More Dyno time!

[M.V.]

Another Dyno run on the weekend & here's the result:
I have to say, I'm pretty pleased with myself

Dyno run 2.jpg

My first run of a couple of months ago is the red one, latest one is the blue one, picked up 5 hp with jetting changes.

First run was 45 pilot jet, needle in the middle position & 142.5 main jet. After that, I dropped the needle down one & it felt a lot better in the midrange, two positions was too lean.

For this run I had 45 pilot jet, needle lowered one position & 132.5 main jet, dyno operators advice was to raise the needle two positions, which I did when I got home & that seems to have evened out the couple of dips you can see, one was really annoying at about 4K rpm.

$40 well spent!

I know I should be happy with 75, the bike's only lost 3HP (or 5, depending on who you talk to) in 16 odd years, but I can't help thinking about how to get more... I reckon cams, a hone, new rings & maybe swap the head to the one from my old engine (lap the valves & clean up the inlets first), it's only got 20K on it... Still, 75hp is not bad for an engine of unknown provenance from the wreckers.

Pretty happy for now!

[powerfish_2000]

MV,
very nice. Sounds so simple. I've had a factory pro kit fitted recently, would really be interested in the figures on the dyno to get the most out of it. Might have to venture off to Dynobike myself.

[Quan-Time]

nah, thats great..
You will find that when the bikes are measured from the factory, they are measured at sea-level in nice dry rooms. So the air is as dense as possible. So if you are higher up in wet air, you can loose quite a bit of power.

If you want to check your shims and cam timing, thats probably your best bet. If you pull the head off, clean everything WELL, and lap the valves in.. You can gain 3 - 5hp in that alone.

[M.V.]

Sounds like a plan Quan-Time, just need some spare time to do it in now...

I am noticing a couple of flat spots around 4K & 5K rpm, but only on really slow throttle openings... Seems to hesitate a touch & then pick back up, so I think I might have gone slightly too lean.

I'll drop in a 135 main jet on the weekend & see how that goes.

[trixi]

Before you pull the heads off your bike to grind the valves etc . Do a compression test. Sure checking the clearance is always a good idea. But if your compression is in spec don't expect any miracles from doing a "home valve grinding" job.If your bike had any real maintenance issues it would not respond to carburetor tuning in a predictable or useful way.
Power figures always need to be taken with a pinch of salt. There are different ways of measuring it. Different types of machine to do it on. Many variables come into play. Air density/ humidity probably being the most relevant. This is affected by temperature and height above sea level amongst other things.
If you always go back to the same dyno guy on the same dyno you will get a good set of comparison readings. Especially if he can figure in compensation for temperature /humidity variables. But trying to 2nd guess Japanese power figures is a difficult science. You can be sure that they always use very favorable circumstances to arrive at the numbers they get.

[M.V.]

These figs are from the same dyno, different days, all the air temp/density etc readings are on there.

Mainly want to swap heads because there is some cam journal wear & this engine has unknown kms, my old one only had 18K on it when the big end went...

Might as well do the rings as well though, see if I can't use a bit less oil!

[trixi]

Sure nuff, Didn't realize you had other motives for tearing down your motor. Sounds like a plan! Never had mine dynoed . It's standard apart from Full Remus Stainless/ Alloy exhaust. Uses no Oil but has a bad 2nd gear glitch. Am i alone in thinking that this gearbox is not one of Yamaha's better attempts?

[Killerwhale]

Sure nuff, Didn't realize you had other motives for tearing down your motor. Sounds like a plan! Never had mine dynoed . It's standard apart from Full Remus Stainless/ Alloy exhaust. Uses no Oil but has a bad 2nd gear glitch. Am i alone in thinking that this gearbox is not one of Yamaha's better attempts?

If you search forum you will find a lot has a dodgy 3rd, much due to running that gear a lot in those winding roads....