What's the maximum RPM you"ve reached?

[Outrunner]

I had my bike up to 38 mph the other day with a digital speedometer that was
GPS calibrated and a digital tach that showed 8310 rpm, I was very surprised
to see that, although it was only for about 4 or 5 seconds. At that rpm my
67cc engine was screaming and vibrating something fierce, and I didn't want
to grenade the thing. I'm running a 41 tooth sprocket, 18mm Mikuni carb,
and expansion chamber. Out of curiosity, what is the maximum rpm some of
you guys have seen?
shft.

 

[Outrunner]

I had my bike up to 38 mph the other day with a digital speedometer that was
GPS calibrated and a digital tach that showed 8310 rpm, I was very surprised
to see that, although it was only for about 4 or 5 seconds. At that rpm my
67cc engine was screaming and vibrating something fierce, and I didn't want
to grenade the thing. I'm running a 41 tooth sprocket, 18mm Mikuni carb,
and expansion chamber. Out of curiosity, what is the maximum rpm some of
you guys have seen?
shft.

Update, I installed a 37 tooth sprocket and I can easily surpass 40 mph up
to 43 mph, at about 8400 rpm, so it is really runnin' well. I plan to rig up a
nitrous oxide system in the near future and will see what the increase in rpm and speed is.

 

[Cabinfever1977]

I thought that most places listed the max rpms of the 66cc engine at around 4500 rpms.
And since youre using a smaller rear sprocket that alone should lower your rpms especially at higher speeds. Im not challeging your equipment,im just stating the information i read and that some people think it would be better to have lower rpms at speed.

 

[Outrunner]

I thought that most places listed the max rpms of the 66cc engine at around 4500 rpms.
And since youre using a smaller rear sprocket that alone should lower your rpms especially at higher speeds. Im not challeging your equipment,im just stating the information i read and that some people think it would be better to have lower rpms at speed.

I'm using a digital tachometer that reads the spark pulses from the plug wire,
so,I'm sure that it is accurate. Riding on a flat roadway that is over 2 miles long gives me ample time and room to wind out the engine. My engine has an 18mm Mikuni carb with a #70 main jet, A tuned expansion chamber,and modified cylinder porting, combined with a modified intake manifold and a slant head.
Running 50:1 Amsoil Sabre gas mix and "tucked in", I assure you that it is accurate data. My buddy has followed close behind me and confirmed my speeds also,so I feel confident of the speed and rpm's reported. Like I first stated, "I was surprised to see that" meant that seeing that high of rpm's. Obviously,I have a well tuned and sweet running set-up. I love it!

 

[foureasy]

10k with a 41t sprocket and 24.5" tires

 

[The 26incher]

Outrunner, could we please see pic's of your bike? Thanks
I really feel like my engine spins like crazy. I would love to have a tach and speedo.

 

[bairdco]

i made two revolutions around the block earlier, probably took me 3 minutes.

 

[Outrunner]

Outrunner, could we please see pic's of your bike? Thanks
I really feel like my engine spins like crazy. I would love to have a tach and speedo.

Here are some photo's of my bike, I have changed the air filter and added a "Thudbuster"seat post for a much smoother ride.

 

[Cabinfever1977]

That really is a great looking bike. I believe your speed,i was just suprised your rpms were so high.

 

[BarelyAWake]

That is a sweet lookin' ride - nice combo of elements for an overall effect, I likes it

 

[Tcams]

Here are some photo's of my bike, I have changed the air filter and added a "Thudbuster"seat post for a much smoother ride.

what kind of carb are you using? Sweet ride by the way

 

[Outrunner]

Thanks Guys, I really appreciate the compliments. Believe me, I was
very surprised to see the rpm's crank that high, but it would run somewhere between 6500-7000 rpm's before I added the expansion chamber. I felt obligated to share that info with you guys so that you
can see the potential of these palm sized engines. These engines
just need to "breathe" a lot better. Now, I've got to work on the pesky
vibration issues!

 

[The 26incher]

That is a very nice bike Outrunner. You know, I have a "Raw" 66cc that I'm telling ya, it spins like crazy and I don't get any vibration? I put an air cleaner, custom intake and "spooky tooth" style expansion chamber. When I put all the parts on, I dropped the clip on the nedle all the way to the bottom. I read on here that guys say they down jet the carb but I think I need more gas. I'm going to make a Youtube video this weekend because I think the bike does 40mph. When I put the pipe on, I gained alot of mid range. My plug looks perfect and I know I could pull a smaller gear. I really think my engine spins close to 10 grand but I don't know for sure. I know a bunch of guys here think that is BS but like I said, I'm going to make a video this weekend to see what it really does. I will have my wife or one of my friends clock me with their speed-o in their car. I think with my 41 tooth sprocket I'll do 40mph. I think I could pull a 36 tooth on flat ground but I dont wont to loose mid range. My engine is bone stock, no head or port work. I just think I got a good one. I am at sea level and the air here in Torrance Beach is nice and dence. O ya, and I run 40 to 1... feel free to call BS (and I could be full of it) but I'm sure the video will tell the true story.

 

[jg767]

9300rpm on a Tanaka 40cc stock

 

[Cabinfever1977]

Instead of max rpms,it should be how long will your engine last or how fast can you go with the lowest rpms. Me thinking that someone turned there idle all the way up for higher rpms. I have my idleing vey low and get 180mpg @ 30mph 44t 26" bike.

 

[K.i.p]

That is a nice looking bike. I think your build is leaching hormones from that "sporty" tank!

 

[Outrunner]

Instead of max rpms,it should be how long will your engine last or how fast can you go with the lowest rpms. Me thinking that someone turned there idle all the way up for higher rpms. I have my idleing vey low and get 180mpg @ 30mph 44t 26" bike.

Cabin, I don't disagree with you at all. The fact is, if you want your engine to
run at less than full throttle at about 25-30mph you need to reducethe rpm's by lowering the number of rear sprocket teeth. That allows the engine to
operate at less than full throttle to obtain better gas mileage,longer engine life and less vibration. It really is fairly simple. My question was to inquire other fellow riders like you, to see what their maximum rpm's are. The engine can max out at almost any speed depending on sprocket gear ratio's.

 

[DanielMaia]

I'm using a digital tachometer that reads the spark pulses from the plug wire,
so,I'm sure that it is accurate. Riding on a flat roadway that is over 2 miles long gives me ample time and room to wind out the engine. My engine has an 18mm Mikuni carb with a #70 main jet, A tuned expansion chamber,and modified cylinder porting, combined with a modified intake manifold and a slant head.
Running 50:1 Amsoil Sabre gas mix and "tucked in", I assure you that it is accurate data. My buddy has followed close behind me and confirmed my speeds also,so I feel confident of the speed and rpm's reported. Like I first stated, "I was surprised to see that" meant that seeing that high of rpm's. Obviously,I have a well tuned and sweet running set-up. I love it!

Where i can find those digital tachometers?

I beat some months ago, 58km/h (speedometer calibrated) on a 44T sprocket..

 

[Outrunner]

The tachometer is a "Tiny Tach", if you Google part #tt226nr, it will bring up several sources to choose from for about $34.00. The Tiny Tach
also will record the amount of run-time logged on your engine and bike to aid in service and maintenance, besides being extremely accurate!

 

[troyboy]

Hi Outrunner,

Nice post. Nice Mikuni Carb also. You ride Harley's too?

Hitting em with some Old School basics. Absolutely true though, allowing more air to come in and allowing more air to exit will give you some great advantages on the stock HT kit.

These motors suffer greatly from air restrictions in the intake and muffler, the black cat being the worst Ive seen yet.

3/4 H.P. can be gained by performing these simple steps.
Port matching your intake or replacing it with a ported intake while getting rid of the kit supplied intake gasket. The supplied gasket overlaps the intake and jug causing fuel resistance. Make your own gasket using some Right stuff gasket maker, yamabond, or ultra Grey ect.

Next is the exhaust, either purchase a high flow ht muffler or a expansion chamber muffler.
If you choose to do the expansion chamber you should upgrade the carb to dial it to its maximum potential.
If you do not plan on upgrading the carb you should just get a high flow muff designed for the Ht's, their half the money and work well.

A balanced crank is the luck of the draw with these kits. Some motors run smooth and some will vibrate your cheeks off. Sounds like you may have shaker.

Nice talking with you on the phone and keep up your dedication here. We need guys like you in this industry.. Let me know when your ready for the juice.

Peace,
Justin