Should I change Roller Weights Max Acceleration RPM 2800 rpm Top Speed RPM 4300

[gmcjetpilot]

Scooter is BMS Prestige 150, GY6 150cc. Level road it tops out at 52 MPH and 4280 RPM. Going down hill +56 MPH and 4500 rpm. During acceleration I'm only seeing 2800 RPM.** Acceleration is OK, up to 35 MPH, adequate to keep up with surface street traffic. From an Android app these are some times (not sure how accurate):

0-50.0 mph 19.5 seconds
0-37.3 mph 8.35 seconds (230 feet)
1/8th mile 16.0 seconds @ 46 MPH
1/4th mile 25.25 seconds @ 51 MPH

** Bought one of those $10 inductive Tachometers off eBay and it reads 650 RPM at idle. I think it is working properly.

Don't want to waste time and money chasing my tail. I called a scooter parts sales. They talked me out of high performance CDI and rollers saying it would make only small difference. I did NOT take rollers out yet but I understand BMS brand has 17 gram rollers stock, which is heavy. Most 150cc scooters are in the 15-11 gr range.

I think 15, 14 may be 13 gram will be a small change, adding slightly to acceleration without loss of top end? WHAT YOU ALL THINK...

[humanbeing]

That Tachometer 99.99% reads half of the REAL rpm...

[ben2go]

What he said. There's supposedly a fix involving resistors. A search on the web may turn up some info.

[gmcjetpilot]

Originally Posted by humanbeing

That Tachometer 99.99% reads half of the REAL rpm...

Well not sure, but the Tach is reading idle RPM correctly. There is a setup setting to tell the Tach how many pulses per crank rotation. I have it at ONE, one pulse per crank rotation.

As I understand CDI on four stroke scooters has a lost or wasted spark system, firing every crank rotation, both top of compression stroke and exhaust stroke. On a two stroke it makes sense to fire every crank rotation. I will try setting 2. This will double the RPM reading as follows:

Idle 1300
acceleration 5600
top speed level surface 8600

That does look better except for the really high idle. However by sound I can tell that the idle is down around 650 rpm. It is possible it's not reading the higher RPM correctly. I have the wire wrapped around the spark plug wire almost 3 turns. I will add a turn and see if that helps. Also per my above post as ben2go suggested will try resistor or capacitor trick.... however by SOUND the bike seems like it is revving adequately... I am sure it is down 1000 rpm or more in actual ideal engine RPM with these rollers, but then again it is running fine.

The question of Tach accuracy aside (assume they are lower), I'm guessing that the stock heavy rollers keep the RPM down during acceleration. That is not all bad. On a manual shift motorcycle or car you don't always ring-out the RPM's, just motoring around. \

Going faster, I packed on some pounds, and being heavy I am guessing is not helping top speed. I could go for exhaust mod, bigger carb, cam, big bore kit... yada yada yada. I see YouTube videos of people modifying Ruckus scooters and going nuts when they get to 60 mph. I get it, but frankly I think I am going to sell this scooter. I own a BMW R1150RT but it's too big to take out for a quick run to the store. I also have a Hawk 250 I have not ridden much. However that thing does have power and manual gear box. However for utility that little scooter with big flat floor board (can put a case of water or beer on it), under-seat storage and top box on back, I can go to store for some grocery.

[gmcjetpilot]

Originally Posted by ben2go

What he said. There's supposedly a fix involving resistors. A search on the web may turn up some info.

I found this:

If your tachometer needle is bouncing or reading too high:

Problems with Early 12V Signal Style Tachometers, If your tachometer needle is bouncing or reading too high: If the car’s tachometer RPM reading is too high when the engine is running, or the tachometer works OK to a certain RPM, then stops or starts reading incorrectly, we recommend installing a resistor in line with the tachometer wire and coil's negative
( - ) terminal. This helps to lower the voltage spike at the coil's negative terminal to resemble a set of points, allowing the tachometer to read the ignition module's signal correctly.

The type of tachometer will determine which resistor is needed. We have found that a 10K ohm ½ Watt resistor fixes most problems and suggest starting with one of these. If you find it doesn’t fix your problem, you might need to use one with higher resistance, like a 15K ohm ½ watt or 20K ohm ½ watt.

A resistor will work in the vast majority of applications, but there are a small number of tachometer designs that will require a capacitor. We recommend using a .01 Microfarad 500VDC or 1000VDC capacitor.

I have possibly low RPM reading not high as this article suggest, but I am all for experiments. I'll try both resistor and then capacitor...

Bottom line I am holding off on the roller weight modification (to lighter ones). I will let the next owner try that. A lighter weight rider will get faster acceleration and a MPH or two higher top speed. The scooter is running great, RPM really SOUNDS great at 45 MPH, hummm. At top speed 52-56 MPH the RPM is high but not like it is crazy over REV'ing. I would not want it to ring-out much more than what I am recording as 4500 RPM at that speed (at least for extended periods). Although I'm sure the engine can handle that RPM or higher all day.

For 90% local streets 35-45 mph is the speed limit. However we have some surface roads that have 50 mph posted. Of course drivers are doing +5 to +10 MPH or more. A scooter that can easily get to 65 would be nice (even get on freeway to hop over to next exit). However I decided I'm going fold on more modifications to this bike to make it faster. It is fast enough for most needs in the city... It's running great. Of course I'm curious of what rollers or sliders do by first hand experiments on this scooter, but like they say, if it ain't broken don't fix it.

[ben2go]

1300 rpm is the proper idle speed.