My 130 mpg 2-stroke Minarelli bike

[xavi]

Believing in the bike''s document it says 4.7 kw wich is about 6.3-6.4 hp right? Also my friend take it for a ride and told me that the piston must have been changed into 75cc. That s the usual procedure when rebuilding an engine around here... previous owner told me the engine has been rebuild... also this engine when pulling to the max makes crazy high r pm. ..never take it to point of stop pulling.. imagine...but it feels like is going to desintegrate lol
about the speedometer a friend behind me told me I was going 55 km/h and it was right in my speedo. But cars speedo tend to be high than reAl speed too... also the km country could give more then real. But I will make a comparison with my car in daily comute and will now for sure.

[jkv357]

You are currently running a 50:1 ratio on oil, have you tested performance and/or economy with more oil?

Typically a 2-stroke will make more power with more oil, which seems opposite of what you'd expect. The additional lubrication and increased sealing of the rings contribute to better efficiency.

Might be worth a try. It may be noticeable, especially because you are only dealing with a few HP. Not sure if it would translate into better economy or not.

Here's a recent purchase of mine -

2000 Derbi GPR with a factory 75cc engine


It's got a 24mm Mikuni Flatslide carb and an Arrow pipe, and does about 70 mph. I'm running premix 32:1 Redline ester race oil, but we won't talk about the FE...

[xavi]

that's a nice ride! it has 6 gears right?
If you drive for better mpg how much mpg do you get?

If I had your sport bike I would use premium ester oil, but my bike is a 23 years old, 3 gear utility bike that can't go to highway roads, used to go from A to B if the trip is short... So I use semi-synthetic and not fully synthetic oil...
Also the mechanic told me to not use more then 2% since I make short trips...
If I use 3% oil in short trips it could isolate the spark plug and get the exhaust with to much oil crap...

[user removed]

Here is my 1965 Honda 50 aka Super Cub.

regards
mech

[xavi]

very nice! twice the age of mine! they are almost indestructible!
it's 4 stroke yes?

[user removed]

Yes 4 stroke, 3 speed with mechanical and centrifugal clutch, original paint not restored, survivor. 170 mpg last time I checked, but it only averages about 10 miles per month.

regards
mech

[xavi]

That's a finding! and original painting even more. incredible how it makes 50 years with same painting!!! Wanna trade for mine?

[jkv357]

Originally Posted by xavi

that's a nice ride! it has 6 gears right?
If you drive for better mpg how much mpg do you get?

If I had your sport bike I would use premium ester oil, but my bike is a 23 years old, 3 gear utility bike that can't go to highway roads, used to go from A to B if the trip is short... So I use semi-synthetic and not fully synthetic oil...
Also the mechanic told me to not use more then 2% since I make short trips...
If I use 3% oil in short trips it could isolate the spark plug and get the exhaust with to much oil crap...

Yes it's a 6-speed.

I've only had it a short time, and I'm still working on getting the jetting right. It's tuned for high RPM power, so it's pretty soft until 7500 or so. I don't think it will ever get 1/3 of the mileage that you are getting.

I understand why you are running less oil then. The GPR loads-up easily, and takes 4 or 5 minutes of riding to stop smoking. It doesn't run well until it's hot and cleaned-out. Not exactly practical for a daily rider - but a lot of fun.

Excellent numbers you are getting!

[xavi]

Update:

Try to mount the sprocket in the weekend but it didn't fit in the chain! Was to wide, so yesterday I went to the garage and they take 1,5mm of sprocket metal and now it fits.
So mounted it last night and take it for a small test ride...
Results are amazing: it is so much better, I now can give some use to 2nd gear, 1st and 2nd gear are smoother when changing gears, now it goes so much better, top speed much better also, feels like a bigger bike, and don't feel so much the lack of more gears...
when uphill in 1st and 2nd didn't notice any difference (could notice big difference if I take a passenger I supposed, but "I ride alone") the only thing I felt more was when in 3 gear and pull the throttle to max, at low revs it goes well, but in the mid rpm range it slows a bit, then entering high rpm it goes better again... I think it happens before, but now it is more noticeble...
Also I'm using for the 1st time a 95 "regular" petrol (the pump didn't have the premium) and with this petrol the engine is noisy, pulls worst, and make more smoke. With 98 octane premium is so much better. Can wait to waist this tank to putt premium again (in 3 liters I put every tank, the cost of premium petrol over regular is peanuts, and it makes a big difference too)

Conclusion: If it was possible to add 2T the bikes behaviour would suffer a lot.
As it was, the gearing was to much short, maybe because of some extra hp to 75cc rebuild.
As it is now is perfect, the gear are a right match to engine real "performance". So couldn't be happier, because after all, it will give me some more mpg too!
Amazing how one extra T on the sprocket transforms it into a completely diferent bike!

[cRiPpLe_rOoStEr]

Originally Posted by xavi

Also the mechanic told me to not use more then 2% since I make short trips...
If I use 3% oil in short trips it could isolate the spark plug and get the exhaust with to much oil crap...

Those carbon buildups around the electrode are a serious issue. Anyway, if you were using either synthetic or semi-synthetic a difference in mileage due to a change in the oil dosage would be less noticeable.