CR250 power valve block off

[Gerry MacNutt]

I need a block off for the power valve on a 2002 CR250 so I can start building a back up motor. So who sells such an item and would prefer from the USA or Canada if possible.

[shaun everard]

Like every other tuning mod and tuning information required just go straight to Ian Harrison at www.viper-racinguk.co.uk

[Gerry MacNutt]

Thanks, yes i know Ian is the man, it is just that parts out of the UK have crazy shipping costs, so I would prefer one from this side of the pond or could we import him to the states and have him set up shop in California?

I will be buying an ignition from him but little bits sure would be nice local.

[John Michael Dillon]

You can lock the stock power valves open. The block off's are kinda a pain. They need to be fitted.

[Gerry MacNutt]

I don't mind fitting one

[Darryl Bertram]

You should try Eddie Sanders Racing, ESR out of California. I purchased their kit for the '99 cylinder and I guess they might do one for the later models. I found these guys pretty helpful.
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Australian American Racing

Aussies in Texas

[Ian Harrison]

Hi Guys

I believe that ESR (and ourselves) only produce powervalve blanking kits for the 1992-2001 series cylinder induction motors.

Unfortunately, because of the internal shaping of the 2002 powervalve pockets, it is practically impossible to design a powervalve blank that would fill the voids and still be possible to fit.

We half-fill the channels with Devcon paste, then bed the valves into it, insert the shaft and rotate it until the valves are in the fully open position.

This squeezes the excess Devcon out, which can then be smoothed into the voids (more added if required).

When the Devcon is cured, the exhaust port can be shaped using conventional porting tools. (we usually top-up and smooth the Devcon once a year).

As a "belt and braces", the power valve fulcrum can then be locked into position with adjuster bolts in the original cable channels. You can also invert the fulcrum and drill/tap a 6mm hole through the back of the powervalve chamber and put a bolt through the front cable nipple hole in the fulcrum.

However, the fulcrum is quite fragile and can crack, so these days we tend to just weld a tag to the shaft that bolts into the original shaft locking plate hole. It's simpler and easier and economical. Having said all that, I've never known Devconned power valve flaps to move and break free.


In fact, if you need to remove the powervalve flaps so the cylinder can be repaired and replated, it's a horrible dirty job, using an oxy-acetylene torch to burn away the Devcon and break the bond with the flaps. This then requires thorough cleaning (scraping and shotblasting) before sending away for re-plate. in short a pain in the backside. We did 2 today . . !!

The pockets/valves in the 2003 cylinder are a more intimate design and with careful working of the port window, good results are obtained without the use of any filler. The only problems with this are availability and the fact that an '03 cylinder comes without flaps and shaft, whereas with an '02 they are included. So the conversion from '02 to '03 cylinder, requires the initial purchase of the powervalve flaps.

The '05 cylinder is a similar story to the '03, but the removeable front of the cylinder means the powervalve blade is the closset fitting of all. However, there is more tuning work to be carried out on an '05 cylinder for superkart use. We are currently working on a solution for the '05 cylinder that does away with the (expensive), powervalve flap and shaft altogether.

It is possible to fit the '05-'07 cylinder direct to any crankcase induction series crankcases. The '02-'04 crankcases are weaker but have a larger reed-block cavity. The '05-'07 cases are stronger, but have a more restrictive reed block cavity.

Shipping costs are not too bad from the UK. Door-to-door for a fully tuned complete cylinder is £35.00 ($52.50 USD). You also don't get charged the UK VAT (tax) on the tuned cylinder which saves you £139 ($210.00 USD) on what a British customer would pay, but you would be responsible for any US import duties/charges.

I can also arrange competitive prices for collection of engines for work/repair/return.

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

[Christian Garcia]

Ian would you recommend the powervalve mod for a Sprint kart? Plus I know they make a cdi that can control when the powervalve opens and closes. Or do the benefits come from smoothing out where the power valve goes, cause I know the area around that thing is horrendous. I didn't know the 03 was nicer as far as the powervalve goes..[/u]

[Gerry MacNutt]

[Ian Harrison]

Hi Gerry

There dosen't seem to be any problem associated with using the stock valve flaps, so we have never sought to have any made in ali. However, I take your point that the O/E flaps are hard and it makes them more difficult (well slower actually) to work, but easier to get a good finish. Just a matter of the correct tools for the job.

Christian, it is really the benefits of smoothing over the voids. If I was looking to use electronic powervalve control (and there are some benefits to be had, particularly for tight short tracks), I would just use the '03 or particularly the '05 cylinder. We aren't allowed to use electronic powervalve control on Superkarts in the UK.

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

[alan speyrer]

Gerry, Ian sells a nice power valve kit for the Honda cr 250 engine. There is another American made power valve kit for the Honda. Go to rtschassis.com. I have there power valve blanking kit in one of my two Honda cr 250 engines. In the other 250 engine i have installed Ians power valve kit. Both kits are nice, However the kit made by rtschassis.com is cheaper, no international shipping charges, and there is less machining to do when installing the rts kit. rts also sell tons of OEM and Aftermarket honda cr 250 parts.

[Ian Harrison]

Hi Alan

Gerry is looking for a power valve blank for an '02.

Neither our nor the RTS (BAM) blanker will fit the '02 as explained above.

However, thanks for the plug . . . . . (pun intended)

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

[Sam Zavaglia]

Ian,
You do go to a lot of trouble to explain and post photos of your solution for benefit of Superkarters. I think that is very generous of you when others are trying to copy and/or beat your package.

In my years of karting (lots of them), I've seen everytime that those who try to save a dollar end up spending more $$$ and time to never even get to the same base line or correct advice when comparing the best option available.
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www.samzavaglia.com

[alan speyrer]

Sorry Ian i thought yours and the rts fit the 02 cyclinders.

[Ian Harrison]

Hi Alan,

No problem

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