TUNING GAUGES engine. we .He really talking abour a The gauge is calibrated in percentage the baffle cone of a two-stroke engine. mixwre of fuel and oiL If yOll rjchen poilJ[.s. Once you .set [he je[[ing wid) A permanenr female pipe flfring (I/Ij rhe pre-mix ratio (20: 1 as opposed w rhe ride and feel merhod, yOll cm ;el in.) musr be welded [lI the side of the 30: 1), rhere is more oil and less fuel in rhe calibrJrion screw on (he gauge so exhausr pipe in order ro fasten the rhe same volunle ofliquid, which eftec­ rhe needle is pointing to 100 pelcenL sen;or. The weld-on firring secup is also rively leans (he air-f1Je1 ratio. Thi~ fau 'W'hen rile air densiry ch'lllges, the RAO used on the temperature g.lIlges. :JIld gives rhe clever (uner one more rool ro gauge \vill show the relative petcenr of the fltring can. be plugged wjrh a ) /4-in. use ",.hen lhe corren jn is nor available change. Usin.g a calculator, you ca.n mak pipe flUing when rhe gauge is not or whe)) nooe of rhe ~tamhrd jets are mulLiply the percentage change shown in use. This gauge is ideal for four­ exactly right. You can richen rhe jerring on the Ri\.D gauge by rbe jet slz.e and srroke engine;. hy slighc1y reducing rhe pre-mix ratio determine the correc(cd jet size for rhe EGT Gauge-The Eel gauge (Ies~ oil). YOH can lean the jerLing by ai r density. The pilot/slow aod main jet measures rhe (emperature of the g.lses in increasing rhe pre-mix rario (more oil). h:lve Ilumber sizes lhal correldle wilh lhe exhaust pipe by means of a tempera­ Changes in the pre-mix rJ(io affect rhe rhe R.A..D gauge, but the needle dip ture probe fasteoedGorr into the ex.hau;r jetting over (he elHire (hronle-opening pOSItion CJn only be eStimated. pipe, 6 in. from the piston. This rype of (ange. bu( rhe changes in rario musr be Normally for eVety two main jet incre­ gauge enables you co rune the carb small ro preVCnt excess wear From Jack menr;, the needle (lip 1l1llSr be .ldjusred jerring 'UIO rhe pipe togerher, [,Iking of lubricating oil or Fouled plugs from one notch. advantageEric of (he facr (h.1r cxh;tust pipes roo much oil. AF Ratio Meter-'1 he M meter are designed- with a precise temper,{tur<: Pre-mix oils are formulated for a rneasure~ rhe percenrage of oxygen in ill mi nd. Fairly narrow range of pre-mix rarios. (he exhaust gases and display; rhe An. exnau;r pipe is designed to rerum YOIl should examine Lhe oil borde for approximare air-Fuel ratio of rhe carb. a compression wave ro the combusriol1 the oil manufacturer'~ suggesrion on the The gauge disl>I.lys AF ralios from 10: 1 ch.lmher JUSL before the exhaust pon pre-nllx ratio. All produccion rwo-stroke to 16: I. The optimum AF (Jrlo tor a dose;. Most pjpes Jte designed for d dirt bikes have a sticker on the rear rwo-srroke engine is 12:1. The M gauge peak temperaru re of 1.200 degrees fender suggesriog rh:lt yOll set Lhe pre­ utilizes a lambda sensor thatMotion is inserted l<"ah renheic. Most din bikes are jetted mix rado ro 20: I. That sticker i~ pur inro rhe cellLer of lhe exhausl Slream, LOO rich, which prevellLs Lhe exhJust rhe!(:: for legal purposes. Always refer ro approximarely 6 in. from the piswn in gase~ from reaching rheir design temper­ lhe oil manufac[Urer's suggesrion on rhe headel pipe of a four-stroke and in arure> so power Output suffers. pre-mix rarios. In general, ~mall­ Somerimes JUSt leaning Lhe main jeL .lnd displacemenr engines require a richer the nee<lIe-cJip po>Jtlon make~ .1 pre-mix ratio than do large-displace­ drama(ie di Fference. ment engines because sm;llkr engines Oigirron i.~ the mosr popular hrand have a hif!,her peak rpm (hJn IJrger Forward of" FGT gause. It measur~ borh F.CT engines. The higher (he engine revs. (he Jnd rpm. The f!,<luge is designed for br( more l11bric.lfion ir requires. of racing .lnd is nor suited for wet weather cOlldiriol1s. h i.s designed In 1ll0l!III Oil TU IG GAUGE the han(Uebars so the rider ,-an foclls ill There Me three rypes of gauges that on if. Once YOLL perform the: h,rseline prote.."Sional tuner; use ro aid carb jetting: jerting, send rhe rider Olll on the bike 1. RelJrive-air-densiry (RAD) gauge with the FCT. The rider Oh~li"'L rhe 2. Ait-fuel (AF) rario merel EG I' [Q give you f(·c -k I n the ll4,:(.o; ­ 3. Exhausr-gas-remperalure (EC ;T) gduge sary jetring chang s, Oln<; Iii j till):. is The following is J description of how dialed. lise rI {(h()ITlU~'f ill <.lIel..k rln:, each gauge funerionsProperty and irs advantages. peak rpm of Ih.:'n~IIL' OJ) ,h,' JUl1~~l RAn Gauge-A RAD gauge is the srraighr of the r.l ~nJ,-k. 1'0r e~,'ll1ple. If best choice for dirt bike~ because of the lhe peak rpm exceeds the poim of r11-:: convenience, bur (he gauge is no good engine'~ power-peak rpm, ch.;I"i;;1O rhe unles.s you ger (he jetting perfect. The rear sprocker (Q a highel fir, Jriv,- I.nio RAD gauge provides yOLi wirh an indi­ (rear sprocket wid) few r eeth) 1I1lLi! til­ catioo of bow much the air density The number one cause of stuck throttle condition IS rpm drops inlO Ihe l rgcl Iduge. All changes, helping you compenSJre for a bad throttle cable. Improper routing caused this EGT gJugc i,s ideal for di rt miLk hi t",; the eflects of changes in the air temper­ ca ble to fray above (he carburetor. Tile cable should and karrs, where peak rpm I III . ',mil ' aruce, altirude, and b;lromerric pre~'llre. route through the center of the head·stay brackets. is critical. 99 Top-end rebuilding is the most frequem or auto parrs s[Ores. Buy the threaded air, causing the mixture to run lean and and cmtiy service romine on rwo-stroke type, and make sure the kit comes with overheat the engine. When the wer seal dirt bikes. Every year, dirT bike riders an adapter that matches the spark plug wears, the cr:ll1kc;lSe sucks in rranny wasrc loads of money on rap-end partS threads of your engine. oil, clLlsing theGorr engine co run rich and rhar didn't need to be replaced, or they Performing a compression tesr is evenrually wet-foul the spark plug. make costly misrake~ while performing simple. Stan by removing the spark plug, A crankcase pressure lest involves repairs. This seC(ion provides the dos and threading in rhe adaprer, and holding the the use of a vacuum pump wirh spark don'rs ro easy rap-end rebuilding, pius throttle wide open with the kill button plugEric adapter and rubber plugs to block some tips that aren't printed Irl your on. This prevenr~ any spark and enables -off the intake and exhaust manifolds of facrory service manual. the engine to draw in maximum aitHow. the cylinder. The pi~ron musr be posi­ Then kick-Start the engine several times tioned ar BDC to allow the transfer BEFORE YOU ST R \lnril rhe needle on the pressure gauge pores co be wide open, linking the bore Thoroughly wa~h your bike because dirr peaks. The pressure reading depends on and the crankca.'e. The hand pump sruck ro the underside of the rop frame twO main facrors: the compression ratio produces vacuum pressure up to a Stan­ tube could break loose when servicing and the altitude at which rhe engine is dard setting of S psi. The notmal ;HJd hll inro rhe engine. Use a sriff plastic tesred. The <..:ompressionMotion ratio will also bleed-down pressure loss is 1 psi per brush and hot soapy warer to clean off depend on wherher or not the engine minute. Cylinders with complicated the gtit and grime around the base of the is equipped with exhaust valves and exhausr valve systems can be difficult to cylinder, on the carbutetor and intake the condition of the wives. When rhe block off air leaks and harder ro tesr. boot, and especially underneath the rap exhaust valves are in the closed position, Crankcase pressu re tesri ng lei ts are ftame rai!. Degreaser can be used on the compression rario will be greater available f'rom Morion Pro. metal surfaces, bur take care nor to leave d1an if the valves are carbon-sei7.ed in rhe If I Sllspecr thar an engine has an air it on rubber or gasker surh\ces. open position. The difference may yield leak in the crankcases, I do d visllal test. Forwarda pressure reading of 25 psi. The guality Starr by power-washing rhe engine TOOLS of compression testers varies gready. clean. Theo remove rhe magnetO cover. You'll need at least some 3/8-in.-driveof The main thing thar a compression Spray thc magneto clean with an merric sockets and box wrenches tester can idemi£~{ is a change in condi­ aerosol can of brake cleaner. Make sure (open-end wrenches will round off rhe tion. Whenever you rebuild the top end, to lise a non-chlorinared cleaner.