VM30 tuning...

So, I have a bit of a balancing act going on right now.
Pilot is #15, and when air screw is out 1/2 turn, it idles at it's best, and starts it's best. After this setting for a few days driving my plugs soot up.
If I go out 3/4 turn on the air screw, it doesn't start as good, and the idle is a bit hoppy/lean, if I adjust the idle screws a tiny bit, it goes from 2500 rpm to nothing. But after driving the plugs look great, nice tan/grey.
So I'm thinking I need to leave it at 1/2 turn out so it starts and idles at it's best, and since most of my driving is at low throttle positions I need to drop the P-5 needle jet, a size to P-4 or P-3 or go with the 176 series, and it sounds like I'd start at the P-8 or P-7? Sounds like they are about 4 sizes difference between the two? Sound about right to anybody? Thanks
 
Get the bike warmed up, get it on the street and hold steady at 20mph in 3rd gear. You should be able to hold this speed without adjusting the throttle position. If you're having to tweak the throttle to hold the speed, your pilot jet is still too small.
 
Thanks Sonreir. So i did the test at lunch.
To start it, it was set a 3/4 turn out on the air screw, wouldn't start, so I changed it to 1/2 turn out, and it started, had to use the choke for a second. Warmed it up good, and idle was high so I lowered that a bit.
It passed the test real well, I went for one mile at 20 mph and it stayed steady and ran well the whole time. When i got back home I checked my plug, and the soot that burnt off the plugs from having the air screw 3/4 turn out, had came about halfway back, so by the end of the day I'm sure it'll be completely sooted again.
I also tried adjusting the air screw again, and if I go in or out any amount the idle falls off fast. So I'm thinking the pilot system is good, and the needle jet needs to be smaller?
 
After setting the pilot system, you'll want to tune the main jet.

Find a nice long stretch of road with little or no traffic. Do a 5th gear run at wide open throttle from 30mph to 60mph and time yourself. Repeat with larger jets and see if your time gets better or worse. If better, try larger jets again, if worse, go smaller. Repeat until the best 30-60 time is achieved.

Also... if you find you're lugging the engine in 5th at 30, you can do a 40-60 or 40-70 instead. Try to use a wide range though, it helps to average out an inconsistencies in timing.
 
Sounds great, thanks. I didn't think to do the main next, I know I'm off there already because if I use WOT now it bogs down. It only goes up to speed if I open it slowly. I'm assuming it's because it's lean, I'm at 145 on the main jet, and because I only have larger jets, I'll try going richer first.
 
Well, I was at 145 for the main jet, went to 155. I was in fifth at 30, also tried 40, and when wide open throttle it just bogs and won't catch up. Jumped up to 170, same drill, and it bogs at 40 but then catches up but not very good, so time to order some larger main jets. Thanks for the help.
 
The issue isn't whether or not you're bogging...

You need to use a stop watch. You're measuring times and looking for the quickest.
 
OK, so if I'm idling at 30 and crack the throttle wide open and it bogs and won't speed up...What I should do instead is roll into the throttle as quickly as possible without any bogging, and time accelaration.
What I was thinking is that I'm still too lean, and until I get rich enough so that when I crank the throttle to wide open quickly and don't have any bogging, is when I should start the timing/jet changing process...but maybe with the Mikuni carbs and the older engine, it won't work out so that I'll ever be able to go wide open instantly and not have any bogging, instead it'll always be a roll to wide open, and finding the right main jet so I can roll into it the quickest?
Hope that makes some sense?
 
I think that's a good strategy. Once things are dialed in, you should just be able to crack the throttle and the bike will respond.
 
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