Hi guys,

Was hoping for some assistance. I just got my bike dynoed. It's running well on WOT above about 8k rpm but below that the mixture looks lean on WOT. Is this normal? It's an MC28 with Tyga pipes / airbox lid / 030 card / wiresplice.

Thanks
Jim

Sorry forgot the chart

More importantly, how does it ride?

Don't draw any conclusions from a single dyno plot. Unless the person running the dyno made fuel mixture measurements on both pipes at multiple throttle/RPM levels you cannot draw conclusions from a single plot.

Rides well at WOT above 8000rpm and hesitates at 7k as per the graph. On the needle I think it's way rich. Runs poorly. Hesitates all the time. I guess the question I have is what exactly do the HRC parts do? I've bought a set of needles so I'll try the leaner set. Do the HRC X and Y valves allow more air or less than the stock parts?

We've almost always run either without a lid, an HRC airbox, or pod filters, and the MC28 with the full HRC carb kit has always carbureted very well.

What needle/clip are you running?
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Andy.
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It has stock needles and stock X / Y joints Andy. I've got HRC needles and X / Y joint on the way in the mail.

I have an mc28 with the same items you listed above. It was way too rich. I got my hands on both hrc and jha needles plus the air jets. I've since sorted things out and it works perfect from 3k to 12.5k with not hesitation.

You can read what I've done in the members section. Keep in mind I'm on the coast in a highly humid area. So what works here may not work for you. I'm running really lean on the lower ends.


http://www.nsr250.net/forums/viewtopic.php?t=13124&highlight=

Thanks mate. That was a good read. As it happens 155 main jets are what I settled on as well and the top end is good. The conditions here in Brisbane are probably similar to your neck of the woods so it's not surprising. I'm seeing all the same things you saw with stock carbie parts. On the needle it a seems way rich so I plan to try the leaner HRC needles. What interests me is the mixture at 7k at WOT. The bike did multiple dyno runs. The plot I attached is WOT and it is way lean at 7k. I'm thinking these HRC X/Y joints must make quite a bit of difference and it's likely they allow less air into the engine than the stock X/Y joints?

The hrc air jets have much smaller holes, so they would tend to make the bike richer, but the hrc needles are much leaner so they seem to work well together.

I am running the jha needle which is about midway between stock and hrc on the taper.

Well I'm pleased to say that with the HRC X/Y joints and C needles the bike is running pretty well. Especially in the midrange and WOT. If I'm slowing down slowly, after the engine has been revved with a closed throttle, the engine seems to surge a little until it settles into an idle. EAnyone have any suggestions. I was thinking it may need richer pilot jets?

I'd be inclined to try the richer B needles.
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Andy.
NSR-WORLD.COM

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Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

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