Starting Point with oversize carb

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I’m new here and new to the Blaster community. I’m very familiar with two strokes but I’m coming from MX bikes.

I just picked up a cherry all original 91 Blaster from the original owner. It probably has 10-12 hours on the whole bike and is completely totally stock. Truly a barn find. I just brought it home last night but the owner tells me he put a new stock replacement air filter in and cleaned the carb. I don’t believe it’s ever had any other wrenches turned other than the occasional oil change. Again, I’ve not had time to even take the seat off yet but I expect to find whatever it was originally equipped with in place. Air box lid/snorkel or however they come.

In my infinite wisdom, I have gotten carried away and agreed to buy another Blaster I found on Craigslist. This one supposedly has a fresh top end, brand new FMF pipe and silencer, and a Keihin PWK39. I’ll be buying this one mostly for these parts, and also as a donor for it’s hydraulic brakes. The guy claims it rips and I’ve talked with him enough that I believe him to be a fairly competent tuner.

My questions are....is the 39mm carb way too much for an otherwise stock (minus a pipe and maybe some intake mods) Blaster? Is this a common conversion? I actually have a spare PWK38 from my KTM 250 that I could slap on one of the blasters if that’s not too much carb. Is there a recommended starting point with the jetting on a PWK 38 or 39? I’m capable of fine tuning but I’d like s good reference point.

If this is way too much carb like I expect it may be...where should I start with the stock Mikuni?

Also for the intake side...what’s the best way to go? Is there simply a lid or snorkel that I can remove from the stock air box? I’d like to use the factory foam filter and don’t want to run a pod filter or anything like that.

Anything else a newb should know?

Thanks
 
WELCOME !!
That's a pretty big carb for mostly stock engine.
These have a snorkel, lid then filter in air box. Depending on other mods, removing snorkel + one size, lid + one more size. Make sure you have a quality filter.

Reason I say that about the carb is I have no lid, Vito's reeds, FAT BASTARD pipe, 3mil crank, heavily ported and still run stock carb.
Look through this thread https://www.blasterforum.com/threads/what-jets-are-you-using.28981/ might find something. Also the search function works great on here.
Maybe someone else will chime in that has experience with larger carbs.

Also, be careful of "New top end" those cheap eBay engine kits have poor quality and reliability. When a new cylinder, piston, head , and gaskets cost less than a Wiseco piston you have to wonder.
 
Thanks for the input. I too would think that a PWK39 would be way too much for a 200 in a mild state of tune. I may pass on this thing once I see it, but like I said I’m mostly interested in the brand new pipe, silencer, and brakes.

From looking through that thread you linked and doing some searches, it would appear most people just up the main jet a few sizes. Does nobody mess with the pilot, needle diameter/taper/clip positions, slide cutaway, etc?

I’m pretty picky with jetting and am used to altering my setup regularly depending on temps and riding conditions. I’m coming from engines in much more aggressive states of tune, though...maybe the milder Blasters just aren’t as picky?
 
38/39's are mainly only run by drag guys where full throttle is all that matters, and the occasional big bore guy who thinks bigger is better .... it is not, especially for a trail blaster
the stock carb is fully capable of handling all the mods you list, and even some heavy porting and head mod.
stick with the stock carb.
 
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I have a large toolbox full of needles, jets, slides, gaskets, floats, and assorted spare parts for the Keihin PWK. if I wanted to slap a PWK on just so I had better parts interchangeability with my other bikes, what size would be optimal for a mostly stock blaster? 28mm? 33? 35?

Thanks
 
28 max for a stockish blaster
 
I’ve decided to pass on the second blaster that has the 39mm carb. Too many weird things going on with that one.

I’m going to do a few basic things to this cherry 91 I’ve got though. I have ordered a toomey pipe and silencer. I’ll be ditching the airbox lid and swapping out the main and lowering the clip on the existing needle per their instructions. I’ll keep my eyes open for a good deal on a PWK28...if I’m not mistaken there are a few 80 MX bikes that use those.

I’d love a baseline on how to set up a PWK28 if anyone had recommendations..
 
Reason you don't see anything about needles and slides is because stock works just fine for most applications. That being said I run Vito's needle, it was designed for that pipe.
Don't think I've ever seen anyone change a slide even when adapting a carb from a 85/125 change the slide. That's getting pretty deep into tuning.
I've never, and don't even remember how/what it affects. That happens when you get old.:D

You seem to know a bit about 2s. I suggest you port your engine and get the head modified. Ken O'CONNOR vids on youYouT, get sport port templates from Ken, or send him your cylinder.
The power increase from porting/pipe will blow you away.