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Dt125R '92 Engine Rebuild Problem

#1 User is offline   zaf 

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Posted 03 April 2017 - 03:00 PM

Hello to all, :wave:
i have put new piston 59mm on my dt and when accelerate, the engine is not running whell.It makes a noise like smasing metal and i have to close the throtlle until the speed is reduced to 70-80km/h.Until 80 everything is ok.It seems like misfiring at high revs.
i have check and relpace some parts like:
CDI
HT coil
sparc plug & pipe
Puls coil
stator coils

The stock curb is 28ss Micuni and from 240 main jet now is 250 and pilot jet is 25.The needle in 4th position.
The air filter is new Twin air.
The power valve is working perfect( i have reduce the valve body because it was near the piston rings)

I'm very confused and ican't enjoy the bike... :cry:

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#2 User is offline   zaf 

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Posted 05 April 2017 - 03:39 PM

Hello again!
Today when i drive back from the office i reduce the fuel flow to the carb by setting the fuel tap not full open and the DT was running better without detonations ,I guess i have tou adjust the carb floater... :ponder:

ps. The needle is in position 2 not 4 :biggrin:

#3 User is offline   tzrtony 

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Posted 05 April 2017 - 04:19 PM

Hi Zaf, it could just be that your jet is too big. but without running a tune on it there is no real way to tell properly by how much.


If you ever get any issues with the engine, head over to the TZR section, as we share the same engine.

I would run through spankys 2stroke tuning guide (found in the manuals section of the TZR sub-forum)
that is a DIY idiots guide to tuning.
I call it an idiots guide as absolutely anyone can follow it and get it somewhere near right :) lol. but follow it to the letter. http://www.125ccsportsbikes.com/forums/public/style_emoticons/default/thumbsup.png

#4 User is offline   zaf 

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Posted 05 April 2017 - 05:16 PM

View Posttzrtony, on 05 April 2017 - 04:19 PM, said:

Hi Zaf, it could just be that your jet is too big. but without running a tune on it there is no real way to tell properly by how much.


If you ever get any issues with the engine, head over to the TZR section, as we share the same engine.

I would run through spankys 2stroke tuning guide (found in the manuals section of the TZR sub-forum)
that is a DIY idiots guide to tuning.
I call it an idiots guide as absolutely anyone can follow it and get it somewhere near right :) lol. but follow it to the letter. http://www.125ccsportsbikes.com/forums/public/style_emoticons/default/thumbsup.png

Hi tzrtony,thank you for your reply! :cheers:
About the mainjet the stock was 240 and the pilot 25 for 1991-1992 year models.Because of the 59mm (from 56mm)piston I was afraid that
the fuel could be lean for high revs and I cheked the spark plug and it was dry.So thats why i put 250 mainjet...

Anyway I'll check spankys tuning guide and i hope to have the DT running like before, without any issue.

to be continued...

This post has been edited by zaf: 05 April 2017 - 05:17 PM


#5 User is offline   zaf 

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Posted 25 April 2017 - 06:40 PM

Hello,

After the adjusting of the carb ,detonations in high revs was still there so I desided to
open the cylinder head and i noticed that the top of the piston was about 1mm higher from the top of the cylinder :surprise: .I think that its not right because everyting will not
be in proper position ,from the timming ,the fuel ports,the compresion will be higher.
I will try to put base gasket 2mm to see if the piston will level with the top of the cylinder.
Can this cause detonations?

#6 User is offline   zaf 

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Posted 25 April 2017 - 07:07 PM

...how much has to be the squish clearance ?
My cylinder head is 3bn on 3mb cylinder...

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