Top Speed, 80cc Chinese motor? what is the record?

[mapbike]

38-40+ MPH is easy with the right engine set up like starting with a Dax "GenIV" lower, these engines are so much better balance than many of the others and with some good clean ports and a good tuned carb and good flowing exhaust, they will do 40MPH no problem if the gearing is right, I weigh 215LB currently and with a 34 or 36T sprocket I've seen 45+ MPH on two of my bikes running the Dax GenIV lower built up nice.

Map

 

[lucajo16]

Ive taken a bet that my current bike im building cant go 50. If I can get it to spin at those 8-9k RPM's then it should be possible. I also told the guy that im doing most of my engine work. I cant wait I gotta buy so many cool parts and do so much work! ^_^

Anything I should know about previous set ups before building? I plan to get a set of worksman wheels which are used for industrial bicycles, Im sticking with a 44t but will gear down at the last minute. I can do it I just need to plan accordingly.

 

[bairdco]

my race bike now has a modified ktm expansion chamber, mm ashtray head, 22mm mikuni and "backwards" engine (carb's in the front, exhaust out back.)

24" wheels and a 37t sprocket. and it weighs 53lbs.

i gps'd it at 46mph. it still revs out with that sprocket. i could easily pull a 28t and hit 50+, but it's geared for the relatively short straights at the gokart track and needs to be quick out of the turns. this season i'm gonna try out a 40t. sacrifice some top end to gain more torque outta the twists.

the key to top speeds is gearing. if you're designing a bike to do nothing but go ast fast as possible, you'll need to sacrifice low speed quickness. a low gear, a looong straightawsy, and just let it freight train along until you get there.

the trick is building a motor that won't run out of torque to pull such a low gear. putting a 30t on a stock china and you'll go nowhere, slowly.

i call bs on speeds over 40 with an untouched stock

 

[bairdco]

stupid phone... stock kit with stock sprocket.

but a stock "tuned" engine (ported, jetted, perfect mixture and ideal conditions ) can hit 40, even with a 40t sprocket.

on the right bike, of course. a junky, heavy, wobbly cruiser isn't the right bike.

as i mentioned, my race bike weighs 53lbs. a full fendered cruiser with heavy duty wheels can weigh 80+. that'll wreck your power to weight ratio.

if i ever build a "land speed record" bike (that'd never pass bonneville tech) it'd be an aluminum framed, skinny tired, long, low and lightweight death bullet.

 

[lucajo16]

My bike is a 70's or 80's Murray 26in....no wally world. I knew going in that I'll have to mod the engine. But hay if I get it to go that fast I might as well start a company to build race and higher quality engines. XD

 

[LandSpeedRecord]

I have to make a GPS run. My last bike was a GSXR 600 and the sensation of speed is so different on this. I am really hopefull we can come up with a class at Bonneville or come up with our own venue. I built the bike in my profile pic to learn and develop toward top speed. New CG from gasbike with a billet head, mildly ported, piston cut out on the intake side to match the port, soldered and drilled the main jet, removed the airbox left just the filter, mostly gutted stock pipe with no end cap. The bike is aluminum framed, just over 22 lbs with aero wheels and bladed spokes, 700x32 tires at 85 psi. I have almost the first gallon run thru it of break in fuel. Took it on a mildly rolling road and it would seriously scream when held WOT. I cant wait to find out how fast and share. Then gearing and more mods and more runs ha ha it will mever end.

 

[mapbike]

I agree with you 100% bairdco...

Ive got two old bgf engines that even with a good flowing exhaust and a couple other mods wont hit 40 with a 36T on the rear of a 24" or 26" wheel.

These two engine will vibrate your fingernail out above 30mph and neither will get over 34mph accept going down a hill

I agree stock china girls with 44T sprockets dont do 40mph in my experience.

 

[Davezilla]

I've got mine up to the 41 to 42 mph range using a 44 tooth sprocket, but very true... it won't do it in stock trim because first off it lacks the power needed to get there, and it'll rev out somewhere around 7k rpm. I think the quickest I got mine with a stock engine and 44T sprocket was around 25 to maybe 28mph.

I'm running a modified KTM exhaust pipe, Fred head, and some pretty extensive porting so it can spin up to almost 10k rpm and still make plenty enough power up there. Mine does feel like it's reving out at 41mph, it gets there fairly quickly and ducking out of the wind or streaming behind a truck won't get it any faster, I did hit 42 once but I'm thinking that road may have been just slightly downhill and I was streaming behind a big truck, and it wouldn't budge over that speed on that road. On a perfectly flat road it'll hit 41 and that's all it'll give me with this gearing.

 

[LandSpeedRecord]

I am off work tomorrow. I am going to go try to run the rest of the breakin fuel thru it. It's a pretty tall order on this thing, I have riden it quite a bit and the gas dissapears very very slowly ha ha.

 

[Davezilla]

I am off work tomorrow. I am going to go try to run the rest of the breakin fuel thru it. It's a pretty tall order on this thing, I have riden it quite a bit and the gas dissapears very very slowly ha ha.

been riding mine almost every day for almost 2 months with the same tank of gas... After this tank runs out that'll be my seond tank thru this engine since I put it back together last summer... I try to ride it everyday, but I only go about 2 miles a day on it to get breakfast, and I'm running full throttle most the way there and back...

 

[mapbike]

That's very good top speed for that big of a sprocket, none of m current engines will twist as high as yours is, My Kulana bike as it is right now will do 43-44 on the flat with a 36T rear sprocket, not sure what my rpms are at that speed.

base engine is a dax GenIV lower, ports just cleaned up nice, ramped piston on transfers and exhaust, 6cc Fred Head, Speed carby, exhaust is a small diameter pocket bike chamber being fed with some1" ID flex pipe that is actually to long for high rpm power I think, I think header pipe is about 13-14".

this engine maks good hill climbing power and runs comfortably smooth from idle to WOT and cruise speed in low 40's.

This same engine ran faster with a short home built basically straight through exhaust, it would hold a steady 45-46 mph on the flat and on a slight declining area of road it would stick the speedo on 48-49 mph and then level back down to 45-46 on the flat.

I wanted to quiet it down a little so I put the current exhaust on it and it knocked 2-3 mph off my max cruising speed but it is quieter.

I've got mine up to the 41 to 42 mph range using a 44 tooth sprocket, but very true... it won't do it in stock trim because first off it lacks the power needed to get there, and it'll rev out somewhere around 7k rpm. I think the quickest I got mine with a stock engine and 44T sprocket was around 25 to maybe 28mph.

I'm running a modified KTM exhaust pipe, Fred head, and some pretty extensive porting so it can spin up to almost 10k rpm and still make plenty enough power up there. Mine does feel like it's reving out at 41mph, it gets there fairly quickly and ducking out of the wind or streaming behind a truck won't get it any faster, I did hit 42 once but I'm thinking that road may have been just slightly downhill and I was streaming behind a big truck, and it wouldn't budge over that speed on that road. On a perfectly flat road it'll hit 41 and that's all it'll give me with this gearing.

 

[LandSpeedRecord]

I am stashing a tiny container of 2 cycle oil on the bike in case i need to premix at a gas pump someday. What I am seeing so far and with what Davezilla told me it is probably a silly precaution? I am going to give it my very best to burn some gas in this thing tomorrow on my day off though.

 

[bairdco]

I am off work tomorrow. I am going to go try to run the rest of the breakin fuel thru it. It's a pretty tall order on this thing, I have riden it quite a bit and the gas dissapears very very slowly ha ha.

i never break-in my engines gently. i build them, gas 'em up and go full throttle from day one with a normal mixture ( i use opti2 at 100:1 on the strret bikes and racing oil with castorbean oil at 20:1 on the track)

my race bikes, i mod the heck out of them, race it up and down the syreet and take em to the track. or work all night before the race and hope it runs on the morning.

my first bike was the only one i followed the recommended break in procedures, and it was the slowest bike i've built. the engine never performed well.

i've built stock kits with the stock nt carb and pipe, but matched and ported the intake and exhaust, cleaned up the poorly casted transfer ports, intake burrs, etc, and pushed 40+ on the first rides with a 36t sprocket and 26" wheels.

if you get a good engine and put it together right, thers no need to baby it.

 

[Davezilla]

I'll agree with that... on my first engine I broke it in rather easy with a richer oil mix and all, but when I decided I wanted to get some performance out of this I tore that engine down and went back up with a Dax bottom end, a new piston and new rings, the jug only had about 30 minutes of run time on it so I ported it and reused it. Put the engine back together, mixed up my 100:1 Opti2 mix and rode it like I stole it ever since. i'm on my second tank right now and almost done with it, then I'll either rejet it or put a bigger carb on it for better midrange and top end.
I'd say it's run in plenty well now because about 3 weeks ago it wouldn't budge over 35, then it hit 38 the next ride, then went up to 41 after a few more rides and hadn't improved from that point. Been looking at a block of aluminum and my CNC machine all day deciding whether or not to make an adapter to put my 20mm Tillotson carb on the bike... only thing that stopped me today was just enough customers coming in that everytime I sat down to make the cods for the cnc someone would drive up for an inspection or alignment... I'll have some free time tomorrow after hours tho so I may make up the G code then...

 

[Theon]

You'll like the 'Tilly'. Make sure you can SAFELY reach the tune knob while your riding.

 

[mapbike]

i never break-in my engines gently. i build them, gas 'em up and go full throttle from day one with a normal mixture ( i use opti2 at 100:1 on the strret bikes and racing oil with castorbean oil at 20:1 on the track)

my race bikes, i mod the heck out of them, race it up and down the syreet and take em to the track. or work all night before the race and hope it runs on the morning.

my first bike was the only one i followed the recommended break in procedures, and it was the slowest bike i've built. the engine never performed well.

i've built stock kits with the stock nt carb and pipe, but matched and ported the intake and exhaust, cleaned up the poorly casted transfer ports, intake burrs, etc, and pushed 40+ on the first rides with a 36t sprocket and 26" wheels.

if you get a good engine and put it together right, thers no need to baby it.

I do the same thing basically, I may ride for a couple miles while watching and listening to things making sure I didn't overlook anything and then its balls to the wall and I break it in like I plan to run it.... have always done every engine I ever built this way, if it fails it was gonna fail anyway because something wasnt right to begin with.

 

[Davezilla]

You'll like the 'Tilly'. Make sure you can SAFELY reach the tune knob while your riding.

Very true... it's just 2 small screws kinda tucked in at the botom of the carb on the side... I may need to make a plastic or aluminum knob I can reach while riding since I seriously doubt I'd be able to get a flat screwdriver in that slot at 40+ or under full acceleration...

 

[LandSpeedRecord]

The only thing i am doing on the break in gallon is dead dyno oil. Then will switch to sythetic. I pin them as soon as they are up too temp right after assembly.

 

[Davezilla]

I've always broke in my 2 smokers with good quality dino oil but after lots of discussion in here I decided to just go with the opti2 right from the get go and at 100:1. I figured either everyone who did it is wrong and I'll be out $35 for a jug, piston, and rings or they're right and I wont need to mix up a batch of dino mix.... from that little personal " experiment" tho I noticed it breaks in just fine and the rings seat at about the same amount of run time. I got over 30 years 2 stroke experience so this was a tough decision to make, but since these engines are cheap and parts are cheap I decided " why not try it" and it worked just the same.
The only thing I do different during break in with these is to keep the rides short so it cant overheat and leave the carb jetted on the rich side. Speaking of which... I'm about ready to dial in the jetting and that'll free up a few more rpm there too, but switching to the Tilly carb real soon anyway so I'll just leave the jetting alone and tune that carb once its installed.... no need to swap jets there, just set the low speed and high speed screws and done... which is another reason the Walbro and Tillotson carbs are so appealing when it comes to performance. I'll stop on the break in subject here tho because it tends to start some heated discussion since everyone has their own methods and almost all of them work just fine...

 

[LandSpeedRecord]

Davezilla, thanks for trying that and sharing. It's fine if one person only wants to break in their motor on west bound, even numbered streets, on odd numbered days that end in the letter y. These pistons and jugs are quite inexpensive and fun to try things with so I for one want to hear different opinions and results, more data = more knowledge. It hit me on my drive home, I ultimately want to run at Bonneville. Even if I can go as fast as my hopes which is unlikely that will mean at least 2 plus minutes of full load wide open throttle at max RPM. That is a lot to ask of that poor little air cooled motor. I am really going to have to be conservative with porting, gearing, basically everything if I want to be sure it will hold together. I have not found the opti2 locally and was going to run the Stihl factory oil at it's recommended 50 to 1 for know. Any Tucson locals know where to buy the opti2 locally?