Just got the CT3 through an MOT, so can do some road testing.

Couple of things.....I believe I have put it back to standard gearing (45 teeth rear: 16 teeth front), but at 6000 revs in top gear the speedo reads 40 mph. 5000 revs is about 30 mph.

Is that normal?

Also, it has just had a rebore, so I don't want to push it too hard, but it really struggles to go above 5000 rpm.

I had introduced an air filter, but it is the same with or without.

Checked the timing, and its as close as I can get it.

Any suggestions from all you experts out there?

Should the sprockets be 15/45? Top speed when new was around 70MPH.

Should the sprockets be 15/45? Top speed when new was around 70MPH.

But at what revs?

14 hp at 6,350 rpm.

70 seems a bit optimistic but i would have thought you could push her to 60 without too much bother

But what are the revs for a certain speed in top gear?

But what are the revs for a certain speed in top gear?

F*ck me, do don't want much, do you? You can't even be ar5ed to say please or thanks!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

It you have some information on the bike - including the gear ratios that are found in most manuals;

Click the linky for an online basic calculator LINKY

or

Click this linky to get one in Excel that will show you graphs of every speed by gear by revs LINKY

You're welcome

Click the linky for an online basic calculator LINKY

good link, thanks

Bit of caution here. I have a 78 DT175 just out of rebore, and it will not make 70s speeds. After much fidgeting, re-jetting and leaving out filters and such, I WAS able to get it to seize up. I believe today's petrol makeup is partially accountable, and in the estados un-unidos THE ETHANOL MANDATE is causing even more problems running vintage machines.

Luckily my DT just had a heat seizure, started up and ran fine after cooling a bit. It's caused by a too-lean mixture, but one of my country-mates burned a hole in his piston because of it. I had just attempted to push the DT to 70s-era speeds and you could really feel the heat. I have since gone to bigger jets and make sure to leave the air filter installed, as Yamaha cuations leaving it out WILL cause a lean mixture.

All this I gleaned from this forum. These guys lurking in here should get paid.

I just posted this comment in another thread about gearing mods.

"If you know how to really tune the bike and make adjustments to fuel, timing, air flow, exhaust, jets, etc. to compensate for the possible strain your initial change may make on the bike - go wild. Otherwise, go standard. "

Inspired by the wisdom of DirtyDT.