READING AND UNDERSTANDING SPARK PLUGS
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The spark plug in your Zuma has two primary functions: 1. To ignite the air/fuel mixture 2. To remove heat out of the combustion chamber Spark plugs transmit electrical energy that turns fuel into working energy. A sufficient amount of voltage must be supplied by the ignition system to cause it to spark across the spark plug's gap.This is called electrical performance. Additionally, the temperature of the spark plug's firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called thermal performance and is determined by the heat range selelcted. A spark plug cannont create heat! It can only remove heat. The spark plug works as a heat-exchanger by pulling unwanted thermal energy away from the combustion chanber and transferring the heat to the engine's cooling system. The heat range is defined as a plug's ability to dissipate heat. The rate of heat transfer is determined by: 1. The insulator nose length 2. Gas volume around the insulator nose 3. Materials/construction of center electrode and porcelain insulator The Gap of the spark plug is extemely important.Always check the gap on every plug before installation;plugs are not always pre-gapped at the factory. The correct gap for the Zuma is: 0.020~0.030"(0.6~0.7mm). Spark Plug Torque is often overlooked. It is most critical as it directly influences spark plug temperatures. A spark plug can only transfer heat effectively when it is fully seated on the cylinder head. The correct torque for the Zuma is 14.0lb-ft (2.0kg-m) The recommended factory plug for a bone stock Zuma, (not modified) is an NGK BPR7HS. For a modified Zuma a BPR8HS, and for a fully modified racing Zuma BPR8HIX. |
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The insulator nose length is the distance from the firing tip of the insulator to the point where insulator meets the metal shell. Since the insulator tip is the hottest part of the spark plug, the tip temperature is a primary factor in pre-ignition and/or fouling. The tip temperature must remain between 450C~850C. If lower the insulator area surrounding the center electrode will not be hot enough to burn off carbon and combustion chamber deposits. This can lead to misfire and fouling. If the tip temperature is higher than 850C the plug will overheat which can lead to pre-ignition detonation and big time engine damage.
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ZUMA FINAL DRIVE INSTALL 02-11
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Remove Kick Starter, Plastic Cover, and outer case. Drain the oil. Be careful when removing the outer case and you will not tear the gasket. |
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Item on left is Variator Item on right is clutch Remove 17mm nut & bell housing The clutch will want to turn, have some one hold it or use an impact wrench. (Cheap Electric impact wrenches are available at places like Harbor Freight and Tools. They are worth their weight in gold!) Remove clutch. (Not necessary to remove large nut, clutch will come off without removing nut.) |
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Remove the final drive cover This requires removal of 6 screws, cover has locating dowel pins so you will probably have to "wiggle" cover to get it off. |
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Remove transmission. These are the original gears and what you are removing. On the left is the shaft that the clutch is on, and on the right is the main axle. |
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These are the replacement Athena Gears and new bearing If you put the new shaft in the freezer overnight and the bearing in the oven on low for about an hour, you can slide the bearing on the shaft and tap down into place using a piece of pvc pipe as a bearing driver. (This assumes you do not have an hydraulic press at your disposal.) Pay attention to the direction of the helical cut gear and install the new gear onto |
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 Note the gap when installing into new final drive gear. Maintain this gap.(the same technique of freezing and heating can facilitate installation into new main gear.)
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Assemble main axle into case |
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Put Clutch shaft into case, install gasket, use new one if necessary, tighten up and add oil. Re-assemble remaining pieces. |
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Exploded diagram of Transmission |
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Remove Kick Starter, Plastic Cover, and outer case. It is NOT NECESSARY to drain oil as there is no oil behind the cover. |
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Be careful when removing the outer case and you will not tear the gasket. Item on left is Variator Item on right is clutch |
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Remove 17mm nut The variator will want to turn, have some one hold it or use an impact wrench. (Cheap Electric impact wrenches are available at places like Harbor Freight and Tools. They are worth their weight in gold!) Remove nut, washer, claw washer, and fan. |
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Now you can slide the belt off crank shaft. Be careful not to lose small washer on end of crankshaft sleeve. Then you can remove back part of variator. |
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Be careful not to remove this piece which is behind variator. |
| Place rollers into sliding sheave |
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Put Cam over sliding sheave and carefully slide onto crank shaft |
| Place Washer back onto shaft. The washer IS NOT A GOVENOR! For proper working it must be there. |
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Put on belt and then fan and claw washer. Please note the amount of spline on crankshaft is getting less as you add items. This is normal. |
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Place funny looking washer on crank shaft, There will be just enough splines left for this to engage splines. It is critical that all items that are splined engage the splines on crankshaft. This is not difficult, just requires paying attention. |
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Put on flat washer and then 17mm nut |
| Done! |
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Exploded diagram of Variator |
| 1 GEAR, PRIMARY DRIVE 2 BEARING 3 OIL SEAL 4 BEARING 5 CLUTCH CARRIER ASSY 6 SPRING, CLUTCH WEIGHT 7 SECONDARY FIXED SHEAVE COMP. 8 SECONDARY SLIDING SHEAVE 9 OIL SEAL 10 O-RING 11 PIN, GUIDE 12 SPRING, COMPRESSION 13 SEAT, SECONDARY SPRING 14 NUT 15 NUT 16 PRIMARY SLIDING SHEAVE COMP. 17 Roller WEIGHT 18 CAM 19 SLIDER 20 COLLAR 21 WASHER, PLATE 22 V-BELT 23 SHEAVE, PRIMARY FIXED 1 24 WASHER, CLAW 25 CLUTCH, ONEWAY 26 WASHER, CONICAL SPRING 27 NUT |
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Problem: After scooter is warmed up, the "off the line" ability diminishes. Reason: Clutch pulley is not returning to lowest gearing, i.e., you are starting in too high a gear! Cause: Grease, gunk, etc on secondary fixed and sliding sheave is thick and dirty & won't allow to operate correctly. Solution (refer to above diagram): Remove 16,15,14,5,12 from the secondary pulley assembly and put aside. Remove the secondary spring seat (13) from the secondary sliding sheave (8), "twist and pull" Remove the two guide pins (11) Separate the secondary fixed sheave (7) from the secondary sliding sheave (8) Now all the original gunky grease is exposed. this needs to be cleaned up. use rubbing alcohol. Apply fresh lithium soap grease on the inside of the secondary sliding sheave (8), be generous. Re-assemble the secondary sliding sheave (8) and secondary fixed sheave (7) with the guide pins (11) Apply more lithium soap grease in the guide pin slots and around the outside of the secondary sliding sheave (8) Actuate the secondary pulley assembly back and forth and then clean up any grease that has seeped out, being careful not to get any grease on the sheave faces. Clean Sheave faces with alcohol! Reassemble |
| Below are various pictures of this procedure. We did not put up every step, you obviously have to get the clutch off the scooter and then re-assembled and back on. |
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| PROBLEM:The two Phillips Screws holding the gas cap together get loose, then fall out. This generally only happens when cap is installed and you are scooting down the streeet. Needless to say this results in screws, springs, and all manner of bad stuff falling into your gas tank, not to mention a gas cap that doesn't work! | 
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SOLLUTION: Remove cap and carefully remove ONE SCREW AT A TIME. |
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Apply one drop of Blue Loctite to the screw and replace and tighten in gas cap. Then do the other screw the same way. |
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| Double Check tightness and replace gas cap on tank. | 
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08-11 CARB FIX
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| On 2008 - 2011 Models the throttle will only open part way. Modifying the throttle cam to allow it to turn fully will solve this. Can be done with hack saw or dremel tool. Careful where the shavings go! Test by turning throttle and observing if slide fully retracts. |
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Please note the location of the air screw. On the 2008 - 2011 models there is an aluminum colored plug in the hole covering the adjustment screw. |
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These Mods change your 2008 - 2011 Zuma from a Scooter that can barely get out of it's own way into a good performing fun Zuma! The picture on the right has the area to be removed outlined in red. If you have questions about your 2008 - 2011 Zuma, we have answers! |
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2008 - 2011 Zuma Fixes: While we do not advocate tampering with the intake or exhaust of an EPA regulated vehicle we know that you would only do it if you were going racing on a closed course! We offer the above advice and or parts so you can go racing and keep up with the older model Zumas! All products are Legal Only for Racing Vehicles and are not intended for use on pollution controlled street vehicles |
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| Model | Oil Weight |
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Quantity OZ's |
| 50cc '02-'11 | 10wt | 88 cc | 3 oz |
| 50F '12-'15 | 10wt | 88 cc | 3 oz |
| 125cc '09-'15 | 10wt | 104cc | 3.5oz |
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Assembly: Piston: Make sure opening in the ring straddles the ring locating pin on the ring land. After installing on the piston make sure it expand and contract freely. If they do not, swap the two rings. (On single ring pistons this does not apply.) Check for free movement. Install wrist pin bearing on the rod. Use a drop of oil on and rotate to spread on inner race of rod. Immediately before installation of the cylinder, WASH the cylinder with dishwashing soap and water. Scrub all the ports and the bore. Dry thoroughly with a lint free cloth. Make sure cylinder is both dry and clean. Slip the cylinder over the piston while compressing the ring(s) with one hand. Make sure ring ends are straddling the ring locating pin on the piston ring land. Rotate crankshaft and make sure piston moves up and down freely. Install head gasket. (if Head gasket has a raised ridge. It goes up.) Install head. Torque head nuts to 11-ft lbs. using a cross pattern. (If you are using the oil injector, don't forget to hook up oil line!) (Do not add oil to the gas tank!!!!) Break In: It is important that during this break in time the RPM is varied constantly. Do not run at a sustained RPM for a long time. If you are cruising at 35mph for a minute, change to 40mph, etc. Do not put on the stand and let idle for any part of the break in period. Engine needs to have air going past it and the RPM constantly varied. Yamaha circlips are difficult at best. Pay particular attention to seating them properly. Yamaha head gaskets have a ridge on them. The ridge goes up. Polini requires the use of a "long reach" spark plug such as an NGK B9ES
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HOW DOES A 2 STROKE WORK
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At the point where the spark plug fires, fuel and air in the cylinder have been compressed, and when the spark plug fires the mixture ignites. As the piston moves downward, it is compressing the air/fuel mixture in the crankcase.
As the piston finally bottoms out, the intake port is uncovered. The piston's movement has pressurized the mixture in the crankcase, so it rushes into the cylinder, displacing the remaining exhaust gases and filling the cylinder with a fresh charge of fuel. Now the momentum in the crankshaft starts driving the piston back toward the spark plug for the compression stroke.
(Two stroke Engine operation |
WHAT IS A VARIATOR
| What the heck is a Variator and how does it work??? Here's a little animation of one in action. The explantion follows |
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| This document was originally written by Scott (AKA Scootnfast) on the ApriliaForum website. We have done a bit of editing so that the average scooter head can understand, but all the photos and info are his. We have requested his permission to reproduce this. We have been unable to contact him, so we stole a great deal of this, but it is stolen with total admiration for the author, his writing and illustrations! Thank you Scootnfast!.....the squids |
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One thing people regularly wonder about is how a CVT (Constant Variable Transmission) works. (If you are one of those people, you need to get a life!) CVTs are used mostly in scooters, like the 50cc Yamaha Zuma. If you've ever been confused about that strange little transmission in your scooter, this should help clear things up a bit. CVTs are quite simple in design, but since every part must work in concert with all the others, it can be difficult to visualize their operation, and understand how each part fits into the whole. The drawings are not to scale, but are meant to just give you a better idea about what is going on. |
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Lets start with the front pulley of the variator. This is where your roller weights and ramp plate are located. This image is a cross-section of the front pulley, showing the front half of the pulley, the belt, and the rollers sitting against the ramp plate. This is how the transmission looks when the engine is running at low RPMs. |
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Now as the RPM's of the motor increase, the centrifugal force pushes the roller weights outward (number 1 in picture). The roller weights push out and onto the angle plates surface. This causes the rear half of the pulley to move toward the front half of the pulley (number 2 in picture). When the rear half of the pulley pushes to the front pulley, it forces the belt out to a higher gear ratio (number 3 in picture). This is the basic operation of the front pulley. Faster engine speeds cause the belt to go outward. |
| O.K. now, I can tell some of you are not paying attention. There will be a quiz on this, and the results go on your permanent record! |
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If you are thinking about getting a new variator, let me first start by telling you that it will probably not have any effect on your over all top speed. What it will do is give you a more steady acceleration. The distance that the rear half of the pulley can travel pretty much remains the same. Meaning that it will only push the belt out as far as the stock variator will which results in the same high gear ratio as the stock variator. The key difference between the stock and performance variators is the angle on which the roller weights travel and the angle on the angle plate in the rear of the variator. This will only help give you a smoother, more constant acceleration. Now as for the different weights for the rollers. It is really rather simple. The heavier the weight, the more force will be applied to the angle plate forcing the rear pulley half forward faster. If the roller weights are too heavy, it will force the gear into too high of a gear too fast. I like to use a 10 speed bicycle as a comparison. From a dead start, if you are in 10th gear, it is very difficult to get going. But if you are in first gear, it is very easy to get moving. the same principle applies here. You want the weights to keep you in first gear, and as the RPM's increase, it will gradually step the gears up until it reaches tenth gear. If your roller weights are too light, then there will not be enough force to push the ramp plate out and the rear half forward. This will result in good acceleration, but a low top end. You will simply remain in a low gear for too long. As the engine speed finally gets moving enough to move the pulley forward and raise your gearing, you will be above the RPM of peak horsepower for the engine, and it will not have the power to get you moving. |
| Now it's getting good! Where else can you use the old 10 speed bike analogy! Doesn't get any better than that! |
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This image is a side view of what the ratio looks like in low gear. You will see that the front pulley is small, and the rear pulley is large. This is like first gear of the 10 speed bike. |
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This image is what the gear ratio looks like when the roller weights are pushed out and the rear half of the pulley is forward. The belt is pushed out to a higher ratio. This is like tenth gear on the bicycle. |
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Now the other factor in this equation is the rear pulley. The rear pulley has a spring holding it together. This is your contra spring. The front half of the pulley is also torque controlled. There are angled grooves that the pulley travels on. As torque is applied, this limits the belt from traveling in too quickly. Likewise, as you go up a hill and torque is applied to the pulley, it is supposed to force the pulley together giving you a lower gear ratio. |
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This image is what the rear pulley looks like at low rpm's. The spring is forcing the two halves of the rear pulley together, holding belt outward, and keeping a low gearing. As torque is applied to the belt, the halves of the pulley begin to separate, pulling the belt inward, which raises your gearing. The stiffness of this spring determines how fast the pulley halves expand, and how strongly they return to their original shape when the torque is lowered again |
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This image is what the rear pulley looks like at high rpm's. Notice the spring has been compressed, and the belt has moved inward. |
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If your roller weights are giving you good acceleration, and a good top end, but when you approach a small hill the scooter slows drastically, this may be caused by having too light of a contra spring. The contra spring helps push the rear pulley back together when torque is applied to the rear pulley. Say you are running good at say 50MPH, and you slow down to 35MPH. If you then try to accelerate, and you have hardly any acceleration, this can be caused by having too light of a contra spring. When you slow down, the spring is supposed to push the rear pulley together into a lower gear ratio. If the spring isn't strong enough, the pulley will remain in a high gear, and then when you try to accelerate, there isn't enough power to push you because you are in too high of a gear. On the other hand, if your spring is too strong, then the roller weights may not be heavy enough to force the belt out all the way and into it's highest gear ratio, and you won't be able to reach your top speed. If you go with a stiffer contra spring, you may need to go to a slightly heavier roller weight. Likewise, if you go to a softer spring, you may need to go to a lighter roller weight. There is a very fine balance that you must achieve between the contra spring and your roller weights. This is only accomplished through trial and error. |
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This is an exploded diagram of the stock Yamaha Assembly |
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So what do we do with all this stuff? Clean and adjust! Do not use a caustic carb cleaner, as this is a Taiwan made carburator manufactured from the finest of materials! LOL! Use contact cleaner or solvent. On the main jet & pilot jet, hold up to the light and make sure they are clear. If not run a small wire through to un-plug.(the main jet is probably clear, the pilot is probably not!) Aslo, hold up #8, the needle receiver. Run a small wire in the 5 pin holes on the long part of the needle receiver. These holes are critical to smooth running, and clog quite easily particularly if scooter has sat for a long time. Float level is set at factory and we do not suggest you adjust it. Generally it is right on. Should be 15-17MM from gasket surface with the float just touching the float valve. Check all parts for wear, replace if worn. Check slide for free movement, check hoses for cracks or wear. After reasembly adjust idle for your preference. AIR SCREW: o.k. here's the deal. comes from the factory 1 1/2-2 turns out. Usually this is ok, however if you have been experiencing "coughing", "starving for gas" turning throttle and bike gasps then catches on.......then......adjust air screw all the way in and then back out 3/4 to 1 turn. This is the sollution to that problem, not changing main jet.
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14mm Taiwanese Del Lorto Knock off |
| Main Jet | 80 |
| Needle Receiver | 2.085 |
| Needle/Clip | 3N24 3/5 |
| Main Air Jet | 2.0 |
| Slide Cutaway | 3.5 |
| Pilot | 44 |
| Bypass | .8 |
| Needle Valve | 1.8 |
| Starte Jet | 48 |
DELLORTO
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| Carb | 19mm Del Lorto |
| Main Jet | 75 |
| Needle Receiver | 262AU |
| Needle/Clip | W9/2 |
| Main Air Jet | |
| Slide Cutaway | 3.0 |
| Pilot | 45 |
| Bypass | |
| Float Height | 15mm |
| Starter Jet | 60 |
| Velocity stack is removeable on both carbs. You can use air box with either. |
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| Carb | 21mm Del Lorto |
| Main Jet | 92 |
| Needle Receiver | |
| Needle/Clip | ?/2 |
| Main Air Jet | |
| Slide Cutaway | |
| Pilot | 50 |
| Bypass | |
| Float Height | 14mm |
| Starter Jet |
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So what do we do with all this stuff? Clean and adjust! Do not use a caustic carb cleaner. Use contact cleaner or solvent. On the main jet & pilot jet, hold up to the light and make sure they are clear. If not run a small wire through to un-plug. Float level is set at factory and we do not suggest you adjust it. Generally it is right on. Should be 15MM from gasket surface with the float just touching the float valve. Check all parts for wear, replace if worn. Check slide for free movement, check hoses for cracks or wear. After reasembly adjust idle for your preference. AIR SCREW: o.k. here's the deal. comes from the factory 1 1/2 turns out. Usually this is ok, however if you have been experiencing "coughing", "starving for gas" turning throttle and bike gasps then catches on.......then......adjust air screw all the way in and then back out 3/4 turn. This is the sollution to that problem, not changing main jet. |