Hi

I have done some searching around the forums, but I am still unclear, hence the new post.

I have an MC28, standard but with Tyga chambers, 2deg advance and are to order the 300kit.

Although I do have a set of PJ38s ready to go, I have been looking into boring out the standard MC28 carbs. The rationale is that this is to be a streetbike and run on high octance unleaded.

I have been offered a set of MC21 carbs with the HRC kit fitted. From what I understand, part of the HRC kit requires the removal of the power jet and changing the needles and mains accordingly?

Are the MC21 + HRC (and perhaps a bore out) a better option than MC28 carbs that have been bored - for the road. In my previous life I used to race a late model RS125 and found that although the PJ system made little difference when running avgas, it was actually usefel and made a difference when running Elf unleaded. I also had the BPS/Sabre ignition system that was complicated but great.

thanks for any advice...

cheers

Simon

Your money would be better spent [and saved!] on tuning a 250.

Mark my words.
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Vampire?

I ran a pair of mc21 carbs on an mc28, it didn't go notably better or worse than on '28 carbs.

Re. the HRC jet kit yes, the HRC jet kit has the power jets blanked off, bigger mains and adjustable needles. Once it's set up you'd struggle to tell a bike with the PJ working from one with them blanked though adjustable needles are nice if you need to adjust the needle postition.

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Hi , i had 2 bikes , 1 with mc 28 carbs and 1 with bored 21 carbs . After we bored the carbs both bikes were allmost identicle on the dyno . The 28 carbs were unbored .
I have a few graphs of my 300 vs my trick 250 if you are keen .
We have sorted out the teething problems ,
I LOVE MY 300'S POWER

Neal wrote:I have a few graphs of my 300 vs my trick 250 if you are keen .
We have sorted out the teething problems ,
I LOVE MY 300'S POWER

Oooooh controversy!
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I am confident that my 300 is the strongest NSR out there

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If I have to take the carbs off once more...

Neal wrote:
We have sorted out the teething problems

That's what they all say!

How did you manage that? By lopping 1500rpm off the redline?!
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Vampire?

Thanks for all the great feedback.

Neal, I am keen to see those graphs please. Without wandering into the murky depths of the eternal 250 vs 300 debate, I am at least going to give the 300 a try! A friend here swapped a 600 for a 300 kitted NSR that was poorly setup by someone who knew little about smokers (yeah, I know, thats why he bought a 300 kit haha!). Anyway he did a recent trackday here (I think that NSR Tom was there too?) and for someone who used to race a HRC F3 kitted NSR and an RS250, he was pretty impressed with it. The problem with racing them here is that you are up against 3 cylinder, 450cc GSXR600s, 80hp SV650s and fast tigcraft 450 singles and 550 twins..

I still dont know what to do about the HRC MC21 carbs, perhaps I just get them and try them out...

You`d be mad not to get the MC21 carbs if they come with an HRC kit.

Even though an MC28 will struggle to ever make over 55hp (in the real world, not the daydreamers' world!) with a standard card, if you do set about properly modifying it you will need all the adjustment & special bits you can lay your hands on. HRC jet kits are selling for £200~300 these days. Have a look on Yahoo auctions & you'll often see a box of goodies with a dozen bids or more going for 30,000+ Yen.

Remember, Honda was long past looking for performance when the 28 came out, & the whole bike was softened for the street. The carbs are a bugger to work on (try adjusting an HRC needle in a set, then do it on an MC16~MC21 & you`ll see what I mean), the suspension is soft (although the SP front is a good cartridge design), the Pro-Arm flexes (in-built passive steering), and the ignition is flat.

A 300`s not going to have much impact unless you get an HRC card, & even then (again, in the real world) you'll be lucky to see much over mid-60`s. Still, at least with a standard PGM-IV the chocolate pistons might last a bit longer.

Hmmm.... let me think.... 300 kit, £1200.... Tyga pipes to fit the 300 barrels, £500... HRC card, probably £200+.... all for an unreliable 65-68hp!
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Vampire?

Oh bugger...why did I start...

Even if I threw money at making it a fast 250 - are there still parts out there? If a fast 250 is merely one that has been matched, flowed, ported and really well setup - then what is to stop the same being applied to a 300? (well, I guess the main consideration is the less than ideal bore/stroke ratio of the 300).

I spent years racing a fast RS125 filled to the brim with stuff and that really did take two years of careful setup, recording and diligent use of the weather station (2 stroke racers best friend!) and also tuned a RG50 bucket from nothing to... well... something less than nothing. Can't the PGM-IV curves even be dealt with to some degree by selecting the optimum curve and then fooling the gearbox sensor?

The MC28 doesn't have a gearbox position sensor.

Mid 60's from a 250 will can be achieved for next to nothing, and by the sounds of it, your experience should get you there pretty quickly under normal circumstances.

You're on a hiding to nothing without an HRC card or a decent PGM though (i.e. PGM-II or PGM-III). What good is a 20% capacity increase when the ignition can't even produce the goods for a 250?
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Dodgy - Is your bike intended for track only or road and track riding ?
I have some good info on the 300 kit and will pm you .

If someone paid 1200 for a 300 kit that he could get hold of good luck to him , how often does the F3 stuff come up for sale and at what price ?
This was the easier way to get HP for me .

dodgy wrote:The problem with racing them here is that you are up against 3 cylinder, 450cc GSXR600s, 80hp SV650s and fast tigcraft 450 singles and 550 twins..

I've not had a run against one of those Ozzy 450s yet but i've had a real good run with one of the SV650 pro-twin guys and the 300 is a perfect match in a straight line. Jason Easton on that Tigcraft SVX550 was pulling high 1:13s at Manfeild... To my 1:21s - but that's got far more to do with his riding than any differences in machine performance.

My engine is not optimised and no doubt if someone running the same spec put the effort into tuning it up like Neal has with his 300, then there's no doubt it'd have the measure of those SV Suzukis and with the right riding (which ofcourse is by far the biggest factor), would be running at the front in F3.
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oh dear...a 28 with a 300 kit, Andys dream bike ...I have been watching this thread with interest as I have a MC28 with a tuned 300 kit on it as well, although I have yet to set to work on it so cant really offer an advice as I have no experience. It currently has RS carbs but as its going to be a road bike it will go back to either MC28 or MC21 carbs as the PJ38's have no idling circuit...MC21 carbs are probably the best to go with if you have them.

I have also learnt that although a lot of guys on here are very knowledgable...they are also very biased and in my opinion they also dont always know everything they think they do .

My advice if its a streetbike though is top leave it as it is and enjoy it . If you do modify it then keep us up to date with your progress and how it goes, and take any advice you can get from Neal as he seems to be having good results.