All Things CR250

[John Benson]

Thanks Riley and Ian. I never thought there would be that much of a change, then today looking at the mycron ,lap 2 was the fast lap and lap 6 was over a second slower .And at that point I know the tires and driver were doing better! Guess I will have to bite the bullet and add that second rad.

[joe lecompte]

http://www.tillotson-racing.com/collections/racing-1/products/hm-1-unlimited-all-stars-jr-drag

[Johnny West]

Ian,
I just ran your Ign on Joey's CR. Better every where. Thanks for your help. I'd post the dyno sheet but don't know how to post photos.
_________________
Johnny West/West Racing

[Ian Harrison]

Hi Johnny

Great stuff, I'm glad it's all ok.

If you e-mail the image of the dyno run to me, I'll post it up for you.

Did I send you the other info you asked for. Not sure if I did? Again let me know and I'll e-mail it to you by 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

[Dan Davis]

I thought I would add my post and Ian’s response from the thread http://ekartingnews.com/viewtopic.php?t=120783 before I reply below since it applies here.

[Dan Davis]

Firstly, Thanks for the quick and graciously thorough response Ian! Always tops!

OK, here it goes…..it’s gonna be a long one!!

I purchased the 2004 cylinder as a lightly used stock spare at a good price from Troy Miller prior to asking you about your thoughts on cylinders through PM a while back. Yes, you can imagine the look on my face when I saw the exhaust port and I spent plenty of time in that area with the die grinder. I have not yet filled the voids around the locked up power valve flaps and probably won’t for my first running of this engine (I only have the on track time dyno at my disposal) but may be looking into that procedure (as posted by you a while back) to further improve exhaust flow in and out of the cylinder in the future.
I did notice the rear skirt of the 2004 cylinder protruding deep into the intake tract and I performed some surgery on that part of the skirt to accommodate a bit more flow capability. The 2005 cases were also sculpted to increase flow capability while being careful not to enlarge too much with regards to crankcase volume. All mods always experimental of course.

Your assumptions are absolutely correct concerning the port timing values and how I achieved them. I am embarrassed to admit that I did not notice that an aluminum spacer was Yamabonded to the base of the cylinder when I began setting up the cylinder and couldn’t turn back the clock after porting was done.
One of my first decisions after deciding on the 2005 domed piston and single keystone ring (a design I prefer over flat top dual flat ring) and acquiring the inexpensive stock head from an ebay transaction, was to set up the head and squish band flush with cylinder deck as described earlier…..a method I’ve always used on 125 Cyl/head combo’s without head gasket. As you imagined, using stock base gasket was not an option as the piston was well below the cylinder deck. So, to answer your question, I am using whatever spacer thickness that was already attached to the cylinder and fabricated a very thin base gasket (from a standard brown paper grocery sack approx. .006”/.152mm….Ok, stop laughing at me!) and I did have to raise the exhaust and transfer ports a bit. I have plenty of Yamabond on hand so applying the spacer to the cylinder base should it need to be removed isn’t any trouble.

With regards to the cylinder head, I always cut the squish band near to parallel between the piston crown with around 1/2 to 1 degree more angle for safety to prevent the deadly combination you referred to above.
Lucky for me, I have friends here in the Air Capitol (Wichita, Kansas) that have offered to assist me with the machining of the cylinder head. I’ll probably model the combustion chamber to achieve the needed CCV and shape and write a program to cut the chamber, squish band, and O-ring groves in one set-up using a multi tool NC machining center.…..we’ll just see how that goes. We’ll probably do a couple of preliminary cuts on some scrap aluminum plate prior to mounting up the Honda part and with any luck, it’ll be spot on after the machine is turned loose on the head. At that point, the machining can be easily repeated on the same head or a new one if damaged from internal component failure in the future. Plenty of work for sure and certainly not the easy route to take especially if one doesn’t have similar resources at their disposal….but it is a learning experience and all in good fun!

On to the inlet. I was surprised to see the very unfamiliar looking configuration of the VF3 reed valve assembly for 2005 engine when it arrived…..more work for me, YAY! As I’m sure you know, the stuffer inlet is severely offset to the left side for use on the motorcycle. In an effort not to make the stuffer inlet any larger than necessary to keep volume down and try to keep a somewhat linear increase in the intake cross sectional area from carb throat through reed valve and into the crankcase, I decided on grinding the existing opening to the right creating an opening with a dimension of approximately 50-52 mm wide (can’t remember exactly from where I sit right now) which roughly centers the opening in the valve. Next is to machine a 1/2” thick adapter that will blend the round intake boot opening to the new opening in the reed valve. Not what I would consider an ideal transition length but should be adequate for starters. I tend to agree with you about the Mikuni boot possibly being too stiff for rough track applications and will be taking that into consideration. I currently use a Swedetech reed valve assembly on my 125 engine which is also very short and very stiff and have not had excessive issues with the carb coming loose…..not to say it hasn’t happened. Usually the issue was from a broken clamp but that boot is thick and the carb literally snaps in to place prior to tightening the clamp.

A side story: I remember completing at least half of a 30 min. CIK125 race a few years back while holding the carb in place with my right arm and shifting the RH side gear change lever with my left hand while keeping the wheel in position with my left knee. It wasn’t desirable or terribly quick exiting the turns while I downshifted to say the least and had pain in that right shoulder from reaching somewhat behind my body for the rest of the season…..likely stretched or tore ligaments or something. Funny how I didn’t notice that at all during that race and I’d rather not do that again. The leaned back seat in a superkart might make it easier to hold the carb in place but in a competitive race, there is little to no chance at any success at that point.

As of now, my plan is to use a 40.5 mm PWK pump around carb system (due to intake angle) and my current Vortex CDI that I used on my cylinder reed engine (I need to refresh my research on that topic from earlier in this wonderfully informative thread concerning ignition component combination), and my current Viper Racing exhaust system. I haven’t much looked into the carb setup as of now and if there is room between the float bowl and cases, I may machine my reed valve/boot adapter to angle slightly downward to level the float bowl as much as possible. That combined with the updated front engine mount available for case induction Hondas and maybe I can make use of the VHSB?? I just haven’t gotten that far yet.

I hope to get all of this work done before early May and possibly before mid April of this year for my club’s first events. We’ll see how that goes.

Incidentally, I am still preparing an order for you to be placed within the next couple of weeks including several Maverick chassis components that were bent up at HPT incident last season as well as your exhaust header for this 2004 cylinder.

I’ll keep you posted and will report back here as this project progresses.
Thanks again for your input here Ian. It is certainly greatly appreciated.

[Gerry MacNutt]

[Ian Harrison]

[Chris Reinhardt]

[Dan Davis]

Thanks for the photo's Ian. That new cylinder/head combo looks very interesting!!

Would you happen to know the P/N of the Mikuni carb boot in your picture above?

Gerry,
Up until this particular build, I have always run cylinder induction CR250's so the double ring flat top piston is all I have experience with. However, I do have plenty of experience with the little brother of the 2005 domed single ring in 125's (also 2005) and am pleased with it's performance as an alternative to the high priced RS piston we used to use. I'll be giving it a try and will let you know how it all goes. Proof will be in the performance/lap time comparisons and realized temps I suppose.
Thanks for your input!!