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1991 DR350 Dirt air filter and big bore question

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So I am looking for some answers on where to go with my build on my 1991 DR350 dirt model.

First I need to check to see what is actually in the engine and what condition it's in.

I recently purchased this bike and it obviously needs some help.  It needs the clutch cable replaced as well as the splined arm for the clutch and I will add the decompression lever back onto it.  I also purchased a tub of DR350 parts that included an additional stator off of a newer DR350 with lighting (I'll be using this to make it street legal), a new Weisco piston set that is a larger bore, gaskets, cam, gears and some other parts that will be nice just to have for spares.

If/when I tear it down and redo the engine....

My questions are:

#1-With the air filter that is currently on the bike (K&N style) I am not a fan of that style and usually prefer the other foam brand (Uni Filter) with the prefilter as well.  Anyone out there that has tried several filter options? Would I be better off to find a stock air box and do the mod to it? Keep what I have or get the Uni Filter which would need the airbox anyway?

#2-The Weisco piston that came in the tub of parts (brand new with wirst pin, rings and clips) is only an 80.00mm bore (3.1496) and stock being 79.00mm and 3.11ish.  Which is basically a one size up replacement piston for the stock one that seized and needs honing to replace.  How much difference is there is the stock vs the 385 kit?  How much difference with stock vs the 83.00 mm (4mm larger over stock, 367cc according to Weisco) piston?  I don't really want the 440 kit but a little more out of the stock engine would be nice.

My other plans are to abandon the current exhaust and do the GSXR 1100 can exhaust on it.  I have access to a machine shop (brother works there) so I also plan on cleaning up the ports and possibly redoing valve seals and whatever else it needs.

Here are a couple pics of what I have in its current condition.59136576c1970_DR350airfilter.jpg.f0fc10ef28e34b0d74fc13a1eb6c654d.jpg5913655b6430d_DR350Front.thumb.jpg.6246f6c82972223a887132f6f4a12f5e.jpg591365d7226e6_DR350side.jpg.3b22651d4f1ae21a749682ec70f535fb.jpg591365e2c3042_DR350left.jpg.e6f27b3df8d092904118cfcfc4fd0850.jpg

 

 

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#1-With the air filter that is currently on the bike (K&N style) I am not a fan of that style and usually prefer the other foam brand (Uni Filter) with the prefilter as well.  Anyone out there that has tried several filter options? Would I be better off to find a stock air box and do the mod to it? Keep what I have or get the Uni Filter which would need the airbox anyway?

yes find a stock airbox & boot.

no dont mod it.

get a foam filter for it such as Uni or twin-air

 

cant answer you engine questions, but the more important thing is the condition of the head/ rockerbox journals, cam & rockers

 

 

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