Post by 90GTVert on Feb 15, 2010 7:30:36 GMT -5
This information was provided by stepthrutuner.
I bought a cheap chinese scooter in '03. Name brand was Tuohe. It was 139qmb powered. Bought it new. Seller clamed it would do 45mph. It would only do maybe 38? I set about trying to remedy this as inexpensely as possible. As far as power is concerned minimizing flow restrictions into and out of the engine, proper jetting and a Denso 0.4mm tip irridium plug got me to 45 and with proper gearing (upgear) would have gotten me to 50. I would estimate I gained approximately 40-50% in power by improving high speed airflow.
My modifications included:
Size-matching exhaust port/headpipe junction and smoothing imperfections on either side.
Sawing muffler apart, removing baffles and rewelding. A small round steel disc was tack-welded about 3/8" immediately behind muffler exit to break up and spread out exhaust pulse. Unmuffled 50s are extremely piercing to the ear and I had to take it easy around the cops.
Filing down cv carb brass butterfly pivot spindle and butterfly retaining screw so that around 2-2 1/2mm remains on either side of the butterfly. Leading edge of butterfly when fully open was also tapered slightly on non-resting(when closed) side to prevent as much turbulance as possible in the airstream as it parted above and below the butterfly at WOT. This really made a difference. Probably increased flow area by 10+%. The smaller the carb bore the more effect this technique has.
Polished inside of intake manifold and matched to head port.
Adapted K&N automotive valve cover vent breather(was just like oiled cotten air filter) to carb for air filter. Cost around $13.00. Can't remember adaption details but may have involved metal vacuum cleaner suction nozzle glue and pvc pipe/coupling.
Irridium plug (these things do provide advantage through consistent firing under a wide range of conditions).
Main jet was drilled progressively with plug-reads and seat-of-pants evaluations made as to power and delivery thereof. At point of performance drop-off jet was filled with electronics solder and redrilled to next to last size.
Transmission modifications:
Ground 1mm from variator spacer length very carefully while constantly rotating spacer for even material removal. Chamfered(beveled) remaining sharp edge slightly. This lets belt ride out slightly higher on vees for slightly higher-speed gearing. Inner surface of variator can be marked with a magic marker to see how far out belt is riding. If obtainable, 1mm diameter larger roller weights would help here too. But bigger weights would disaffect initial take-off.
I tried drilling my roller weights to reduce weight but botched the job and wound up having to order weights from the U.K.(only place I could find them at the time) to get the weight of 4.2g I desired. Subsequently I have been able to successfully drill rollers for my '02 Derbi Atlantis reducing the weight from 7 to 4.5 grams. Hint. Use plenty of lube while drilling.
Removed weight in identical locations from the three clutch shoes by drilling and grinding(same effect as installing stronger springs) and final matching of weights for higher rpm engagement and quicker take-offs. Note. Removing the weight the fartherest away from the pivot has the most effect.
Installed home made bushing behind torque-driver spring(can't remember what I used) to help hold up RPM on acceleration and up hills.
Scoot would now do 45-47MPH @10,700RPM. I am confident that 50MPH would have been easily obtainable with an up-gear kit. Take-off would jump you ahead of traffic at lights easy.
These are very inexpensive techniques that yield substantial results. The tools are really the most expense, but once you have them you can work on any number of scooters.
Word of caution. These things break piston rings when rpms get in the mid elevens or so(and a little birdie didn't tell me). So watch that tach going downhills. Another reason for upgearing.
Positive note. This particular scooter with trailing-link (or is it leading?) front suspension and skinny 10" tires would lay into a curve fostering a lot more rider confidence than my telescopic-forked, fat, 12 inch-tired European Derbi.
The Tuohe's drum brakes. Not so good.
Nice things to have when scooter tuning:
Electric impact wrench. 120 VAC model for the power. About $30-40.
For weighing roller weights, a simple, hand-held letter scale. Harbor Freight has a digital scale that may be even better. On sale about $13.00.
Suggest www.drillbitcity.com. Great selection of inexpensive good quality twist bits. The ones at Harbor Freight, if you find one in their odd packaged assortments to suit your purposes, are very brittle and break very easy.
0.001" digital or dial calipers. 0-6"range.
An Installed tachometer. Northern Tools. Small engine section. EMC digital with hour meter. About $45.00. Not very responsive, but who's shifting gears anyway? Ha. Ha.
I installed one of these inside the dash in the available plastic to the right of the speedometer under the "glass" in my present Derbi. Had to install a tiny incadescent lamp inside the tach for night time illumination. That was a b*tch. I just glued it on the China job with no illumination.
Sewing needles can be used to drill jets. Cut them off square with a pair of sharp diagonal wire cutters and carefully deburr the corners leaving the full width. Clamp it long ways in a pair of vice-grips and spin the jet on the needle by hand. Not real fast and you have to make small-change cuts. Use the calipers to measure needle diameters.
Tips for night riding: Install the brightest headlamp bulbs your generator will handle. Remove some of your speedometer illumination lamps so that you can barely read the speedometer and obscure your high beam indicator if it is glaring in your eyes. You can see down the road so much better and if you've hopped up your scoot you need all the help you can get.
Happy scooting and may your asphalt abrasions be mild to non-existant.
Reg
I bought a cheap chinese scooter in '03. Name brand was Tuohe. It was 139qmb powered. Bought it new. Seller clamed it would do 45mph. It would only do maybe 38? I set about trying to remedy this as inexpensely as possible. As far as power is concerned minimizing flow restrictions into and out of the engine, proper jetting and a Denso 0.4mm tip irridium plug got me to 45 and with proper gearing (upgear) would have gotten me to 50. I would estimate I gained approximately 40-50% in power by improving high speed airflow.
My modifications included:
Size-matching exhaust port/headpipe junction and smoothing imperfections on either side.
Sawing muffler apart, removing baffles and rewelding. A small round steel disc was tack-welded about 3/8" immediately behind muffler exit to break up and spread out exhaust pulse. Unmuffled 50s are extremely piercing to the ear and I had to take it easy around the cops.
Filing down cv carb brass butterfly pivot spindle and butterfly retaining screw so that around 2-2 1/2mm remains on either side of the butterfly. Leading edge of butterfly when fully open was also tapered slightly on non-resting(when closed) side to prevent as much turbulance as possible in the airstream as it parted above and below the butterfly at WOT. This really made a difference. Probably increased flow area by 10+%. The smaller the carb bore the more effect this technique has.
Polished inside of intake manifold and matched to head port.
Adapted K&N automotive valve cover vent breather(was just like oiled cotten air filter) to carb for air filter. Cost around $13.00. Can't remember adaption details but may have involved metal vacuum cleaner suction nozzle glue and pvc pipe/coupling.
Irridium plug (these things do provide advantage through consistent firing under a wide range of conditions).
Main jet was drilled progressively with plug-reads and seat-of-pants evaluations made as to power and delivery thereof. At point of performance drop-off jet was filled with electronics solder and redrilled to next to last size.
Transmission modifications:
Ground 1mm from variator spacer length very carefully while constantly rotating spacer for even material removal. Chamfered(beveled) remaining sharp edge slightly. This lets belt ride out slightly higher on vees for slightly higher-speed gearing. Inner surface of variator can be marked with a magic marker to see how far out belt is riding. If obtainable, 1mm diameter larger roller weights would help here too. But bigger weights would disaffect initial take-off.
I tried drilling my roller weights to reduce weight but botched the job and wound up having to order weights from the U.K.(only place I could find them at the time) to get the weight of 4.2g I desired. Subsequently I have been able to successfully drill rollers for my '02 Derbi Atlantis reducing the weight from 7 to 4.5 grams. Hint. Use plenty of lube while drilling.
Removed weight in identical locations from the three clutch shoes by drilling and grinding(same effect as installing stronger springs) and final matching of weights for higher rpm engagement and quicker take-offs. Note. Removing the weight the fartherest away from the pivot has the most effect.
Installed home made bushing behind torque-driver spring(can't remember what I used) to help hold up RPM on acceleration and up hills.
Scoot would now do 45-47MPH @10,700RPM. I am confident that 50MPH would have been easily obtainable with an up-gear kit. Take-off would jump you ahead of traffic at lights easy.
These are very inexpensive techniques that yield substantial results. The tools are really the most expense, but once you have them you can work on any number of scooters.
Word of caution. These things break piston rings when rpms get in the mid elevens or so(and a little birdie didn't tell me). So watch that tach going downhills. Another reason for upgearing.
Positive note. This particular scooter with trailing-link (or is it leading?) front suspension and skinny 10" tires would lay into a curve fostering a lot more rider confidence than my telescopic-forked, fat, 12 inch-tired European Derbi.
The Tuohe's drum brakes. Not so good.
Nice things to have when scooter tuning:
Electric impact wrench. 120 VAC model for the power. About $30-40.
For weighing roller weights, a simple, hand-held letter scale. Harbor Freight has a digital scale that may be even better. On sale about $13.00.
Suggest www.drillbitcity.com. Great selection of inexpensive good quality twist bits. The ones at Harbor Freight, if you find one in their odd packaged assortments to suit your purposes, are very brittle and break very easy.
0.001" digital or dial calipers. 0-6"range.
An Installed tachometer. Northern Tools. Small engine section. EMC digital with hour meter. About $45.00. Not very responsive, but who's shifting gears anyway? Ha. Ha.
I installed one of these inside the dash in the available plastic to the right of the speedometer under the "glass" in my present Derbi. Had to install a tiny incadescent lamp inside the tach for night time illumination. That was a b*tch. I just glued it on the China job with no illumination.
Sewing needles can be used to drill jets. Cut them off square with a pair of sharp diagonal wire cutters and carefully deburr the corners leaving the full width. Clamp it long ways in a pair of vice-grips and spin the jet on the needle by hand. Not real fast and you have to make small-change cuts. Use the calipers to measure needle diameters.
Tips for night riding: Install the brightest headlamp bulbs your generator will handle. Remove some of your speedometer illumination lamps so that you can barely read the speedometer and obscure your high beam indicator if it is glaring in your eyes. You can see down the road so much better and if you've hopped up your scoot you need all the help you can get.
Happy scooting and may your asphalt abrasions be mild to non-existant.
Reg