paulrev3 Posted February 13, 2006 Report Share Posted February 13, 2006 I have an 02 Beta Rev 3 - Feels choked up when opening throttle, have cleaned air filter chamber and replaced filter, checked reed valve. Recent bottom end re-build + new piston and rings. Have also tried adjusting air screw in/out. Has anyone got any ideas and if poss a carb diagram. Cheers Regards Paul. N Quote Link to comment Share on other sites More sharing options...
neonsurge Posted February 13, 2006 Report Share Posted February 13, 2006 I assume you've stripped the carb and cleaned the jets etc.? The Mikuni VM-series carb is pretty simple and you can get at the main jet by simply removing the carb (loosen the two jubilee clips, twist and pull), removing the large bolt on the bottom of the bowl and unscrewing the jet. You can see exploded diagrams and download tuning manuals on Mukini USA's site (as well as numerous other places). Quote Link to comment Share on other sites More sharing options...
clarkp Posted February 15, 2006 Report Share Posted February 15, 2006 "Have also tried adjusting air screw in/out." Aye, there's the rub... Starting at the beginning...I'm assuming you're running the standard-ish 145 main jet and either a lean 27.5 pilot, a nice 30 pilot jet, and your carb slide needle clip is still in the middle position. And I'm sure you know that all of the carb circuits work in concert with each other so it can be difficult sometimes to identify the root of the problem, however, in the case of the machine "four-stroking" as you indicate - I would look to the air screw as long as all of the above are in line (main, pilot, etc...). You say you've 'tried adjusting air screw in/out', but do you really know what you're doing, or are you just whacking about with carb settings? I don't know how much experience you have with adjusting carbs, but you can really hose yourself with indiscriminate adjustments..much like a computer - change only one thing at a time and make a note of what happens. The air screw turned out even a half a turn more than necessary can cause your bike to four-stroke at mid to WFO throttle. Try turning your air screw in until it seats lightly, then back it out 1.25 turns as a starting point. Then refer to the online Mikuni manual for the final air screw adjustments. In a nutshell, set the idle up a bit and start opening the air screw by 1/4 turn increments - you want the revs to pick up smartly when you whack open the throttle off idle, but you don't want it to take a long time to return back to normal idle. Open the air screw until you achieve this balance. My guess is that your air screw is open too far. Quote Link to comment Share on other sites More sharing options...
paul w Posted February 19, 2006 Report Share Posted February 19, 2006 i had similar problems with my 04 270. i checked and adjusted ignition and changed carb settings. all had a slight effect on running but did'nt fix the problem . so, i stripped down the top end and gave the full lot a THOROUGH de-coke, it now runs sweet as a nut, dont get me wrong on this, there was'nt lots of carbon build up, but there was enough to spoil the performance. give it a go , i managed to re-use the gaskets and as long as your carefull on removing the rings it should'nt cost a penny. (proper yorkshire repair!!) Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.