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
Forgot to add- I currently have a FMF pipe/silencer and this quad will primarily be run in the sand.
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.
Forgot to mention the bike is an 1987, so I am assuming the carb is as well. How can I tell one year from the next? The slide looks great on both sides. Actually the inside of the carb was very clean, I just wanted to make sure, so I am deep cleaning it. I will have to see what jets are in it. I was thinking about sending it down to him to have that done, but before I did that, I wanted to make sure the bike will run. I have never heard it run as pieces were in boxes when I got it. T
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
The PWK dosent allow for enough air at idle / slide closed so stalling can be an issue on the big engines. You have to run a slightly longer than stock slide stop screw (metal screw from keihin will be in all the way with no lock nut). On the up side, they are crisp with the right slide - im running a top trimmed #6 on a 41mm, and offer great performance mid to top. Bumping up my slide a c*n! hair should solve it, ive just learned to deal with it for now.
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
you have any more springs left? Only reason i havent put it on as i was needing to get a lock nut like the oem steel. I took off the lock nut to put the oem in all the way and lost it.
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
On the side opposite of the Mikuni manufacture logo there are two squares on the intake side.
Top square has 43B and 00
the bottom square has T7 and 15
I do not see any other stampings with the exception of Japan
The main jet is 440 I can't read the stamping on the pilot jet
It does not matter what year Mikuni TM 38 you have. We can make either one perform equally well.
That's a 87 Carb -
Sending it to Motorgeek (Halls!!) is never a bad choice to get it worked.
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.
The mikuni just got sent down to Hall's Precision. Thank you Jerry, I appreciate all of the knowledge and it was nice talking with you.
Can this quad benefit from a lectern alcohol carb??