300 Kickstart ratio change? No - cylinder change.

[bikerpet]

I've just picked up a 2020 Evo 300 to replace my 2017 Beta 300.

Generally feels pretty much the same (but shinier!) with the notable exception of starting. The new bike is vastly easier to kick over.

On the '17 I had to get right up over the starter and give a really solid kick to spin it over consistently. Any sort of half hearted stab and it would usually laugh at me.

On the '20 I can give the most mediocre stab on the lever and it spins right over.

I'm left wondering if they changed the starter ratios or if the engine has lost compression.

I looked up the part numbers and there's only one difference, but I've no idea if it's significant:

• 007.03.439.80.00    PRIMARY DRIVE WITH CUP (2020 model)
• 007.03.435.80.00    PRIMARY DRIVE WITH CUP (2017 model)

So have the ratios changed (seems unlikely given only one component has changed) or is my engine low on compression?

Thanks

Edited June 23, 2021 by bikerpet
Updated Title to reflect the answer.

[faussy]

Same flywheel weights on both bikes?

[bikerpet]

Just now, faussy said:

Same flywheel weights on both bikes?

As far as I know. But it really doesn't seem like an inertia thing - it's just much easier to prod over at any speed.

Maybe I'll take a peak to be sure. Potentially I need to pull the head off and take a look inside I guess, reluctant to do that on a bike I've only had one day though!

[bikerpet]

I just made a little video comparing turning over the two bikes.

Big difference! But I'm not really sure how either of them compare to other people's Evo's.

The '17 had the head & cylinder off about 100 hours ago and was in perfect condition. It doesn't seem to have changed in compression or performance since then.

Vimeo kicking over video

[tshock250]

There's a slot machined vertically in the barrel to aid starting on the later evos.

 

[bikerpet]

7 hours ago, tshock250 said:

There's a slot machined vertically in the barrel to aid starting on the later evos.

 

 That would explain it. Certainly makes a big difference.

Looking at the parts list numbers it appears the cylinder changed in 2019.

Thanks, I'm happy to have that mystery solved. You'd think Beta would have talked it up a bit more really.

[overdale]

tshock250 is absolutely right - the latest 300s are real easy to start. 

There is a small short slot going up the barrel from the exhaust port, and the depth reduces as it goes away from the exhaust port. 

So there is exhaust leakage (lower compression as the piston rises past the exhaust port) as you kick the bike over at very low speed compared to tick-over . 

Once running, the piston passes the slot so fast that the exhaust leakage is negligible. 

[trapezeartist]

Clever idea.

[portman]

Yes, clever idea.  I guess the 250s might also have a slot since my friend's 2021 250 is much easier to kick than my 2016 model (both standard, not factory versions).