July 28, 2013 at 6:18 am #5135
I’m not sure if this is the best way, but click on this link to go to the “All Things CR250” topic in the Cassic EKN Form.
This was started in Jan 2009 by my good Superkarting friend, Erik Frank. Since then it had 400 replies and 124,000 views!! I can’t even beging to imagine the hours that I and others have spent researching and posting good and valuable information.
Hopefully anyone can access all that information for years to come and perhaps that thread can continue in this topic on the new forum.
July 28, 2013 at 10:13 pm #5181Roger MillerParticipant
would propose that we have a sticky topic for this, and maybe a couple of other historical links in the same place.
August 11, 2013 at 7:45 pm #6724
Hi Ian ,
just wondering if any more work had been done with the HPI box and ’02 stator flywheel?
August 12, 2013 at 4:17 pm #6835
You can forget running an HPI box with an ’02-’07 stator.
We have developed a fantastic basic programmable ignition with Zeeltronic that works with the ’02-’07 generator (ignition only, no powerjet, powervalve or quickshift). This is designed around our UK regs.
New ’02-’07 Generator (if required) – £200.00
New Rectifier Regulator (if required) – £40.00
New Coil (uses standard Honda CR250) – £39.00
Programmable box programmed with 2 Viper Curves – £245.00
Bespoke Wiring Harness – £40.00
August 29, 2013 at 11:22 am #8420
<span style=”background-color: rgba(255, 255, 255, 0);”>Hello Ian
I have had a chance to use a Dyno
To test my cr250 based engine after getting a good baseline. I put carb (38mm mikuni )on flow bench got a baseline. Then taper bored and worked the bell area. To a 20% increase .
Re installed on engine and. Reran the pulls. And the graph layed right over the first runs
So next I put a 44mm on just to see. And it did same!!!
Now I’m confused (I have V force reeds). Is that the limit of motor or is there a restriction I need to be looking for? Any ideas
Thanks in advance
Sent from my iPad</span>
August 29, 2013 at 12:48 pm #8431
Sounds like you engine can pull all the air it can swallow through a 38mm venturi
On our fully race tuned CR250’s we find the optimum size to be 41.5mm. However, a 38mm will give exactly the same power up to about 9,500 rpm. It’s only really the last 1,000rpm from 10,500 to 11,500 were you begin to see an appreciable difference of about 2 Hp at say 11,200 rpm. Of course if your engine is in a lesser state of tune and doesn’t pull those kind of revs or the power drops off after 9,500 rpm, then your wasting you time, effort and money. Can you post up a dyno graph for us to see?
August 29, 2013 at 1:45 pm #8438
<span style=”background-color: rgba(255, 255, 255, 0);”>Pic
Sent from my Verizon Wireless 4G LTE Smartphone
August 29, 2013 at 1:49 pm #8439
<span style=”background-color: rgba(255, 255, 255, 0);”>Pic
Sent from my Verizon Wireless 4G LTE Smartphone
August 29, 2013 at 1:51 pm #8440
Sent to your email
August 29, 2013 at 5:51 pm #8457
I’ll pick your e-mail up at work tomorrow.
I’ll try one of mine to see if it works. Could do with preview on here!!
OK, if your on photobucket you have to click on the “insert image” icon in the EKN message box and copy and paste (only requires a left click to copy) the “direct” link from photobucket.
Shame the window is now so narrow. Much prefer the old version EKN forum!!
August 30, 2013 at 1:01 pm #8535
Here are Stephen’s dyno plotting points. That’s a very generous dyno. No 250 single 2-stroke race engine ever made 37 FtLb of torque at 9,000 rpm. . . . . I’d guess about 15-20% over the top. Most likely be around 55 Hp at peak and around 29Ft Lb of torque. Anyway, as long as you always use the same dyno you can at least make valid comparisons as you make any improvements:
October 21, 2013 at 10:46 am #13280StockMoto JoelParticipant
I have a spare CR250 Engine (believe it is a 2001 – 2003?) for sale (used) .. $950, email or PM me if you are interested. Thanks, Joel
October 22, 2013 at 8:32 am #13392Chris HegarParticipant
What gas were you using for testing Ian?
January 27, 2014 at 8:14 am #20399
I have noticed that long track 250 single owners have been ending up on the side of the track too often due to engine failure here in Northern California. It seems we have been running too lean. Is there anyone that could go over the basics as to how to establish a baseline for jetting, a good starting point, and what preparation should be done at home so that when you get to the track you are not overwhelmed. Also, I have noticed that a common sticking point (pun intended) is mid throttle jetting point. Anyone care to give advice?
I realize this is too broad but it is off-season and I could use some help. If we don’t help each other so that we can at least start fininshing some races there won’t be anyone left to race with :)
January 27, 2014 at 5:49 pm #20430
Larry ,get someone to hack Anthonys computer for his jetting program!
January 29, 2014 at 5:49 pm #20621TonyParticipant
Hey John – I don’t have a jetting program, it is all stored upstairs in the old grey matter – for a starting point anyway!! Then tuning to the track by how it feels, looks and sounds on the day right – yeah right!!
What is going on with your program – have you sold your PVP and heading to the 125 class still or are you going to stay with the lads and get your finger out :)!!?? Just kidding – I think your kart is working pretty good, just needs a few tweaks and you are right there!!
January 29, 2014 at 8:55 pm #20631TonyParticipant
John – I was looking at my data, checking RPM, EGT etc. trying to dial her in!
I know what you mean about the Dellorto carb – I have a few of them, I found them pretty complicated, however I think once you have figured it out it is a very tune-able carb; Ian knows how to tune them – that said I think he has switched to the TMXX carb.
And talking about engines – there is nothing wrong with your Honda – I had nothing for you – my speed is in my karts handling – when I came upon you exiting the carousel your engine pulled a couple of lengths on me very easily – get that kart dialed and you are right there my friend!!
January 30, 2014 at 8:02 am #20664
My idea is to let the European’s beta test the new barrels this year before we make any rule changes here, and that’s because they have more participants than grid spots and can afford to make a mistake, whereas we have just enough participants to break even on paying for the event, so we can’t afford to alienate any of our participants.
January 31, 2014 at 12:32 pm #20757Andy KikerParticipant
I have never found the 250 single to be very jet sensitive. once you have a good setup and it is not blubbering and exhaust temps are not to high leave it alone. Unlike a 125 you do not have to be right on the verge of detonation for it to be fast. I run the same jet almost all the time unless there is extreme air changes or you go to Miller in Utah.
January 31, 2014 at 2:49 pm #20760
Andy, please tell us what carb, pipe and ignition you were using. Tell us what piston and piston-cylinder wall clearance, head volume, and reeds. How often do you need to change the top end and then the crank? Thanks in advance :)
February 1, 2014 at 6:16 am #20777Andy KikerParticipant
Larry, To start I currently run a gas gas and have for the past many years. Before that that we ran a 2001 and older version of the Honda with very good results . I have never ran the case induction Honda. It was Anderson prepared with Dellorto carb, Anderson pipe and silencer (very quiet), digital PVL non programmable with Anderson ignition curve. (stock Honda ignition curve is the worst for our application), Stock Honda piston with stock clearance. I think it is 2.5 thousandths. any time we put a new piston in we always ran 2 to 3 easy sessions for break in. Head volume I think was around 22 to 22.5. v force reeds. Top end with ours was a matter of keeping an eye on the bottom edge of the skirt at the center it would start to crack. time of this to happen varied. I will say RPM was the key to making them last longer. if you kept it under 11000 things last much longer. over 11000 and I was replace much more frequent. I am no expert on this stuff. I always left the motor setup to the engine builders. I just replaced parts as needed.
You guys are very lucky to have your own expert right on here with Ian. He is very knowledgeable and willing to answer almost any questions. and is spot on with his answers.
as Anthony said above getting your chassis to carry more turn speed will do much more in cutting your lap times than anything you can do to the motor.
February 3, 2014 at 3:53 am #20851Chris ReinhardtParticipant
This year should be a real learning experience, but my Cobalt will have a CRF450 EFI on it. Once I get it dialed…….. It “should” adjust itself…….
Another thing you guys should be discussing is what carb, and what fuel system (pump, tank, pickup, return, etc), and if there’s a g load area, ie left or right sweeper that’s causing a fuel starve…. Study the pistons, lean 4 corner stick, cold seize, ignition deto seize, over heating, etc…
February 21, 2014 at 9:28 am #22424
Never mind……I just looked at some decent pictures of a 2005 cylinder for sale….it appears that the bolt circle and bore are concentric unlike the 2002-2004 version.
Flat Top piston and chamber it is!
February 22, 2014 at 3:07 pm #22521
Never mind……I just looked at some decent pictures of a 2005 cylinder for sale….it appears that the bolt circle and bore are concentric unlike the 2002-2004 version. Flat Top piston and chamber it is!
That’s right Dan, the ’05 went back to the bore being concentric with the bolt circle.
Flat top piston and chamber is the way to go!
February 27, 2014 at 12:43 pm #22865Chris ReinhardtParticipant
Looks real nice Dan, I like it!!!! I took a couple of Solidworks classes last year, we had access to the 3d printer…. The stuff we could make…..
I would be inclined to think that was a work related freebie? There’s plenty of isolation for the carb, you could certainly have that model CNC’s out of some billet alum, or maybe delrin….
Also, I would seal around the two bolts that hold the rubber adapter on, a potential air leak….
February 27, 2014 at 1:45 pm #22867
That’s a pretty accurate inclination there Chris ;-) ……In fact, I need all the freebies I can get to even hit a couple races throughout any given season but this kind of stuff is just about as much fun for me as piddling about behind the wheel.
Yep, I plan on using Yamabond between boot and adapter as well as the bolt heads. The boot is a Mikuni/Kimpex 07-105-01 which are common on snowmobiles and cost as little as $10 delivered. If I were to use Aluminum in the future, I could eliminate the nut pockets on the inside and just tap the holes.
Next up, build fixture to deck couple of cylinder heads, cut o-ring grooves, and comb. chambers on a CNC machining center……luckily I have a buddy that sells those things and has one in his showroom to demo at the moment…..that equals free rent and maintenance for him on one of my CIK125’s for a couple of events. ;-)
March 26, 2014 at 5:54 pm #24559
I’m at the point where I wanna work on timing curve anyone have any to suggest??
January 17, 2022 at 7:48 am #114943Robert HorvathParticipant
Get more performance from your Honda CR250
by adding twin carbs In making it breathe easier by adding a VForce 3 Reed Valve System and twin carbs. Experts claim that two smaller 30mm to 38mm throttle bore size carburetors (Mikuni or Keihin) on race 110 octane gasoline are better than one big one – they both passed about the same or a little more CFM but the smaller two carbs give a higher flow velocity ( that means more suction and quicker throttle response ) and add more low-end torque with two main jets now ! The VForce is from Sharkshifter, the twin carb intake manifold is from V-Twin Harley Products By Cycle X of Hazelhurst, WI. But the intake adapter plate to go from Honda to Harley is very easy to make but you’ll have to do that yourself with a small piece of about 3/8′ thick aluminum plate-just copy what I did in my YouTube.—Just go to YouTube and type in “Get more power from your Honda CR250 by adding twin carbs” as all the parts that I used are listed in my comments from Bob
1) Won Overall shifter grand champion for the Year 2014 #92 team Craig Hemmen driver and Bob Horvath crew chief Elkhart Lake Road America kart club
2 ) Won Overall shifter grand champion for the Year 2016 #92 team Craig Hemmen driver and Bob Horvath crew chief Elkhart Lake Road America kart club.
Thanks Bob H
- This reply was modified 5 months, 1 week ago by Robert Horvath.
October 21, 2013 at 4:09 pm #13312
The 2001 is a “jug read” motor (reed block on the cylinder)
The 2002 and 2003 are “case reed” (read block on the crankcase).
Engine numbers are on a small stainless steel plate riveted onto the crankcase next to where the gearchange shaft goes in.
The first 2 numbers indicate the year:
63 = 2001
64 = 2002
65 = 2003
October 21, 2013 at 6:59 pm #13330StockMoto JoelParticipant
Thanks Ian.. appreciate it.. will check it out and update the post.
October 22, 2013 at 1:15 pm #13406
We have to use 99 Octane unleadead, which is what the dyno runs were done with.
We have also run MS109 unleaded, which gives great power, but is like a dry-Martini for your engine. Get the jetting wrong and it’ll end in tears!
I also test on Q16 (for the US market) and Avgas 100LL (for the Aus market).
With either of the latter fuels you can run much higher compression and ignition advance, without detonation, but I have found the trade-off between bottom-end power and over-rev renders little or no impression in terms of actual lap time.
January 27, 2014 at 5:17 pm #20427
Good points and I have your e-mail on the same subject. What you have asked is a very wide ranging subject, which will take a good deal of thought and time to answer in a way that will help everyone. I’ll put my mind to it next week. For the last few months and the next few days 99% of my focus is on completing and achieving registration, in the UK, for our new Viper SK250S (250cc single cylinder) Superkart motor.
January 29, 2014 at 8:37 pm #20629
If you don’t have a program on your lap top, what were you looking at all day at Sears while the rest of us were thrashing? :) Yes I’m staying with the 250, and getting a 125 for practice! Larry ,all I know about the Dellorto is there’s to many things to change for my pee brain. I like my Mikuni ,once I got the float level set it’s been good. I know you have a 257 which is a higher level race engine ( I am hoping the club will allow some rule changes so the CR guy’s can compete on a level playing field,that EVO barrel above would be a nice start) so not sure how it would work for you.
February 21, 2014 at 8:00 am #22412
Well, it’s been a year since I’ve worked on my case induction CR250 project….it’s just been sitting there patiently waiting on me to get back to it while I drove a 125 and a TZ250 kart at select events last year. I am currently working on resolving my cylinder head issue for a 2004 CR250 cylinder for which I intended to fit a 2005 domed piston.
As I began modeling a combustion chamber to cut into a 2004 cylinder head to use the domed piston, I realized that I would need to cut the chamber excessively deep into the OEM head to obtain a 20cc CCV (without spark plug hole, approx. 22cc’s with) and a 1.2-1.3mm squish clearance. This is mostly due to the piston dome consuming approximately 7cc’s of volume keeping in mind that my chamber must begin flush with the cylinder deck rather than inset into the bore due to the existing porting in the cylinder. The piston depth in the cylinder at TDC then is equal to the squish clearance value.
I have concerns that this will make the combustion chamber casting thickness too thin and possibly even break through since I have not cross sectioned a head to verify casting thickness.
This leaves me with a couple of options to use this cylinder:
1. Use a flat top piston to gain approx. 7cc’s of volume. This is probably the easiest option but I really would like to use the 2005 single keystone ringed piston.
2. Explore a different head. Expressly, the 2005-2007 cylinder head for which I know nothing about except that it was designed to be used with the domed piston I would like to use.
Based on previous posts by our favorite technical expert on CR250’s, I think I already have a clue as to the answer of my question….which is no but don’t have a definitive answer, so here it goes:
Can a 2005-2007 cylinder head be fitted to a 2004 cylinder? I’m guessing the answer is no because of the offset bore/chamber relative to the stud pattern on a 02-04 cylinder (assuming that the pattern and or bolt circle is even the same) but I haven’t seen one to be able to tell.
Thanks in advance,
February 27, 2014 at 9:13 am #22849
Experimenting with 3D printing to make a carb. rubber adapter for 2005 CR250 VF3 reed valve. It is angled slightly downward but is tough to see in the photos. The material is a bit on the brittle side but seems to be impervious to intended race fuel. It is a urethane acetate material. There is a better materiel available that has similar properties and is less brittle but I don’t have access to that at this time. Hopefully, thickness of adapter will overcome any potential damaging stresses and vibration. Time will tell. Fun-Fun!
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