Knocking Sound

[grahambaskin]

Hi guys,

i have a beta rev 3 2007. i'm only a novice rider its my second bike, i love the bike to ride but i feel a little disapointed with it because its seems to be one problem after another. first it was the carb, that seems to have stoped but now i hear a knocking sound when giving the bike throttle, only when moving in the like of fourth gear, not any lower. when i wheelie it knocks but when im only playing about in low gears its fine, but as i said in the higher gear it knocks CAN SOMEONE GIVE ME SOME GOOD NEWS PLEASE.

[the addict]

Try a higher octane fuel first 98/99 that may cure it straightaway or add some octane booster to the mix, knocking is sometimes just pre ignition in the cylinder

Edited June 5, 2008 by The Addict

[dan williams]

Agreed, higher octane gas. Even though the throttle setting is the same in the higher gears you are putting a heavier load on the engine and that can cause detonation to be much more prevalent. Also realize pump gas is notoriously inconsistent. Even premium fuels like Sunoco Ultra which I used to run until I got a few bad batches. A car is so mildly tuned it'll just suck it up and run lousy but a trials bike tuned to within a gnats *** will let you know immediately when you've got a bad batch. See if you can get your hands on some race gas. It won't make any more power but it will dramatically reduce the occurrence of detonation and it's consistent batch to batch.

[the addict]

Always tried to run the Beta on 50% Avgas and 50% super unleaded they love high octane fuel

[grahambaskin]

Cheers guys,

i will try this hope it works, so will i use complete super unleaded or mix it with unleaded. does the make of oil mix matter i use castrol tts.

[the addict]

Use super unleaded only 100% and 70mls of TTS in 5 litres of fuel, it might also be possible the knocking is actually lack of fuel especially if it happens up hills or whilst doing wheelies, if the high octane doesnt make any difference (still keep using it though) the carb might be running out of fuel whilst pointing up hill etc, there is a float extension for the Rev 3 which holds more fuel in the bowl or your float height may be set wrong. Could always get a 4rt and forget about all those carb problems altogether though

Edited June 5, 2008 by The Addict

[grahambaskin]

one more thing guys does all two strokes like the higher octane fuel? the reason i ask is that my friend has a montesa it never knocks, and i always get the p*** taken out of me when were out.. i take it that this fuel is fine in all two strokes.

[grahambaskin]

A four stroke is one bike i would love. maby next year.... or the year after!!!!!!!!! never was on one but they sound lovely and flat.

[the addict]

The sherco I had last year seemed to run ok on anything, no difference at all with Avgas so didnt bother, I think the 315 likes good fuel though, the 4rt will run on anything that is liquid

Edited June 5, 2008 by The Addict

[dan williams]

Whether four stroke or two stroke the octane required depends mainly on compression ratio. A higher temperature in the combustion chamber is what causes detonation so anything that raises the mixture temperature too high before the proper ignition time will cause detonation. That includes advanced ignition timing/poor cooling (yes mud in the radiator) /lean mixture/ flogging the engine under heavy load. Different fuels will spontaneously ignite at different temperatures. The trick in an engine is to maintain the mixture temperature and pressure just under the point where the fuel ignites without the spark.

The common misconception about race gas is that it makes more power. That has a grain of truth to it but the main feature of higher octane fuel is that it has a higher flash point so it self ignites at a higher temperature then lower octane fuel. This allows more aggressive ignition timing and higher compression ratios to be used. It also allows for a leaner mixture since there is less need for the cooling effect of fuel vaporization.