betabell Posted May 22, 2018 Report Share Posted May 22, 2018 I have a new to me 2004 Beta Rev3 270cc and I don’t think it runs correctly but I am not sure. The bike is supposed to of had a full rebuild by the last owner including a re-plated cylinder and new piston etc. The bike start first or second kick and seems to have lots of power. What concerns me is that when you blip the throttle about 30% + it revs cleanly but then as it is dying down you get a sort of uneven roughness and a couple of loudish bangs/ coughs. I am not a mechanic and am not familiar with this engine. I don’t know if this noise is just normal overrun of excess fuel or if the carb is not set up correctly and the bike is to lean or reach? It may be low quality fuel or a problem with the timing, or if there is something more seriously wrong with the bike. Any advice would be greatly appreciated. As a side note should I use super unleaded or normal unleaded? The reason I ask as I have been told conflicting things. I know lots of people run super unleaded but I was told by a Beta dealer a few years ago to use normal unleaded? What is considered old fuel and not suitable for use in bikes? I always use to think that anything older than 6 months should not be used but I have read about people saying not to use fuel that is over 30 days old. Sorry to squeeze multiple issues in to one but I think they may be connected. Thanks James Quote Link to comment Share on other sites More sharing options...
zerorev3rev4 Posted May 22, 2018 Report Share Posted May 22, 2018 Is it pinking on shutting throttle is there a vibration when rpm coming back down Quote Link to comment Share on other sites More sharing options...
markparrish Posted May 23, 2018 Report Share Posted May 23, 2018 I have a 2007 model and the previous owner told me to use the super unleaded (97) which I have done - I don't get the effect you describe. Hope you get it sorted. Quote Link to comment Share on other sites More sharing options...
lineaway Posted May 23, 2018 Report Share Posted May 23, 2018 Fresh fuel and a new spark plug is the first place to start. Quote Link to comment Share on other sites More sharing options...
goudrons Posted May 23, 2018 Report Share Posted May 23, 2018 (edited) Beta's handbook states to run them on "super grade unleaded". They pink and knock on anything less than 97 ron. They are also quite fussy with the float height setting due to the angle of the carb, you might find some help on here to set it, though you should be able to find a handbook to download for it on the web somewhere, any Rev 3 book from 2002 to 2007 will do. (2000, 2001 were similar but certain parts like forks and airbox were different and 2008 had a different carb altogether) If someone has had it apart, did they put it back together properly? I'd check the timing at the very least. Edited May 23, 2018 by goudrons Quote Link to comment Share on other sites More sharing options...
mcman56 Posted May 24, 2018 Report Share Posted May 24, 2018 I have a rev 3 that will pop in the exhaust when chopping the throttle off, sort of a Pop...Pop...Pop I chased/ tried everything you can imagine to eliminate the issue but it is still there. I tried all different fuels including race gas by the can. Other bikes I have ridden will do that occasionally but mine does it a lot. Otherwise, it works fine. It was sold as a 200 and I put a 250 top end on it. The top end is from a different year so maybe that has something to do with it. When Beta sold 270 kits, I noticed that there were different kits for different years but I could never find out was was different. Quote Link to comment Share on other sites More sharing options...
markparrish Posted May 25, 2018 Report Share Posted May 25, 2018 Ah...yes, mine does the "pop pop" thing as well - I think it's quite normal and I quite like the sound (which comes from the exhaust). Maybe you should video it making the noise and post it so others with more knowledge than me can diagnose it? 1 Quote Link to comment Share on other sites More sharing options...
markparrish Posted May 25, 2018 Report Share Posted May 25, 2018 here is mine - hope the link works. Just started so running cold and a bit rattly! Quote Link to comment Share on other sites More sharing options...
mcman56 Posted May 26, 2018 Report Share Posted May 26, 2018 The popping I can get from mine is like adding up 5 or 10 of those pops. It only happens when winding up the engine and chopping the throttle off. Quote Link to comment Share on other sites More sharing options...
markparrish Posted May 28, 2018 Report Share Posted May 28, 2018 I think if it was mine, I'd run it on super unleaded as recommended and just enjoy it - if it is running well and has power as you say, I think you should have some fun with it. Quote Link to comment Share on other sites More sharing options...
betabell Posted June 22, 2018 Author Report Share Posted June 22, 2018 Thanks very much for every body’s comments. I sorry I have not replayed sooner but I have been busy and have not had the time to play with the bike. I have run the bike with a new sparkplug and super unleaded. This has made no difference as far as I can tell. I shall run the bike on super unleaded if that’s what the supplier recommends. I got the petrol from a Gulf petrol station as this is what is nearest to me but next time I buy fuel I will try a different brand? Has anyone had good results with a particular brand? Zerorev3rev: It’s more of an noise that I was initially worried about but yes you do feel a bit of roughness from the engine. Goudrons: I was a little cautious diving in to the carb as it starts easily, ticks over and seams to deliver the right amount of fuel if you wack the throttle open. By that I mean I have had bikes that when you open the throttle there is a lag and splutter as the carb float bowl does not have the correct amount of fuel in it. Also the carb does not leak. I have had a rev3 250 and I know what an absolute a*** the carbs can be, my 250 liked to wee everywhere. I will probably dive in to the carb and clean it and get a rebuild kit and fit gaskets etc. I have no idea if everything has been put together ok. I have no idea how I check the timing on these. How do I go about that? Mcman56: Yes the noise could be normal for this model of engine. I also wonder if it could be excess fuel along with the fact that the engine could be a bit tight from the rebuild. Markparris: Yes I will upload a video that a good idea. Mcman56: Yes that sounds more like you described when the engine has been wound up and the throttle is chopped off yes the pops are louder as you described. Quote Link to comment Share on other sites More sharing options...
betabell Posted June 22, 2018 Author Report Share Posted June 22, 2018 Quote Link to comment Share on other sites More sharing options...
mcman56 Posted June 22, 2018 Report Share Posted June 22, 2018 That is what mine does. I think many bikes do it to some extent but mine was the worst. Advice on line suggests an air leak in the exhaust system allowing air into the pipe that then causes un burnt fuel to ignite in the pipe. I went as far as bubble testing the pipe under water and fixing all pin holes but it still does it. I also notice a little pinking when rolling along with the throttle barely cracked open and suspect these are related. It does not pink under any other conditions and other wise runs fine. It did the same thing with a mikuni and keihin jetted rich or lean although rich jetting did reduce the popping. It sounds like some KTMs do something similar It looks like you are missing the skid plate. Quote Link to comment Share on other sites More sharing options...
2stroke4stroke Posted June 22, 2018 Report Share Posted June 22, 2018 Having owned a Beta in the past (for 12 years) I would say that sounds normal. Try running without a tickover, as we used to do decades ago, and the noise should disappear. It is the inevitable result of allowing mixture in to the motor on the overrun. Having satisfied yourself on that you can set the tickover to suit then just enjoy riding the thing. 1 Quote Link to comment Share on other sites More sharing options...
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