Suddenly running better

cityevader

New Member
May 11, 2008
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Santa Cruiz, CA
I've been battling engine performance for awhile now on my PK-80 with 44T, 25:1 synthetic oil and 91 octane, my weight 180 lbs. It just didn't want to come up into 2 stroke rpm range unless it was going downhill. On the flats and particularly on a slight grade, it would surge between 2 and 4 stroke running. Steeper grade had less surging. Clearly a mixture issue, but without an RC engine-like mixture screw, it simply sucks! (hmmm, a Saito 4 stroke radial engine in-frame? Nice!)
Resealing manifold and carb, checking float, needle, and seat for debris, moving mixture needle clip into all four slots, matching intake/exhaust manifold ports didn't help. Scouring this site came up with nothing else to really go for.
So I took it on it's maiden voyage to work (20 miles one way) with an estimate 75 miles of break in roadtesting, and a few miles into the way back it just suddenly, miraculously, started to run consistently! No more surging, just smooth operation...nice!
I still wish it had more power on the hills, as even a very modest incline loses a lot of speed, but overall, much happier now. Wish I knew what changed!
I guess it is true, the firt 100 miles or so should be just ridden through without worrying too much about performance.
 

Pablo

Master Bike Builder & Forum Sponsor
Dec 28, 2007
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It takes an amazing amount of time to break the engines in, relative to new modern tight toleranced 4 strokes. 2-3 FULL tanks.

What kind of plug and wire are you using?

I'm finding my stock exhaust system is really holding me back at this point and I could do with some port work....then I will lap the head and install a new HG all at the same time. Will be fun to feel the difference.
 

cityevader

New Member
May 11, 2008
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Santa Cruiz, CA
All components used came with kit. Was planning to change them out soon, but haven't because the problem didn't feel ignition related. (I've got a well-tuned assometer having been a mechanic for so long, and experiencing a problem is typically enough to know where to go to resolve it). I'd estimate about 1.5 gallons were run through it for breakin.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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up north now
Sounds a bit rich.

Also, the 91 octane is a waste of money.

All my builds would pull my 200# up a hill and have some spare power doing it. 44T sprocket, stock baffle.

Finally, you won't see an improvement in performance as far as break-in goes until 250++ miles. Vary the throttle and engine load often, and don't baby it.
 

cityevader

New Member
May 11, 2008
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Santa Cruiz, CA
hmmm, interesting. I've read in several places /suppliers, that 91 octane was important, I wonder why? Perhaps useful for breakin since it "burns slower" to prevent pre-ignition and reduce likelihood of damage? But then again, aren't 2-strokes lower in compression to begin with, reducing likelihood of pre-ignition? 87 it is!!!!
 

cityevader

New Member
May 11, 2008
170
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Santa Cruiz, CA
Hey hey! Skyliner is back!
How did your move go? Smooth I hope?
Settled in enough to do your planned sea level boost bottle before/after time/distance/speed trials?