assemblies below are a bit on the pricey side, but we have to make them up by hand. One good thing about these seats is that once you have one of them it's a part that is good for the life of the carburetor.
 The needles  are inexpensive and you can replace them as needed without buying a whole needle and seat kit. These kits are also package with the needed inlet needle spring for the carburetor you have which can also be purchased separately.

EC-014
Un-captured Ram Flow Tillotson needle and seat kit for all HL and HR series Tillotson carburetors. This is an un-captured needle and seat assembly that was designed years ago for all alky carburetors used for dirt racing. The seat is hand machined and the inlet needle is made from a Viton ® tipped needle for the special machined seat that has holes machined in the side of the seat to increase the fuel flow.
As with all of these special seats one is good for the life of the carburetor and the replacement of the inlet tip needles can be purchased for replacement as needed.

EC-014A
Captured Ram Flow Tillotson needle and seat assembly for all HL and HR series Tillotson carburetors. This needle and seat assembly is the same as the EC-014 but comes with a captured arm and captured Viton® tipped needle. This type of needle and seat kit is preferred for Asphalt Sprint tracks, Jr. Dragsters and 1/4 Midgets where fuel delivery is needed in a hurry. In short a faster fill on the wet side of the carburetor helps increase the torque of the engine from the start.

EC-014B
Ram Flow captured inserted needle and seat assembly for all HL, HR, and European Formula A and Formula Super A
carburetors. This needle and seat assembly we make up can pass more fuel than any on the market. It comes with a blue needle that is machined on the sides to allow fuel to travel up the sides of the needle. The seat is machined with a series of holes through the sides to also allow fuel to get into the wet side of the carburetor faster and an insert that fits into the bottom of the seat to control a perfect seal for the needle to rest on.
This seat was designed more for the gasoline carburetors. For Direct Drive and Sprint 2 cycle racing this is the answer to solve fuel starvation.

EC-014C
Ram Flow un-captured needle and seat kit for HL-166B,C and HL-357A,B carburetors. With the Tillotson pipe line now being filled with the Viton ® tipped needles and the nickel seats we can now offer this complete kit with the new nickel seat, gasket, Viton ® tipped needle, fulcrum arm and special inlet spring for an up date of the carburetor that you have. This kit is recommended for dirt carburetors on gasoline or alky.

EC-014D
Ram Flow captured needle and seat kit for all HL-166B,C and HL-357A,B carburetors. This is the same type of needle and seat kit as the EC-014C but comes with the captured needle and captured fulcrum arm. This kit is recommended for the sprint tracks and small Jr. Dragster engines. Gas or Alky.

EC-MIK 34-37
Mikuni Ram Flow un-captured needle and seat assembly for BMC-34 carburetors. This is an un-captured needle and seat assembly and works perfect for asphalt or dirt for this series of carburetor. The needle we make for this kit has a Viton ® red tip needle. The seat gets TLC handwork and comes with a copper gasket to assure you of no leaks around the seat surface. A new fulcrum arm and special needle inlet spring is also included with the kit. This kit will serve all your needs for gas or alky as a fuel. This needle and seat kit also helps off set the nightmares of fuel control and setting the pop-off pressure in the Mikuni carburetor.

Inlet needle springs:
 002 alleged to be usful for high pop off pressure in mcculloch carbs
 003 pops off at about 8-9# tilly application
 009 pops off at about 1# more tilly application
 24b-299 is similar to the 009 spring but has an extra coil (top and bottom) that can be cut off to lower spring height.

(pop-off springs) In these springs we have several different ones that we keep in stock. We’re not going to list all of them because there are three different springs that handle most all needs. All three of these springs have a double wind coil on each end. This lets you cut off one full coil on one end or both and leave you with the must have flat bottom spring for constant inlet spring tension. Along with these special springs we have made a shim kit with .010 thick shims.

  shim kit 712 shim pac 10 pcs. is .005
  shim kit 713 shim pac 10 pcs. is .010

Shim Kit. There are enough shims here to do two or three carburetors. That is if you don't drop them in the grass.

Viton ® is a registered trademark of DuPont Dow Elastomers

d
on gaskets
gaskets are pretty much identical on all dble plate kits and same goes for triple plate.
they mostly do not interchange between though so don't be buying a double stack KIT for a triple and vise versa.
me, i just buy diaphrams and gaskets by the ten and use as needed.
needles do vary.
needle springs universal same as needle seals and tiny washer.
seats are where things get different and there are several styles of inlet fulcrum retainers.
there are different throttle parts just match to bore and rod unless modifying carb then rods can be changed as needed.
hope this helps for now
daveCool
when you rebuild an old carb the adjustment needles on used carbs are mostly usable but have a little surface corrosion from sitting.
always take out and inspect adjustment needles and if possible the needle bore.
if you don't a rough needle will grind away material inside the inlet bore seriously messing up carb fuel inlet ba1ance.
even what looks like a nice smooth needle may be crap.
so careful inspection under magnification is critical. it will reveal damage issues the naked eye may miss.

besides you absulutely should be replacing the o-ring seal in the needle package.
a bad o-ring will leak a huge amount of air and allow the carb to "self-adjust" from vibration.

i've found that a quick wire wheel brush up with a brass wheel followed by light polishing with 000 steel wool cleans them very nicely.
under 7x magnification they are pretty smooth.


i wire brush everything needle point threads and adjustment section.
i then coat them in light oil.
They look a lot nicer than knarley rusted old needles installed in a clean fresh carb.

dave
ordered some new parts from e.c. birt
pulled a couple of sample carbs to rebuild.
the ec parts are prime.
especially the increased flow seats.
a handy guy could copy the work done but for the price why bother.
the high flow intake tubes are just silly too.
daveCool
i am gonna start with using the needles found in the carbs.
the overall plan for this thread is pretty complex.

first i've broken down a alky karb to separate components and half assed numbers near them to get everyone on common ground as to what things are.
i also did a photo group tutorial on the dycom or sharpy inking and how to sand flats flat.

the next step will be installing the new seat and parts and setting pop off.
i've bought 4 different spring tensions in groups of ten.
on the exact same carb i'll be testing the pop off of each spring in each group and creating a graph.
i'm also seeking out ANY info i can find on pop off pressure for alky carbs and will be posting what i find.

after i get that all done i have a brand new set of 334a's that i will be building as alky carbs.
on that project we'll be starting with it as a stock carb with ec birt alky parts added.
we'll track test it with 25% then 50% then 75% then full alky.
if we see a drop off we'll do some drilling but SteveO was supposing that they might flow fine as found and i want to do tests before drilling.

at some point i also hope o find a decent replacement spring for the mcculloch bdc carbs.

i have an exotic idea for the mcculloch bdc involving narrowing the venturie to reduce airflow.
the main reason a bdc double pumper is needed is the airflow as found in the double stack is to much to push ba1ance charge of alky through .
it seems to me if i reduce airflow i can get the bdc14 workable with alky.
But that is a whole other thread .

dave
so heres the pix of carb rebuilding area.
also some pix of a torn apart carb.
kinda rough but as time passes this area will evolve.

ok first the 120 is sand paper grit per sq inch.
120 grains per sq inch to be exact.
the multible numbers are the various grits of sand paper i'll be using on the flats.
the picture illustrates how fine the grain gets as you progress upward.

i don't use the number 13 very often superstitious i guess.
#10 not sure where that is i think the screws were gonna be 10.
heres the list
  1. low needle
  2. high needle
  3. low/high needle springs, they rolled away from thier number #@!&%
  4. needle washers
  5. needle o-ring seal
  6. fuel inlet
  7. fuel inlet gasket
  8. fuel inlet screen (i usually toss those on alky carbs)
  9. top plate fuel inlet
  10. screws
  11. fuel flaps
  12. gasket
  13. ---
  14. second plate
  15. diaphram
  16. gasket
  17. inlet lever spring
  18. non captured inlet lever
  19. inlet lever fulcrum rod
  20. inlet lever fulcrum rod screw
  21. inlet needle (typically these are metal,one show plastic alky version)
  22. inlet seat
  23. inlet seat copper seal


bye
d
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next tip
replacement screws are priced outrageously on the carb parts sites.
i suppose that's because of the labor to buy,bag and ship.
heres the screw specs all available at mccmaster carr or any bolt depot.
the main cover bolts 6 total are called

main cover screws 90280A153 Fillister Head Slotted Machine Screw, Zinc-Plated Steel, 6-32 Thread, 1" Length,

lock washer for plate screws 92146A540 18-8 Stainless Steel Split Lock Washer, No. 6 Screw Size, .25" OD, .03" Min Thick,

inlet cover screw90277A147 Binding Head Slotted Machine Screw, Zinc-Plated Steel, 6-32 Thread, 7/16" Length,

hold down screw for gem reed plate 90277A105 Binding Head Slotted Machine Screw , Zinc-Plated Steel, 4-40 Thread, 3/16" Length,

throttle shutter screw (short) 90283A105 Zinc-Plated Steel Pan Head Slotted Machine Screw, 4-40 Thread, 3/16" Length,

throttle shutter screw (long) 90283A106 Zinc-Plated Steel Pan Head Slotted Machine Screw , 4-40 Thread, 1/4" Length,

throttle shutter plate screw lock washer 91113A005 Zinc-Plated Steel Internal-Tooth Lock Washer, No. 4 Screw Size, .27" OD, .01"-.02" Thick,

fulcrom rod hold down screw 91802A107 18-8 Stainless Steel Oval Head Phillips Machine Screw , 4-40 Thread, 5/16" Length,

air filter/intake adapter screw 92196A271 18-8 Stainless Steel Socket Head Cap Screw, 10-32 Thread, 5/8" Length,

intake nut lock washer 98438A240 400 Series Stainless Steel External-Tooth Lock Washer, 1/4" Screw Size, 0.51" OD, 0.02"-0.03" Thick,

intake manifold nut course thread 94846A029 Zinc-Plated Grade 5 Steel Thin Hex Nut, 1/4"-20 Thread Size, 7/16" Width, 5/32" Height,

intake manifold nut fine thread 94846A505 Zinc-Plated Grade 5 Steel Thin Hex Nut, 1/4"-28 Thread Size, 7/16" Width, 5/32" Height
i have a considerably better understanding of the tilly alky carb now.
i've redone several and track tested them and have gotten extremely good results.
i have one more race (cuddeback) to do and then i should have time for pix.
as winter sets in i'll be posting all the stuff i've sharpened up on during this season.

the scope of this thread expanded into setting up dual carbs.
as soon as i get time to load pix and add text.

i have always liked dual carbs but was told except for the hartman gears there wasn't a good simple linkage set up.
the gem set up works really well but the long cable makes removing a single carb a real pain.

i'd bought out a fellow with several cresent dual carb mechanical linkage set ups but never could get one to work correctly.
i've let it ruminate in my mind and finally the correct set up popped into my head.
i'll be posting the how to's on that as a separate thread along with the gem dual and the hartman gear dual.
the nice part about the cresent stuff is it's mostly stock tilly parts re purposed and repackaged.
so getting parts should be simple??

anyway first tech hint which i'll be repeating.
removing the weltch plug is vital in any good rebuild.
the issue is theres almost ZERO wiggle room for drill bit penetration.
if you go too far you just scrapped the carb.
E.C. Birt suggests using a milling machine or bridgeport or recutting your drill bit to a shollower angle.
all easay stuff for the gearhead/machinist but a little harder for a home style shade tree guy.
so i thought about it a little.
most people have a dremel tool or at least a small hand drill.
so here's what cha do.
get a small round head diamond burr home depot even sells them.
install in power tool and grind , at an angle, a hole through the weltch plug.
as you're grinding lift the burr every few seconds to check progress.
you'll see when you just break trough the steel plate.
STOP as soon as a hole appears.
as long as you don't try to go straight in it's impossible to drill through the carb floor if you pay attention.
pry the weltch plug out with a small hook tool.

at least this way you save a trip to the machinist and don't need to own a bridgeport.

After you check the three holes for sizing carefully install a new welsh plug.
a small punch is needed to tap the center of the arch in the welsh plug to trap it in the hole.
further sealing the welch plug with epoxy is advised.


A side note:
Steve Welte has advised super glue seems to work well on sealing the welsh plug when you replace it.
he also reports having had no problem drilling the plug out with a 1/8" bit, SLOWLY.
 Get a hole in it and pop it out with an awl.

dave l.
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