Can Reeds Really Improve Response?

[mcman56]

I have a 2008 Rev3 200 and the response is quite soft.  I ran it with a 250 top end for a while and it did have more power but the response was still soft.  It has the fast throttle and Keihin carb.  Everything is in good shape and overall it runs good.  It does have the Boyesen dual stage reeds.  Could a reed change make a significant improvement in response?  There is no add on flywheel weight.  I have thought about shaving weight off of the flywheel but am concerned about making an expensive paperweight.  I recently had a 2016 Beta 125 apart.  It has a little tiny flywheel and impressive response for a 125.   

[konrad]

Have you played with the ignition timing?  Generally, advancing ignition timing will help bottom-end power/response at the expense of high-RPM power and possible detonation.  I also find that a combustion chamber with minimal squish clearance and a sharper blend radius (both of which increase turbulence and therefore rate of combustion) will create a more explosive "hit."

Edited July 5, 2019 by konrad

[nigel dabster]

does it have a weight on? Boysen reeds are the best, so changing wont make it better.

Is compression good?

Edited July 5, 2019 by nigel dabster

[konrad]

2 hours ago, johnny_rotten_dab said:

avgas???

Are you asking if he is using AvGas or suggesting that he do so?

Below is a link to my write-up on leaded fuel:

 

 

Edited July 5, 2019 by konrad

[Bilko]

The Rev 3 200 is soft also the 250,should have tried a 270 bit sharper than the 250. if possible,machine the flywheel will make it pick up a lot quicker depending how much you take off,go too far and suffer no bottom end grunt.i once bought a sy250 because they were supposed to be docile.got it home went out to try it.Thought i was on a motorcross bike just a touch of throttle and it was off like a rocket.checked timing to see if it had been altered,but no.Happened  to see a Scorpa 250 flywheel for sale on e bay.didn't look the same as my one.rechecked mine that's when i noticed it had been machined down.

[mcman56]

I checked the reeds and I actually did not have the boyesens installed.  I installed them and fully advanced the timing.  There is a noticeable improvement.  I have a 26mm OKO and  wonder if it could improve response over the Keihin.

It is interesting what this site says about Keihins on 125s.  https://trialendurodirect.com/product/gas-gas-pro-performance-kits-ppk5/

The Keihin carburetors make a BIG difference to all GG Pro models. The standard 26mm Dellorto carbs are great for production because they carburate perfectly and rarely change whatever the conditions. The Keihin carbs are 28mm so that’s 2mm bigger than the dellorto which increases top end power, this is why all the top riders use them. Also because of the 2mm bigger bore they make the bottom end power very smooth and clean. The carburation is a little more tricky to set up and can vary in different conditions but the Keihin carb we supply should be spot on for all 250/280 and 300 Pro models. Only maybe a slide change is necessary. Fitting the Keihin carb to a 125cc will improve the top end power alot but you lose quite alot of bottom end which is maybe not a good thing for a 125. It depends on ability of rider and conditions used.

  

[lineaway]

 Quickest way to change the response is to add a tooth or two to the rear sprocket. The 200/250 Beta`s are a timid type motor. Just takes some clutch work to make it come alive.

[mcman56]

Except for turning, I don't use the clutch much.  Do you have any suggestions on developing that skill?  Do you try to rev and dump or hold high rpms and feed?  

[lineaway]

 Best practice is on long steep loose hills. Rev and feed. Do this till you are use to it. The dumping comes in when you throw an obstacle in at the end. Which is basically what is happening when you watch someone do a splatter. It does not need a lot of revs, just more than you would without the clutch. Great to learn as that is what slippery riding is all about.

[konrad]

4 hours ago, mcman56 said:

Except for turning, I don't use the clutch much.  Do you have any suggestions on developing that skill?

One finger, and one finger only, always on the clutch lever.  Ride a gear higher than you normally would.  This will force you to quickly develop the skill.

[konrad]

On 7/6/2019 at 3:23 PM, mcman56 said:

Also because of the 2mm bigger bore they make the bottom end power very smooth and clean.

I would take issue with the reasoning behind that statement.  Generally, a smaller bore will produce a higher air velocity thorough the carb which will help low-rpm response.

If there is a low-rpm improvement with the Keihin / OKO it's because they are flat-slide-carbs (versus the Dellorto which uses a round slide).  The smaller volume under the flat slide makes it respond quicker because fuel is pulled through the need jet quicker.

A larger bore has the potential to flow more air for high-rpm use.  On just bore size alone, a 28mm carb provides 16% more area than a 26mm carb.  However, additionally, a flat-slide carb will flow more air than the same size round-slide carb.