Combustion chamber shape, squish, compression

The Tecno was used from Ebay, without spacer. I wasn't too far off
though, I had 2 stock Vino spacers of 0.9mm each.

I tried one spacer tonight. I believe it still has full belt travel,
with 4gr weights, and no hesitation on takeoff.

Haven't checked the rod play, will do that next time cylinder is
off.
 
Well hi again!

As the Btitish would say, I've run into a spot of bother.

Here's what's hapening:
I was getting promising results with the high compression head.

It hasn't been running too well the last couple of days, till
this morning it was hard to start. Once running it would die
at around 8k, unless you brought the rpm down.

Checked compression, and it was up to 135lbs warmish.
The plug however, was all but destroyed. Signs of melting
on the tip of the ground electrode, and cracked insulator.

My question is a general one. Can a cast iron, air cooled cylinder,
be run with 135lbs compression, at high rpm (11K+) with proper
jetting and timing of course. Should it be able to stay reasonably
cool when properly set up? If so, I'll keep working on it.

Tuning differences I have from low 100lbs compression setup,
which gave no problems:
Increased main jet from 120 to 125
Retarded timing by 1 degree.
Spark plug heat range is NGK 8
 
Last edited:
StepVino said:
Well hi again!

As the Btitish would say, I've run into a spot of bother.

Here's what's hapening:
I was getting promising results with the high compression head.

It hasn't been running too well the last couple of days, till
this morning it was hard to start. Once running it would die
at around 8k, unless you brought the rpm down.

Checked compression, and it was up to 135lbs warmish.
The plug however, was all but destroyed. Signs of melting
on the tip of the ground electrode, and cracked insulator.

My question is a general one. Can a cast iron, air cooled cylinder,
be run with 135lbs compression, at high rpm (11K+) with proper
jetting and timing of course. Should it be able to stay reasonably
cool when properly set up? If so, I'll keep working on it.

Tuning differences I have from low 100lbs compression setup,
which gave no problems:
Increased main jet from 120 to 125
Retarded timing by 1 degree.
Spark plug heat range is NGK 8
Click to expand...

Aloha, I would forget about this compression thing.... Instead get a proper shaped and distance squish. Also with all the timing, and jetting you are doing, you need to have an EGT guage. I think you are lucky to not have smoked the piston yet and caught it just in time with the damaged plug. Seems of course that you are running too lean, but where in your RPM/Load range is your mixture too lean or too rich? You need a simple $85.00 EGT/CHT gauge available at an aircraft supply or on ebay to avoid a meltdown. frank
 
StepVino said:
My question is a general one. Can a cast iron, air cooled cylinder,
be run with 135lbs compression, at high rpm (11K+) with proper
jetting and timing of course. Should it be able to stay reasonably
cool when properly set up? If so, I'll keep working on it.
Click to expand...

yes, been doing that with some street & trackbased setups & they run it for a hundred kms at a time with no problems.
 
StepVino said:
Great takeoff power (after initial hickup), and best of all, full speed
rpm down to 11.something k . Still close to where the power is. See? I
am starting to accept that peak rpm close to max power is best :).
Top speed was around 55mph.
Click to expand...

Just a side note on this; with both the Malossi Variator and Torque Drive Pulley combo, my scooter now jumps right up to 9,800 rpm @ 20 mph and just stays right around the 10,000 rpm mark all the way through top speed, (Clutch grabs @ 6,500 rpm). This is with 7.5g rollers. I can now say that I have experienced what Adas and Big B are talking about as far as narrowing your operating range, and that the Malossi Variator and TDP work better together than separately. The one obvious benefit I have experienced is the acceleration response time seems to be quicker. I'm not used to having it wound up so high at slow speeds, lol.

scootertrog
 
Yes, they know that of which they speak :)

Is the TDP Malossi also? Just one half, or the complete pulley?
Would you say Malossi variator makes a noticeable difference
over the Tecnomoto? (Almost embarassed to ask this...)

I'm eperiencing close to same thing. Now have 4gr rollers, and back
to 2x0.9mm spacers behind finned pulley. Without 2 spacers, 4gr
actually acts too heavy.

It now pins 10.5k right from a stop, no hesitation whatsoever.
It then settles to 9.5k for rest of accel, eventually creaping up to
low 11s . It guzzles gas like a drunken sailor, but feels great. Max
rpm must have come down because of the extra enrichment.. not sure,
but it was always lower with high compression head anyway. After
the last severe beating, it doesn't seem to have lost any compression.

I didn't have anything bigger than a 125jet, to stop the meltdowns,
so I had to temporarily plug up two holes at the top of the needle jet.
This might be the reason for the low gas mileage.. bad atomization.
Plug looks good now, after ~1mile wot plug chop. Speed is low to mid
50's, but tranny now seems to be set right for upgears.
 
StepVino said:
Yes, they know that of which they speak :)

Is the TDP Malossi also? Just one half, or the complete pulley?
Would you say Malossi variator makes a noticeable difference
over the Tecnomoto? (Almost embarassed to ask this...)
Click to expand...

The Torque Driver Pulley is just the one half (with the grooves). By itself, the Malossi unit isn't any better than the Tecnomoto, although the Malossi inner sleeve may be pressed in with closer tolerances, as I've never heard of anyone breaking it loose. The roller ramps do have a different profile, and perhaps the back plate too. Like any manufacturer, they design their parts around the other parts they make, so it was no surprise that the Malossi works better with their TDP than the other brands. I would expect the same results from Polini, Metrakit or any other same-brand combo.

scootertrog
 
Big B, nice healthy sound your scooter makes.

Off topic..
Wanted to record the sound... maybe as a project do a frequency
analysis.. like a spectrum analyzer. Can't get Windows XP sound
recorder to record the sound from the video. It wants a microphone...
Stupid hardware designers.. the sound is right there coming out of
the speakers.

Thanks scooterdog for the info. I have been wondering about
the supposedly bigger Malossi variators. That would mean that
the rear pulleys would turn even faster... But at 2:1 (approx)
stock ratio, engine at 12k, the rear pulleys are already turning
at 24k! How much more can they take... I've never seen bearing
specs higher than 20k. Even now they must be stressed out,
although never heard of a rear bearing failure.
 
Just wanted to post an update.. not too much hapening,
but did bore the carb out again.

I'm planning to fix the intake, and try to make the V3 reeds fit
better, so the back reeds aren't tougching the case.

The bored stock carb is close to 17mm now. It's having problems
of course, but once you get going it's fine. A little dangerous.. 1 out
of 10 times, opening the throttle from stop, the engine bogs. Had to
raise the needle (now +2), drilled out main jet to 135 from 125,
retarded the timing some more, now -2 degrees.

Here's the progression of the stock carb:
stock throat, oval, and now big rectangle.

Can't try for top speed yet due to bald rear tire... would have
to put 36lbs in it, but don't trust it anymore. Also need to
swap to the lower compression head.

2i0bqip
 
Nice work you have done! That will give some more preformance!

It's cool you try to push your std setup little steps futher everytime instead of going for the full expensive parts!
 
Thanks Big B.

There's still the mystery of why the top speed didn't go up,
with about 700 more rpm, after shortening the header.
You remember I tried heavier weights, but it didn't help,
top speed was the same at 11.8k, and 12.5k. I'm
wondering if the transmission heating up might have
something to do with it. Maybe hotter belt is harder
to push up the variator.. more sticky.. I don't know,
but I will also try venting the transmission.
 
forget tuning the stock carb without the airbox 135 mainjet is way too big but still it didn't make any difference, why? b'coz the needle is too thick, you can even run it without a mainjet & still it won't make any difference.

if i were you i'd start looking for a PHBG19 to 21mm carburator.
 
tiba_karotsu said:
forget tuning the stock carb without the airbox 135 mainjet is way too big but still it didn't make any difference, why? b'coz the needle is too thick, you can even run it without a mainjet & still it won't make any difference.

if i were you i'd start looking for a PHBG19 to 21mm carburator.
Click to expand...

Hi Tiba, I have been looking at carbs for a while, but wasn't planning
on getting one till after I get the scooter to 60mph. No gears, no carb,
no crank, it's really close!

I haven't tried running without the main jet lately. Maybe I should
test that again.
 
StepVino said:
Thanks Big B.

There's still the mystery of why the top speed didn't go up,
with about 700 more rpm, after shortening the header.
You remember I tried heavier weights, but it didn't help,
top speed was the same at 11.8k, and 12.5k. I'm
wondering if the transmission heating up might have
something to do with it. Maybe hotter belt is harder
to push up the variator.. more sticky.. I don't know,
but I will also try venting the transmission.
Click to expand...

Just to try:

Put the lighest weights in you have. Just to see what happends. Maybe with alot of RPM you can get higher speed. (with bored carb and other adjustments)
 
i think your drivebelt is worn thats why you are losing speed even though revs ar up, we tested this on a stock Zip SP, with a worn belt it could only muster 80kmh but after replacing it with a new belt it did 85 to 88kmh.

something to consider.
 
I have 8gr weights I can try, that should do something :)
I'll line up the reeds first, and bore out the inside of the
intake manifold.

Tiba, it very well might be the belt. It's longer than stock,
and had major rubbing problems at the beginning. Have been
slowly grinding the case, every time I have taken the cover
off. I think it's ok now, but it has lost a lot of dust.
 
tiba_karotsu said:
forget tuning the stock carb without the airbox 135 mainjet is way too big but still it didn't make any difference, why? b'coz the needle is too thick, you can even run it without a mainjet & still it won't make any difference.

if i were you i'd start looking for a PHBG19 to 21mm carburator.
Click to expand...

Tiba is right! That OEM Teikei carb Yammie uses on the Vino is just about the worst carb I ever had to work around, with maybe the exception of the Gurtner carb on a Peugeot Speedfight.

Step,
Yamaha sells an 18mm carb (it's a Mikuni) as an OEM part, not sure what bike it comes stock on, but it would be an ideal fit if you wanted to stay with a Japanese-spec carb. It could be used later for a mild-to-decent 70cc kit if and when you upgrade. I've actually swapped out the Mikuni OEM carbs on CPI's with this 18mm, it even used the same slide assembly, lol.

scootertrog
 

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