Pinned Honda CBR250RR MC22 Specifications

Guys does anyone know the inlet and exhast valve diameters of various CBR250's?

I can't find it anywhere in any manuals or on the net

 

I believe its 19.978-19.993 but yeah I remember it being 2cm diameter pretty much from memory.

 

actually the figure i gave above 19.978-19.993 was the lifter diameter so ignore that. There is seat "cutter" diameters early in the workshop manual that is saying 17mm and 21mm which might be the accurate diameter but unsure.

 

thanks Damus, I did come across those measurements also, difficult to know for certain what the cutter diameter refers to however

I think this will come down to someone actually having made measurements as I've been unable to locate the size in any of the honda documentation

 

I thought I had tracked this info down before on google, I needed the valve diameter to do exhaust calculations when I was intending on modifying the stock exhaust. From memory the source was not 100% reliable.
As you see below the part numbers for inlet and exhaust are different so the dimensions differ one way or another.
The inlet valve part no. is 14711-KY1-000
The ex valve part no. is 14721-KY1-010
I only needed a rough estimate at the time, but being that I want to know for a fact my self what the real diameter is I have done some further googling.
Valves on Honda mc17 mc19 mc22 mc23 mc31 are the same "allegedly", knowing this may help in your searches.
One EXTREME method I have used was to measure on the screen the sizes here http://www.aliexpress.com/item/Gift..._3&btsid=c196e6f4-3276-4e46-bcfe-1b44bbc34dce
It says they are "real life size photos" however of the 3 photos available in this particular link the photo sizes differ.
Taking a ruler to the screen though I did do a measurement of 22mm and 18mm.
If that was scaled down it does correspond with the 21mm and 17mm of the valve cutter diameter.
I would almost put money on the fact that the diameter would be 21mm and 17mm but without measuring with one in your hand there would be no 100% guarantee and I highly doubt anyone will be quickly forthcoming with the info in the near future.

 

I posted on the dedicated CBR250 forums to see if I could hit some luck

http://cbr250.com/forums/cbr250-forum/21113-valve-diameters-lengths-~3-5mm-stem-valves.html

Measurements taken from used valves
inlet :- 3.48mm stem dia. Head 18.95 mm. o/all length 80mm

Exhaust:- 3.46 mm stem dia. Head 16.52 mm o/all length 79.4 mm

I'd say any assertion by sellers that all of the models use the same valves are incorrect, you only have look at the specs on page 1 of this thread to see the differing stem diameters.
Speculation: The valve sizes may also change across models like the FZR250's from 2KR -> early 3LN -> later 3LN/Zeal

The search continues...

 

The workshop manual does have some inconsistencies and some mistakes in it (not many but it is worth taking into account its not perfect). Going off part number would be the best course of action in terms of comparability.
These are Honda genuine inlet valves for part number 14711-KY1-000
http://www.ebay.com.au/itm/HONDA-CB...309041?hash=item2ef411e4f1:g:3mcAAOSwFV9Xw6GB
It might be worth asking the seller to take a measurement or 2.
Even if I pulled my engine apart it wouldn't be as accurate as brand new Honda genuine OEM in the packet valves. I have purchased OEM parts from tokyo japan in the past and they are the real deal.
That is probably the best bet if they will give an answer that is.

 

Did you see any improvement from the dyno tune and exhaust gas’s analysed?
I own a 1991 mc22 with some small work “i.e” mc19 cams and head, cbx1100 reg/reg, bigger jets all round, carb sink/full rebuild, head was ported and cleaned up, entire engine was asid washed, inspected, new bearings though out and rebuilt,ect
runs and rides like an absolute dream, currently have a second mc22 engine going into a small off-road buggy to, would like to see any improvement’s out of both, thanks for your time
Enjoy

 

Hi Zack,
I have never quite understood what real difference there is between the MC19 cams and the early MC22 cams. Are they really different? What does fitting the cbx1100 reg/rect do? I would not have thought this would give a performance gain.
Spending time on a dyno is likely to yield an improvement for you. You might find running bigger jets is not the best.
I have set up my early MC22 track bike on the dyno after being disappointed with the way it felt on the track. We just changed the jetting after a number of runs and played with air filter configurations. We started with about 35 bhp at the wheel and ended up with 42. The feel on the track was much better, but the engine still runs out of puff at about 17 - 18k rpm. I feel there might be a little more to be gained by playing with an aftermarket ignition module. I suspect it might be over retarded at high rpm. Our final jet setting was leaner than standard.

 

Yeah I seen that after I had posted the comment, no harm in trying tho, thanks bud


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There slightly larger lobes alowing it to breath a little better, you can feel the difference, it’s massive in response and smoothness when going up in the rpm, from idel to redline is all crisp and snappy, love it and I couldn’t be happier
I have a set of aftermarket carbs I’ll be using on the buggy build so hopefully it should push close to original numbers with everything done do it
The upgraded reg rec provides a more stable current and not only that it’s lighter and will last a lot longer, looks better and dosnt get as hot asweel

Ahh okay, what iv found with my exhaust system and airbox, the jets I’m currently running work perfect, a little on the ritch side but I still get around 330-360kms out of a tank and that’s giving it a hard time on track so can’t complain

I’ll look into what you have said tho, iv been thinking about going back to 102-105-105-102 agin but I’m unsure

I have a aftermarket cdi ready to be put on, haven’t had time to set it up yet, been sitting in my toolbox for almost a year now haha, I’ll get around to it eventually, I don’t think there will be much of a gain in power, more response and feel/smoothness


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Hi Zack, I have never directly compared the cams. But from the specifications, I believed that the J,K, L & N versions all run the same cams. So early MC22 should be the same as MC19.
From my dyno testing, the power drops pretty sharply beyond 16k rpm. Playing with the ignition map might enable the power to be pushed a little higher up the rev range and give a few more usable revs to play with on the track. A waste of time on the road though really.
Have fun with your project and keep us posted.

 

Ah okay, comparing my original mc22 cams (L) to the mc19 cams was around 1.4mm from memory, dosnt sound like a lot but did improve it overall so it was worth $100 and around an hour to do, can’t complain, and yes the later 93^ have a restricted head and slightly smaller cam lobes, they have a restricted cdi and a lower rev limiter, I think it was about 500rpm difference
Yeah your not wrong, I’ll hopefully be getting mine back out on track soon and see how she go’s, just a quick question tho, can you run a mc19 fuel pump with a mc22 carb’s and harness? Just been looking into ideas due to how far away the fuel tank is from the engine on the buggy, not only that the tank is about the same height if not a little lower so it won’t have gravity on its side eather, not sure if the vacuum line would work effectively

Will do, I’ll start a build thred soon, just need to make sure this engine will actually work without being a week point


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I do not see why you couldn't run an MC19 pump with the MC22 carbs. I think float chamber needle valves are similar and pump is fairly low pressure so flooding should not be an issue. I run a pump on a motorcycle engined race car that I have. I simply run a fuel rail across the top of carbs. One side of the rail is fed from a pump and the other side bleeds back to the tank via a filter. This effectively means the carbs see very little fuel pressure. Equivalent to gravity feed from a tank above.

 

Legend thanks mate, I wasn’t sure if it would just flood it or give it not enough fuel up in the higher rpm’s, I’ll do some testing, besides what’s the worst that could happen right


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Here's what the fuel rail setup looks like on my race car.

 

Hi,

Does anyone know if there is a diagram for VP20 carbs? I understand the basics of CV carbs, but why are there 4 small air intake holes? I figured this would be the best place to ask.

Any thoughts are appreciated