50 CC chinese engine tuning

[pdegroote]

Originally Posted by dirtbkr188

Apparently, in France they call the bike a moped, as seen on the MASH homepage HERE.
Looking up the engine number posted above, I found the information shown below.

Sorry, it looks like the manual is wrong. The engine states: 139FMB. (the engine you showed is a 125cc, my engine is a 50cc)

[pdegroote]

Originally Posted by Bruces

Looks like a Suzuki clone to me

That is possible. It could also be based upon the Honda 50cc four-stroke.


regards

[dirtbkr188]

Originally Posted by pdegroote

I also checked the compression and it produces 6kg/cm² (some 86 PSI). That may be the reason it feels sluggish.

You might want to try a valve adjustment of 0.05mm - intake and 0.08mm - exhaust, for starters, and see if the compression improves.

[Thumper]

Since the manual indicates the larger engine, I am sure you can swap in that 150, if you can get away with it. It's not an expensive engine. Displacement is the most effective mod possible, and it would be stealthy. Do they inspect it that closely? You could just do it during Winter.

[pdegroote]

Originally Posted by Thumper

Since the manual indicates the larger engine, I am sure you can swap in that 150, if you can get away with it. It's not an expensive engine. Displacement is the most effective mod possible, and it would be stealthy. Do they inspect it that closely? You could just do it during Winter.

It is an option. But the ECU will need to be reprogrammed.

There are also 70 and 85cc kits available. But these also need reprogramming of ECU.

[Thumper]

Originally Posted by pdegroote

It is an option. But the ECU will need to be reprogrammed.

There are also 70 and 85cc kits available. But these also need reprogramming of ECU.

Are you saying it's a 50cc with EFI ?
If so, I guess it would need an ECU flash.

If it's a CDI system, it might be simpler. Maybe the 150cc engine comes with a carb and peripherals like CDI/coil.

[pdegroote]

Originally Posted by Thumper

Are you saying it's a 50cc with EFI ?
If so, I guess it would need an ECU flash.

If it's a CDI system, it might be simpler. Maybe the 150cc engine comes with a carb and peripherals like CDI/coil.

Yep, EFI with ECU. That didn't do much for the power though, and still a low compression of 86 PSI.



I agree a carb & CDI would be easier to tweak. (up to MY 2019 or 2020 it was a CDI that was easily derestriced. Alas, EU regulations (EURO 5) made an ECU and EFI a requirement.



I am looking around to see if I can find a trustworthy source for reflashing te ECU.

[Barnone]

"A 139fmb big bore kit is available for the 139FMB OHC Cub Engine. A big bore kit can be used to increase the performance of an ATV or dirt bike by replacing the stock cylinder bore and piston with a larger version. This provides more displacement, increased combustion flow, and more torque."

Google "139fmb big bore kit" or "k157fmi big bore kit"

or

"A big bore kit for a 139fmb engine requires a cylinder, piston, crankshaft, head, and gaskets. Some recommend replacing the engine instead of trying to modify the existing one. A 125 cc pit bike engine can be purchased for around $300, and there are also many inexpensive and reliable drop-in replacement engines available."

I don't know if it would work but I would prefer the engine swap if it can be fitted.

[krat]

In both the U.S. and the rest of the world a 50cc scooter with CV transmission is considered a moped, in spite of the prejudices exposed here.

All states specifically have exemptions and laws directed at these bikes and specifically refer to them as "mopeds".

It is doubtful that your bike makes more then 2 hp since that is about the limit the law allows for them. My state limits them to 1.8hp. They are also legally limited to not over 30mph in most U.S. states.

Since you have a full license you are exempt from this restriction and can modify your bike. You will also need to register it as a full motorbike at that point, or so they say. From my experience there are no rolling dynos or such in my area.

Most of the restrictions on Mopeds are mechanical rather than electronic, as so many think. There is no electronic rev limiter.

There are several mechanical restrictions on your 50cc engine.

First thing to do is tune the bike properly. Rejet the carb to an 80-90 jet and install a good quality spark plug.

Second, get rid of the stock exhaust. Replace it with a high performance glass pack and eliminate the CAT.

Just those two actions took my 50cc from 25mph top speed to around 40mph and increased pulling power substantially.

And I am an adult, 5'10" tall and weighing 230 pounds. With just that tuning action I nearly doubled the top speed.

There are tricks that one can do with the weights in the variator and the clutch springs but I have found them of marginal benefit.

The one thing that is a benefit is the installation of a "big bore kit". The normal ones will increase your engine capacity to 80cc and it will increase your HP by a proportional amount. Over here they cost less than $50 and can be installed by a competent wrench turner in half a day. Less if it is your second or third go. No modifications to the crankcase are required for the 80cc kit.

Carb rejetted, engine tuned, exhaust replaced and "big bore kit" in place and you have an 80cc scooter capable of 50-55 cruising speed.

Most of the people here consider scooters a waste and improving them more of a waste but I feel the same way about pouring $2000 of high tech mods on a 250cc Chinese bike that is worth $1500, just to get 75 mph out of it instead of 65mph.

[dirtbkr188]

The OP's bike is a 50cc vertical cylinder engine with EFI, it doesn't have a CV trans or a carb.

[Thumper]

Originally Posted by krat

In both the U.S. and the rest of the world a 50cc scooter with CV transmission is considered a moped, in spite of the prejudices exposed here.

All states specifically have exemptions and laws directed at these bikes and specifically refer to them as "mopeds".

It is not prejudice, it is history. Mopeds hit the street in the late 60s, and 70s. They were clearly and physically marketed as bicycles with pedals. Perhaps you ran out of gas, or just tooling along at 5 to 10 mph and looking at the trees. You could pedal. THESE are mopeds. Anything without pedals are scooters.

Here are a few classics!









Who cares what governments classify them as


ELECTRIC mopeds are back in spades
NO, they are not scooters, they are electric mopeds. You can pedal them with, or without electric assist.

[pdegroote]

Originally Posted by Thumper

It is not prejudice, it is history. Mopeds hit the street in the late 60s, and 70s. They were clearly and physically marketed as bicycles with pedals. Perhaps you ran out of gas, or just tooling along at 5 to 10 mph and looking at the trees. You could pedal. THESE are mopeds. Anything without pedals are scooters.



Who cares what governments classify them as


ELECTRIC mopeds are back in spades
NO, they are not scooters, they are electric mopeds. You can pedal them with, or without electric assist.

It looks as though various regions have differing definitions of "Moped". In my neck o' the woods (Belgium) scooters can be moped's or motorcycles. Depends on the displacement. Anything below 50CC is a moped, anything above is a motorbike.
A scooter is defined as a two-wheeled vehicle with the engine attached to rear wheel. The engine is thus part of the unsprung weight of the system. Could be 50CC or more.

A moped is also any other two-wheeled vehicle with a displacement of less than 50CC, whether this has pedals or not.
I am not claiming this is wrong or right. It is just the way things work over here. That it may be confusing to others is without doubt.


What I have at hand is a fuel-injected motorbike of less than 50CC (49.5CC).

[pdegroote]

Originally Posted by krat

I
It is doubtful that your bike makes more then 2 hp since that is about the limit the law allows for them. My state limits them to 1.8hp. They are also legally limited to not over 30mph in most U.S. states.

I am surprised as a honda 50CC engine is stated for approx 5HP.

There is no technical limit imposed on the power over here, only on the max speed of the moped.


The engine is fuel-injected (no carb, no cdi).





regards