How fast can your 80cc really go?

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All stock "80" on a mountain bike, sustained 26mph all day long. Sometimes she'll get up to 30 on a flat... but this is obv due to all the planets being in perfect alignment on a tuesday - but only if it's an odd number day of the month and I remembered to sacrifice the goat the night before.

mebbe...

Although... I've been thinkin of replacing the knobby tires w/cruiser street tires, this might give me another 1-2mph :D
 
rickie h said:
so how are you guys readng your rpms?
Click to expand...

I think some of these guys use an electronic speedo that is still set for KMPH but choose to read it as MPH. Explains a lot of the ridiculous claims. :rolleyes:

I calibrate my wheel diameter with GPS then enter that number in subsequent builds with similar bikes. Also check periodically thereafter.
 
.flg.All right, I can see that I am going to find and dust off my 2 stroke Hi Pro notes from MMI to keep up ya'all. reading this whole forum this morning got me to thinkin that as a true test bed I will have to build a bench top output shaft dyno and sorce an accurate 2 strock tac. I would like some imput if anyone has tried this before
 
On Level Ground, My 26" Mountain Bike normally runs at 31 MPH top speed, it has a sputtering sound and not as smooth as climbing a slight hill. Today, after 1 1/2 hour ride and tank was near empty, the engine smoothed out and my GPS speed went to 40 MPH. This lasted for about 2 miles. I would like to hear it run smooth all the time. I suspect I am running the oil mix a bit heavy and may be fouling the plug. Any suggestions?
 
1 1/2 miles from my home is a nice long down hill. 3/4 of a mile long. i put thinner tires with no tread on 2' 90 PSI. i get to the top of the hill put my head down and start my speed run. stock set up 44 tooth. after a few seconds the motor rpm's clean up and start to clime. i hit 38MPH. i can only hit 28 on flat ground and the motor misses allot
 
my bike hits 35mph stock grubee starfire gt4 66cc motor, mind you I am 6' 8" 260 lbs.... my little brother is 6'1" about 180, he can do 45-47mph on flat ground on my bike. It didnt really hit me that he went that much faster untill this crazy lady pulled up beside my brother in her car with her thumbs up saying "your going 45!" then she immediately slammed on her brakes because she wasnt paying attention and was about 20 feet from a stop sign while doing her thumbs up driving maneuver lol. My bike does have a computer on it with trip/spedo functions which really helps when I'm driving near a cop with a radar gun in a 25mph zone, normally I drive around balls out throttle pegged just cause.
 
The first day out on my "Shake down" run; A cop pulled me over.
I was traveling down the sidewalk, (I live on a rather high speed road) and he pulled me over at a cross street. He told me HE was doing the speed limit, (45) and I was slowly pulling away from him.
Thank GAWD he had a sense of humor. He just laughed & said;
"Be careful old man & PLEASE keep it below light speed!
(made my day :))"
 
Weight and height does make a difference in loading down the engine.
Mine is up to 34 on level ground, now that the engine is broke in and I am running 24:1 mix. I only wish I could get it to climb these hills in Tennessee. I had to do some pushing this weekend to get over a few of them here.
 
23-24mph 3/4 throttle zoom 80 slanthead... 28mph max at WOT.. feels like the motor is about to asplode... 44tooth.. sum ting wong. 24:1 mix...

gee, could my intake possibly be my problem?..
 

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no, not a bmx... was a serious question though, Thanks chrisme.

P.S. 38mph is quite possible on a 44tooth.. so, thanks again.
 
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What kind of riding conditions are people hitting their speeds in? I just got mine to 58kmh which is the fastest yet but the wind became unbearable and I had to back off. It is very windy and cold here at the moment and the roads Im testing on are rough and hilly country back roads. I wonder how much speed I would gain on a long dead flat road with calm weather. My ears are actually hurting after that ride!
66cc 9 speed shift kit, expansion chamber, high comp head, boost bottle.
 
Here is how to tweak another few mph or kph: try fully synthetic oil. At 24:1 non-syn oil, I topped out at 28 mph on flat road. With 50:1 syn oil (20 cc per liter) and 3 cc per liter of Marvel Myster Oil (supposed to help clean carbon out of the cylinder), I topped out at 33 mph (53 kph) on flat road. I also run a jackshaft kit and a shift-geared wheel. That and I drilled a half dozen 1/8 inch holes in the end of my muffler pipe. The holes allow exhaust gas to exit with less restriction with only minor noise increase. RPM was 4800 or so, so at wide open throttle, I am still not over-revving the engine. Bad vibrations start at about 5200 rpm (Maybe I will fix). I weigh 245 lbs. If I weighed 145 lbs, I'd go a lot faster due to less wind drag.

MikeJ
 
there's a school zone down the street from me, with the digital, "slow down!!!" sign-type radar detector. the street's new. smooth, and just barely downhill. i went passed it the other day and it registered 20-something. i looked around, no cars, so i knew it was radaring me and my bike.

i made numerous runs at it, and in full tucked, almost sitting on my rear fender-mode, i clocked 37.

(i also made sure there was no cars (or cops) around doing 37mph at the same time...)

bike: 100lb. 60 year old beach cruiser,12 guage spokes, bendix coaster brake, no front brake, "80cc" starfire, 36tooth sprocket, dried out and cracked original Carlisle Aggressor 26x2.125 tires...

me: 135lbs, usa made converse lowtops with no socks (size 8.5,) short haircut, 1980's protec helmet, sunglasses...
 
Hi all. As far as I can tell, I've never been able to go any faster than 33.4mph. When I did hit that speed, I backed off of the throttle. I then cruised for a bit at 24.9mph, and the bottom bearing broke, my piston was jammed, and my chain snapped. It was horrible. You guys are getting 40mph? And then some? I'd love to know what I'm doing wrong! These engine kits are a blast, I wish people would just drop the cars and get with the program! lol. Anyways, I'm always up for some tips to perfect my engine! Take care.
 
I'm kidding about going 60 on a 44t :P
I usually cruise around 25. I have hit 35 once. Seems a bit fast without having gears.
 
I have the CH80 that Chris Hill replaces bearings and does some other
stuff too. So it is really a stock engine with beefed up bearings. I cruise an
easy 25-28 mph with little strain on the engine.
 
rickie h asked "so how are you guys readng your rpms?"

Here is what I did: I learned about inductive pickup digital tachometers. Huh? Go to SenDEC Products Group - Home and look for "inductive meters (surface mount)". A product called TinyTachs uses the same hardware. A wire wraps around the spark plug wire 4 or 5 times. The meter senses the number of spark plug pulses per second and displays. There is one pulse per crankshaft revolution. If you get a tachometer: wrap the pickup wire around the sparkplug wire and then route the sense wire perpendicular to the spark plug wire, else the display will show twice the true rpm count. Cost was less than $45 delivered to your door. Instructions are fairly simple to follow.

MikeJ
 
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