VM24 w/ pods rich idle issue.

I haven't had a chance to do anything. Will tinker with it this weekend I hope.

Will update on what I find

So i've been tinkering with this all morning.

First, i used another carb bowl and blocked the choke port in the bottom of the bowl with a a bit of hot glue. AFRs on that cylinder did not change. So it's defintely not some weird choke issue.

second, i took an old main jet and soldered the end of it, essentially capping off the main jet. That cylinder idled at 16+AFR and, of course, immediately pegged full lean with any bit of throttle. I'm surprised the needle/needle jet have this much affect on the idle. Ill the diagrams ive seen say its 1/4 throttle or higher.... Anyways, good to know.

I pulled a needle out and took some measurements. No markings, but right off the bat its .5mm longer than a 5DL31 and it has 6 slots. These measurements dont match up to any 5 series mikuni needles. They are more aggressive than a 5DL31
a 58.48
b 23mm ish
d1 2.50
d2 2.50
d3 2.26
d4 1.76
d5 1.27
d58.5 .92mm

When i got the carbs they were clipped to #4 and i put them to #5. I have moved it back up to #4 and will try that out. Putting the unknown needle at #4 side by side with a 5dl31 at #3 shows it should be pretty close except for the more aggressive taper on the unknown needle.

Also, i took inventory of my spare parts. I have:
4x y63 (same as 5DL31)
2x 5DL31
4x 5DL35

]If the needle is stainless steel, it might be a dynojet needle.

And yes, depending on the shape, the needle position has a huge effect just off idle and light cruise.

First thanks for the update. Sounds like you have been busy finding the solution.

It probably is a dynojet needle then. I cant find a spec sheet with all of their needles and specs... not terribly important i guess.

So i got the needles back in and went for a test ride. It definitely needs a re-sync but off idle AFRs are much better.

Idle is still around 13.8.
1/8 is around 12.5 (used to be ~10.1)
1/4 is around 13.5
around 1/2 is a bit lean though. I saw some 14-15-16 AFRs.
Full throttle is ok around 13.8/14

What are your guy's thoughts? If i bump the needle up another clip, the 1/8 will be better, maybe even too lean, and the 1/2 throttle will definitely get too lean. Im thinking a half clip higher on the jet needle and go up to 115 from 112 on the main jet?

What outside temperatures are you dealing with? And are you testing in high humidity or very dry (desert) type environment.
AFR's change a bit with temp and humidity.

I try to do my tests around 70 to 75 deg on an average humidity day. That is about the midpoint of the weather I typically ride in.

Are you holding the throttle at those positions and letting the bike get up to speed?
At any rate, the your 1/8 is a bit rich. It will run fine but gas mileage will be a little low.
Your 1/4 would be ok if it was getting richer at larger openings, but I'd rather see 1/4 at about 13.
Your 1/2 is definitely too lean. 13.8/14 is more a target for 1/8 doing light steady cruising (60 to 70 mph).
If you twist and hold to 1/2 throttle, it should start out in the 11's or even 10's, and as the RPMs increase, the AFR's should sweep through the 12's and hopefully end up right around 13 at redline.

Be aware, most throttle stops are set so the WOT goes slightly past fully open. That is, the slide goes beyond the maximum opening of the carb throat. That is a little safety device to enrichen the mix at WOT in case someone is just holding it to go top speed. That's fine, but it gives a skewed representation of your jetting. Because just slightly off WOT, when the slides are exactly at fully open, it will be leaner than the throttle-stop position. You can adjust the stop for testing purposes, or just remember to not go to WOT and stop your hand just short of WOT for testing.

If your results were on my bike, I would lower the needle yet again, probably half step using a shim, then put in a larger main. If you see any throttle higher than 3/8 going beyond 14, let off the throttle and get a larger main.

It is a bit colder but I haven't seen a difference at the rich spot with lower temps.

I havent been following that process exactly. Will do more testing and see how it goes.

I luckily have some brass spoke washers that are perfect for half clip positions woooo

Thanks again.

Don't mix Dynajet main jets with Mikuni. Dyna jets are to be used with their needles and the numbers on them do not match Mikuni's numbers. It will drive you crazy trying to tune the carbs if you start mixing them,

The carbs had type A 118 mikuni mains. I am using type c mikuni mains right now and they're drilled out to 115ish (I'll buy some when I figure out what I need)

As for the testing, Half slot higher clip made 1/8 too lean as well as everything else.

If I could figure out what dynojet needle this was and find one that gives me #5 slot 1/4 + throttle and #3.75 slot 1/4 and lower throttle id do it, but I'm happy enough with the way it is at #4.... So it looks like I shouldntve screwed with the jetting at all and just ran it the way it was to begin with!!


I think I'll be buying a newer bike with EFI for next season anyways.

When you lowered the needle by half step, did you also increase the main jet? It was rich at 1/8 and lean everywhere else, so lowering he needle was to lean out 1/8, but a larger main would be needed to compensate for everywhere else.

The numbers on Dynojet jets are in hundredths of mm, but I don't know what the numbers on some Mikuni jets mean, if anything. They don't seem to correspond to a diameter. Tk jets are in hundredths of mm and some Keihin are in hundredths of mm.

I did go up to a 115 from 112, but the 115 bit didn't do much so they were probably already close to 115.

I currently have 118 mains at slot #4 with resynced carbs. Runs ok, but there is a rich hesitation right off of idle. 1/8 throttle and higher is fine. I will test out this setup today and maybe go back to 3.5 slot on the needle with this larger main. Maybe a 120 main or higher, whatever it needs. I got fed up with this whole thing last night but I feel better after sleeping on it hahaha

I guess I probably haven't seen a genuine mikuni jet. I am fairly confident on the jet sizes as I have micro bits to gauge them.

Did another test run for 118 mains and #4 clip.

idle a tad rich. around 12.8 to 13.1. need to tweak the idle screws.
off idle to 1/8: still rich and chokes a bit
1/4: perfect for cruising at speed... ~14.5, almost too lean
1/2 3/4: great, they end up around ~13
full throttle tad rich but workable. ~12.5. I may have been too far open and hit that over rich safety feature. not sure.

I still plan on trying the #3.5 clip on the needle though i am a bit worried about 1/4 throttle. If everything else is ok i might try 1.5 CA slides or those little .5mm jets that target the lean 1/4 throttle range and screw into one of the ports in the carb mouth.