[drewmanley]

Hello all! I'm in Richmond, Virginia. I have to ask: What are the stock settings for the idle set screw and the air mixture screw? I've just gotten this 500 and can not seem to dial in the carb. Thanks, all. This site has already been a big help.

[ace.cafe]

Hi Drew,
Welcome!

There's probably more to it than that.
But the answer to the question that you asked is that you should get the bike started and set it to a medium-high idle with the large headed idle screw, and let it warm up.
A good place to start with the position of the bleed screw is about 1.5 turns out from fully seated in.
After it's  good and warm, turn the bleed screw in and out, until you acheive the highest idle speed you can find by doing that. Leave it at that spot.
Then lower the idle speed with the large headed idle speed screw, until it's a good steady idle that isn't so low that it seems unsteady. Around 1000 rpms is what you want.

Probably, you're going to be looking at some jetting changes, but maybe it might be okay as it is, if a previous owner already did it.

[drewmanley]

Thank you! that is the info I was searching for. Carb is still jetted stock. 117.5 main. I forget the # on the other. I've been wanting one of these for a bit now. I was happy to get rid of my hardtail to pick up the shocked beauty.

[drewmanley]

The carb seems to be happy flooding all over my sneakers. Gotta do something about that...

[ace.cafe]

If the fuel feed hose isn't leaking, then you have a dirty or worn-out needle/seat shut-off valve, or float level problem.

A 117.5 main jet is too small for most places in the US, unless you are right at sea level, and even that might be too lean for there.

But get the leaks and other stuff handled first.

[NJ Riff Raff]

Here's a question. I know that turning in the air mixture screw  carb things up and turing it out leans on the VM28. What about the idle stop screw. Does tightening it in to raise the slide inside richen further or lean further at idle?

For instance after chasing my tail for a while trying to find the setting for these two screws I'm currently trying one turn out with the air mixture and have to fiddle with the idle stop screw by turning it in a little raising the slide to start the bike. Once warmed up I turn it down to a slower idle.

I was having real hell trying to find a consistent idle. The idle was all over the place no matter what I did. I'd stop at a light and one moment it would be fast. The next light slow and the slightest adjustment of the idle stop screw would send it either really high or really low. I think my accelerator cable may have been to blame as when I went check for free play it seemed to be hung up a little where it enters the carb. The cable has so clearance space from the bottom of the gas tank to enter the carb. I think I may have fixed it just by checking the free play.

The one turn out seems to give me a very slow but steady tick but a definite fiddle to get the bike started. But if someone has other ideas on this setting please chime in and also I'm very interested in my initial question.

I should say that I have an 08 final edition military, stock air filter and 50's style exhaust with 27.5 pilot.

[Chasfield]

All the idle stop screw does is minutely raise and lower the main carb slide air and fuel control needle assembly to make some main circuit contribution to the idle running fueling - which probably means that idle mixture strength kind of hangs on an interaction between the idle and main circuits.

Air leaks in the mounting rubbers (very common) might be the cause of erratic idling. They can open and close depending on vibration and temperature levels and you would never get a reliable idle. The throttle cable routing into the carb is pretty tight and as you suggest it might have been hanging up there. I made an extra ferrule out of an old steel pen top to make the cable square up more where it enters the throttle top. The one bonded on the cable was a very loose fit and I decided that it also might be letting a bit of air in.

I have found that if pilot circuit air screw needs to be set further in than normal then it might well give the correct petrol/air mixture ratio for combustion, but there just isn't enough of it for easy starting. A larger pilot jet, with the air screw wound out to the stock 1.5 turns, would probably work better all round.

[drewmanley]

A buddy of mine tells me that the plug on the bottom of the bowl , covering the idle circuit jet , needs to be drilled out in order to make it adjustable. That is a fine plan on many carbs. Just not this one. When did I find that out? After drilling, of course. I'm off to the parts store, in hopes they hve a used bowl lying around...

[ace.cafe]

A buddy of mine tells me that the plug on the bottom of the bowl , covering the idle circuit jet , needs to be drilled out in order to make it adjustable. That is a fine plan on many carbs. Just not this one. When did I find that out? After drilling, of course. I'm off to the parts store, in hopes they hve a used bowl lying around...

From this point on, please consider "your buddy" to be good for having a beer with, but do not seek his advice on carburetors anymore.

We can actually tell you the correct answers here.
Oh, and please put the drill in a safe place where it won't do any more damage.

[drewmanley]

I am in total agreement! My local Brit parts store gave me a new carb for a song. Fortunately, my voice is not so bad. Should have this beauty purring by the afternoon.

[ace.cafe]

I am in total agreement! My local Brit parts store gave me a new carb for a song. Fortunately, my voice is not so bad. Should have this beauty purring by the afternoon.

Here's my "guesstimate".

Use a 27.5 pilot jet, and a 125 main jet..
Set the idle bleed screw to 1.5 turns out.
Warm the bike up with an idle speed a bit higher than you'll want it.
Then turn the bleed screw in and out until you achieve highest idle.
Leave it there, and lower the idle to about 1000 rpm with the the large headed idle speed screw.
Ride around and see how it does.
It should be very close to correct.

[drewmanley]

OK, I put in new carb. Turned on fuel, and the first thing that happens is it floods everywhere. No leaks, mind you, jut spilling right out of the intake. Immediately.

[Chasfield]

Hmm, sounds like the float needle isn't seating, allowing the fuel level to rise into the throttle aperture via the jets or other drill ways.

Maybe the float has a leak and isn't floating. Or the float lever mechanism is bent, or at least way out of adjustment , so that it doesn't put pressure on the float needle to shut off flow, no matter how high the fuel level rises.

[otteryboy]

Hi Guys,

This sounds a lot like like the problems I have been having, in the form of irregular idling and overflowing carb. It was all sorted out by renewing the needle valve for the float and setting the float height. Also sorting out the fuel leak with a rubbing of soap on the thread of the float chamber drain plug.

Mine too is a bullet 500 but the main jet on the Mikarb ( you may remember I ditched the Amal carb that was fitted) is 110 .  I have jetted up to 115 main jet and it is a different bike -better!

But I am wondering why you seem to go for bigger jets like 117.5 and 120 or more?
I am talking of course in the context of standard air filter and silencer. My bike is running better than I have had it before, which was dire! Is there more to be gained with an even bigger jet (in the UK)

I did move the needle to the bottom ( most rich setting) as well as fitting the 115 jet.

All the best, Otteryboy

[drewmanley]

I have now even switched out the needle for an actual rubber tipped one, and still it floods. I know the float works, as I have tested it in water. Also, the float position seems good, since it seems to set the needle, while taken apart. Hmm.