curious as to what main jets y'all are running on your rigs. what main jet comes stock on the mikuni?

I'm running a 2011 prodrive with IM heads, MM exhaust and mikuni and appear to be running very lean and i think it has a 160 main in it now, but could be 165. i bought the carb kit from setx performance.

any does any one have a good website to order a new tiny tach from? mine has stopped working properly.
if anyone has similar mods to mine could give me some info what size main jet would be better suited for my mods?
thanks

I had a 160 mainjet in my mikuni when I got it from boat doctor. I think that's wut they unusually put in them. Wut makes u think it's lean?

the new spark plug is still a half shade off white. and sometimes when i kill the motor, it deciders it going to keep running for a another couple seconds, isn't that from the motor being hot/lean and combusting on its own? I'm not sure and it dosent always do it. i'll turn the key off, it will stop firing and almost stop, then fire another couple times then it normally stops.

oh, i thought this post was about the jets in the hot tub i used to put my willy on when i was a kid...

I had a 165 with just carb and exhaust and it was too much

It depends on temperature and elevation... what works for me probably wont work for you!

I ran mine with the 160 today, because I couldn't find a freaking mikuni round jet anywhere in this stupid town, but it was a brief run because the motor definitely is running too lean. I think the needle needs to be adjusted on to the richer side as well.

What causes the motor to run for a second or two after you kill it? Mine does it too.

I got all these parts from yall last week...
IM heads, Mikuni 42mm carb, Q-Pipe
Fresh 90 octane fuel (from a clean, waterless tank) RC12YC plugs gapped to .020 (same plugs it comes from factory with).

SO- maybe a colder plug?

Try the autolite app 3923's. Lots of us using those with good results. Gapped at 35 instead of 20

Ran with the 167.5 today... looked at plugs, they looked as if I just took them out of the package after a mile and a half of 3900 RPM.... tried a 170 next (biggest I got since I didnt think I would need it) and the same thing.
So- what could be causing this? No air leaks... air temperature 45-60 degrees, 300' above sea level. Oh yea- I tried autolite APP 3923 gapped at .035 during this run...

Also- the bottom end is very boggy, if you grab a handfull of throttle from 800 RPM idle, it will sputter and die, and will put out a little bit of black smoke as well on the bottom end (almost as if the choke were on, but it is not)

The needle clip is on the 3rd one up from the bottom. I'm not super familiar with the other adjustments on the carb. There's got to be somebody wondering the same thing...
Thanks in advance for help!

First make sure you have full throttle travel with your throttle cable. If you are only getting 3900 RPMs in the water with heads, exhaust, and carb you may not be getting full throttle travel (note this is assuming you are trimmed at the optimum position while running). Clamp down your throttle handle at the tiller then make sure the throttle on the carb is fully opening (there should be no play). Depending on your throttle cable, you can move the adjuster or bend the bracket that holds the throttle cable at the carb until you have full travel. I am also assuming your valve lash is set correctly (0.004-0.006 for stock cam).

The Mikuni has different circuits that you tune independently- Idle (0->1/8 throttle), Mid Range (1/8->3/4), Full (3/4 +). Do you have a tuning manual? If not- Google Mikuni HSR Tuning Manual and download the PDF. Read the whole thing (doesn't take long) and then read on in the post.

Get your Idle/off Idle set first and go up. Adjust your pilot air mix screw to get a smooth idle and crisp response off idle (get rid of the bog you describe). Screw in the adjustment screw until it bottoms out and back it out to set it initially about 1 3/4 turns out. Then on a warm motor, micro tune until you get a stable idle and crisp response off idle.

After you get the Pilot screw at the position for the best throttle response, if you still have a little hesitation as you transistion past 1/8 throttle then try adjusting when the Accelerator Pump kicks in. Adjust the #1 pump adjustment screw referenced in the tuning manual to reduce the gap between the pump rod end and plastic lever (standard setting is 2mm). This is a minor adjustment and you should have a crisp response through the acceleration.

The jet needle size determines the performance between 1/8 and 1/4 idle. I expect the standard jet needle (-97) should be fine for your setup. The E clip position on the jet needle determines the fuel flow 1/4->3/4 throttle only.

The main jet is your primary adjustment for 3/4 throttle plus. Use the roll off method described in the tuning manual and you should be fine. A 165 will probably work for your mods (and altitude) but if you want more cushion install your 167.5 (you aren't doing time trials). Assuming your main is fine, then you can set the E clip position on the jet needle so your transition from 3/4 to full is smooth both accelerating and decelerating.

If you are expecting coffee colored plugs after a mile and 1/2 run you will never see it. You are looking for a ring at the base of the insulator. If you really feel the need to check this, then warm up the motor with a set of old plugs in (~5 mins). Stop the motor and install a brand new set of plugs (wearing gloves helps). Start the motor and without idling go immediately to full throttle and run for about 2 miles then kill the motor (do not idle). Remove those plugs and reinsert the ones you started with. Take the test plugs back and look at the base of the insulator, you probably won't be able to see anything with them unless you chop the threads. This is an expensive way to do it, or you can take the advice of all the people on here that run a similar setup and altitude and assume the main is the size you need, then tune from there. Note, those 3923's are cooler plugs and should be fine.



Hope that helps you. Others may chime in if I left something out or scewed something up in the description above, haven't had much coffee yet.