Post derestriction jetting change on a 1998 Dtr de03
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I just bought a 98 Dtr that was already derestricted with open powervalve etc. it sometimes likes to bog down at any throttle when cold and id like to know if anyone knows what the issue could be. My thought process is that its either a clogged or too small main jet and i just wanted to confirm my theory with people who have experience with this exact motorcycle. Thanks in advance and cheers!
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I just bought a 98 Dtr that was already derestricted with open powervalve etc. it sometimes likes to bog down at any throttle when cold and id like to know if anyone knows what the issue could be. My thought process is that its either a clogged or too small main jet and i just wanted to confirm my theory with people who have experience with this exact motorcycle. Thanks in advance and cheers!
@Dougster Most two-strokes are a bit boggy when cold and this is also when most engine damage occurs so warm it up carefully keeping the revs low for the first couple of miles.
If you mean the powervalve is pinned open, that is probably the source of your problem. Pinning the powervalve makes the DTR very difficult to ride as it robs it of low-end power without gaining any top-end.
As far as I'm aware the DE03 model ran the 5-wire servo; these are easier to find and cheaper than earlier 3-wire versions so if you don't have one on the bike ATM it might be easier than you think to sort this by having a look around eBay, Facebook DTR pages etc.
If the jets in the carb at the moment are what your manual says they should be, don't stray from this setup until you've got a servo fitted and working, it's a massive improvement to the DTR riding/ownership experience (particularly off-road) as you don't have to thrash the bike everywhere to make it do anything.
Look around eBay for a pulley/housing as well, these are the same as on most other YPVS-equipped Yamahas including the RD350YPVS, TZR/TDR250 and TZR125 (the "29L" on the inside of the pulley housing is the RD350YPVS model designation). Buy genuine powervalve cables from Fowlers (Yambits pattern ones are the wrong length) or make your own here, it's no more complicated than replacing gear cables on a mountain bike: https://dt125r.co.uk/post/28693
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As @HOTSHOT-III has stated, if you're not running a powervalve then this will hinder performance. If your model has restrictions on it still, then this may have been why the powervalve was pinned. Certain CDIs close the powervalve after certain RPMs, limiting the top end potential.
All of which can be worked around these days with no real dramas.
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@HOTSHOT-III i did a testride today and it likes to backfire in the mid rpm range, could that be caused by the pinned powervalve aswell?
@Dougster Even with a pinned powervalve the bike should pull smoothly right through the rev range, just with very little power until it comes on the pipe at 6-7000rpm.Actual backfiring could mean a CDI unit issue but this is quite rare; a lot of midrange running problems on the DTR are caused by a blocked emulsion tube in the carb.
If you've just bought the bike I'd do a full carb clean including the emulsion tube (the brass tube the main jet screws into). A lot of people (including bike shops) miss this and don't realise it comes out because you have to screw the main jet back in without the brass washer and tap it gently to remove it from the carb body. The space between this and the carb body gets blocked with moisture, dirt etc and blocks more and more holes in the tube until it just starts fourstroking and won't rev out one day as this controls the mid-throttle fuelling. Make sure the air supply to this is clear as well, it's the small brass tube on the right of the carb body just in front of the carb-to-airbox rubber. You should be able to blow through it, but only just.
You can also make future carb cleaning easier by bypassing the carb with the carb warmer hoses which come from the cooling system. These are only really needed to stop carb icing in countries with really cold winters but they serve another purpose which is to make the cooling system self-bleeding when refilling, so you don't get air gaps at the top of the cylinder head and unlike a lot of two-strokes you don't need bleed bolts in various places on the cooling system. Whilst you're getting the carb off, you can retain this feature by running a single hose directly from the banjo on the cylinder head to the one on the thermostat housing so you don't have to mess with the cooling system next time. Don't forget to check the coolant level in the radiator after doing this
