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Discussion Starter · #1 ·
Guys need some help,im stuck!Need to know what size drill bits to use to drill the jets and the dump tubes on a keihin 38mm PJ. Some people say .120 on the mains.Do i need to drill or just buy a larger set of jets. I know this is permanent on a keihin, thats why im doing this on a spare carb. Any help or tips would be greatly appreciated thanks! oh this is on a 89 trx250r if that makes any diff. thanks again everyone!!!!!!!!
 

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AS far as size to drill on a 250R im not sure, you will however need to have a needle specifically suited for alcohol on your size bike. You will also need to drill out whats called the " Dump Tube" which is the tube the needle goes thru and at the bottom of that tube is where the mainjet screws into and you will need to drill mainjets as you can not buy .118- .125 sized mainjets. A .120 is a 3mm size hole which would be a 300 size keihin main. You will probably also need to install a powerjet in the carb to feed it the fuel it needs at WOT. Drilling the dump tube is the one real permanent change top the carb that can not be reversed.

Honestly, I would have someone else set it up for you or at least get you the proper needle, powerjet etc . Many of the site sponsors on here are knowledgeable with 250Rs and alky.
 

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The absolute best way IMO is to buy a reamer to get the hole size exact. When drilling brass the bit tends to grab and get pulled through very quickly, and a little movement will make the hole a different size.



If you could find a lectron or mikuni to start with, you could backtrack and correct any accidental problems.
 

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Mikuni has changable dump tubes if u use a mikuni start with a 120 main n tube needle is a dp4 on the 38-41.5 flat slide carb, start with it raised all the way up rich is safe install a power jet and start with it all the way open. You can always lean it out if needed
 

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Guys need some help,im stuck!Need to know what size drill bits to use to drill the jets and the dump tubes on a keihin 38mm PJ. Some people say .120 on the mains.Do i need to drill or just buy a larger set of jets. I know this is permanent on a keihin, thats why im doing this on a spare carb. Any help or tips would be greatly appreciated thanks! oh this is on a 89 trx250r if that makes any diff. thanks again everyone!!!!!!!!
I'm with bubba make sure you use reamers. Depending on your engine set up I would use a .120 reamer and an EGQ needle. Make sure to use a pump and bowl don't mod the floats.
 

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Discussion Starter · #6 ·
thanks everyone, all the info is greatly appreciated, cooler weather here now,alky will be a good winter project
 
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