2001 Reed Blocks and Inlet Rubbers

[Ian Harrison]

Hi Guys

A couple of e-mail questions have encouraged me to revisit this subject.

This is also timely as at the moment we have 3 x 2001 motors in the workshop for rebuild and modification and we will be spending some dyno time to optimise the setups.

The 3 blocks that we will test are as follows:

V-Force 3
ESR Billet Block
Standard 1997 Honda Block with 2 Petal Reeds

Here are 3 pictures of the blocks:

V-Force on the left, ESR in the centre and Honda (less it's stuffer) on the right






The main carb rubber we will be using is the Honda Straight induction Rubber as pictured below. This brings the carb angle back to about 17.5 degrees which is ideal for carb operation. It also has a very small volume taking into account the change of shape to match the reed block. We have always found this to give the best response:


We will also do do tests using the straight Honda RS Rubber on the Honda Reed block. This will leave the carb at a 30 degree angle well within it's operational spec. The rubber requires a little adaption to fit the reed block, which will require modification and production of a special stuffer. Those of you who have looked at a GasGas inlet system will be familiar with this kind of arrangement although the latest ones I've seen use an "upturned" RS short angled rubber to allow the carb to clear the crankcase (but increases the angle).


There are 2 versions of the V-F3 block. The first is the one intended as a replacement for use on a motocross bike. The second is the one intended for the ATV and matches (more or less) perfectly with the straight rubber. If you buy the motocross version there is a lot of work to do on the stuffer as the inlet is smaller and offset. See below: MX on right, ATV on the left.


The ESR block came with a spacer. This pulls the reed block back to give more clearance, but increases the crankcase volume by a nominal 53cc. With advances in pipe design primary compression is not as critical as it used to be and we will try this with all combinations.


I would be grateful to hear of anyones experiences or differing approaches and will report on our findings as and when we run on the dyno over the next week or so.
_________________
Ian Harrison
Viper Racing UK
www.viper-racinguk.co.uk
sales@viper-racinguk.co.uk
+44 7984 225 564
+44 161 343 2009
Championship winning Superkart race team 1997-2012

[Mark Croslyn]

Ian,
Interesting stuff. Keep us informed on the outcome. Looking thru some of the older stuff, duel stage reeds and early carbon. Couldn't seem to tell much difference. Now that was 10 years ago so I know they have come a long way.

[FIROUZ HAGHIGHI]

Ian,

i just want to say thank you for all you do to make our sport even better with your great input and information you sharewith us. please keep us posted with your finding with the reed block test.

best wishes

firouz haghighi
team texas
USSK

[Andy Locuson]

I run a cr 250 on a micro sprint. and for the most part everyone uses the honda stright with the v-force reeds. I belive that is really the best combo

[Sid Swift]

Hello Ian,
Try the V-force 3 w/spacer the ATV stuffer and the straight intake
It's been the best set up I have found to date--and have found to
to work well on many different engine combos--ie. singles and
multiple cyls.as well --good luck and hope alls well with You and
Yours--keep Us informed on the testing
Thanks and best regards SID SWIFT

[Chris Reinhardt]

Ian, is there enough room on the cases to run a dead straight intake? I'm thinking with the V-Force or the ESR you could fabricate a plate with a Mikuni intake rubber bolted to it. We did that with the 125's and you can tune the volume by using a different thickness plate.

CR

[Ian Harrison]

Hi Chris

On the 2001 CR250 you can run a 39 VHSB Dellorto with either the straight (angled down), Honda ATV Inlet Rubber or the dead straight (in all respects) Honda RS rubber, in either case either with or without spacer block.

The carb does come a little close to the strengthening web, but there is clearance.

Of course you can slightly relieve the boss/web or indeed totally remove it (as we do with our '02 motors).

Other carbs with wider float bowl may have more of a problem.

I alway try and keep the volume and the length upstream of the reeds as small as practically possible.

Best Regards

Ian
_________________
Ian Harrison
Viper Racing UK
www.viper-racinguk.co.uk
sales@viper-racinguk.co.uk
+44 7984 225 564
+44 161 343 2009
Championship winning Superkart race team 1997-2012

[Chris Reinhardt]

Ian, again, why not use a piece of either 3/8 or 1/2" aluminum plate bolted to the back of the reed block and one of these suckers bolted to your plate?
http://www.sudco.com/Carburetor/SudcoMikuniCatalog.pdf

That's about as straight and short as you can get the intake track...

CR

[Ian Harrison]

Hi Chris

We did use these bolt on flanges right back at the start of our developments for the '02 CR250 and very useful they were.

The isolation they provide is minimal and not really ideal in my eyes for a bone-shaker CR250. Fine on a smooth 125 or tandem twin.

In fact the one we favoured was off a TM 125 Rotary and produced especially for the 39VHSB. Nothing particularly wrong with that or the technique, except you end up with 2 components rather than 1.

Also if you want to bring the carb angle down, you end up with an angled sandwich plate and quite a complex CNC machining job, or ages with a die-grinder as opposed to a simple off the shelf economical part.

The final thing although irrelevant from a performance point-of-view is that the bolt on flange with a sandwich plate looks a bit of a "dog's breakfast".

I'll dig out one of our angled prototypes which used the bolt on flange and post a picture of it along with the rubber that was produced as a result of the development work. You will then see exactly what I mean.

Really the initial objective is to see if there is any kind of an advantage from a perfectly straight tract. If it warrants further investigation then we will look at alternative prototypes to maximise benefits. From our developments with the '02 motor I know the RS rubber works.

Believe me we know only too well how easy it is to spend huge amounts of time and not inconsiderable amounts of money chasing up blind alleys. Hopefully we are a little wiser than we were in the early days

We will be on the dyno over the next week.

Best Regards

Ian
_________________
Ian Harrison
Viper Racing UK
www.viper-racinguk.co.uk
sales@viper-racinguk.co.uk
+44 7984 225 564
+44 161 343 2009
Championship winning Superkart race team 1997-2012

[Chris Reinhardt]

Money might be better spent figuring out how to keep them from shaking so bad!!! Maybe a one off crank?

CR

[Ian Harrison]

And you think we haven't

Visit Falicon or Crankworks, then glue your dentures in with Devcon

Sorry Chris - Old News and Way-Off topic

Next

Ian
_________________
Ian Harrison
Viper Racing UK
www.viper-racinguk.co.uk
sales@viper-racinguk.co.uk
+44 7984 225 564
+44 161 343 2009
Championship winning Superkart race team 1997-2012

[ted dale]

Ian its so easy to stop the vibration BUY A GAS GAS
_________________
Anderson gas gas

[Chris Reinhardt]

Ted, I was thinking the best manifold for a CR250 is a Wiwa Gas Gas 250!!!
All kidding aside, I honestly think that it would be real hard to compete with the other guys motor unless you can reduce the vibration by a whole lot!!!

CR

[Ian Harrison]

Hi Ted

Who says I haven't

Ted, can you tell me what type of motor Chris races

CR250 vibration never did me any harm - - - - did it

Chris, read the woefully out-of-date bit under my signature. Add 4 new 2009 British lap records, winners of the 2009 MSA British Championship and 2009 UK Cup winners. Now comment on the success, competitiveness and value for money of the ubiquitous CR250.


Best Regards

Ian

p.s. I haven't
_________________
Ian Harrison
Viper Racing UK
www.viper-racinguk.co.uk
sales@viper-racinguk.co.uk
+44 7984 225 564
+44 161 343 2009
Championship winning Superkart race team 1997-2012

[Chris Reinhardt]

I guess nobody runs Wiwa's in the UK!!!!
Ian, I don't doubt your abilities, but that Gas-Gas is a monster!!!

CR

PS What happen in 08 and 09?