Carb tuning HELP
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Bought my DTR few month back was lacking power in first and second gear, looked at the carb and it had seen better days so I decided to clean it. Put it back together and it ran the same. It came with a dep pipe so after some research decided to rebuild it with the suggested parts for the dep pipe. Put a 5DP39 needle in, 22.5 pilot jet and 260 main. Started with needle clip on the second from the top and it started well and idled okay but bogs and dies as soon as you put revs on. Since moved the clip to position 3 and 4 and still the same although slightly better. Runs and doesn’t bog with choke on. Another thing is the air screw is making no difference to idle no matter how far out I turn it even though I’ve just replaced that as well. Any help is appreciated TIA
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Hi there,
I would leave the carb settings alone. DEP themselves don't even recommend changing the settings for their setup.
There can be several factors for poor running, a lot of this is well documented on this forum.
Probably the key one here that I am sure @hotshot-iii would say is the emulsion tube in the carb. Often gets overlooked and clogged.
Cleaning it verbatim won't help, it'll need pressing out and properly cleaning, before reassembly.
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The most easiest carb to get ahold of is probably a
Dellorto PHBH 28mm. Found on restricted RS's, they're widely used and reknowned for being easy to jet.I run a
Dellorto VHSA 32mmcarb on my DTR.The reason I've gone with this carb, although rarer and harder to find, is that they were factory fitted to the
TZR 125 RR Belgardawhich effectively ran aDT125REengine. Which just gave me nice confidence that it was a solid choice to make.Another great carb, albeit harder to tune, is the
VHST 28mm.So keeping the size the same as the Mikuni, but this time Flat Slide instead of Round Slide like the
PHBH.Remember, bigger is not always better. Going from 28->32 doesn't necessarily mean more performance. Fair enough if you're giving the engine a tune up, but if your plan is to keep it relatively stock, then sticking to 28mm isn't a bad idea.
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@DeeTeeArr Definitely 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 (which is how the air atomises the fuel) until it just starts fourstroking and won't rev out one day as this controls the mid-throttle fuelling. Just chucking it in an ultrasonic cleaner usually isn’t enough; you have to actually remove everything from the carb body, physically make sure all the jets and air passages are clear, then reassemble. Make sure the air supply to the emulsion tube 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.
I'd also echo what @calum said; it shouldn't really be necessary to re-jet just for a DEP exhaust and the OEM TM28SS is the best option for the DTR if you can save it. It's well worth soaking the carb body and all the jets in alloy wheel cleaner for a day or so as this always brings carbs up like new even when people restore bikes twice the age of the DTR.
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