O.S. engine MAX-90FSR User manual

INSTRUCTIONS FORTHEO.S.TYPE 7DCARBURETTOR
This carburettor incorporates an automatic mixture control device which ensures that the enginereceives a
correctlybalanced mixtureof fuel and air at allthrottle settings. Itprovides steady revolutions and a
smooth response, even to abrupt operation of the throttle. Adjustment, when required, is very easy to carry
out.
1.5~2.0mm
Fig.(1)
Three adjustablecontrols areprovided on the Type 7D
carburettor.(See photo.)
•The Needle-Valve:For adjustingthe mixture strength
when the throttleis fullyopen.
•The MixtureControl Screw: For adjusting the mixture
strengthat part-throttleand idlingspeeds, toobtain
steady idlingand smoothaccelerationtomedium speeds.
•The ThrottleStop Screw:For settingthe positionwhere
the carburettorrotorisclosed.
PROVISIONAL SETTING
The use of a muffler-pressurizedfuelsystem is recom-
mended. Open the Needle-Valve1 1/2~2 turnsfromthe
fullyclosedpositionbeforestartingthe engine.
ADJUSTING THE CARBURETTOR
1)Set the throttleveryslightlyopen fromthe idle position
(See Fig. 1)and startthe engineinthe usual way.It is
preferabletohave thethrottleonlyslightlyopen,toavoid
unnecessarilyhighrevolutionswhen theengine starts.
2) Now open the throttlefullyand graduallyclosethe
Needle-Valve until the engine is running at itsmaximum
speed.*
*Warnings
(a)Do not close the Needle-Valve to too "lean" a setting, as this
willcause overheatingwhichmay resultininternaldamage
and reduced enginelife.Set theNeedle-Valveapproximately
1/4to1/2turnopen (i.e."rich")fromthe peak r.p.m. setting,
even thoughthiswillslightlyreduce r.p.m. on theground.
(b) Make sure that the engine is fully "run-in" before operating it
continuouslyatfullpower.(See engine instructionleaflet.)
3) Havingset theNeedle-Valveasdescribedabove,closethe
throttle.The engineshouldidlesteadilyand continuous-
ly.(Ifit stopsimmediately,firsttryturningthe Throttle
Stop Screw clockwisea few degrees to raise the idling
speed a little.)
(a)If,however, the engine idles unevenly and smokes a
good deal when the throttleis re-opened, before
pickingup speed, itis probablethatthe idlingmix-
tureis too rich.In thiscase itwillbenecessaryto
adjusttheMixtureControlValveby turningthe
MixtureControlScrew 1 5 to30 degrees clockwise.
(b)Alternatively,iftheMixtureControlValveisset too
lean, the engine may stop when the throttleis
closed, or itmay idle fora fewmoments, then speed
upvery slightlybeforecomingtoa stop.Re-opening
the throttleunder these conditionswillusually
result in theengine cuttingout abruptly,without
smoking.Correctiveactionis toturntheMixture
ControlScrewabout15 to30degrees counter-clock-
wise.
MixtureControl Valveadjustment is not unduly critical,
butdo notturn the screw more than 15 — 30 degrees at
atime.
Carry out adjustments progressivelyand patiently,re-
membering the symptomsof richand lean running,
quoted above,untiltheengine responds quicklyand
positivelytothe throttle.Do not alterthe Needle Valve
settingwhileadjustingtheMixtureControlValve.
Warning:
For safetyreasons, itisadvisable to stop the engine before
carryingout adjustments to the Mixture Control Valve or
ThrottleStop Screw.
ThrottleStop Screw
MixtureControl Screw
Needle Valve
Photo(1)

Note
Once the correctcarburettorsettingshave been established, it
shouldbeunnecessarytoalterthem. Such slightneedle-valve
readjustmentsas may berequired tocompensate forvariationsin
atmosphericconditionswillnot normallyaffectthe othertwo
controls.Slightreadjustmentsmay benecessary foroptimum
performance if differenttypes of fuel, glowplugs or propellers
are used.
VENTURIINSERT
This carburettoris fittedwitha venturiinsertforgeneral
use.If,however,higherpower output is required,it is
permissable to remove the insert.
MixtureControlScrew
Venturi Insert
MixtureControl
ValveSet-screw
Donot removethisnut.
HOWTOREMOVETHE VENTURIINSERT
1.Unscrew the ThrottleStop Screw and withdraw the
throttlerotor.
2.Remove theMixtureControlValveSet-screw and care-
fullywithdrawMixtureControlValve.
3.Extractthe venturiinsert.
4.Reassemble the carburettor.
CARBURETTORCLEANLINESS
The correctfunctioningofthe carburettordepends on its
smallfuelorificesremainingclear.The minuteparticlesof
foreignmatterthatarepresentin any fuelcan easilypartial-
ly obstructthese orificesand upset mixturestrengthso that
engine performancebecomeserraticand unreliable.
Itis recommended thatfuelis passed through a filterwhen
the tankis filledand that a good in-linefilteris installed
between the fueltank and carburettorand, furthermore,
that thisfilterisfrequentlycleaned toremove dirtand lint
that accumulateson thefilterscreen.Finally,occasionally
remove the needle-valveholderfromthe carburettoras
shown in Photo (2)and extractany remainingforeign
matter that may have lodged inthe location shown in
Photo (3).
MixtureControl
Valve
Rotor
Dirt and fibrousmatter
mostlyaccumulatehere
PARTSLIST
Photo(2) Photo (3)
The specifications are subject to alteration lorimprovement without notice.
Description
MixtureControlScrew
Mixture Control Valve
"0"Rings
Throttle Rotor
Mixture Control Valve Set-screw
Throttle Lever
Universal Link
Throttle Stop Screw Assembly
ThrottleStop Screw
Throttle Stop ScrewHolder Assembly
Nipple No1
CarburettorBody
CarburettorRubber Gasket
Needle ValveAssembly
Needle Valve HolderAssembly
Ratchet Spring
Needle
"0" Ring
Set-screw
Removethis with
8mm spanner
CodeNo.
26681603
29081305
24881824
29081200
26881311
26881406
26881424
27181600
27181620
27181610
22681953
29081110
29015019
27381900
27381940
26711305
29081952
24981837
26381501
6-153-chomeImagawaHigashisumiyoshi-ku
Osaka 546, Japan. TEL [phone]
FAX.[phone]
©Copyright1992by O.S. Engines Mfg.Co., Ltd. All rights reserved. Printed inJapan.
60130080-19710