@duxky229 Supermoto is an interesting concept but also quite a major change to the bike; if you're just getting started with DTRs it makes sense to get what you have as good as it can possibly be before you start modding. Avon TrailRiders in the recommended sizes on the stock wheels give plenty of grip on tarmac and are still blocky enough for light off-roading when it's bone dry. Replace inner tubes and rim tapes. Michelin Trackers and rim locks if you want to get serious on dirt.
Tips and tricks; copied and pasted as people ask the same questions over and over again on Facebook etc. so I typed them out in a Word document in the end. Hope some of these help:
High rpm misfire? HT lead
Possibly could be the HT lead as they break own on DTRs causing this exact problem. The actual coil is very good quality so it's well worth fitting a new lead; you can cut off the very top of the coil's outer case where the lead pushes in with a junior hacksaw, pull out the old lead and solder the new one to the coil output for a really good connection. Then re-waterproof using Shoe Goo and electrical tape. Looks messy but no-one can see it under the tank, and you should notice a performance increase as the leads deteriorate over time. Much better option than just buying a new pattern coil as these often have different specs to OEM which can cause other issues. Fit a new NGK cap while you're there, try to get the type that's moulded into a single piece of rubber.
I had a high-rpm misfire once, after trying everything else we replaced the HT lead in the manner described above which took around 1 hour on a summer's day so the engine was neither stone cold nor up to operating temperature when I took it for a test ride. It wheelied out of the driveway without me even trying, and I couldn't believe how much better the performance was at all engine speeds. Made a big impression on me as I was 17 at the time and I'd spent practically a weekend trying to fix the bike and getting nowhere.
Don’t gut stock pipe
Don’t gut the stock pipe. The DT125R/DT200R styling was based on the 1988 YZ250 and the expansion chamber is about the same physical size. Within that there was enough space for an appropriately-sized, functioning expansion chamber for a 125cc road/trail bike and enough noise suppression material for the bike to pass a noise test (whereas the YZ is for closed-course competition which is why it has a single-skin racing exhaust). If you chop it open with an angle grinder and rip all that stuff out, it will not only sound like a wasp in a tin can but also you’ll probably lose power as you no longer have an expansion chamber which matches the porting/carb/crankcase volume etc. By all means take the washer out of the header pipe but the stock pipe and silencer aren’t restrictive besides that; I’ve owned several full power French import DT125Rs which have all revved to 10k+ rpm with the stock pipe. In fact in one case I bolted on a DEP silencer and the bike immediately refused to rev higher than 9k; this was cured by refitting the stock silencer.
Rear caliper pattern seals leak
Buy a genuine piston/seal kit from Fowlers. I bought an eBay rear caliper rebuild kit once, cleaned the caliper completely including the seal grooves, put it together and bled it and there was a small dribble of brake fluid on the back of the pad on the piston side. Wiped it off and it came back several times, so I cleaned up the (old) genuine piston/seals and put them back in as I wanted to go for a ride that evening and it cured it, no issues for a couple of months whereupon I bought new genuine ones. Compared the seals, the eBay kit seals are slightly smaller in cross-section than genuine which is what causes them to leak.
HEL braided hoses make the best of the stock brakes and it's well worth reconditioning master cylinders as well; I always had good results with genuine front and Yambits rear.
Enduro/Greenlaning preparation
Run fork gaiters if you want acceptable fork seal life; Polisport ones are very good but you have to enlarge the vent holes at the bottom with a leather punch to stop them ballooning under full travel. If you weigh any more than 140lbs, XT600 fork springs and 500cc per leg 15W oil makes the bike jump a lot better (i.e it actually can jump without bottoming everywhere) and a YSS rear shock can be adjusted to match the fork setup (I had to run mine with +16mm preload over stock and rebound on position 29 out of 30). Chain; run 40-50mm free play or using all the rear travel will destroy the bearing behind the front sprocket. An O-ring chain takes an extra 0.5bhp to turn; when you're working with YZ85 power/XR600 weight you'll notice this so run a D.I.D 428HD and just keep degreasing and re-lubing it after every ride. Get a load of spare D.I.D split links the correct size/spec for like £1 each and just use a new one every time the chain has to be removed. Get a decent grease gun and re-lube all rear suspension bearings after every off-road ride/jet wash. Fit a grease nipple in the headstock and seal up the slot in the stem for the steering lock with heat shrink tube and cable ties. Get 3-4 Yambits air filter elements and devise a system for cleaning and re-oiling them so you can quickly fit a fresh one. Wash them in petrol (wear gloves) and use foam filter oil. Yamaha did a very poor job of gluing the carb-to-airbox rubber when the DTR was new and being downstream of the air filter, this will allow the motor to suck dirt. Seal this up using a petrol- and oil-resistant glue such as Seal-All (the airbox needs to come out to make a proper job of this so do it at the same time as replacing the shock). Likewise replace the 5mm air filter foam (eBay) on the back of the element holder where it slides into the airbox using more Seal-All. Run genuine throttle and clutch cables; these are pricey but good quality, and those £12 pattern throttle cables are responsible for a lot of DTR engine meltdowns (the OEM cable automatically synchronises the carb and oil pump on pre-’99 bikes). Keep the Autolube unless you want to waste time rejetting and run a good quality synthetic two-stroke oil (JASO FD is the Japanese industry standard for racing two-stroke oil so look out for this, doesn’t have to be expensive, I used to run Exol which is about £30 for 5 litres). Lube all cables after every jet wash; this more than anything delivers striking cobra responsiveness and a cable oiler costs £5 from Yambits. The stock pipe is fine but if you want an aftermarket one, run a Tecno (same as Athena but half the price) expansion chamber; this is a good mid-range pipe and makes the bike pull strongly from 5k rpm which is more useful off-road than screaming top-end. DEP silencer fits the Tecno well. Run a 100/80W P45T halogen bulb in the stock headlight; Yamaha cheaped out and fitted a 45/40W candle from new but the actual light is the same unit as 900cc+ Yamaha superbikes of the day and the DTR's AC lighting means high wattage bulbs won't flatten the battery. This lights up the trails like a rally car. Make your own powervalve cables from MTB gear cables so you can re-lube them in situ https://dt125r.co.uk/post/28693
Carb Warmer Hoses
As others have said it doesn’t make any difference which hose goes where, and they’re not really needed in a country like the UK with mild winters. However they also serve another purpose which is to make the cooling system self-bleeding when refilling as the one on the thermostat housing comes out above the actual thermostat, so all you have to do is fill the radiator slowly and you end up with no trapped air (this is why bikes like the 350LC and a lot of MX bikes have bleed bolts on the head and barrel etc.). So it’s useful to just run a single hose from one banjo straight to the other and bypass the carb; you still retain the self-bleeding cooling system but it’s a lot easier to get the carb off for cleaning, jetting and float height changes etc.
