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Author Topic: More jetting Q's -- 73 CR250  (Read 7902 times)

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Offline Gippslander

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More jetting Q's -- 73 CR250
« on: March 31, 2011, 12:40:15 am »
Am about to put a 36mm Mikuni on my 73 CR250 -- otherwise very standard motor -- on 2nd overbore.
I have -- Slide 2.5, needle 6DP1, needle jet Q2.
Any "baseline" suggestions for main and pilot?

Also -- strangely the bore is 37 mm not 36 -- probably just a manufacturing tolerance -- that and the casting being a "bit rough" at the bottom of the slide bore (about 30% area not machined -- still as cast -- so it seems a bit light on for metal at that point) -- and HL500 (I think it was him) telling me that his CZ ran poorly with a new Mikuni until he found and fixed a crappy "orifice" (no toilet jokes please!) all makes me think Mr Mikuni may not have misplaced the Q control the Japs are proud of.
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Offline Freakshow

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Re: More jetting Q's -- 73 CR250
« Reply #1 on: March 31, 2011, 01:40:06 am »
what size was it before ( the carb) and what jet was in that?
id be thinking in the 340's main if its a reed.  but the other info will give you a closer crack at it.
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Offline Gippslander

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Re: More jetting Q's -- 73 CR250
« Reply #2 on: March 31, 2011, 09:08:19 am »
It's a non reed setup. Had the standard Bing 53 but was not an easy starter -- so am trying a Mikuni.

The Mikuni was ordered "to suit" my engine and although the supplier has always given me good advice before I am wondering about the jet sizes supplied being Main 430 and pilot 35. The motor "just runs" and fourstrokes non stop.

Also, I am thinking that maybe it's not the jetting and that it's the carby just flooding -- because the engine is constantly wet with fuel.

As an aside -- when I was trying to dry her out by kicking with open throttle and fuel turned off and the side plug out it fired for a moment and ran with two foot flames out the spare plug hole -- after that I sat down and looked at the bike in amazement for a moment -- 00 compression and it ran a little bit  ???

So tonight I will try again starting with checking the float level and then tipping the bike over for a while to drain anything out of the bottom end and then trying to start, maybe with some starter fluid.

The reason for the jet question is that I'm just not sure -- 430 is a big hole for a non reed 250.
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Offline jimg1au

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Re: More jetting Q's -- 73 CR250
« Reply #3 on: March 31, 2011, 12:39:21 pm »
http://www.honda-elsinore.com/
check this web page out there is some jetting specs in the vintage forums
i think my petrol read valve motor has a 38mm and about 280 main
i have a jetting chart on my home pc that will give you somewere to start
my race cr250 runs on methenol so those specs are no good to you
jim
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Offline jimg1au

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Re: More jetting Q's -- 73 CR250
« Reply #4 on: March 31, 2011, 12:50:13 pm »
from marks swap meet i just googled what you want and got a few hits

Joined: 08 Jun 2010
Posts: 11

 Posted: Mon Mar 07, 2011 9:25 pm    Post subject:   

--------------------------------------------------------------------------------
 
The specs I have are:36mm Mikuni on 73/74 Honda Cr250M
Main Jet:270
Pilot:40
Njet:Q4
Needle:6F5
Slide cutaway:2.5

Hope this helps
 
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Offline Husky70

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Re: More jetting Q's -- 73 CR250
« Reply #5 on: March 31, 2011, 12:53:44 pm »
Ummm... I think it is a Husky250CR?
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Offline Freakshow

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Re: More jetting Q's -- 73 CR250
« Reply #6 on: March 31, 2011, 01:57:13 pm »
Either way 430 sounds wayyy to big.  Check the float vales also hasnt got stuck in open during transit or one of the flooats has moved over and is holding the arm open too.
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Offline jimg1au

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Re: More jetting Q's -- 73 CR250
« Reply #7 on: March 31, 2011, 02:05:41 pm »
sorry but 250 twostroke piston port engine should breath the same
it dont run with what he has now so why not try honda 36mm mikui settings to start with and then do plug chops.

cz250 specs
CZ 250 MX Mikuni VM 36 260 35 Q5 6FJ6 - 1.5

hope all this helps 430 main is somthing a yz465 would run
jim
« Last Edit: March 31, 2011, 02:22:33 pm by jimg1au »
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Offline Gippslander

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Re: More jetting Q's -- 73 CR250
« Reply #8 on: March 31, 2011, 02:36:18 pm »
Thanks all round -- I have a 270 main in the box so I will try that as a starter.

Will carefully check the float and sticking -- probably the reason it drowned it self first go ::)

Will try all that tonight and will report.
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Offline Gippslander

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Re: More jetting Q's -- 73 CR250
« Reply #9 on: March 31, 2011, 07:40:36 pm »
Got a bit lazy -- after work went to the shed -- good squirt of "start ya bastard"  ;D  and it started first kick and it seems to be running ox -- with the 270 main.
Will work on the jetting over the wekend -- lookin good 8)
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Offline jimg1au

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Re: More jetting Q's -- 73 CR250
« Reply #10 on: April 13, 2011, 06:26:25 am »
from marks swapmeet
Husqvarna: Ready to bolt on Mikuni 34mm carb with new rubber intake with manifold adaptor. This came off a 76 Husqvarna WR250 so it should fit many Husqvarna's. Carburetor has a 159 R-O needle jet,6DH3 jet needle,35 pilot,260 mainjet and a 3.3 needle valve assembly.Carb comes complete with a 2.5 throttle valve slide and return spring. $85.00 plus shipping cost. Please e-mail me anytime or call before 8pm Eastern time.

       Rob Kerr
Jackson, MI, U.S.
Phone: (517) 787-6062 | Email
Registered Since 6/30/2006 | 77 Posts
Accepts: Pay Pal
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Offline tony27

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Re: More jetting Q's -- 73 CR250
« Reply #11 on: April 14, 2011, 06:29:16 pm »
Quote from: Gippslander on March 31, 2011, 12:40:15 am
Also -- strangely the bore is 37 mm not 36 -- probably just a manufacturing tolerance -- that and the casting being a "bit rough" at the bottom of the slide bore (about 30% area not machined -- still as cast -- so it seems a bit light on for metal at that point) -- and HL500 (I think it was him) telling me that his CZ ran poorly with a new Mikuni until he found and fixed a crappy "orifice" (no toilet jokes please!) all makes me think Mr Mikuni may not have misplaced the Q control the Japs are proud of.
Any clues on which orifice to check out?
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