Kings of 50cc help with my Scootermotard

[rabidnz]

well affordability is all relative, for the exhaust to cost half as much as the bike seems a lil crazy to me, so i will continue the ebay scavenging Im not sure my pipe is such a big wall to her performance, the baby exhaust port is probably the next thing in the way, but i dont think that can be cured without a cylinder replacement, which in turn will warrant a piston, which in turn will warrant a crank
Just gotta think of the rego and gas savings, not to mention servicing of a single cylinder 2t instead of an inline 4 4t

What is this oil fogging of the pod filter you speak of? Is this caused by your reed valves being worn, causing gas to come back out the intake, collecting the injected oil and depositing it on the filter? Couldnt find anything with the search?
Anyway if this is the case I will make a small extension tube angling up a little, to allow the oil to flow back down to the carb and rejoin the intake massive.

[SS90]

maybe you could even start a thread about power valves and why they arent in 50ccs

I may have to get a pipe program and build one myself, tack it up and then have the welding done by someone a bit tidier than myself, as pipe prices are pretty ridiculous, looking at least 200 pounds, plus god knows what shipping, plus having to then cut and twist your expensive new pipe, just not worth paying 700 bucks for a scooter exhaust imo

Uh, oh....

The "Stand off" question....

I think what you are referring to is the situation where a tuned engine is running "off the pipe", and the resulting mistimed exhaust pulses (sometime referred to as resonance ) as well as intake resonance cause problems with the intake tract, causing a situation where the the incoming air/fuel mixture meets with a closing reed /or disc valve, causing this incoming charge to revert back out the intake to atmosphere.

In all truth, an engine that performs like this is fairly normal, and in actual fact, this occurs at such a low RPM (well, low as in terms of BELOW any real power, and, as such, well below any reasonable operating rpm for a tuned racing engine....like for example if a tuned racing engine starts producing usable power at say, 7000rpm, up until 10,000 rpm....you may well find this engine has a"standoff" situation about, say, 4,000 rpm...)

In such a scenario, you operating the engine at tis low rpm is a complete waste of time.

My advise id´s to not worry about this "standoff", it occurs far below operating rpm of a racing 2 stroke, and other than a bit of mess for an engine with no air box, it has no real effect on either the power or the main jet setting....needle perhaps.

[rabidnz]

cheers mate, clears it up alot. With the factory tuning of this pipe, nothing even happens till the last 2krpm anyhow, im sure it is standing off badly at low rpms, you can even see it comin out the carb, but its pretty well full throttle everywhere with this lil beast in fact, operating the engine wont even wake up for low rpms, so it may not be such a problem. I guess i will find out. hopefully soon, as my carb and manifold and filter arrived today, but the fecking manifold is bent into an oval out of the packet, looks like something has smashed it in the courier van, and im going to send it back to scootling, as for that price i expect something bloody perfect.

[F5 Dave]

Hum, yea.

Im not saying your not correct Dave, but would you be able to elaborate why a variable exhaust port height/trapped compression ratio is unsuitable for a fiddy.......... You and I both know why, but clearly Mr Spotty here does not.... and it could make for some interesting discussion.

Grammatically that should be ". . you're not correct. . ." . But of course I am -and I should know. I'm an internet expert.

The real reason the AM6 engine doesn't have a PV is cost. The only reason RG150s have them is 'cause it was easier to leave it on from the RGV250 origins.

Can you imagine the typical 16ers in UK & Europe trying to maintain such a device with little more than a rounded screwdriver at the local servo?


My point was the AM6 don't got one, so trying to fix it would be the ultimate exercise in futility.

Of course on a tuned racebike the powerspread is somewhat thin. It could seize from lack of use.


I did however at one stage look at making a manual powervalve, principally a sealed half-moon sectioned bolt so one could adjust the port height down for short tracks. Sealing it & the available metal was unfeasible.

[Henk]

Woody

If I recall the gasgas mini motard you took out for a few laps of Mt Wellington with all the road gear fitted and no nylon was a 125.

[SS90]

Grammatically that should be ". . you're not correct. . ." . But of course I am -and I should know. I'm an internet expert.

The real reason the AM6 engine doesn't have a PV is cost. The only reason RG150s have them is 'cause it was easier to leave it on from the RGV250 origins.

Can you imagine the typical 16ers in UK & Europe trying to maintain such a device with little more than a rounded screwdriver at the local servo?


My point was the AM6 don't got one, so trying to fix it would be the ultimate exercise in futility.

Of course on a tuned racebike the powerspread is somewhat thin. It could seize from lack of use.


I did however at one stage look at making a manual powervalve, principally a sealed half-moon sectioned bolt so one could adjust the port height down for short tracks. Sealing it & the available metal was unfeasible.

Fair enough.

For my latest fiddy plan, I would like to incorporate a power valve, and like you I thought a bout a self made blade, but it would seem that is not feasible.

Do you remember the Honda "Beat", it was a 50cc water cooled CVT scooter in the eighties/nineties.

It simply used a foot pedal operated version of Hondas "V-Tac" (anagram time)

Which, simply had an extra chamber cast in the side of the cylinder head, and when the valve was open (normal operation), it allowed for a lower trapped compression (higher volume), which gave an increase in performance outside the expansion chambers tuned rpm range, and when the valve was closed (pedal down), it raised the trapped compression ratio (lower volume i.e, only that of the combustion chamber), allowing the correct trapped compression ratio for the tuned rpm range of the pipe.

Simple, and, no real maintainance (like you say, spotty youths with blunt screw drivers)

They had a LED rev counter to show when there was enough rpm to operate the valve........

A modernised version of that would work on a fiddy racer I believe, just adapt a Rotax system (the vacuum operated units) that operate the blade type systems to actuate a valve on a bespoke cylinder head.

It sounds easy.... I'll make one after lunch.

[Spearfish]

Uh, oh....

The "Stand off" question....

I think what you are referring to is the situation where a tuned engine is running "off the pipe", and the resulting mistimed exhaust pulses (sometime referred to as resonance ) as well as intake resonance cause problems with the intake tract, causing a situation where the the incoming air/fuel mixture meets with a closing reed /or disc valve, causing this incoming charge to revert back out the intake to atmosphere.

In all truth, an engine that performs like this is fairly normal, and in actual fact, this occurs at such a low RPM (well, low as in terms of BELOW any real power, and, as such, well below any reasonable operating rpm for a tuned racing engine....like for example if a tuned racing engine starts producing usable power at say, 7000rpm, up until 10,000 rpm....you may well find this engine has a"standoff" situation about, say, 4,000 rpm...)

In such a scenario, you operating the engine at tis low rpm is a complete waste of time.

My advise id´s to not worry about this "standoff", it occurs far below operating rpm of a racing 2 stroke, and other than a bit of mess for an engine with no air box, it has no real effect on either the power or the main jet setting....needle perhaps.

I guess I made it sound like a bigger problem than it is, all I meant was that once you get the jets right it can go off song again in just a few hundred kms giving the impression something else is wrong other than a simple dirty filter.

If fogging or stand-off occurs mostly before getting "on the pipe" can it happen again once I've gone past the peak and revved high enough to be off the pipe again?

[Yow Ling]

It simply used a foot pedal operated version of Hondas "V-Tac" (anagram time)

Which, simply had an extra chamber cast in the side of the cylinder head, and when the valve was open (normal operation), it allowed for a lower trapped compression (higher volume), which gave an increase in performance outside the expansion chambers tuned rpm range, and when the valve was closed (pedal down), it raised the trapped compression ratio (lower volume i.e, only that of the combustion chamber), allowing the correct trapped compression ratio for the tuned rpm range of the pipe.

From Wikipedia

"Honda V-TACS

The "V-TACS" - Variable Torque Amplification Chamber System - works differently from the "AETC system" and it will only work when it is used in conjunction with a tuned muffler. Tuned mufflers/expansion chambers increase power but only at the RPM they are designed for and can actually cause a power loss outside their tuned RPM. "V-TACS system" takes advantage of using an expansion chamber without losing power outside the expansion chamber's tuned RPM. Within the head and cylinder of the engine, there is a chamber that is sealed by a valve. This sealed chamber is vented onto the exhaust port when the valve is open. At low RPM this valve is open, this has the effect of increasing the exhaust manifold volume and negating the power loss that would normally be apparent at low RPM with an expansion chamber. At mid RPM the valve is closed, this enables the expansion chamber to work. It is identified by the head and cylinder, being much larger than normal for its displacement, the cylinder balls is also cast with the wording VTACS on it.

V-TACS was a foot-operated power valve system made by Honda on some of its small two-stroke bikes and scooters, like the Honda FC50."

My understanding is that it changed the volume of the chamber at low revs and killed the mistimed exhaust pulse, it just makes it less bad off the pipe

[F5 Dave]

. . .
Do you remember the Honda "Beat", it was a 50cc water cooled CVT scooter in the eighties/nineties.

Only that they had a belt driven water pump that a mate used on a bucket. . . .or was that the Lead (125 version with an unfortunate name if you think about it)

For my latest fiddy plan, I would like to incorporate a power valve, and like you I thought a bout a self made blade, but it would seem that is not feasible.
.......

A modernised version of that would work on a fiddy racer I believe, just adapt a Rotax system (the vacuum operated units) that operate the blade type systems to actuate a valve on a bespoke cylinder head.

It sounds easy.... I'll make one after lunch.

yeah I have a couple of vacuum units left over from my Trinity kit. Yamaha had experimented with variable comp on the YZR500, not sure if it really progressed any. Theoretically you could get away with steeper baffle cone & get acceptable over rev.

Most powervalves work for road & dirt applications masking the negative effects of the pipe when out of frequency. On a 50 or any small high output 2 stroke you only really care about 2000 rpm. It's death anywhere else anyway. If you had a PV that operated quick enough in that area you could extend the peak power a little, giving a useful increase in mean power in between gear changes.

[SS90]

From Wikipedia

"Honda V-TACS

The "V-TACS" - Variable Torque Amplification Chamber System - works differently from the "AETC system" and it will only work when it is used in conjunction with a tuned muffler. Tuned mufflers/expansion chambers increase power but only at the RPM they are designed for and can actually cause a power loss outside their tuned RPM. "V-TACS system" takes advantage of using an expansion chamber without losing power outside the expansion chamber's tuned RPM. Within the head and cylinder of the engine, there is a chamber that is sealed by a valve. This sealed chamber is vented onto the exhaust port when the valve is open. At low RPM this valve is open, this has the effect of increasing the exhaust manifold volume and negating the power loss that would normally be apparent at low RPM with an expansion chamber. At mid RPM the valve is closed, this enables the expansion chamber to work. It is identified by the head and cylinder, being much larger than normal for its displacement, the cylinder balls is also cast with the wording VTACS on it.

V-TACS was a foot-operated power valve system made by Honda on some of its small two-stroke bikes and scooters, like the Honda FC50."

Wikipedia Ist für Schulkinder und die Hersteller von 3 Rädern Fahrzeuge, die hinter einem anderen Fahrzeug abgeschleppt werden.

[SS90]

From Wikipedia



My understanding is that it changed the volume of the chamber at low revs and killed the mistimed exhaust pulse, it just makes it less bad off the pipe

My bad, yes it changed the header volume, not the trapped compression, it was another anagram that changed the primary compression, I just cannot recall it just now...... Yamaha I think it was, just trying to find something that the "Hoi Polloi" could relate to.......

[F5 Dave]

So the hole is actually in the head for that to work? No I haven't seen one.


Ideally you have a floating head like Rainey's bike used for a while I believe. Didn't Polini make some kit? Can't have done much, all sort of went away like antidive.

[SS90]

Only that they had a belt driven water pump that a mate used on a bucket. . . .or was that the Lead (125 version with an unfortunate name if you think about it)


Most powervalves work for road & dirt applications masking the negative effects of the pipe when out of frequency. On a 50 or any small high output 2 stroke you only really care about 2000 rpm. It's death anywhere else anyway. If you had a PV that operated quick enough in that area you could extend the peak power a little, giving a useful increase in mean power in between gear changes.

This is where The crux of the whole situation exists..... 50s have this anomaly of having a disproportionate amount of power for the displacement, however, it is over such a small rev range ( 20000 rpm....... I wish....something like 1500rpm is best I can do, and, short of a 7 Speed gear Box ......... (hence my sudden interest in variable volumes)

The Top guys over here all take different approaches for the Same results..... The Same Peak Power and torque, very different exhausts, and very different Cylinders....... But the frightening thing is they all have the same parts cost (not labour, just parts) €10,000 (yup $NZ20,000)..... This years winners had 27ps by all accounts.....

[F5 Dave]

well it depends what you call 'in the power', the rev range used is more decided by the gear box ratio spacings.

That is crazy money & wayy more crazy power. So these are the silly rev monsters? what basis are they starting from? that is 540hp per litre. I struggle to fathom that. Top flight GP bike is 400. Drag race engines?

[Spearfish]

well it depends what you call 'in the power', the rev range used is more decided by the gear box ratio spacings.

That is crazy money & wayy more crazy power. So these are the silly rev monsters? what basis are they starting from? that is 540hp per litre. I struggle to fathom that. Top flight GP bike is 400. Drag race engines?

Google: "Polini Big Evolution" for info.
Big money, big power, small life span.
I would imagine they would be a hell of a lot of fun on a sprint track but the cost would kind of go against the best parts of real bucket racing.