Author Topic: DT230 Performance and Improvement  (Read 4568 times)

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Offline motorindustries

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DT230 Performance and Improvement
« on: October 30, 2014, 04:07:50 PM »
Found out some interesting info to help the DT230 punters out there...

Having rebuilt the whole bottom end of mine, I was concerned about putting it back together and it having another soft seizure like it did the last time I rebuilt the top end. FYI, Serco still have sleeves for the DT230 barrel on the shelf and provide an aftermarket piston kit from the DT200.

Found out from Mikuni... the DT230 carby was 'molested' by Yamaha to meet emission regs...meaning they leaned the carb to the point of starvation. Mikuni don't supply larger aftermarket jets, needles, etc for the DT230 carb.

Found out from Serco... the only reason Yamaha would have drilled the hole in the OEM DT230 piston is to help with fueling...meaning the carby is toooooo lean. Therefore the DT200 piston kit supplied by Serco to match the Serco sleeve should work fine with the appropriate fueling.



So...found out the DT230 carby specs
MIKUNI TM30x1
Main Jet:   #165
Jet Needle:   6DHY40-4   
Pilot jet:   #22.5   

and found out the WR200 carby specs
MIKUNI TM30SS
Main Jet:   #210
Jet Needle:   6DHY40-3
Pilot Jet: #35

So...got onto boats.net and ordered the WR200 Main, Needle and pilot carby parts and...ferk me! What a difference to this little bike. I have finally discovered what a DT230 should really go like. My mechanic neighbour even commented that it is the best he has ever heard my DT230 run.

This is one mod every DT230 owner should do.

Robo

Offline motorindustries

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Re: DT230 Performance and Improvement
« Reply #1 on: October 30, 2014, 04:10:35 PM »
Part numbers for the above and are from a 1995 wr200

1 x needle set = 3xp-1490j-10
1 x jet, pilot (#35) = 193-14142-35
1 x jet, main (#210) = 137-14143-42-a1
1 x washer, main jet = 137-14153-00

Also need to open up the airbox by drilling holes in the top and remove snorkel if you haven't already

Cheers
Robo

Offline gearhead86

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Re: DT230 Performance and Improvement
« Reply #2 on: October 30, 2014, 10:49:43 PM »
Quick question; does the 230 carb have an adjustable air screw?
I'm from Canada eh.

Offline motorindustries

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Re: DT230 Performance and Improvement
« Reply #3 on: November 10, 2014, 09:10:43 PM »
Quick question; does the 230 carb have an adjustable air screw?

Sure does

Offline Masatu

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Re: DT230 Performance and Improvement
« Reply #4 on: February 04, 2015, 11:07:48 PM »
so are you saying I can just switch those parts for my OEM parts and it will run even better?

Offline motorindustries

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Re: DT230 Performance and Improvement
« Reply #5 on: April 03, 2015, 09:22:30 PM »
so are you saying I can just switch those parts for my OEM parts and it will run even better?

Masatu,
That is correct and here is some more info that might be helpful.

The use my DT230 gets can only be described as brutal, 100kms a day of full throttle running for a couple of k's to get away from cars doing 90 to 100, then intense stopping to get off the road before a tin lid tries to run me over again. If I'm very lucky, I can get 4 weeks out of set of Organic brake pads on the rear, just to give you an idea.

And with the jetting the same as the WR200 as discussed a few posts ago the little ring dinger is transformed. Six months on with the WR200 jetting, I was due to give the power valve a service. I was 4 days too late and snapped the power valve, which nicked the rings and of course another rebuild was on the cards. Off came the head again for number ??? rebuild (I really can't remember how many times I've done this now). But this time instead of seeing a piston with the usual mega hot spots and countless scores both on piston and bore, they were pristine. I shart you not, I could have reused the piston and just put some new rings on it. Not something you can normally associate with a DT230 rebuild.

So now I've got proof, the jetting on the DT230 MUST be changed, the stock jetting will kill your DT230. Get the snorkel off, change the jetting and here's another tip...get rid of the power valve. I just unplugged the power valve motor and left it there, but pulled everything else out and put the same cap which goes on the right hand side into the left (I had a spare which I had previously broken trying to lever it out with a screw driver).



As I discovered the power valve is also a major constrictor which does not open as far as it should, which is to do with more emission crap. And yes I had the power valve cables adjusted correctly. Apparently fitting an older DT200R CDI will allow things to operate as intended. Performance difference without the power valve is astonishing, you would not know it's the same bike. The 4 stroke characteristics have of course gone, but with a little clutch abuse the DT230 will take off quicker than it has ever before. I already had the stock chamber on and thought I'd give the stock muffler a try as well. Couldn't believe it, the stock muffler gives the little ring dinger the perfect amount of back pressure to compensate for the removed power valve.

So, for all DT230 owners out there, your little 2 smoker will thankyou in many ways if you try this:
1, remove air box snorkel
2. install WR200 jetting
3. remove power valve and cap hole
4. put stock muffler back on if you've taken it off
5. GO LIKE STINK.

Here's mine now with close to 50,000 kms...DT230's rule.



Offline EMMS

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Re: DT230 Performance and Improvement
« Reply #6 on: June 22, 2015, 05:36:19 PM »
Great write up there mate!
I know I'm in the wrong place, but would the WR200 jets work better on the DT200 as well?
Ive never touched the jetting on mine and it doesn't feel like it revs out cleanly or freely enough.
1993 DT200
1980 DS80 Gone
2007 PW50 Sold




DT200/125 Expansion Chamber Mod, How To Video!

Offline CBR600

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Re: DT230 Performance and Improvement
« Reply #7 on: July 28, 2015, 08:37:09 PM »
What is the power jet rated at ?