length of air intake before carb

[redorchestra]

Does It matter how long the air intake is before the carb.
I bought some awesome silicone hose.
Check it out:
cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130266837894&ssPageName=STRK:MEWNX:IT
I cut off one of the legs but left the other so that the air filter comes out from under the fender into the open air near the cooling fan. Id say it is about 20cm (8inches) long.
I don't know if its the new hose or the heat of summer but I seem to running rich.

On a related topic
I know what the idle screw does on the carb. It raises the slide up or down a little to get more or less air into the carb.
What does the other screw do exactly. I know it works for the high speed mixture.
The mechanic I took my scoot to screwed it all the way in. What does it adjust? What is the change that it makes to the carb?

I have more questions but I'l try not to ask to many in one post :stars:

Thanks

[190mech]

Ive got a long hose on mine;
49ccscoot.proboards.com/index.cgi?board=2perform&action=display&thread=497
but its much larger than the carb inlet and should cause no restriction,a small hose with the same diameter as the inlet will become more restrictive the longer it gets,,
That other screw is the idle mixture screw,on Mikuni type carbs,"in" is rich,"out" is lean.If he screwed it all the way in ya have an air leak or clogged pilot jet or too small pilot jet.

[redorchestra]

Jul 31, 2010 5:14:24 GMT -5 190mech said:

Ive got a long hose on mine;
49ccscoot.proboards.com/index.cgi?board=2perform&action=display&thread=497
but its much larger than the carb inlet and should cause no restriction,a small hose with the same diameter as the inlet will become more restrictive the longer it gets,,
That other screw is the idle mixture screw,on Mikuni type carbs,"in" is rich,"out" is lean.If he screwed it all the way in ya have an air leak or clogged pilot jet or too small pilot jet.

How exactly do the Mikuni type carbs work?
My idle mixture is quite simple.

The screw hits a ramp carved into the slide.
The further in the screw is the higher the slide is at idle.
The higher the slide is, the more air it gets.
So On my carb in is leaner

It's the other screw, the high speed adjust, that I don't understand!

[90GTVert]

Thats just idle speed, not mixture. It's the same as holding your throttle open a little.

[redorchestra]

so BOTH screws are for idle. One is idle speed the other is is idle mixture?? really confused now

[drawkward]

The way I look at it is the screw in your diagram is for controlling how open the slide is (how much air/velocity is let through the carb). The other screw is controlling how much air get's mixed with your fuel during atomization through the jets. I'm probably way off - but it's just how I make sense of it.

With a well sealed engine, your idle should change when adjusting both screws, I believe.

[190mech]

Here is the Mikuni manual,it will explain in depth just what each part does;
www.mikuni.com/pdf/vmmanual.pdf

[redorchestra]

Yeah Both of those explain it quite well.

Thanks guys

[Fox]

The thing that lots of people get wrong is they think the air screw affects the high speed mixture (main jet) but that's false. The air screw only affects the idle jet mixture. It's called the "Idle Mixture Screw" It has nothing to do with wide open throttle performance whatsoever really. It's job is to fine tune the idle mixture so your scooter idles smoothly. There is a factory setting but the setting changes with weather changes and elevation changes so each scooter will have a sweet spot on the screw depending on your geographic location and the seasons. That's why the screw is there. If the factory setting worked for everyone everywhere then there would be no need for a screw. It's something that needs to be adjusted periodically but again, it has nothing to do with the high speed mix. The mix screw can sometimes cure a stutter or hesitation when the throttle is opened.

Correct me if I'm wrong here, but I think that different oil ratios on a 2T will also affect the idle mixture setting.

[redorchestra]

The guy at the shop had closed my mixture screw right down. I thought it was too rich so I changed for a smaller jet. I'll go back to the bigger jet and adjust the mix myself.

[90GTVert]

Aug 1, 2010 13:27:01 GMT -5 Fox said:

correct me if I'm wrong here but I think that different oil ratios on a 2T will also affect the idle mixture setting.

If you premix, the mix ratios affect the mixture throughout the powerband. If you mix 2% oil, that's 2% less fuel passing through your jets.

[redorchestra]

so... is this right? The only thing that affects the mixture of wide open throttle is the jet size!
The screws are only for idle speed and idle mixture?

[190mech]

Right,but the needle and needle jet determing mixture ratio through most of the rest of the throttle settings,thats where a lot of folks fry their engines.I have been setting my needle a bit rich since I holed a piston a while back..

[Fox]

Aug 3, 2010 4:46:10 GMT -5 190mech said:

Right,but the needle and needle jet determing mixture ratio through most of the rest of the throttle settings,thats where a lot of folks fry their engines.I have been setting my needle a bit rich since I holed a piston a while back..

The other factor is how restrictive the air filter is. If you change a stock scooter's air filter to a hi-flow UNI or K&N style foam sock filter you will most likely need to enlarge the main jet size or raise the needle so the fuel/air ratio remains the same otherwise you end up holing a piston or burning an exhaust valve etc...

It's so simple really. You know how if you blow on burning embers they flare up and get hotter? That's due to an increase in the oxygen level at the source with no increase in the amount of fuel. Same thing happens inside the engine. You increase air flow but not fuel quantity and the fire gets hotter resulting in great performance but increased engine wear. It's a balancing act to keep the combustion at the optimal temperature where you get the best performance without damaging the metal. (Brown spark plug)

It ain't rocket science... It common sense once you understand fire in general

[redorchestra]

Aug 3, 2010 11:39:54 GMT -5 Fox said:

It ain't rocket science... It common sense once you understand fire in general

It is kind of rocket science. Well some of the scoots out there are rockets for sure.