Pilot jet up, or main jet down?

[4T_Goblin]

So I found some years old shed weed out back recently and of course I had to try it out. Here's the result.

On my Vader I'm running 35 pilot, 110 main in a genuine mikuni vm22 from Niche. I have an aftermarket pipe from Venom Motorsports which is the same as the stock but minus the cat. Polini pod filter. After a long ride my bike gets weak, leading me to believe it's getting lean, like the main jet is drinking up the reserve before the pilot has a chance to refill the bowl. By weak I mean the idle gets really low and it will stall. Always starts back up with a lil throttle crack. So I have to keep some air flow.

Here's the shed weed talking-

Should I pilot jet up to 38/40 from 35, or drop my main jet down to 105 from 110?

This is a genuine mikuni, stock (per their website) is 30 pilot/100 main. I went up initially because A) I didn't know quite what I was doing, and B) I jetted up because I thought I should due to the filter letting in more air than the stock box and the pipe being more open than stock.

If you have some shed weed go smoke it up for best quality answers.

Thanks for humoring me

[braindead0]

you are mistaken if you think the main jet is starving the pilot for fuel. The pilot jet does not 'fill up' the bowl.

Check the fuel tank vent, if it's not venting properly over time the tank will vacuum and that will starve the engine for sure.

[4T_Goblin]

Yeah my mistake I know fuel comes through the float valve. And the pilot is not responsible for the filling of the bowl. But rather it's the main component in the idle circuit. It's the shed weed
Definitely will check the vent hose. It's something I look at every once in a while but I forget to check it more often. Good reminder.

[Bob Kelly]

Hard to say with the little discription you have given on how it runs !
my guess is that it is running good but later on in the ride it starts to starve for fuel
there for as the other guy said fuel vent is probably not venting from the gas tank
I concur with that assessment ! it's also possible that your float level is set a bit low
I would quit using your shed weed till you figure out the bike, before you cook it ! and seize a piston !
larger pilot jet is ONLY if the engine needs it to idle correctly
larger main jet is needed only if your running lean at WOT ( wide open throttle)
no "I think it will need it" ideas work here, so put the stock jets back in it and assess
if it needs it.... it may not ! you do not put in new jets just because you put on new air filters Some times it is needed but only some times Opening up the exhaust usually does mean jetting changes because they have the engines so de-tuned to pass emission standards now days..... but making changes to the carburetor without knowing which way to go or a reason to do it is totally folly !
put the stock jets back in and then tell us how it runs down to the last nitty gritty detail
...for example ...there is a slight pause when it comes off of idle when I give it throttle ( too small pilot jet or simply not adjusted correctly)
or it takes off great until i reach mid RPMs and it slows down accelerating (too small main jet)
and what is the color check of the plug looking like ? is it white, brown or black ?
yes you must pull the spark plug and look at it to see <GRIN>
a carburetor works somewhat like this.... at idle speed your fuel is regulated by the pilot jet and fuel air screw, at mid range RPM it's working off the needle jet ,jet needle and throttle valve cutaway, at wide open throttle and top RPM's it's solely on the main jet.
.... this is a close approximation and each carb works a bit differently from any other but the principal is correct the carburetor is made in such a way that all 3 of those settings interact with each other as well so the transition between just off idle and into mid range there is a grey area where both are working to provide the correct fuel air ratio and the same goes for when the jet needle is all the way up that transition period needs to be a smooth one ...
do a plug color check when you notice the running low on power (Stop it right then and pull the plug) I almost bet you it will be very white.... and that is unhealthy for your engine !
....Bob....

[4T_Goblin]

https://youtube.com/shorts/KDf7d7oTEMY?feature=share

Here is the idle right now. This is with 37.5 pilot, AF turned out a 2 turns. Just experimenting.

I'll go back to the stock jetting but do a 21mm float level.

Yes the bike runs great but then after 10 minutes of riding with a long run of WOT is when it gets weak. I have some hesitation in the mid range if I snap throttle open too fast. I'll get the needle clip placed next but it's not really hindering my riding fun.
The float came stock at 26mm. I believe mikuni sheets say it's supposed to be 21mm but now I'm seeing the effect it has even with a few mm difference.
Last plug check it did it was almost good just a little on the lean side coloring

My clip is in the 3rd position, I reset it and the AF screw (to 1.5 out) every time I adjust a pilot or float level.

When I ride it sounds like I need to go to position 4 and it should take care of the hesitation. I've reprioritized to getting the idle tippy top.

[Bob Kelly]

Well good sounds like your on it then.... I'ed be concerned about that "little lean"
you were talking about.... before I would move the needle clip I would put in a larger main jet and try it....
back in the 1970's changing the jet needle was a absolute NO-NO ! now you hear of guys changing them at the drop of a hat.... personally I can't see that because it messes up the fuel air ratio all over the mid range scale , where changing the main jet will only make it a bit richer from 3/4 throttle on
I remember playing with the float level in a Mulkini carb in my younger years and the small amount of changing made a huge diference ! ...
and on my 2012 250R Ninja if their not "SPOT ON" you will have problems all over !
but those carbs are a nightmare to get clean ! been into them 2 times and I have to do them again because their not clean yet ! ...their a bitch ! that idle passage way is a bugger to get clean after setting for a few years !
....
I got my RX4 on the bike stand and the side stand off and shortened so it won't fall over now that I lowered the front and back.... stock it would fall over if the front wheel was turned all the way to the right... so I had to fix that !
....
Bob.......

[4T_Goblin]

Good note on the clip setting.
I think about getting an early 2000's ninja 250 all the time but not until I'm sure about getting a carb right. I'm getting closer. This mini bike scratches that itch for now. At least there's just 1 easily accessible carb to deal with lol.
I do have a 50cc 4 speed too that I love but I got it cheap enough I could put a ZS190 or Lifan150 in it later on

[krat]

Your carb does not warm up, your engine warms up and changes the requirements placed on the carb.

When something changes as it warms up it is usually due to expansion and contraction of the metal parts due to change in heat.

As that cold engine warms the super tight clearance of your valves reduces to nothing and the flow of air/fuel/exhaust changes with it.

I have noticed that everyone on this forum tends to adjust their valve clearances super tight on a cold engine. I have also noticed a lot of specs being mixed between metric and Imperial without proper conversion tables being used.

Check your valves and adjust to the proper specs. It does not matter what you do to your carb if your valves are screwed up. They every one come from the factory wrong and when people adjust them, if they adjust them, half the time they are adjusting to the wrong specs on an engine at the wrong temp.

[4T_Goblin]

Originally Posted by krat

Your carb does not warm up, your engine warms up and changes the requirements placed on the carb.

When something changes as it warms up it is usually due to expansion and contraction of the metal parts due to change in heat.

As that cold engine warms the super tight clearance of your valves reduces to nothing and the flow of air/fuel/exhaust changes with it.

I have noticed that everyone on this forum tends to adjust their valve clearances super tight on a cold engine. I have also noticed a lot of specs being mixed between metric and Imperial without proper conversion tables being used.

Check your valves and adjust to the proper specs. It does not matter what you do to your carb if your valves are screwed up. They every one come from the factory wrong and when people adjust them, if they adjust them, half the time they are adjusting to the wrong specs on an engine at the wrong temp.

Yep they are adjusted to .003" intake and .005" exhaust

[4T_Goblin]

Update: I'm back to 30 pilot, 100 main, float bowl level at 21mm.

The bike sounds good, runs good all the same, still wants to die out after a long run when I come to a stop, unless I feed it some throttle crack.

I did notice a little oil coming from what I think it's the lower valve tappet cover, could be a bad gasket from spilling gas on the motor. I'm looking at Grom gasket sets to find a replacement. I Found something at partzilla that appears to have these o rings. I don't think this is related but maybe the fact that there is oil pooling in the lower tappet has something to do with it?

The bike always turns back on with a little throttle crack. I'm wondering do I need to turn the idle screw in further?

I did have an issue where I overfilled the crankcase with oil, and I had a white smoke issue for a minute. I've since correct the amount of oil. But I can't detect a leak anywhere that I think it would be the crankcase seal having gotten pushed out.... Other than some not so good looking oil, like gas got in again, in that cover.

My plug was looking good on a plug chop. I ride for about 30 minutes because I started to have fun. I cannot post pictures on here as they are too large for forum to handle.

Everything works great, to just still having this little issue with dying at stops

[Bob Kelly]

Sounds like you have the idle very low..... should be around 800RPM at an absolute MINIMUM 1000rpm is normal.... a single cylinder needs a faster idle ! than a twin does.
....
adjust the air/fuel screw at idle (when the bike is warm) for the fastest idle and then about 1/8 turn more (out) and you should be perfect....
if your doing alot of full throttle riding I think I would go the next step up on the main jet (from stock) just to keep the heat down.....
....it's a thought !
Bob....

[4T_Goblin]

Thanks Bob

So my idle is set at 1500, I was thinking about raising it closer to 2000. With the idle screw.

The bike idles decent. Others have said they have a really hard time fine tuning these VM 22 round slides, and that they have better luck with flat slide.

I went just about every which way on the AF screw and it just didn't appear to be making any difference. Perhaps I need to lean it out a little more

I'll get back on that little screw later, I've just had to take a break with work and it raining on my free days.

[franque]

It could be that you're lean on the pilot jet, so lean in fact that turning the screw doesn't change much because it's so lean. Does it run better off idle with the choke, or half choke engaged?

[4T_Goblin]

Originally Posted by franque

It could be that you're lean on the pilot jet, so lean in fact that turning the screw doesn't change much because it's so lean. Does it run better off idle with the choke, or half choke engaged?

I had this problem even with the 35 pilot. So I don't think it's too lean in the pilot.
I've gotten adjustment changes from the AF screw but it just seems like it wasn't affecting it as much as it should. It could be the vm22 just isn't the easiest to tune.

I never have to turn the choke on, it cranks right up, even between weekends. Last time I had the choke on it revved up really high so that's another reason I don't choke it. This was so long ago .

I think it's a venting issue

[4T_Goblin]

Update: I drained the tank, used pipe cleaner at the nipple to ensure freedom of clog, and put new fuel line on. Got my lines elevated better, got the bubbles out, the seem to be staying out on my last rides.
Replaced a valve cover gasket as well.

So I still have the stalling issue at stops after long run.
Research says that's a lean mixture. I richened the AF mixture some, trying just 1 turn out instead of 2, and main jet up to 105. the spark plug was dark, should have looked before because I couldn't tell if it was dark from the richer main or the AF.
I jet back down down to 100, tried 1 turn out, still rich, new plug again, tried 2 turns out, more lean, but my spark plug looked better. It's just a confusing issue to have.
So my last couple runs I want stalling out but I did hear a valve come loose, tomorrow I'm gonna tighten the valves up.
Overall the bike performs well I think the 100 main is fine and i got a new top speed of 61.

It's confusing.

So it's running good, had some successful runs without stalling, but the idle does dip below 1000 here and there, got some top speed. Maybe the valve cover gasket played a bigger role than I thought possible, maybe not lol

Valves to be tightened again tomorrow