DIY takeoff tips?

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anim8r

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Jul 15, 2011
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I had a car pass me as I left a stop sign on my 66cc yesterday. It was pretty stupid move, I thought, but at least I didn't get hit. (what I learned yesterday: some drivers are b!tc#es & m0+#3rfuc%3rs, so daily brake checks are a must.)

So I'm wondering about diy solutions to improve my takeoff speed. So far I don't think my top speed is a concern....it feels like it goes pretty fast & I still haven't had it as fast as it'll go. But the takeoff is a little sluggish, and I don't have any more money for the bike for a while. Any suggestions? Maybe some tuning tips?

66cc BGF chinagirl with upgraded hardware
no shift kit
standard exhaust
 

Tohri

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Aug 28, 2010
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People's Republik of Massachusetts
The shift kit is the only thing that will really help your off the line accel. it's a good idea overall, these motors do Not make good power at redline, the ports are wrong. you'll see an improvement overall, but REMEMBER to upgrade your rear wheel/hub, Deraileur and Casette/Freewheel. The Shimano Megarange is ideal for our bikes, the 34T-11 are more ideal, but the 34-14 7 speeds are cheap and durable.

with a range like that, it's like being able to choose between a 64 tooth sprocket, Down to a 30, and 5 more in between. So yes, you'll be able to stand on your rear wheel off a stop, and cruise at your peak power, not at Peak RPMs
 

anim8r

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Jul 15, 2011
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I guess the "no-money" parts weren't clear enough lol....does anybody have tips for WAY less than a few hundred dollars?

Looking for stuff I can do in the shop, not stuff I can shop for.
 

Tacomancini

Member
Mar 18, 2010
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Pittsburgh
You could go to a larger sprocket, a 48 tooth could be had for cheap, improve takeoff but in trade for top speed.

Also, increase the idle speed so the engine is revving higher allowing you to slip the clutch to assist you earlier.

I'm one of those opti 2 oil guys, I swear it increased my low end response. But if you are running a standard decent two stroke oil at a high ratio like 18:1, 20:1, after break in of two to three gallons of gas switch to 32:1. That helps, although I recommend make the jump to opti if you can find it.

Three other cheap upgrades that I believed helped a lot with low end torque, you could pick any one of them and they would probably help: better fuel petcock let's fuel flow with less resistance in the low rpms, the HD fuel filter for the NT carb helped with air flow, and super cheap, get a better spark plug by Ngk, like a b6hs ( this is a must and is even better with new plug wire). The spark plug is a no brainer really. All these upgrades are available at sick bike parts. I'd you were to find 70 bucks, u could do their expansion chamber exhaust which would absolutely increase low end torque. That's of course on the high end of low budget.

Also, make sure there are no air leaks, the revv should sound crisp, Rrooom rrooom.... Not rrrrrraarraraaaaroooouuuuummmmmnnnn. If it seems slow to return to idle you probably have air leaks or something weird happening somewhere.
 
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Tacomancini

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Mar 18, 2010
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Pittsburgh
Also, couple a diy things:

The cheap DIY airflow filter made out of a tuna can with holes drilled in it, and a sponge inside is quite popular and free. Search the forums for examples. Others drill holes in the plastic of the stock air filer to increase air flow. Thats a two minute fix.

I have seen folks extend the length of the clutch arm to increase leverage on that part. You could for example put a sheath around it to make it longer. This makes the clutch action easier, and can help you to slip the clutch more like a car's clutch functions, so more assistance off of the line. The trade off here is that you are harder on the clutch, but you can replace the clutch pucks later. This reminds me of another cheap upgrade from sick bike parts, a Teflon clutch cable. It stretches less, and reduces drag allowing you to use your clutch more aggressively for take off. Ten dollar upgrade there.
 
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decoherence

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Aug 23, 2010
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sebring,fl
larger rear sprocket.
it will do exactly what you are looking for.
faster take off with a sacrifice of top speed.

shift kits will not make one take off faster.
it is used for one to select ratios.
to take off with a shift kit you use the large gear.
the OP's problem wasn't to take off quick & have great top speed.
in fact all the mods posted here will not help take off ANYWHERE as much as a gear change.

the other option is to peddle when taking off.
it can help greatly.
 

BarelyAWake

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Jul 21, 2009
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While it does sound like all the OP needs/wants is a different rear sprocket (sacrifice top speed for acceleration/inexpensive easy mod) I thought I should mention "shift kits will not make one take off faster" is incorrect, in fact that's what they do, all they do.

Provided the finals are the same, having multiple gears only improves acceleration, granting you both low gears for take off and high gears for cruise speed - shift kits do not improve top speed as that requires more power, a common misconception. They actually (very) marginally reduce absolute potential top speed vs a direct drive single speed due to additional friction & drag, though it's so slight it's a sacrifice worth making in my opinion.
 
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decoherence

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Aug 23, 2010
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sebring,fl
While it does sound like all the OP needs/wants is a different rear sprocket (sacrifice top speed for acceleration/inexpensive easy mod) I thought I should mention "shift kits will not make one take off faster" is incorrect, in fact that's what they do, all they do.

Provided the finals are the same, having multiple gears only improves acceleration, granting you both low gears for take off and high gears for cruise speed - shift kits do not improve top speed as that requires more power, a common misconception. They actually (very) marginally reduce absolute potential top speed vs a direct drive single speed due to additional friction & drag, though it's so slight it's a sacrifice worth making in my opinion.
that is granted you have the gearing set that way as you said.
also granted one has the gearing set different would have different results.
THAT is the purpose of shift kits.
more gearing options.(abet a large price tag or time & ability to make one's own)

but we both can agree that the OP's problem is screaming larger rear sprocket.
not a sock filter, shift kit, or a fast looking paintjob. lol
 

anim8r

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Jul 15, 2011
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That's the kind of stuff I'm looking for.
decoherence-- I've got a 44-tooth sprocket now. That's one of the bigger ones, isn't it?

I wonder now if I'm being too gentle with my clutch. I always pedal at take off because I've just read on so many posts that it's a good practice. I guess when this freezing rain lets up I'll try taking off with a little more aggression & see if my low take-off speed is just my own fault. (I've got a bad feeling about the answer lol). I'm also using a Al.Fisherman-style clutch cable roller mod.

So what about using a more open air filter & a better spark plug? Do they really provide any noticeable performance boost? I'm starting to think about homemade expansion chambers...
 

Tacomancini

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Mar 18, 2010
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Pittsburgh
Yup. For reference, I'm 220(hopefully) and my bike is an old schwinn collegiate probably clocking in 45 pounds before the motor. I have a 66cc as well and live in the very hilly city of pittsburgh, so taking off at lights that are halfway up a hill has proven challenging.

I don't want to steer you wrong, a 48 tooth gear will absolutely get you a better take off 100%. Someone mentioned a smaller wheel, but even a thinner tire like a 1.5 will get you better mechanical advantage. If you need immediate results without tinkering, a 48 tooth or larger is an inexpensive solution that will do what you are looking to do. The trade off is that you will lose top end speed, and find that the engine is revving higher than it was before to achieve the same speed. For me I decided to stick with my stock 44 tooth as my city gear and try to get better take off performance in other places.

All the other stuff I mentioned buys you little improvements that add up. A b6hs (or the better bp6hs) Ngk spark plug is a must, it's cheap, and it will have your engine performing better. I'd recommend getting a better plug wire. The thing is the cdi's are kind of weak, so the better plug and plug wire help so that healthy-ish spark gets to the engine. The lower the rpm, the flakier the spark is with these engines so these things help. But at least start with the plug.

Also, this is a use at your own risk, but opti 2 oil did wonders for my low end. As I mentioned before going to a higher ratio of 32:1 with scooter pro oil helped a tick or two, but opti did wonders for the engines performance.

Plus, maybe drill holes in the eyeballs of your red skull, see if that helps so your engine does't have to suck as hard to get air at lower rpms. That costs you nothing. Others have posted on this forum for other exhaust mods that remove the innards of the thing to help with exhaust flow and ultimately performance.

You have to pedal to start, but you can try engaging the clutch earlier. It will be harder on the clutch pucks, but you can replace those. If you can do it without stalling out then you know it's there to use when you want to take off more aggressively. The mod you did will help.

Also, are you fully broke in?

I’m hoping that after fine tuning and splurging on this baby I'll be able to go to a 40 tooth sprocket and still have strong take offs. http://www.sickbikeparts.com/catalog/product_info.php?products_id=83&osCsid=n6efim2sf12ubkpcra71eavj06
 
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biken stins

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Jul 11, 2008
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Might open the exhaust more or even make one to reduce restriction. It may cut down top end some but may increase take off and be louder. 6 of 1...
 

anim8r

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Jul 15, 2011
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Yup. For reference, I'm 220(hopefully) and my bike is an old schwinn collegiate probably clocking in 45 pounds before the motor. I have a 66cc as well and live in the very hilly city of pittsburgh, so taking off at lights that are halfway up a hill has proven challenging.

Also, are you fully broke in?

I'm about 150 & I miss hills. It's flat as glass for miles around here except for one little valley. I'm definitely being too easy on the clutch.

On the other hand, nope...it's not broken in yet. I've only got about 25-40 miles on it. Using Lucas semi-synth at mfr recommended ratio. I'll probably be getting a new spark plug....there's a 2-stroke shop on every street in Michigan.


Plus, maybe drill holes in the eyeballs of your red skull, see if that helps so your engine does't have to suck as hard to get air at lower rpms. That costs you nothing. Others have posted on this forum for other exhaust mods that remove the innards of the thing to help with exhaust flow and ultimately performance.
Thanks a lot for this info....motors are new territory for me. It does feel like it's sucking pretty hard at takeoff, & that's probably why I've been gentle with it. I'll try a few things to get more air in there.
What happens if I get too much air? Will it overheat?
 

Tacomancini

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Mar 18, 2010
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Man I had a big response then browser crash. Guess its better for everyone.

The gist was: after break in you can increase your oil ratio and the engine will become stronger and more responsive. Spooky tooth told me 20:1 for first to gallons, then raise it at your own risk,.. Cough cough 32:1. But I see that Lucas is good stuff, but I'm not sure if you are following the engine or the oil's recommended ratio. My latest engine I broke in at 100:1 with opti 2 from the start, and it's stronger than my other engine. Could be a coincidence, there are folks that are skeptical of opti. I did find that raising my ratio in my first engine increased low speed take off performance. My second engine broken in from start with opti 2 has a much better take off. But you better take that with a grain of salt, it's just my experience. I defer to the experts on this board. I'm very green.

As far as drilling the holes, I would think that you'd be safe as it would just be a slight increase in air flow. The proper thing to do however would to do a "plug chop" to determine if you are running rich (healthy amount of fuel mix to air and safer) or lean (too much air to fuel mix and bad for your engine). That's definitely worth a search on this forum for more details.

Also, you want the throttle response to sound crisp. I wasn't sure what that was with my first build, but I could tell that it was anything but crisp. That was due to air leaks where my carb attaches to the intake manifold, as well as a sticking throttle cable. Long story short, you don't want air leaks, and lube throttle and other cables. I think I've got it sounding pretty good now: audio - http://db.tt/rfzy9TzU Video - YouTube - Broadcast Yourself.

Spark plug is a must I think, kind of a gut check thing that you want to know is quality . Also setting the idle a bit higher with the screw can help for take offs during break in.
 
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anim8r

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Jul 15, 2011
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I took my air filter cover off to drill some holes in it, I noticed the sponge was wet at the bottom. Some fuel is splashing out of the carb, apparently. Should I be worried?
 

BarelyAWake

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Jul 21, 2009
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No worries, blackblow is normal on unreeded two smokers, but an automatically oiled air filter isa good thing too lol ;)
 

anim8r

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Jul 15, 2011
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Ok, now I'm looking at instructions to do a plug chop. Says to get a new plug & run it WOT for a 1/2 mile, then shut it off & remove the spark plug at its hottest temp.

Removing the plug while hot...won't that risk screwing up the socket?
 

BarelyAWake

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Jul 21, 2009
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Let it cool. Those "instructions" are crazy, that's a great way to pull all the threads out of the head (heat expansion). o_O
 
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