6 replies to this topic

[skippy1234]

hi all just treated meself to a 04 rev 3 ,while riding today i noticed a knock every now and then when i blip the throttle not all the time but noticeable any ideas thanks

[Dan Williams]

Welcome to the wonderful world of high compression. Although there can be other causes Betas are known to have the knock from using pump gas. A lot of us have just given in and run race gas. That gives you the crisp throttle response Senior B riders like me demand (and can't use). You can try raising the needle a notch or two to see if it helps but it will soften the power a bit. There really is no substitute for the good go juice.

[paul w]

my 04 250 did the same, its either pilot jet too small (sorry cant remember the sizes) this will be worse this time of year due to the cold. (presuming you are in UK).
But i also used to de coke (polish the piston crown and the head) frequently, this always stopped the Ping on my bike as it is usually pre ignition.

[Steve_E]

paul w, on 04 February 2012 - 05:40 PM, said:

my 04 250 did the same, its either pilot jet too small (sorry cant remember the sizes) this will be worse this time of year due to the cold. (presuming you are in UK).
But i also used to de coke (polish the piston crown and the head) frequently, this always stopped the Ping on my bike as it is usually pre ignition.

Pilot jet is 30 standard with a 150 main.
Sounds like your bike COULD be running lean or the timing is too far advanced.
The odd knock is noting to worry about though on a beta, Probably piston slap.
Look on the beta website technical information for the timing setting pic.
Changing to the factory spec jets 27.5 pilot and 145 main will transform the bike.
Actually come to think of it it may be running lean because someone has adjusted the floats to try to cure the leak from the overflow.
We have played with many betas to try to cure this and the only solution is to leave the floats 1.5mm above level and live with the odd leak when the bike is leaned over. There is info about the mikuni carb fix to stop the leak but this starves the bike, and kills initial throttle response, Lots of people rave about it because it stops the leaking but they are not mechanically minded enough to realise the symptoms of it running lean after.
This is just my experience don't take it as gospel do what works for you.

[skippy1234]

the chap i got the bike off had a new stator fitted 2 months ago would that make timing out- i was used to my techno this rev 3 has loads of power a little more than i,m used too

[Steve_E]

skippy1234, on 04 February 2012 - 06:33 PM, said:

the chap i got the bike off had a new stator fitted 2 months ago would that make timing out- i was used to my techno this rev 3 has loads of power a little more than i,m used too

www.betatrialuk.com/content/view/64/51/[/img]

heres a link to the info.

My beta has the rare faint knock & Im running higher than standard compression, Have my timing advanced & I'm running leaner jets all to make it perform like a wild animal!!!

[pindie]

If it helps mine was running rough at the weekend due to the cold weather. Get some heat in it and it cleared up nice. Also use Tesco Momentum 99 octane fuel.