Tom125mx Posted August 29, 2013 Share Posted August 29, 2013 hi all, I have to admit, that I was a little bit disappointed about the topspeed of my 78 dt125mx. --> not more than 90km/h (55mph) .. maybe the speedometer in inaccurate... my kawasaki ke 125 (1978) appears more powerful and is faster as well.. ... how fast should it go? ... any obviouse modifications to improve power? ... does the 175 barrel/piston/barrelhead fit? if yes: what else need to be changed in order to have the full dt175 power? thx in advance tom Link to comment Share on other sites More sharing options...
Moderator Airhead Posted August 29, 2013 Moderator Share Posted August 29, 2013 morning Tom, first check the exhaust header, you may find a sleeve in there that you can take the dremel cutting disc to. Yes the 175 barrel and head will fit straight on. Also some of the early bikes had a 22mm carb but it would go better with the 24mm version fitted Link to comment Share on other sites More sharing options...
Tom125mx Posted August 29, 2013 Author Share Posted August 29, 2013 oh. fast response thx!!! is the barrelhead of the 175 identical with the 125? the 125-175 conversion seem to be the most obvious change cheers tom Link to comment Share on other sites More sharing options...
Moderator Airhead Posted August 29, 2013 Moderator Share Posted August 29, 2013 yes if you can find them a 175 convert is easy Link to comment Share on other sites More sharing options...
Tom125mx Posted August 29, 2013 Author Share Posted August 29, 2013 is 90km/h resp 55mph ok for the dt125mx? shouldn't it be a bit more???? tom Link to comment Share on other sites More sharing options...
Ttaskmaster Posted August 29, 2013 Share Posted August 29, 2013 Topspeed as indicator for full horsepower. My kawasaki ke 125 (1978) appears more powerful and is faster as well. Top horsepower for any given bike kicks in at a certain number of revs, depending on your bike model. Yours reaches its maximum of 14HP at 6500rpm. Your statistical top speed is given as 68mph (110kph), meaning you'd have to rev it pretty hard to get much faster than you already are. The '78 Kawasaki, by comparison, is rated at only 10HP at 6300rpm, topping out at 58mph (94kph). Bear in mind though that as these things get used, they do drop in performance. Also, it depends how you rev it and govern the throttle. If you're going along and whack the throttle open, you will be stressing the engine too much and it will actually lag in performance. If you gradually increase the throttle, building your speed up you'll find you eventually get a higher top speed... eventually. A trick I used on my 125 Dragstar - Gear 1 was for moving off. Gears 2-3 were for playing in traffic. Gear 4 was for high speed moves (50-65mph, overtaking, etc) and getting up toward top speed. Once at around 65mph, I'd then shift to gear 5 and just cruise along, but slowly increase throttle over about 30 seconds to a minute. I'd then end up with a top speed of about 74mph. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted August 29, 2013 Moderator Share Posted August 29, 2013 my 175 will do 70 if I cane it but it's more comfortable at 65...I wont do it for long stretches though it seems a bit risky and I dont trust modern ethanol fuels!...I have one more tooth on the front sprocket to raise the gearing slightly Link to comment Share on other sites More sharing options...
Moderator Cynic Posted August 29, 2013 Moderator Share Posted August 29, 2013 Same here. She will do 70 but 7krpm is my normal max. I think the 2 compare on top speed. The extra cc counts for plugging the muddy lanes not tarmac tearing. Link to comment Share on other sites More sharing options...
blackhat250 Posted August 29, 2013 Share Posted August 29, 2013 One other factor " How heavy are you ,,, 60mph will be tops, and remember Twinshock barrels are 4 stud . and MX 5stud... Link to comment Share on other sites More sharing options...
Moderator Airhead Posted August 29, 2013 Moderator Share Posted August 29, 2013 MX 125 = 4 Stud John Link to comment Share on other sites More sharing options...
Tommy xs Posted August 31, 2013 Share Posted August 31, 2013 One other factor " How heavy are you ,,, 60mph will be tops, and remember Twinshock barrels are 4 stud . and MX 5stud... In other words if your a fat bastard that's why your bike is slow 1 Link to comment Share on other sites More sharing options...
Tom125mx Posted September 1, 2013 Author Share Posted September 1, 2013 75kg... Not that fat ;-) And it's the topspeed of the dt that is less than the 10hp Kawa ke 125. Adjusted the ignition Timing yesterday. Plus I took away the airfilter. This added another 5 km/h in topspeed Still far away from where i'd like to be ;-) More Tipps? The realistic tip that bring's the 100km/h+ will get a Free Pint!!! T. Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 1, 2013 Moderator Share Posted September 1, 2013 some of the early 125cc bikes had a 22mm carb venturi and the later ones a 24mm vanturi which is better, what is the number stamped into your carb Tom ? Also mr Yamaha had a thing about fitting smaller diameter inserts into the exhaust header pipe, what is the number stamped into your exhaust and have you checked the header, I suggested this earlier but you didnt respond ? It's not advisable to run without an air filter on a long term basis Link to comment Share on other sites More sharing options...
Tom125mx Posted September 1, 2013 Author Share Posted September 1, 2013 Stamp on the carburator is MIC 2A8 00 The numbers on the Exhaustor pipe is 2A8 14610 Does that tell anything to you? Cheers Tom Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 1, 2013 Moderator Share Posted September 1, 2013 Not sure about the carb, you will have to measure it using some inside calipers but the exhaust has a restrictor tube, I know this because I just bought one myself, I use a dremel speedclick arbor and the smallest cutting disc they supply for it...even then you may have to wear it down a bit in order to gain access looks like the pint is mine then This is the sort of thing you'll find, you can see the end of the tube in this pic although the 2A8 has a longer tube so you'll need a torch Link to comment Share on other sites More sharing options...
Tom125mx Posted September 2, 2013 Author Share Posted September 2, 2013 this Sounds promising!! Would the ( unrestricted) exhaust of a dt 175 fit? Any idea where to get an exhaust? .. I'like to keep the original one... Are there any Tuning Exhausts for that Model available on the market? Cheers T. 1 Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 2, 2013 Moderator Share Posted September 2, 2013 I've tried various exhausts aftermarket exhausts were made by several manufacturers over the years, of course being a 35 year old model they were mostly withdrawn from production personally I have found that the performance of the original pipe is hard to beat, I say remove the restrictor in yours Link to comment Share on other sites More sharing options...
Tom125mx Posted September 2, 2013 Author Share Posted September 2, 2013 ok. cool.. since I want to keep the original pipe unmodified; i'm looking for a second exhaust. any idea where to get a original part from? either used or new? AND: would the exhaust from the 175mx fit to the 125cc barrel? tom Link to comment Share on other sites More sharing options...
Moderator Cynic Posted September 2, 2013 Moderator Share Posted September 2, 2013 looking for a second exhaust. Best of. There are pattern ones by Big One but they are in the later front expansion chamber type. Pick a bodypart for an oe system in good nick. Link to comment Share on other sites More sharing options...
Tom125mx Posted September 2, 2013 Author Share Posted September 2, 2013 hi cynic, maybe my english is not good enough, but I don't understand what that means: "Pick a bodypart for an oe system in good nick"?? can you help me out? tom Link to comment Share on other sites More sharing options...
Recommended Posts