Yamaha TRX850 Enthusiasts Forum

I spent a few hours on a dyna pro dyno today at Projex in Cradley Heath nice friendly guy. My bike was runninng very very rich. We went down from 142.5 to 122.5 and we ended up with this curve. The engine has 68,000km on it and uses no oil to speak of. Is this normal, bad or good?

pretty much normal for a standard TRX especially on a hot day when you can lose a few BHP.

I reckon it's way too easy to get hung up on BHP. My old engineering instructor who was a vintage bike nut - regularly racing Scotts, would allways say when we were pestering him for tuning advice - 'tune your self first'

not that we ever liked the advice, but I did see this old boy beat a GS1000 on an MZ250

Tuned MZ `smokers` are pretty rapid old things, seen many of them whip much bigger machinery on the right circuits.

http://www.bmzrc.org.uk/

look at some of these lap times:

http://www.bmzrc.org.uk/Racing/LapRecor ... fault.aspx

I`m biased, I like MZ`s.

Pretty much as you'd expect from a standard motor with a set of cans

Nice smooooooooooooth curves too

trixynut wrote:Pretty much as you'd expect from a standard motor with a set of cans

Nice smooooooooooooth curves too

Thats good news indeed I knew thw motor was torquey but I was shocked to see 50ft/lbs from 3000rpm up to 8000rpm. How much would big bore headers add to this? What size headers are recommemnded for a std engine?

trixynut wrote:Pretty much as you'd expect from a standard motor with a set of cans

Nice smooooooooooooth curves too

Must agree with Mr. Nut here

Big bore.... ask KillerWhale e.g., dunno how much it would add, but it sure will ad a bit more to it.


Greetz
Gerben

Hi Kenny, that chart looks very good!

Are those the jet sizes you settled on for best performance, or did smaller jets go too lean?

I had a similar result from my first dyno on a std motor(76000km) with just a set of staintune cans fitted. Who ever set it up had rejetted and it was running way too rich. Once dynoed I gained almost 6hp bringing me back up over 76hp.. It certainly gives you a good starting or reference point once set..

What we found was that the main jets didnt have a very large effect on the AFR if we only went down one or 2 sizes. 122.5 was on the lean side so we settles on 132.5 for now. Im planning some airbox mods so I may have to go back up to std 142.5 or higher. The biggest difference now is the bike is so much smoother to ride now and better on fuel I hope.