Slowing Top Speed

StevenMain

New Member
Jul 18, 2016
108
4
0
Texas
So, I took the bike out ALL night with my friend and we raced all over town. Im worried though, I started out topping at 41, I made a new cylinder as my old one had scratches in the plating around 300 miles. The new one I ported "better" and only managed 40.25 (44 tooth)
as the night went on my top speed kept dropping lower and lower and lower and I ended up topping out around 36.5... Is the cylinder wearing out THAT fast? I don't know what else it could be.

Also 41mph was the BEST recorded top speed on 44 tooth to date. Anyone ever logged any faster on GPS? I have done EVERYTHING you can do to this motor.
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,130
164
63
Santa Barbara, CA
If you just put a new cylinder on it the piston rings need to set, you should follow break in procedures again any time you replace the rings, cylinder, or head gasket. It's possible that when the rings get set you will have more consistent performance.
 

crassius

Well-Known Member
Sep 30, 2012
4,032
155
63
USA
while it usually take only a mile or so to get these warmed up enough to run well, it takes 8 to 10 miles to get these motors to stable temps - mixture may be diff once it warms up to that point
 

codyj528

New Member
Aug 10, 2016
3
0
0
TEXAS
If you just put a new cylinder on it the piston rings need to set, you should follow break in procedures again any time you replace the rings, cylinder, or head gasket. It's possible that when the rings get set you will have more consistent performance.
I wouldn't call it new, it had a proper break in then was pulled and gifted to him. 16:1 ratio break-in.

And if $50 is to much to throw away in 1 night, consider a night out for dinner/movies with a chick.... .duh.
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
16
0
memphis Tn
I wouldn't call it new, it had a proper break in then was pulled and gifted to him. 16:1 ratio break-in.

And if $50 is to much to throw away in 1 night, consider a night out for dinner/movies with a chick.... .duh.
Using so much oil basically triples (or more!) break-in time due to rings being overlubricated and unable to properly seal to cylinder wall.
Break-in means rings seating and too much oil can easily prevent it EVER happening.
Poor compression, poor manners and reduced power are usual results of too much oil.
I'd bet $50 your jug was basically new inside regardless of prior use, so it ran like a new top end: poorly.
 

StevenMain

New Member
Jul 18, 2016
108
4
0
Texas
Thanks for the reply, I took the cylinder off today and did more port work to try to hit the magic 10k rpm... plating had definite scores. Not terribly deep but obvious. I've hit 9,733 rpm at 41mph before and the motor is well balanced to with the lightened piston.
 

StevenMain

New Member
Jul 18, 2016
108
4
0
Texas
39.75 mph tonight which is within my range of acceptable. If it wasn't 84 degrees and 78% humidity it would probably be a little faster. (This is at 3am!)

My new question is at top speed the bike surges hard and slow. Once it hits a certain speed it litterally falls on its face entirely for about a whole second, then pulls again for 1/2 a second, then dies for a full second.

There must be a float height issue, fuel sloshing from the slight vibration, or maybe the bowl is running dry due to a filter restriction idk. Any thoughts ?
 

codyj528

New Member
Aug 10, 2016
3
0
0
TEXAS
Using so much oil basically triples (or more!) break-in time due to rings being overlubricated and unable to properly seal to cylinder wall.
Break-in means rings seating and too much oil can easily prevent it EVER happening.
Poor compression, poor manners and reduced power are usual results of too much oil.
I'd bet $50 your jug was basically new inside regardless of prior use, so it ran like a new top end: poorly.
Meh. I couldn't remember the spec sheet but it was more like 20 or 25. Whatever the Chinese called for. And it had about 3 tanks of fuel ran thru it so I'd consider it a ok broken in. Besides. This isn't a gt500 break in.... but you know we drove that thing like a stolen car the first 5 miles off the lot on a 4 hour road trip home. Let's just say my Datsun couldn't keep up. :(
 

Kioshk

Active Member
Oct 21, 2012
1,152
7
38
Connecticut
...fuel sloshing from the slight vibration, or maybe the bowl is running dry due to a filter restriction idk. Any thoughts ?
BINGO.

I've had the same "problem", but I think it's a good thing. It's either that the carb-bowl's fuel is aerated from sloshing (doubtful), or there's not enough fuel getting in at high-revs (probable). Hold down the tickler with your left-hand when it starts happening again and report your findings. Better yet...for safety purposes...bring along a small child for the ride and have them do it.