Engine Trouble Bike wont go faster than 24mph with 36t sprocket

[6blueoval9]

Yes..that's acceptable compression range.

I'm not sure why it won't go faster..if the carb is tuned properly and the plug is in good shape and gapped properly and spark is adequate along with a proper fuel/oil mixture it should be faster in my opinion.

The only bad thing that can be hurting you is you said the exhaust port was ported and you're still using the stock exhaust.

 

[BikePete]

Correct but the engine came with that stock exhaust. Im guessing maybe the engine needs more breaking in?

 

[BikePete]

What affordable exhaust would you recommend for this oval port? 32mm

 

[FurryOnTheInside]

I guess if it's been run super rich I would take the exhaust off and have a look inside. It might, I suppose, be caked in oily carbon. I'd just check that out and maybe try to wash it out with some petrol.
There are some things that you can do to improve the stock exhaust.
Idk if you have done any work on the flange/opening of the header, or opened up the holes in the lower baffle whatsit.

Happy Time exhaust flange

• FurryOnTheInside
• Aug 30, 2017

Opened up the end of the exhaust and made it slightly more oval, and smoothed it.
Ears bent...

I only opened the holes in my own lower baffle whatsit because I was adding an extension for stealth which I knew would slow the flow a bit. I also ground off some welds that were invading into the two internal tubes.

Cheap exhaust, opened

• FurryOnTheInside
• Sep 9, 2017

I opened the 6mm holes to 6.7mm diameter and opened the largest hole slightly too. I ground back...

Idk what exactly has been done to your exhaust port. Just the word "ported" doesn't tell me anything. It should be a bit more trapezoidal than oval shaped at the window, and a bit oval at the exhaust mating surface. All the flow really has to happen in the first moments of the exhaust port being opened, that's why its wider (24.5-25.5mm) at the top (on the "window" inside). Widening lower down or just the middle doesn't help because that's when you're done exhausting and it just loses the fresh fuel/air.

Modified exhaust port

• FurryOnTheInside
• Aug 23, 2017

Opened the outside of the exhaust port a little rounder, and widened exhaust window a little at...

So what is the "porting" that has been done to your exhaust port?
Also are the transfers nice and clean, no casting flash left in them like in this uncorrected stock cylinder?

Serious casting flash

• FurryOnTheInside
• Sep 14, 2017

Upper, lower and intake sides of transfers have severe casting flash causing massively...

Casting flash in exhaust port

• FurryOnTheInside
• Sep 14, 2017

It is common to find the exhaust port window is obscured on the right side by a big chunk of metal.

 

[6blueoval9]

Do you know what mixture of gas and oil you are using?

As far as an exhaust it's hard to say really...most of them aren't really any better than a stock exhaust.

An expansion chamber exhaust is considered the best among them but even some of those are garbage.

The two that come to mind are in the 40 to 50 dollar range.

There is an exhaust called "Thrust" and zeda has a new pipe as well "zeda66" which is probably the better of the 2 but it's 50 dollars.

 

[BikePete]

Thanks Blue and Furry do i have to do drilling in the exhaust to improve it a bit?

 

[6blueoval9]

Do you have a Dremel tool?...a round file maybe?

 

[BikePete]

Yes both. And a drill

 

[FurryOnTheInside]

Thanks Blue and Furry do i have to do drilling in the exhaust to improve it a bit?

Just check out the caked in .... situation first.
Since it was running very rich it could possibly be caked in carbon.
I think the flange opening and smoothing is pretty much a necessity because it is free and has no downside.
Idk about the drilling out the lower baffle plate whatsit,. I just felt like doing it.

 

[6blueoval9]

You see the first pic furry posted?...that hole used to have flat edges where it meets the flange..you want to round those edges off as much as possible without breaking a weld.