kenDAWG Posted January 3, 2013 Share Posted January 3, 2013 after doing a topend rebuld on my little dt125r i fitted some carbon reeds and refitted the snorkel while i was at it took her out for a run and she wouldnt go past the 4,000rpm sounded like there wasnt enough air getting to her so i pulled the snorkel back off and she went fine until 6-7k rpm same sound (she has been well run in now) i have never seen the point in all these holes drilled in air boxes but i couldnt think of any thing else so i drilled out 4 holes the size of 1 pence coins now she runs up to the redline just sounds soooo bloody loud!! any ideas why with a change of topend she would need more air? and will this be ok? cheers ken Link to comment Share on other sites More sharing options...
Moderator Cynic Posted January 3, 2013 Moderator Share Posted January 3, 2013 Easy do the math. 4000rpm = 4000 x 125cc gives 500000 cc of air. Thats 500 litres of air a minute. 10000rpm = 10000 x 125cc gives 1.25 million cc of air or 1250 litres of air a minute. You can get clever with velocities for given diameters and such but it does make you think. Becomes obvious why the power difference between 2 and 4 strokes too. You can halve those figures for a 125 single. As to the different top end. Think on this. If the bore is worn on a 4 stroke she burns oil and loses compression. On a 2 stroke there will be less draw into the cases as charge from above the piston will be drawn down reducing the pull through the carb. Just imagine losing even 5 per cent of the volumes from earlier and the effect on mixture and performance. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted January 3, 2013 Moderator Share Posted January 3, 2013 Confused why you drilled the airbox but didnt try washing the filter first? Link to comment Share on other sites More sharing options...
kenDAWG Posted January 3, 2013 Author Share Posted January 3, 2013 no no the filter was brand new pal, oiled it up lightly also... im guessing like cynic says the topend was worn thefore not drawing as much air as a new topend! just means the bike must have been setup with the worn topend as it was done in a garage before i bought it! not to worry she goes well result ken Link to comment Share on other sites More sharing options...
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