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Discussion Starter #1
Hi guys,

let me introduce first: i'm Jan, from Belgium, born in 1976 and also ower of a 1976 pawpawgreen oem honda Z50 monkey. Been lurking here for the last couple of months :)

I converted it to a motorcycle, as stock look as possible, with a new honda ca. 110cc block, kitaco suspension front and rear, sporty tires, here are some specs:
GB4 cases,
49,5mm stroke, 53mm bore, flat piston,
modified C50 head with roller bearing cam with roller rockers from uma racing.
Takegawa multi plate clutch, hydra actuated and 4 speed manual box.
It's 12V CDI, with simple YX type ignition and batteryless kit.
Exhaust is 'standard style' but obviously much bigger diameter.
I'm running a yoshi MJN TM24 carb at the moment.
Stock wheels on reasonably low profile tires, and 16-24 gearing...should reach easy 120km/h in theory.

The bike pulls very nicely, and i can hear it scream in lower gears, but i'm getting no topspeed. I'm struggling to reach 90 km/h GPS. So i have all the rpm, but not enough horsepower. Especially as this is a oversquare engine, it should be strong up top.
I am a little bit stuck at the moment because i can't get it running the way it should: it should be a very fast screamer, but it's not. After lots of messing with 2 cheapo carbs, both big and small, i changed to the yoshi flatslide TM24 thinking that would be the reason i'm getting no serious top-end out of it. But it didn't make a change. (of course i have fabulous ridiculous throttle response now, but still no top-end. Jetting is correct)

I am suspecting ignition advance now. Idle ignition timing is on the left stripe next to the 'F' mark, but i'm getting no high rpm advance whatsoever. It changes maybe 1 or 2°. I tried with 3 different CDI boxes. I would assume there should be plenty advance added at higher rpms right? My car is 5° BTDC at idle, and 30° at 4K rpm...
So is this advance normal? (basically same advance over full rpm range) and if it's not, what can there be wrong? Is it a simple case of wrong CDI? Do i need a power rev or something? I tried running the bike with just the basic 3 or 4 wires and it makes no difference. So i don't suspect the wiring at the moment. Can the yx ignition voltage supply be too low causing the CDI boxes to run safe mode?

Thanks for your input,
cheers, Jan

270439
 

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Discussion Starter #2
some measurements:
  • CDI power feed: starts at 80V A/C at idle, and then drop a little bit in higher rpms to 60-65V A/C . i guess this is balanced system…higher revs = more sparks = more voltage that gets used up.
  • CDI pulse feed/pickup: starts at 0,7V A/C idle and picks up to about 2V A/C at maybe 5000RPM. So that’s x3. So whatever pickup input the CDI uses as rpm indicator (Hz or volts?), it gets a good reading i think.
 

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Discussion Starter #4
heya, yes, i have tried at least 3 or 4 rear sprockets, the engine should be able to pull this gearing all the way to the end. It has no top-end. It gets to 80 pretty quick, and then falls on its face and takes a minute to get to 90. It feels great at the bottom, which is completely counter intuitive for this rpm-motor.
 

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Discussion Starter #6
i've got the largest possible front sprocket on there without eating the cases: 16T
bigger front will go even bigger topspeed, so not necessary.
 

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I see.

I love that you have upgraded it while making it look like stock. While you wait for someone smarter than me to chip in, can I ask you about your blinkers? Are they stock? The 72-78 bikes here in US never seem to have been offered with battery/blinkers/horn etc so I've been looking at converting my stock 74 into basically a J model, which I assume is what yours is. Do you have a good source in Belgium to find for example the wire harness for your European model?
 

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Discussion Starter #8
naaah, it was a 6V model with almost nothing on there. It had half a headlight and a almost non-existent rear light :D

When i built the bike back up, i started from a 12V replica loom, and i bought some chrome replica blinkers which i think fit the 70's style quite well. I made my own bracket in the rear. I added a horn too. I will use the bike almost daily, so i need it to be safe, reliable and legal. The loom was cut up quite a bit, but it was interesting to see the standard loom to learn how honda engineered the 12V charging and lighting system, i think i used this one as a basis:
http://www.monkeybiker.se/en/electrics-ignition/electrical-components/wiring-loom-monkey-replica.html (these guys are from sweden)
I used a sub-loom with a control pod for the left side, and the right side has nothing (no kill switch, no lighting switch)
I used a batteryless kit (from kitaco i think), so no battery, out of a idiotic idea to save weight even though i am 200lbs :D
We have a big online store here in Belgium called motorkit.com which caters to the quite big minimoto market around here.You will basically find everything there.

I've got stock looking, but much improved rear suspenders, and in the front i've put hydraulic inserts in the original fork. So it looks stock but it rides really great.
 

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I haven't had mine for long so I'm still learning, but one of my goals is too make it street legal here in US, which I understand is a long shot. None of the Z50A were. Surprised to hear that there are battery-less 12V kits, thought some of the reasons for 12V was to have stronger lights and stronger battery. The US bikes has a slightly different frame and does not have the space for a battery among other things. Motorkit looks promising, will snoop around.
 

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Discussion Starter #10
these bikes were 50cc legal in Belgium, 30 mph. Over here, we have to buy replica 125cc monkey frames with papers, and build the bike on such a frame. Then you can legally have 11hp and ride it with a normal car license. Of course plenty of people buy the frame with papers and never transfer the frame and simple ride on the original frame...i did not have 1 time in my life have a cop check a VIN number on any of the motorcycles or cars...so it's possible. :)
 

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Interesting, over here it would be impossible as they inspect the frame whenever you register or change the registration. Where do you buy the 125cc monkey frames, at motorkit?
 

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Thanks, I will look closer at this. I guess the difference between the 50cc and the 125ccis the paperwork. I found a similar frame on an Australian site, but without paperwork.
 

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I'm wondering about the "modified C50 head"..?
I'm not familiar with a C50. Is that a 50cc engine? How was it modified? How big are the ports...valves...etc.
The head is probably the most important part of a big engine. I would think a 50cc head would need some serious modifying to go 75mph.
 

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Discussion Starter #15
hi kirby,
yeah, i don't know exaxctly where that term comes from, but suffice to say i have 22mm port, 22mm intake valve, and 20mm exhaust valve if i remember correctly. plenty big.
i should have 90km/h cruising and 120km/h topspeed with this engine.
basically what i'm most curious about is if anybody has checked their timing with a timing light, and see what it does...in my case, timing at idle = timing at high rpm...which sounds fishy to me.
 

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What trigger does your flywheel have, a dot or a rectangle/stripe. A dot will never advance whatever cdi you are using.
 

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Discussion Starter #17
hi Niels, it's an almost square recangle. It's not a long rectangle.
Today i'm gonna revert back to the oiginal cam and see what gives. Maybe the racing cam is not suited for my motor.
 
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