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Post subject: I'm missing 30kmh from my top speed
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1982RD350LC  Regular Racer Joined: 31 May 2008 Total posts: 354 Location: Vancouver, Canada |
I have a 1982 RD 350 LC and it should ring out to 176km/h (110mph) according to stock specs on this site. But I only get 145km/h (90mph). Here's what I have and I hope somebody can spot the problem.
At the back I have an aftermarket exhaust, so it should help me go at least a little beyond stock shouldn't it. The gearing is 39 on the back and I threw in a 17 tooth gear in the front (1 more than stock) to help the top speed. New chain (R type oil ring).
http://i8.photobucket.com/albums/a3/ron629/2008June7002.jpg
The exhaust is missing that gasket, is that a big deal ?
http://i8.photobucket.com/albums/a3/ron629/2008June7001.jpg
The cylinders have just had their 4th overbore and a stock set of banshee pistons have been dropped in. I'm thinking this is bad, but the compression is 110psi a side. And I've just re-jetted to 230 in the carbs. The oil mixing system is not plugged in, but the oil injection connectors are tied together with the black tubing. I'm premixing 40:1 synthetic oil and 89octane gas. The air box is stock. Yea, I know it's ugly, but I like it that way, but it must be able to move to make up for it's looks. 
http://i8.photobucket.com/albums/a3/ron629/2008June7004.jpg
ron.
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Posted: Sat Jun 07, 2008 7:42 pm
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kaptainkaos Daily Burner Joined: 14 Aug 2007 Total posts: 207 Location: Out o' there an' over 'ere |
If you change your gearing to 17/38 which is standard in the UK, you should hit it.
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Posted: Sat Jun 07, 2008 8:04 pm
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Billy One-handed Stoppie! Joined: 12 Oct 2007 Total posts: 2216 Location: Sweden arise! |
That's strange. I have the exact same problem! I can only go up to 145km/h, not one km/h more, it's like it's restricted to that speed! 
But i think it's the clutch slipping = not enough power to the rear wheel to go faster. I can't understand why it won't go faster other then a slipping clutch..
My bike have an arm-ripping acceleration, but it loses power when going above 130km/h or so.
It might also be bad aerodynamics, and i'm not laying with my head on the clocks either, i think it feels very unsafe so i'm kind of half-laying on it. 
Edit: Here's the thread i started some time ago. http://www.yamaha-rd.com/forum/viewtopic.php?t=51080&start=0
I had bad setup carbs (too rich) and the acceleration was not much to hang in the christmas tree. But it still went 145km/h, and after i dropped the needles one notch, the acceleration became much harder and it easily went up on the 2nd gear, but STILL the same top speed as when it almost couldn't wheelie on 1st gear! So, i think this have nothing to do with the power, i think it's the clutch that can't transfer the power to the wheel.
In my case, i think it's because of the oil in the gearbox. It is oil for cars, and i found out that they often have stuff in it that makes it less friction, and this causes the clutch to slip. 
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Posted: Sat Jun 07, 2008 8:05 pm
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Post subject: poor topend performance
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johnlc Powerband Master Location: John O'Groats |
http://www.yamaha-rd.com/forum/viewtopic.php?t=51975&highlight=
Says it all really 
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Posted: Sat Jun 07, 2008 8:29 pm
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| p51bombay Joined: 23 Jan 2004 Total posts: 9910 |
With that 17T sprocket its quite possible you may not get there. Will it pull redline in 6th?
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Posted: Sat Jun 07, 2008 9:18 pm
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Vindaloobeast Rear-wheel Steering! Joined: 25 Aug 2005 Total posts: 2623 Location: Gloucester |
Gearing yes, tyres maybe but defo 110% needle valves. If the bike stonewalls at 7k ish it slugging too much fuel and any combination of main jet and or needles aint gonna fix it.
Beast.
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Posted: Sat Jun 07, 2008 9:32 pm
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Post subject: Re: I'm missing 30kmh from my top speed
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| jmw |
| 1982RD350LC wrote: |
I have a 1982 RD 350 LC and it should ring out to 176km/h (110mph) according to stock specs on this site. But I only get 145km/h (90mph). Here's what I have and I hope somebody can spot the problem.
At the back I have an aftermarket exhaust, so it should help me go at least a little beyond stock shouldn't it. The gearing is 39 on the back and I threw in a 17 tooth gear in the front (1 more than stock) to help the top speed. New chain (R type oil ring).
http://i8.photobucket.com/albums/a3/ron629/2008June7002.jpg
The exhaust is missing that gasket, is that a big deal ?
http://i8.photobucket.com/albums/a3/ron629/2008June7001.jpg
The cylinders have just had their 4th overbore and a stock set of banshee pistons have been dropped in. I'm thinking this is bad, but the compression is 110psi a side. And I've just re-jetted to 230 in the carbs. The oil mixing system is not plugged in, but the oil injection connectors are tied together with the black tubing. I'm premixing 40:1 synthetic oil and 89octane gas. The air box is stock. Yea, I know it's ugly, but I like it that way, but it must be able to move to make up for it's looks.
http://i8.photobucket.com/albums/a3/ron629/2008June7004.jpg
ron. |
First thing first,
you've overgeard it so return to the original stock gearing and you will find the bike can now pull better and it will go slightly faster at the top end. There is an arguement for dropping it further allowing for more thrust and an even greater top speed but I can't really say much more.
Ditch the R ring, that's eating up anything from 2 - 5 hp, similar to an O ring. The reduction in maintenance VS drag is in my opinion, not worth it and, your tiny RD engine just can't cut the mustard with this sort of chain.
Personally I'd return to the autolube and set it up again from stock settings, although probably nothing, the change in incomming charge and already mixed oil is a pain in th behind so stick with how it's meant to be for reliability and simplicity.
The 4th overbore gives at a guess about 357cc displacement, you might note that the shape of the exhaust port drops down steeply the further out you go so lifting it by 0.5mm and tapering it would help a great deal. It's the same for the transfer ports, although in your circs you are probably looking at 0.3mm at the most, it reduced the top end gusto of the motor ever so slightly, that with the over gearing is probably the cause for the lack of speed.
You're a little less than perfect on compression but well within the bounds of a healthy motor.
Finally, FFS, 89 octane is like cat piss on a bonfire.
Do the bike a big fat favour - use 97 or 99 octane, ideally 101 full lead - really helps with reliability and survivability if you like giving the motor severe grief. You are giving it decent synth oil so do the same with the fuel.
Oh... Last thing, using a light gear oil helps reduce windage loss in a similar way to using a normal chain.
Go for it....
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Posted: Sat Jun 07, 2008 10:22 pm
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1982RD350LCRegular Racer Joined: 31 May 2008 Total posts: 354 Location: Vancouver, Canada |
Thanks guys for all of the replies, I will fill you in with what finally works.
ron
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Posted: Sun Jun 08, 2008 2:56 am
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1982RD350LCRegular Racer Joined: 31 May 2008 Total posts: 354 Location: Vancouver, Canada |
Okay, I said that I'd let you know what I found out so the first thing is that I checked my speedometer up against my GPSr and found that my speedometer reads 10 km/h too slow at 100km/h. I also decided to toss the chain that steels 2-5hp, but just to cut some of the friction losses in it I sprayed it down with WD-40 to loosen it up and then through on some really light oil. I am reading 172 on my GPSr(Global Positioning Satalite reciever) in 5th gear with still more to give but not enough road to do it in. I will eventually take your advice on sprocketing the bike back down to stock.
Thanks for all your help. ron
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Posted: Sun Jun 08, 2008 10:49 pm
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Bare All-gear Wheelie! Joined: 28 Jan 2006 Total posts: 1916 Location: Vancouver Canada |
110 psi (assuming that's an accurate comp reading) ..Ain't great .. on brand New boresw at 4th over .. more indicative of a bore/ring set half thru it's service life.. Maybe running for max speed attempts on brand new bores has affected the sealing.
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Posted: Mon Jun 09, 2008 3:06 am
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| p51bombay Joined: 23 Jan 2004 Total posts: 9910 |
or the rings ain't seated yet. Out of curiosity, in this day and age of population explosion and the speed with which they now jump to "street racing"................where does one test these things without landing in the sin bin?
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Posted: Mon Jun 09, 2008 4:14 am
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KX3 Mmm, Fully Synthetic! Joined: 02 Oct 2006 Total posts: 1217 Location: Québec |
| p51bombay wrote: |
| or the rings ain't seated yet. Out of curiosity, in this day and age of population explosion and the speed with which they now jump to "street racing"................where does one test these things without landing in the sin bin? |
a new law was adopted here on april 1st (no fool here).
Excess speeding fees doubled and many more troubles....
still, lot of room to play 
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Posted: Mon Jun 09, 2008 9:05 am
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