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#26 - Osco
polish carburettor (what carb is it, throttle slide or butterfly valve?), intake and exhaust, run some water into the engine to get rid of the carbon build up, and tune the carb properly

my 50cc 2 stroke sprintmoped should be around 12-13 hp now..
I'm thinking going completely stock now. other than a rebuilt exhaust system. And possibly doing some re-porting. My boss has all of the tools to do that, and he knows what he's doing.

I guess it just all comes down to the fact that I've been realy thinking I could get more than what's posible from this bike.

Problem is, I can't sell this bike. I made a promise that I'd hand it down to someone else when I'm finnished using it. I figure I might as well make the most of what I've got.

When you have 7hp, even one more makes a difference. I figured I could atleast get it to 9.

I didn't even think about Compression with the blower, It's at 9.1:1 stock, so I thaught that would be fine. As for the spark, I'm positive it would be strong enough for the amount of boost a blower would provide. It wouldn't even make 6psi. Though, after considering it, I think polishing and porting is all I can do. which is good enough for me, it's free and it works if you know what your doing.

I wouldent have even thaught about it if it wasn't for you people.

One funny thing is, I once "Boosted" my snowmobile with an air compressor, all it realy did was make the engine rev up faster, but it was fun as hell to hear the thing scream. Unfortunaltey, the reason I did it was because the crank seals where gone, so the only way to get fuel to the combustion chamber was to force it out of the crank with a shot of air. I did it to see if it was just the crank seals, they only cost 10 dollars at a snowmobile shop. I never got around to getting them though.

@Osco

Edit: It's a throttle slider carb.

What mods do you have on that bike? Just polished carb and intake/exhaust?
That sounds like a lot of horse power for a 50cc. Then again, it's 2 stroke. The littlest things seem to make a big difference on a 2 stroke.
#28 - Osco
Quote from DragonCommando :
@Osco

Edit: It's a throttle slider carb.

What mods do you have on that bike? Just polished carb and intake/exhaust?
That sounds like a lot of horse power for a 50cc. Then again, it's 2 stroke. The littlest things seem to make a big difference on a 2 stroke.

just a little more than that
yamaha aerox frame, cut off for less weight, polini 50cc cylinder tuned and ported, the block itself is portmatched and tuned, carbonfiber reedvalve, 24mm JHC kart carburettor, expansion exhaust, racing ignition and upgraded transmission,
I'll try to get a photo up from it's current state
Quote from Osco :just a little more than that
yamaha aerox frame, cut off for less weight, polini 50cc cylinder tuned and ported, the block itself is portmatched and tuned, carbonfiber reedvalve, 24mm JHC kart carburettor, expansion exhaust, racing ignition and upgraded transmission,
I'll try to get a photo up from it's current state

holy cow, that must have cost you a lot.
I'm on a limited budget of $200 for repairs and upgrades, but the upgrades are only what's posible without spending money for aftermarket parts.

I think I'm kind of in a corner as far as getting more power out of this bike without serious moding. I think my original idea of just changing the torque curve is more reasonable.

It's going to take a combination of things to get a noticable power difference without risking the reliability of the engine.

I'm thinking a list is in order.

-advance the timing (even if it does very little, every bit counts)
-advance cam timing (I'm considering it now, but I'm still a bit nevous about messing with valve timing)
-reduce exhaust restriction
-polish ports
-fine tune the carburator to the extreme

Thats all I can think of right now, I want it to be reliable, thats why I'm trying to avoid aftermarket parts. I've read that alot of people put bolt-ons on this bike and it makes it less reliable.

The whole point to this originaly was to change the torque curve so there is more power in the useable range after first gear.
I kind of lost that idea after a while and started getting off the wall a bit.
#30 - Osco
to be honest, it didn't cost me a lot, did most of the tuning and porting work myself, the rest of the parts were second hand or very cheap from a friend of mine, birthdays help too

now trying not to get carried away with my car as I did with my bike
Are you able to use a different sprocket set? If one is available, you can use this method to trade low end torque for top speed.
I think I could get a different sprocket set, I'll have to check it out.
I didn't even think about it, but that could be a solution.

I can't change the sprocket on the transmission, because a bigger one woulden't fit, but I could put a smaller one on the rear.
I'd have to change the chain length, but I think it has a master link already, so it should be as easy as on a pedal bike.

I could even make one, I'd have to do some serious work, but It's possible.

Thats probably the best solution I've got.


Edit:

The front can actualy be increased by one tooth, the original gearing is:

front 14 tooth
rear 46 tooth

and the selection I have to chose from is

Sprocket - Front - 12 Tooth
Sprocket - Front - 13 Tooth
Sprocket - Front - 14 Tooth
Sprocket - Front - 15 Tooth
Sprocket - Rear - 35 Tooth
Sprocket - Rear - 36 Tooth
Sprocket - Rear - 37 Tooth
Sprocket - Rear - 38 Tooth
Sprocket - Rear - 41 Tooth
Sprocket - Rear - 44 Tooth
Sprocket - Rear - 46 Tooth

The front sprockets apearantly run around $14.95 US, and the rears are $18.95 US
I'd have to have them shipped, but it's still well within my budget.
I was actualy planing to get new ones anyway.

Thanks for the ideas guys, keep them comming.
Don't bother porting, as you'll just slow the gas down and ultimately lose power (although you might gain some somewhere, the overall loss will be bigger than the slight gain, and you don't want a racing engine!). Don't bother polishing - this tends to make engines run worse. Notice how, whenever you get to see inside an F1 engine, how they are NOT polished? They are "as-forged" (minus flash removal). And F1 wants every last 0.01hp they can find, especially if it came from polishing.

Your compression ratio, at 9:1, might be fine in general terms, but your engine will bet set up at MBT (this is NOT Maximum Best Torque, which is something fools think) by the manufacturer, and not be a million miles away from it's knock limit. Even though it's 'only' 9:1, to avoid knock (and possibly pre-ignition later on) you WILL need to drop the compression ratio to get any meaningful boost from a cheap, fake blower.

As for sprockets, you'll need to work out the tractive effort at your wheels in each gear and 500rpm increments and decide what you want from your gearing. No point having the bike at 1,000,000rpm whenver you get close to cruising speed, as you just make noise, waste fuel and look silly.

It's all a compromise. Do something and you will lose something else. For $200 I have a suspicion that you WILL lose more than you gain, and ultimately as a road transport device your bike will become slower, thirstier, more annoying and less reliable.

You have been warned.
I've been looking at it from a practical point of view, and gearing changes are the best bet. The whole point is, that as it stands, engine speed at cruising speed in 5th gear seems to be to high.

It hits a range where the engine is at around 7000-8000 and it's cruising at optimal, I can accelerate up to maximum engine speed from there and it seems to be limmited by gears not power. I've been told that the redline for this bike is 10500RPM.

After thinking about it, This whole thing would have been a waste of time without changing sprockets, because the bike is limmited by it's transmission gearing once you get up to 5th.
I kind of feel like an idiot for not realizing that before

So I can get a higher top speed, without lossing hill climbing abillity as long as I get the rear end ratio right.
I will lose some acceleration, but that was the point in the first place, trade acceleration for top speed. I'd just forgoten that the bike already hit the top speed of the transmission.

[attach]43863[/attach]

Here is a chart I made of all the possible ratios and all of the ones I think would be ok. I marked the ones that are questionable in yellow, but for simplisity I marked them as being out of possible range on the chart, even though they are yellow not red.

I'm going to be going over this chart to decide which sprockets to buy, they are well within my budget, and I'd have to change them eventualy. So I figure it's worth a shot.

It's definately easier than moding the engine.
Can you even hit the redline in 5th gear? Unless you want 5th gear to be a cruising gear in which you cannot accelerate much.
I do infact hit redline in 5th gear.

Thats something I'm actualy trying to change with the sprockets.
Quote from DragonCommando :I do infact hit redline in 5th gear.

Does it seem like there would be more power left to accelerate after that? Because, wouldn't you want to make it so that you can just barely get to the redline in 5th gear?
Sorry for the late reply.

It actualy seems like there's enough power to get at least 5km/h more out of the bike as it is.

As it is now though, the bike isn't running full power either, so I can't pin the throttle at max and continue to accelerate. It actualy bogs out if I open it up. It will stop running untill I let off, so it basicaly just rolling stalls. I know whats wrong, it's included in my To-Do list.

After I fix it, I'm going to be able to open it up and I'll definately be running off the end of the final gear of the transmission.

I think the biggest problem is that the bike was designed for entry level motocross and I'm using it for flying around an area that has alot of long distances where the bike can reach its speed limmit. On a motocross track you generaly don't reach the top speed the bike can do horsepower wise, but you usualy gear it to make the most of the power at lower speeds.

However, Honda aparently knew it wasn't just going to be used for entry level motocross so they have a whole range of higher rear end gearing. Plus lower range ones, but I don't need them.
One of my friends has a dirt bike, and he goes through 3 gears just driving across his yard. So I see what you mean about the gearing being way to low.
It's actualy so severe on this bike that first gear lasts only long enough to let out the clutch, and I don't even let it slip that much. Most of the time my take off involves a small amount of front wheel lift, and as soon as I get going I have to shift into second, then redline comes at me like a bullet train and I have to go to third.

Most of the time, when I stop at a road crossing, I just put it in second and take off from there. Can't do that on a cold engine, but once it's warm, it makes enough power to redline 5th on a good straight.
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