PPKJeff Posted June 13, 2015 Share Posted June 13, 2015 Hey everyone, Just bought a new to me 1980 Yamaha DT175. The bike is in mint condition and only has 600 original miles on it. The tac and speedo are in miles not sure if this is originally an American bike or if they all came that way, I live in Canada. Anyway, it runs really well and I have already taken it deep into the mountains, put about 50 miles on it and have no worries about the reliability of this thing. I am having an issue with the top speed. Guys on the internet are saying it should run at 120kph and mine tops out at around 50mph, roughly 80kph? It pulls pretty hard and idles well, but always struggles to get past 7000RPM. It will rev up 10,000rpm in neutral no problem however. I weigh about 200lbs and am a little big for the bike but I doubt that is the issue. Any suggestions? I have tried much yet. Will have a look at the air filter on it first I think. Thanks in advance. Jeff Link to comment Share on other sites More sharing options...
blackhat250 Posted June 13, 2015 Share Posted June 13, 2015 Yeh , jeff " try dropping the front sprocket 1 tooth, it will pull the higher gears to red line, Link to comment Share on other sites More sharing options...
Moderator Cynic Posted June 13, 2015 Moderator Share Posted June 13, 2015 Yep, 50ish is about right, like blackhat said. Upping the gearing takes you up to about 60 ringing its neck. The Australian (India, eastern Europe etc) bikes that came later had more modern top speed. Aussies were getting them up to early 2000's, they get better carburation and torque induction, prob more advanced porting too Link to comment Share on other sites More sharing options...
PPKJeff Posted June 13, 2015 Author Share Posted June 13, 2015 Air filter is good, pulled pipe off and removed baffle, that looks good as well. Was just about to remove carb and check reeds and I noticed that the rear sprocket is a 49 tooth. I believe the stock is a 45 i read somewhere? This could certainly be my issue. I think the not revving to to the redline is pretty normal on these bikes. Link to comment Share on other sites More sharing options...
PPKJeff Posted June 13, 2015 Author Share Posted June 13, 2015 OK will have a look at how many teeth the front sprocket has and order a smaller one, that could help too. I have lots of great trails 5 mins from my door, just don't want to be a nuisance on the highway getting to the trails! Link to comment Share on other sites More sharing options...
PPKJeff Posted June 13, 2015 Author Share Posted June 13, 2015 We had a DT200 up until 1996 here in Canada. I know a guy who has one back in Ontario where I grew up, not very common though, hope find one one day! Link to comment Share on other sites More sharing options...
Moderator Cynic Posted June 14, 2015 Moderator Share Posted June 14, 2015 NO!, you need a smaller rear, bigger front sprocket for higher speed. That will be at the expense of acceleration though. Its a ratio, standard gearing is 16/49 with 118 links. You wont get a bigger sprocket on and you need to make big changes to the rear to have an effect. Not forgetting there is a ratio between the sprocket and the rear wheel its mounted on. A smaller rear sprocket will need more effort to make the wheel turn. 16/49 or 49divided by 16 gives 3.062 for stock ratio. 13/40 gives 3.07 so close to stock, leaving you 2 teeth on the front to adjust but remember the smaller sprockets may affect the chain run. You already have a 45 rear so you could already be at 2.812 with a 16 front, that's a 10% increate already. Not sure there is the horse power for more. But that should give high 50's at 7000rpm. Personally I don't like using max rpm on these old girls, it kills them pretty readily, in top I stay at 6500 to 7000 rpm. (May hit 9 on the way up though, ) Link to comment Share on other sites More sharing options...
PPKJeff Posted June 14, 2015 Author Share Posted June 14, 2015 Sorry, my bike DOES have the stock 49 tooth on the rear. I was thinking of putting a 53 or 54 tooth (whichever I can find) on the rear or a 15 tooth on the front because as it is now, 6 gear is useless on the road. I actually started losing speed when I shifted up to 6 because there was no power there to keep it climbing so I ended up dropping it back down to 5th just to hold it at 50mph. I understand the concept of sacrificing acceleration for top speed when raising the gearing, but this thing just seems like it was poorly geared from the factory, for this type of riding. Link to comment Share on other sites More sharing options...
Moderator Cynic Posted June 14, 2015 Moderator Share Posted June 14, 2015 Sounds like you might have other issues then. Just to check, your not 25 stone or something similar, or going up a respectable grade? I say this as im 13stone well nearer 13 than 14, my DT will rev to the limiter in top, screams its knackers off if I let it to be honest. I will admit that more go would be nice. I think its why I like my TDR250 as that really does feel like a sorted DT with a skip load of extra go. Link to comment Share on other sites More sharing options...
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