Here is a dyno run of my absolutely crap and waste of time 300 - got to beat the others to making this statment Haha

MC21 flywheel, bored standard carbs, Tyga exhausts, etc.

It was running out of steam far too early, even for the useless MC28 that it is. Removing the airbox helped it to breath a little more. I might put the airobx back on though as it makes a little more power around 4,700 Clutch started to slip a bit, so we found some old valve springs off an XR500 or similar - was all that we had at hand.

The dip around 10,500 would be nice to smooth out as would the lack of over rev after 11,500. it should really keep on a bit more after that I would have thought. Perhaps some 300 specific pipes (Matt, Matt??) would perhaps help here. I have the PJ38 set awaiting in the wings for a later date..

Hey bro, what were the differences in setup between the two dyno runs shown on the graph?

Oh and what squish and fuel type are you running? Annnnd was this recorded on Ozzy's dyno?

I think we should formulate a plan to approach Wobbly about designing some custom expansion chambers, what do you think?

I was abit gutted to find this new, alleged '76 horsepower' engine i have here has had the front cylinder nip up at some point... Matt and Neal have explained to me how to remove the aluminium deposits from the bore and how to re-dress the plating so i think it'll be fine but still abit annoying ay?

Congrats on the 65 horses man - if you can suss how to pull that 10K flat spot out too it'll be ALLL GUUUD.
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After years of moaning about immigrants now i am one...

The bike is just way too rich, that's why it did better without the air box, get some jets and go back to the dyno....

Looks to be making healthy maximum power - it's just got a dead spot at 10,000 drops off early and it doesn't look very smooth!

Yeah, you're jetting is definitely out, too rich as Alazorq said. You can get jets off ebay, just be careful that you buy genuine Keihin, not 'Keihin style' jets.

You can get jets off ebay

- Dont support them, support Tyga !

Also check that your pv's are opening as they should with the pipes off, dont just look at the butterfly on the side but at the pv's themselves !

Alzazorq wrote:

You can get jets off ebay

- Dont support them, support Tyga !

I support TYGA, but are TYGA jets genuine Keihin?

Also check that your pv's are opening as they should with the pipes off, dont just look at the butterfly on the side but at the pv's themselves !

Agreed, the butterfly on the side really doesn't tell you much, and I think setting the marks up on the NSR150 barrels that you've got there is a little different than the 250, though I could be mistaken... However I set mine up via the marks on the butterfly and when I took the pipes off recently, I checked the adjustment, and it was WAAAY off. I adjusted them to HRC spec and I've now got a really fast machine! Though, I did do a LOT of other stuff to it at once as well!
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MC21 Honda NSR250. TYGA 300 conversion.


Last edited by anonymous.shyster on Mon Aug 01, 2011 1:21 pm; edited 1 time in total

My MC28 300 put out about 65bhp in a similar set up to you, although had standard carbs. Alot more punch low down and was a really nice set up. I wouldn't expect to be getting much more than that on your particular set up.

I agree racer38. His maximum power is about all that can be expected, perhaps two or three more at the most without any more major work. I think the OP is concerned (or I am, atleast) with the flat spot at 10,000 rpm, and the lack of over-rev. My MC21 happily revs past 12,000 rpm to 13,000 rpm. Granted his is an MC28, but it still should be making power after 11,500 rpm unless the dyno operator is closing the throttle?

The power doesn't look smooth, either. I'd say some careful jetting should sort it out.

Come to think of it, it really doesn't look too bad... I would experiment with one shim under the needle and drop the jets about 0.05mm diameter, i.e go down a size. Take it for a ride, and see how it feels.

If the NSR is running too lean (probably not likely if it goes better without the air box) it can get a dead spot around 9,000 - 10,000 before it 'hits'. Keep that in mind.

Nice to see another 300 ! You should be able to smoothern that graph out with some jetting . The bike will always peak around 11 - 11500 but you may see a better over rev when you jet it .
you will be even happier when you have custom pipes . Are you riding on the road or track ? Pj 38's don't have idle screws

Does it wheelie in 2nd gear ?

Or, seize in second gear..
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If I have to take the carbs off once more...

2nd gear wheelies? Should a 300 do those? Surely you'd have to clutch it!
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MC21 Honda NSR250. TYGA 300 conversion.

Hrc ignition could be the problem with the over rev. The 21 flywheel is good for a couple of horses but not a true substitute if you want every last bit out of it.

Tom, did you not get a fair bit more when you went to the hrc card from the mc21 flywheel??

Just jet the thing half way near where it should be!
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

I have a dual EGT fitted and was getting to 1050 degrees on the dyno, which the experienced operator (and RS tuner) thought was pretty close and would peak around 1200 degrees on the road.

I have already fitted 0.5mm spacers under the carbs.

The only difference between the two runs was the removal of the airbox. The airbox already had the 4x 20mm holes drilled as well. Earlier, lower jet sizes indicated a lean situation with the EGT and the fact that it was making more power as it got hotter on each successive run (as I recall). I ended up with drilling the standard jets to xyz as I had run out of sizes! I may end up going down a size as yet, but I do want to run it on the road and monitor the gas temp first.

It is running BP Ultimate - 98 unleaded pump fuel. Squish is 0.6mm. Head volume is relatively large at 14.2, but I did specify to Matt that this is a road bike, running 98ULP. Hermit, I think yours are 11.8cc.. Alloy deposits are a piece of piss to remove - get some drain cleaner and some thick rubber gloves and it will come off (but watch the alloy).

Some custom pipes could be a very good idea. Neal, are you keen to share your experiences? Hermit, give me a call sometime about your barrel..