I have the Beta Rev4T running great.....Changed the Main jet to #115, Raised the needle all the way, 3.5-4turns out on the fuel screw. I tried a richer low speed jet but returned to std as it wasn't nice. The bike is well tuned - valves are ok, iridium plug is gapped to 0.6-0.65mm, filer is properly oiled. Boy does the bike run really well...... way better than std.

However it still has an occasional miss-fire or something just as the bike is coming off idle. Not every time, perhaps 1 in 4 times..... it has me stumped.

Any ideas out there?

What are climate conditions.. summer arriving for you maybe worth trying slightly bigger plug gap?

Hi,looks like you have sorted out your 4T. Wondered if you could help me. I have a 2008/9 and the idle is very poor, will not run smoothly at the very bottom of the rev range. I see you have fitted different jets-is there any other mods that maybe required? Also how often do the tappets need adjusting? Any info would be welcome thanks.

Well i fixed up the weird idle issue. The mixture screw was only 1.25 turns out rather than 3-3.5 turns. It appears like some moron had been turning it the wrong way. Just wait till i get my hands on him....

Hi Tapscott Yes my bike is running great here are my top tips for your bike....

The factory has a few updates - call Lampkin's to find out - kick start, head gasket, hot start (this is on this web site)

1 The cam chain is self adjusting.

2 Change the oil every 15-20hr, oil filter every second change, factory is 15-50, use FULLY (!!!!!!!) synthetic oil only, 800ml per change.

3 The bike is jetted wrong to pass Euro emissions tests. Change the main jet for #115. Move the needle clip to the bottom grove of the needle (note where the washers are for the needle, and DON'T get the diaphragm caught when the top cap is put back on). 3-3.5 turns (right up to 4 turns if the bike feels like it wants to stall) out on the mixture screw.

4 Make sure there are no splits on the caps that cover a couple of the carb breathers

5 Cut all the carb breathers short so they don't hang down low (it keeps them out of the water)

6 Get an NGK Iridium spark plug, and gap it to 0.6mm

7 Remove the front support/bracket on the rear mudguard - it hangs in the air flow to your air filter and restricts air flow. Stupid thing.

8 Remove an air baffle that is supposed to stop back firing from burning the air filter.

9 Have two air filters and ALWAYS keep a clean one fitted

10 Remove the stupid BETA kill switch & light control - these are often faulty - replace it with a Yamaha square unit.

11 Valves shouldn't rattle. It is more a sewing machine sound. Exhaust clearance=0.125-0.15 and Inlet=0.10mm. You have to rotate your engine forward to do the valves.

12 I ground off the rising hump inside the twist grip - now my throttle is a linear action.

See how these go..... worst case you could need a valve grind or you could have a poorly electrical system (i have heard of one instance) . Again call Lampkin's (very helpful)

Ralphy

I forgot to add....

Fuel float level set to 11mm (this is to the bottom if the floats' casting mark)