Not a real problem but...

GoldenMotor.com

fugit

New Member
Mar 5, 2012
176
0
0
Oregon
Ok so I am a chicken and like keeping it at around 22 mph max. I have put about 250 miles on my latest motor maybe a tad more. Since I ride it only on back streets slow like that there really isnt many places to open her up anyway. But there is this one strech that is smooth road, level, no traffic, and I have opened her up a several times there.

The max I have been getting is about 30 MPH WOT. But today when I went that way and opened her up I was at 30 and then all of a sudden the motor seemed to open up way more then usual. I mean it really stepped it up and she got to 35 mph. It was like she was a whole different motor winding out so much more then usual. So I turned around and did it again with the same result.

The strech is about 100 yards straight and then a slight turn and another 70 or so yards. About 30 yards before the turn both times she just kicked in like nothing else before.

Anyone got an idea why that may of happened? Im all stock 66 cc (bikemotorkit motor) basic carb and switched over to amsoil 70:1 after about the first 50 miles.
 

Cavi Mike

New Member
Dec 17, 2011
189
0
0
Rochester, NY
Engines without an actual redline will do pretty much anything you want them to do - for a few minutes. I assume you're running the stock 50T sprocket on the back? I wouldn't try to go 30MPH again until you go with a smaller rear sprocket. The 66cc is a terribly balanced engine and you're just gonna blow it up by thinking it's going to wind out like a 45cc chainsaw.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
63
up north now
Maybe she's finally broken in.

If you have a 44T sprocket, it's not going to hurt it to run it up once in awhile.

Just be careful at that speed, you're on a bicycle ;)
 

fugit

New Member
Mar 5, 2012
176
0
0
Oregon
Engines without an actual redline will do pretty much anything you want them to do - for a few minutes. I assume you're running the stock 50T sprocket on the back? I wouldn't try to go 30MPH again until you go with a smaller rear sprocket. The 66cc is a terribly balanced engine and you're just gonna blow it up by thinking it's going to wind out like a 45cc chainsaw.
Well I said stock but that was meant only in terms of engine, carb, and muffler. I used the Manic Motor Mounts, Pirate adapter with 44 t, and the smaller 415 chain.

Oh yea I am nervous at 24-30 I was terrified at 30-35 but I just kept saying the lords prayer over and over in my head LOL. I only wound her out for mabey 20 seconds not even. I was too scared :) Usually I, and only on that stretch when I go that way, bring her up to 30 then immediately back down. But this time she seemed to really kick in at 30 and take it to another level I have not experienced yet - so I had to try.

This is a good stretch of road because there is sand on both sides and I hug the right side. If I bite it at least I got a chance to hit sand :)
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
I have one engine that does what yours did. I can be riding at or near WOT then for some unknown reason 'something happens' and there is a noticable change in engine sound and power. It has done this since break-in and continues to this day. That engine has about 1400 miles on it, still runs strong and smooth. My theory is that for some reason at that power setting the air/fuel mix finds a sweet spot and the power rolls in. I've given up trying to find out exactly what happens. If you ever find out, let me know.

Tom
 

fugit

New Member
Mar 5, 2012
176
0
0
Oregon
I have one engine that does what yours did. I can be riding at or near WOT then for some unknown reason 'something happens' and there is a noticable change in engine sound and power. It has done this since break-in and continues to this day. That engine has about 1400 miles on it, still runs strong and smooth. My theory is that for some reason at that power setting the air/fuel mix finds a sweet spot and the power rolls in. I've given up trying to find out exactly what happens. If you ever find out, let me know.

Tom
That was my intial thought too Tom. Question I had in my mind considering that was; Is the engine just experiencing an air leak at the higher pressure or like you say is it hitting a sweet spot?

If it is a "normal" condition I would think you would be able to duplicate the phenomenom/performance level with an adjustable carb ( like the CNS) and the right Oil:Gas ratio.

Thanks for the input!!
 

rustycase

Gutter Rider
May 26, 2011
2,746
5
0
Left coast
My cruising speed on level ground seems to be 17mph, on my fire breathing, flame shooting 48, on the main street of town, the Old Kings Hiway. 24 was flat out WOT with my carcass. 29mph w/ number 1 as a pilot.

Many riders/builders feel different, but I'm good at 20mph, and think a thirty top would be about right for practical reasons. Many fellows build for faster speed.

If your motorized bicycle all of a sudden 'came alive' and began turning higher rpm, it could be the components of the engine free-ing up, all coming into place, and doing what they should do at their best, in harmony... breaking in???

OR, it could be a tad bit of debris causing fuel starvation, or running out of fuel for bad float level... and basically leaning out and developing more hp.
Optimal fuel/air ratio, right at lean will bring most rpm, just not longevity! lol

...watch that sandy road! Very treacherous!

also, it could be the circuitry of the cdi coming in to a loop that allows most advance, which will also bring top rpm capability. and hole pistons and stick rings and stuff like that...

Best
rc

Some builders run a 41T rear which would bring rpms down, and kinda clamp the engine back by putting the brakes on the limited torque it produces.

.
 
Last edited:

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
That was my intial thought too Tom. Question I had in my mind considering that was; Is the engine just experiencing an air leak at the higher pressure or like you say is it hitting a sweet spot?

If it is a "normal" condition I would think you would be able to duplicate the phenomenom/performance level with an adjustable carb ( like the CNS) and the right Oil:Gas ratio.

Thanks for the input!!
Another theory might be the pipe on my bike. This engine is on the Norton bike in my album. It's 3/4" EMT with a stock muffler out at the tail end. Maybe, just maybe, the pipe acts like an expansion chamber after a certain RPM. I'm grasping at straws here, Fugit. Let's just ride 'em and enjoy that kick-in-the-butt when it happens. :)

Tom