1984 Yamaha CA50 budget build!

[markopollo]

well, I'm back!!

its been a while now, (sorry, buncha projects and college)

still trying to find an affordable kit for this thing. (sorry, 200+$ is a bit out of my budget)

seems like I can use a Minarelli vertical 10mm wrist pin kit?

although ill need to find some more measurements before ordering one.

so far im loving it! did some minor hoonigan stuff in the snow and its holding up great!

i might also try to shave the head and deck the cylinder later on as well, (as 7:1 compression isnt exactly performance level stuff)

ill purchase a new kit around march if i cannot find a used one for cheap, possibly add a bigger carb? (although i LOVE using the oil injection, since its so simple to use)

anyone wanna sell me a cheapo top end?

[jbjhillbilly]

$75-80 on a performance variator (Polini or Malossi) will help. The original variators on these and Hondas of the time were packed with grease, and not made with an eye toward performance.

[markopollo]

Jan 17, 2021 22:14:24 GMT -5 jbjhillbilly said:

$75-80 on a performance variator (Polini or Malossi) will help. The original variators on these and Hondas of the time were packed with grease, and not made with an eye toward performance.

Gptta ask, what gains are expected from a performance variactor?

i swapped the roller weights to lighter ones on the stocker and it seemed to help, would the performance variactor give me more top end? or just general engagement? im not sure if i could find one for this motor, but ill be looking out for one.

[markopollo]

Alright, finally gave in and torn down to the motor.

Its actually a pretty high compression cylinder, 45mm bolt spacing (yes!! It'll fit minarelli vertical kits)

Found out hoe they kept the thing with a low 7:1 compression ratio. The spark plug is down so low its hilarious. Probably a solid 10mm away from the head.

I found that i can use a longer spark plug to basically climate any gap and make it into a decent cylinder,
NGK BPR2ES is the spark plug (although is reccomend a bpr7es, as i didnt have that and everything is closed today due to MLK)

Had to space the plug with 2 washers (just used some spare spark plug washer things)
Seems to really have worked!
Id bet with a e3 (the 4 electrode sparkplugs) i could increase the compression even more (as they take up more area)

Also, checked the ports, intake is pretty small, lots of room for improvement there, transfers are eh?, exhuast is ok, but would benefit from some work.
But its BEGGING for a rev plate, as the piston blocks about 1/8 of the port. (Id say a 4-5mm would provide the most benefit here)

[markopollo]

Alright, installed the NGK BPR7ES with one shim (from another ngk sparkplug)

Also removed the the Tin headgasket (about 10 thousandth)

Major improvement all around,
bottom end is great now!
No more 2 bump deal revs right into the pipe around 18mph (according to my speedo) and tops out flat around 45-47ish. (Again, speedo only goes up to 40, pushing past that)

Ill probably leave it as is, since it feels perfect for street riding.

[markopollo]

Well, figured id update this thread.

sadly, after a month of screwing around and bashing it almost daily, I've put about 250 miles on it.

and today, it officially lost compression

what I believe was the cause is that the oil pump had frozen the night before, when I took it out today it was not giving it oil all day and after abruptly stalling in my garage, will not restart, kick start feels super light and the electric start spins it over way too easily.


now ill be looking for a top-end, possibly might see if a 70cc big bore will fit on it when I get the cash.

[190mech]

Ditch the oil pump and PREMIX!!!!

[woodini]

Cool scoot!

[Senna1Rossi]

Is this Yamaha same as a Razz model?

[aeroxbud]

I'm with 190, go premix. You know it makes sense.

[markopollo]

Feb 22, 2021 23:28:06 GMT -5 Senna1Rossi said:

Is this Yamaha same as a Razz model?

its more early jog/vertical zuma based platform, its a minarelli vertical with a weird auto choke head, and a couple of other things (cylinder bank angle is a bit more forward then a jog, varactor is different, case size/length, etc.)


weird part it today it fired up no problem! ran it around town (yeah, bad idea, but it was pumping oil to it)

then it died, and now somethings up with the electrical ( no lights will come on) 


let the hunt continue! 


for premix, yeah, that gonna be the plan once I big bore it (probably gonna be a custom deal, should be fun though!)

im thinking of going polini, but ill need to double check reed spacing and such to see if the stock intake would work. 

[markopollo]

this thing is a complete mystery now.

went ahead and put in the key for shits and giggles, green light popped up and I hit the starter, fired up as if nothing happened!


oil is pumping (cleared it out just in case, seems to be flowing well now) runs perfecto! am able to hit 42ish, performance is good.

I think there is a loose connection somewhere? possibly cold seized it?

I don't know, but it's working!


edit: found the culprit

loose connection to the battery cable and the fuse, cleaned it up and seems to be good. Still doesn't explain the fact that it stalled on me though, guess ill ride it until it does that again. 

[markopollo]

Alright, round 2

Fires up fine when cold, i can ride it till the gas tank runs out BUT, if i kill it then try to restart it, it won't.

Im suspecting a worn top end could cause this? As after a while the rings could be out of spec and cause low compression when in the low rpm range?

Not sure as it seems to have enough torque like it used too, compression is hard to tell.

[markopollo]

Heres a picture of it on todays ride.

[markopollo]

ok, so I've narrowed it down (i believe) that the top end is just worn slightly too much.

so I ordered a Minarelli vertical piston kit (10mm, 50cc) that should be here by next week?

we will see if that resolves the issue, if not I'm digging deeper into the mystery.