Installing new pipe, (Bike is Slower )
Before installing a pipe check the following, it will save you a ton of head aches. Compression 90 LB. is good below this a pipe will only slow the bike down make it worse, if it is order new rings. Look at the variator closely in the cradle area, look for cracks and uneven wear , replace it if these symptoms are present. This will cause the variator to hang in low or high or bog at times, replace it.
A two stroke pipe raises the power band in the motor, depending on pipe construction where the power band comes in, down low, or built for mid and top end, this all depends on how the pipe was designed. after installing a pipe and the trans kit, (Do Not Install the side cover) Start the engine and hold the rear brake and slowly increase the rpm"s untill the clutch grabs, pay attention to the front pulley and see how far the belt is moving up the pulley, 1/4 inch is all right. If the belt is moving more than this one of two problems needs to be corrected. Either the springs have too much tension or the rollers are to heavy, or both? Rule of thumb, for MX racing the Malossie springs 29 8747 either the red or blue will launch the bike, in some instances you will have to use the black ones, (do not lighten the clutch shoes, with the right spring installed the clutch will stay locked up and will last a long time, lightened shoes have a tendency to slip, bike sounds like a bumble bee but is not going any where? for a pipe that has good bottom and mid use part number 29 9605.
Rollers use 3.5 gram to a 5.5 gram roller, experiment with a 3.5 4.0 4.5 5.0 and see what the bike likes. Make sure you install a red or yellow clutch center spring, this applies pressure to the belt at low speeds and forces the variator to follow the belt at higher RPM's
What occurs at high rpm's is this the heaver the weight in the variator the slower the variator will expand and allow the belt to move down inside the variator,(Drive hard into a corner and try to accelerate and the bike bogs) by using a heaver spring in the rear the more gram weight you can install in the variator and the faster the bike will go.
Tune the engine around the pipe:
Install new plug and ride the bike for about 5 minutes, even if the bike is lazy , what you are looking for is if it is too lean or too rich both will cause the bike to be lazy. pull the plug , If its black its to rich, If it is a yellowish or dark brown too lean, a perfect jetting is a plug will look as if it had never been in a motor with just a whisk of tan on the exhaust side of the plug. When you get here the bike is flying. Ha Ha.
To lean the carb. There is 5 slots on the needle move the clip to the top slot this is full lean, The bottom is richer, and see if the bike is responding more positive, By moving the needle this will tell you what the bike needs for jet.
Ok! you have installed the pipe have the red clutch spring in and the belt is only moving a 1/4 inch the plug looks good and the bike is still a t--d. What I have found a lot of times is that the clutch has too much shoe spring and by coming down 500 to 800 rpm's before lock up, the bike will start launching good, what is happing is the motor is overpowering the the belt and causing it to slip,
next no top speed, launches good but no top speed.
There is a ton of variables here I will try to cover all of them,
Roller weight go up a little in gram weight, watch the front pulley to see if the belt is climbing all the way to the top. If not try rollers or a longer belt, most belt part numbers are 780x16.6 30 there is a 780 16.8 30 and a 780 17.0 30 that are longer try one of these.
Trans gears and Sprockets:
Trans gears should be 11-31 this is a 2.81 drive ratio and works good with 16 or 18 inch tall tires.
Sprockets 18 to 19 front 25 to 28 rear I perfer 18-25 for MX and 18-22 or 20 for TT.
In the world of Auto-matic engines , these engines have very little torque, rod ratio is off a ton, So we have to create a false torque to make a 400 lb bike (with rider) run 60mph.
The variator is the key to this by slowing down the action or movement of the belt in the front pulley we are creating torque thru gear ratios. When the belt reaches the top of the variator the torque has reached the lower value of the motors torque. By using 11-31 gears or 12-36 3.0 ratio and 18-25 sprockets we have slowed down the variator increased torque, and still have great wheel speed.
If you use a 32 or 35 rear sprocket on the rear, you just eliminated the variator, this causes the belt to move up the pulley faster, and all you get is a high revving bike
December 2008
This Year we have spent untold hours Testing on a new dyna-jet dyno working on the horizontal and the 85cc YZ85. CR85,KX85 and the RM85 motorcycle engines. for 90 Mod and 105 Super mini, Honda CRF150R and the new raptor 250cc 4 stroke engines,
The CVT 90cc motor I found that most that we dynoed made between 5 to 10 hp at 10,000
rpm's, and dropped off after that, Most interesting was the fuel curve, Everyone of them went lean above 10.000 rpm's! Jet change made no difference, These motors where built by various engine builders from NY to Calif, and some in between, What I suspect is Blow Down timing and reed flutter, Some of the motors I had the opportunity to rebuild, everyone of them the piston dome underneath was completely black, which is a lean condition, the black or dark brown under neither should only be the size of a dime in the middle of the piston, this is a correct air fuel ratio motor.
Some of them even had carbon on the bottom skit of the piston and the top of the rod, which indicates the the exhaust pressure was greater in the cylinder than the intake charge?
30 degree Blow Down has been the norm for years, The little motor needs a lot more TLC
in the cylinder and head plus the expansion chamber to over come this problem.
The Motorcycle engine: YZ85 CR85 RM85
I could write a book on what you can do to make your 85 a turd? I have a YZ85 on a blaster frame that has over 250 pulls on the dyno! And a 104cc motor with upwards of 185 pulls.
I am not bragging, (on the net there is a ad stating 32hp at 12500rpm at the rear tires)
This was my goal, Bone stock 85cc YZ85 motor 15hp at the rear, Ported cylinder and a removable dome head, stock ignition and FMF rev pipe, 18hp, 104cc motor with the same ignition and head and pipe, 18hp! As you can see (what a turd)
After over 200 pulls on the 104 motor and a 103 we are making inexcess of 25hp at the rear,
I am still looking for that 32hp on gas . Not nitro or some other oxygenated fuel. that will blow his legs off if a reed brakes and causes a backfire.
Here is one problem that we found with the CR YZ RM motors they won't rev past 11000, and still make power, You will need to do your own tweaking on every single part. look at the reed cage and reeds, most are too restrictive, look for signs of flutter in the reeds,
The engine has a bad reversion problem. fuel flows out the carb and not in??? causing them to go lean at high rpm. If you are porting your engine use a degree wheel!
Have the intakes open 1 to 2 degrees before the transfers, blowdown 30 degrees port time area is critical. Squish clearence .0028 to .0030. These little motors need crank case pressure, there is a couple of ways to do this. One is not filling the crank area with devcon, this takes away volume, you need this! High compression is another way to kill crankcase pressure, besides that the motor doesn't like more than 8.5 to 1 comp ratio, (175 static compression)
Carb------A BIG ONE! 30mm or 32mm
One major problem with the 105 motors that you need to be aware of is too much stroking will make the piston uncover the exhaust port at TDC. use a piston that does not have the two oil holes for the bridge port,
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If you encounter any problems call us or e-mail us 757-410-0034
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