Okay- so I am in the final stages of getting my bike back together. When I traded for it, a majority of the pieces were in boxes.  Today I am undergoing getting the carb cleaned up and ready.  I have the stock Mikuni carb and also found a Kehein PJK 38 in the boxes. Both were dirty on the exterior but looked pretty clean on the inside. I have decided to deep clean both of them and get them back together. Which is the better carb to use? I have a new top end that has been o-ringed, the correct squish set and what appears to be some minor porting by Jerry Hall. With this I need to use higher octane avgas or racing fuel. That is pretty much it for engine mods with the exception of new piston, rings, billet washers and appropriate roller bearing and boyesen reeds. Will the stock jetting work for either of these carbs? Where should I start? I live a couple hundred feet above sea level here in Washington State.  Thanks in advance

Personnally I think the Mikuni's are easier to tune. Send the carb to jerry and get it bored to 41.5. How does the slide look in the mikuni on both side's? What Style mikuni 87 or 88-90 style. Your jetting will be different. with your setup and the 88-90 carb I'd say start about 420 and work down. My 89 w/ stock ports and carb, V2 reeds and a Q pipe likes a 390 at 75-80 degrees about 600 ft above sea level. Same combo with fmf liked a 380.

What are the numbers stamped on the side of the carb?

One thing I learned early on was the 87 Mikuni Carb was prone to leaning out the motor on deacceleration (need further back up). Seems like the ZIlla crowd likes and uses the 88 and up Mikuni's

Now speaking from experience, I had my Mikuni worked over by Jerry Hall. It starts great, idles, and works well. I rode the sand dunes in 90 degree heat and just recently rode in chilly 50 degree fall weather with a minor adjustments.

On the old site there was post after post and post about people having a hard time getting the idle circuit on the Keihins to run. This may also contribute to the legend of the hard starting Zilla. Just my 2 

This is what he is talking about on the PWK, Right side is OEM idle adjustment, Left is the longer Plastic screw I made with longer spring to secure it.

You can see there is alot of adjustment left

one other mod i did to my pwk was to address running out of fuel at wot.  The mikuni has a great set up for fuel to the bowl.  nice large fuel line port and float seats you can change out orifice sizes.  You cannot do this on the pwk.  I was running out of fuel at wot for longer runs / taller gears.  I moved the foats up to the border line of flooding over and ever so gingerly drilled out the bowl vents to a larger size.  The two bowl vents are just tiny out of the box.  I also lined up the holes on the bowl drain / jet plug with the bowl divots gaining a few cc's more fuel capacity.  No more wot fuel starvation issues to date.

Side note**
If you F up your pwk drilling the bowl vents out, dont cry to me!  i did it pre-beers for increased accuracy 

It does not matter what year Mikuni TM 38 you have.  We can make either one perform equally well.

Okay- so I am in the final stages of getting my bike back together. When I traded for it, a majority of the pieces were in boxes.  Today I am undergoing getting the carb cleaned up and ready.  I have the stock Mikuni carb and also found a Kehein PJK 38 in the boxes. Both were dirty on the exterior but looked pretty clean on the inside. I have decided to deep clean both of them and get them back together. Which is the better carb to use? I have a new top end that has been o-ringed, the correct squish set and what appears to be some minor porting by Jerry Hall. With this I need to use higher octane avgas or racing fuel. That is pretty much it for engine mods with the exception of new piston, rings, billet washers and appropriate roller bearing and boyesen reeds. Will the stock jetting work for either of these carbs? Where should I start? I live a couple hundred feet above sea level here in Washington State.  Thanks in advance

I prefer using the Mikuni carbs in all of the LT 500 applications.  The TM 38 carbs have 3 more tunable circuits than the PJ, PWK, PWM, or Air Striker Keihin carburetors. 

You cannot change the needle jet, float valve size or the air correction jet in the Keihin carbs. 

Ones understanding of what each circuit does and how they overlap is imperative for carb tuning.  Ones tuning ability also has to increase as the number of tunable circuits within the carb increases.  More tuning circuits makes it possible to fine-tune the engine to a higher level than carbs with less circuits.

If a manufacture made a carb that only had one tuning circuit and only made two jets to fit that one circuit, you would have two chances to make that carb work the best it could work.  In this example one of the jets would not necessarily make the engine run up to its full potential but one of the jets would make the carb run at its full potential.

My experience has shown that most professional tuners prefer carbs with more circuits.  Carbs with fewer circuits and fewer tunable circuits are preferred by those with less experience because there are fewer choices to make from a smaller selection of tuning parts.

Can this quad benefit from a lectern alcohol carb??