Honda CR500 jetting guide
What jetting should you run in a CR500?
CR500 FULL MANUAL
Well if you don’t know already, they are extremely HOT running engines. and unless you can monitor your exhaust temperatures we say start fat and go down from there. It is extremely important to run ALOT of premix 40:1, it helps lubricate your crank & wrist pin bearings, keep your cylinder running cooler and has a lot more slippage for the exhaust port where it gets hot as hell. Our Ice racing Oval Motors we will run 32:1 or 20:1.
EXHAUST PORTS Many die-hard racers live and die by drilling extremely tiny holes in the exhaust side of the piston to help with exhaust bridge lubrication and cooling for the cylinder. This is where a lean burn will happen and you will see it first.
TEMPERATURE PROBE for Ice Racing – We run a coolant temperature probe on the EXIT of our cylinder cooling lines, they help us know when the bike is properly warmed up and we can pin it. We won’t give it the beans until about 120 or 130F. With ONE RADIATOR COVERED. What can happen ice racing is when you crank on the throttle hard when the engine is not too warm (under 180f). You can expand the piston MUCH faster than the cylinder walls, resulting in a lean seize. We cover 1 radiator to keep the bike running a constant temperature so it does not fluctuate when off and off the throttle or coasting around or after waiting around. The Cooling ports on the CR500 ARE MASSIVE, and for good reason, a lot of heat is produced from the CR500.
MIX RATIONS & JETTING
Now, this mostly came from the KTM crowd wanting to stop the “spooge” that came out of exhausts. Many offroad dirt bikers in tight singletrack conditions seem to have a lot more excess oil out of their muffler than most, There is a reason for this. The Exhaust temperatures are lower than required to vaporize and use the excess oil on the bike at the required jetting. You can get spooge at any jetting if you are not revving the bike and cleaning out the excess oil that will build up at the bottom of the crank.
MORE MIX = LESS GAS
When you change your mix, two things happen, you either add or take away mix that is supposed to lubricate your bearings. When you take away mix, you will be adding more FUEL to what the bike takes in, which would mean you need to LEAN the jetting out (over fueling). However, depending on the racing and RPM you are at, this can determine if your engine will be at 20-30HR engine or an 80-100hr Engine.
More Lube= less wear on bearings, engine runs cooler, just like in the bedroom.
40:1 or 32:1 Mix Ratio is an industry standard and for good reason. It just works, makes great horsepower and keeps your engine crisp and snappy. PreMix is the MAIN way your rings are sealed on your Cylinder wall, 4 Strokes have 2 or 3 Sets of rings which recycle the oil in the 4 stroke motor, which is why you need to check your oil in the 4 stroke motor as it will be used along the Cylinder wall as lubrication and to seal the rings against the Wall.
Every Mix change must match your Jetting, Altitude & Temperature. Many mountain racers will just lean for the base of mountains and when they get to the top of the climbs their bike will run better and not be bogged down. Until all 2 strokes are on the TPI/EFI freight train. It’s best to understand how jetting works on your bike to prolong its life and power.
We won’t even get into HOT/Cold Spark Plugs!
Our 1986 CR500 at 3500 FEET, 2nd Clip DOWN – Stock Needle – PWK Carb – 40:1 PREMIX runs a 185 MAIN when below -20C. At about -15C We will run a 182
-5c to -10c We will go 178 to 175 MAIN Jet. Anything Above -5 We will go 172 MAIN and 170 MAIN. Depending on our riding style and the amount of time on the Main we will adjust our jetting appropriately.
FMF HONDA CR500 JETTING INSTRUCTION MANUAL
HONDA CR500 JETTING RECOMMENDATIONS
Here are our jetting suggestions for your CR500. We’ve spent countless hours of testing to determine which settings work best when bolting on one of our pipes and silencers to a stock machine. These are recommendations only, based upon our testing at sea-level atmospheric pressure, a 65-80F degree ambient air temperature, a 32:1 fuel to oil mixing ratio on super unleaded pump fuel with a stock motor.
For some models we offer a Power Up jet kit for optimum tuning. Kits may include jets, needles and any necessary hardware and have been developed with the assistance of Dynojet. There are too many variables outside of our control to give you an exact configuration that works perfectly under all conditions. Our
recommendations are just that, a starting point to reference from. Higher elevations, high humidity, hotter temperatures are examples that will require leaner jetting. Colder temperatures are an example that will require richer jetting. If you are unknowledgeable or don’t feel comfortable tuning your machine yourself, find a mechanic in your area who is. FMF Racing is not responsible for problems derived from improper jetting and/or usage.
Always check that your jetting is correct when changing parts that could affect the intake system, exhaust system and any product or change that could alter fuel combustion in the cylinder (ie. aftermarket ignition module).
Check out our website www.fmfracing.com for additional information.
Use the following suggestions when using a FMF Fatty, Factory Fatty, Gnarly, Rev or SST exhaust pipe.