|
Post by jdl357 on Aug 9, 2018 15:50:19 GMT -5
Somewhat new to 4 strokes, got 50mm bbk, should I run an open pod filter or keep my stock one?
|
|
|
Post by gsx600racer on Aug 9, 2018 15:57:00 GMT -5
Stock air box is prefered. Remember to up-jet them main jet. With a pod filter you need to up-jet even more.
|
|
|
Post by scooterpimp on Aug 9, 2018 16:57:28 GMT -5
Yea , the stock airbox seems to work fine (in my experiences) & you dont get thay blahh carb sound...
|
|
PirateLabs
Scoot Enthusiast
Posts: 296
Location: Bowling Green, KY
|
Post by PirateLabs on Aug 9, 2018 17:27:37 GMT -5
I actually like the sound my pod filter makes when throttle is open BUT, as Brent pointed out a long time ago, they make the scoot very sensitive to air temperature changes. I have to tune my carb. for spring, then summer heat, then fall cool weather and then the winter. I carry a tuning screwdriver in my glove box because some days start out really cold here, and then hit upper 70's in the fall. It is a real pain I can tell you. I am glad I saved my old air box and I believe I am ready to put it back on very, very soon.
Bill
|
|
ratdog
Scoot Enthusiast
Posts: 342
|
Post by ratdog on Aug 9, 2018 17:56:58 GMT -5
There is very little measurable power gain with a pod filter. However, they are not all that hard to jet for. If you are getting rid of the egr system, which most people do when they go to a BBK, a pod filter makes things much slimpler. Of course it is not as weather proof, so if you don’t keep your bike inside, I would avoid it. If you do keep the bike out of the elements there is really no reason to avoid them. Just understand that it will lean the mixture out ( more aid!) so you will be needing bigger jets. For the two bikes I am working on, a #85 jet works great. I also made a spacer to go under my needle to give a bit more gas at lower rpms and a 32 polit jet for idle mixture. That’s in a stock size carb
|
|
ratdog
Scoot Enthusiast
Posts: 342
|
Post by ratdog on Aug 10, 2018 5:05:54 GMT -5
I don’t understand how you are “ tuneing” it, if you have the samejets. 99% of the time these little guys are running above 4000 rpm. When you get above about 4000 rpm, the only thing effecting the mixture is the main jet. Now for the transfer from idle to the main jet 2000-4000 rpm, you can change the needle. My needle only has one place for the clip, so I made a couple of spacers to go between the clip and slide. The one I use is just about 3/16”. If I put a fresh plug in it, and put it up on the center stand and run it for about 15 min at 3000 I get a nice tan plug, indicating good mixture ( I put a big window fan in front of it blowing on high. Don’t know if that helps, but in my mind I say I have to have air blowing over the engine.
So the only thing left to “ tune” is the mixture adjustment, which has zero effect once you get past about 3000 rpm. I don’t screw with that at all. I just keep the idle turned up fairly high. These little engines don’t get much oil flow with a low idle setting!
|
|
|
Post by jdl357 on Aug 10, 2018 8:32:31 GMT -5
Never thought of that, but what you're saying makes sense!
|
|
ratdog
Scoot Enthusiast
Posts: 342
|
Post by ratdog on Aug 10, 2018 10:22:28 GMT -5
Well I’m not going to spend the time to teach you how a carb works, so try this. Put a new plug in the scoot and run at 5000 rpms for about 10 min. Shut off while running art 5000, don’t let it fall back to idle. Pull the plug and look at it. If your main jet is correct, you will have a tan plug. Now change your mixture adjustment all you want, and run the bike for 10 min at 5000 rpm again. Again turn off while throttle is set. Look at your plug. I don’t care how much you screw with your mixture adjustment, that plug will be the same
|
|
ratdog
Scoot Enthusiast
Posts: 342
|
Post by ratdog on Aug 10, 2018 13:29:47 GMT -5
Well that’s your story and your sticking to it. Of course it does not match carb theory or test data. I am willing to bet you have never run a plug chop in your life. Pulling a plug that has been thru all sorts of rpm changes tells you very little about the jetting of the main jet.. but that’s fine, I don’t really care. When you have a couple thousand engines builds under your belt give me a call. I have thousands of 1/4 mile runs in my pocket. I have hundreds of hours of Dyno runs in my pocket and I have most likely done several thousands more plug chops then you.
Your mixture adjustment affects up to about 2500 rpm. After that the pressures inside the carb change and nearly all the fuel is coming thru the main jet. The needle is a flow restriction for the main jet . I’m sure you are aware it has a taper. By the time you get into the fat part of your rpm range, the needle is no longer doing anything to reduce flow and 99.9% of your fuel is from the main jet. No matter what you do to the mixture adjustment, when CVT keeps your engine up around 7000 rpm, the mixture adjustment has zero to do with it.
Yes, the mixture adjustment is important for starting and just off idle, but it has nothing to do at 7000 rpm
|
|
|
Post by benji on Aug 10, 2018 19:34:51 GMT -5
Your mixture adjustment affects up to about 2500 rpm. After that the pressures inside the carb change and nearly all the fuel is coming thru the main jet. The needle is a flow restriction for the main jet . I’m sure you are aware it has a taper. By the time you get into the fat part of your rpm range, the needle is no longer doing anything to reduce flow and 99.9% of your fuel is from the main jet. No matter what you do to the mixture adjustment, when CVT keeps your engine up around 7000 rpm, the mixture adjustment has zero to do with it. this is not true. When your WOT, both the main jet AND the pilot jet are open fully and drawwing fuel. The idle mixture screw (or air/fuel screw, depending on what type of carb you have) will have little effect on the mixture at WOT, but it will still effect it slightly. Especially with a stock carb and airbox.
|
|
|
Post by jwinn on Aug 10, 2018 19:47:42 GMT -5
👀 🍿
|
|
|
Post by scooterpimp on Aug 10, 2018 20:29:51 GMT -5
|
|
ratdog
Scoot Enthusiast
Posts: 342
|
Post by ratdog on Aug 10, 2018 21:25:32 GMT -5
O, if the mixture screwed any effect mixture above a few thousand RPM, youcould takeour bike out and make. High speed run, then close off the mixture screw and get. Measurable and repeatable diffnce in top speed. Try it, you will see.
He reason is because where the air fuel path is. Basicly, the polit jet is in a BYPASS path. Look where it gets it’s air from. Tryi blowing down that opening. Takes a lot of pressure, right? ELL you have that pressure when the hrottle is closed, but when the slide is open, why would he air go there when it can flow all it wantsthru the open carb body
You can run the engine with the mixture all the way off, or 5 turns open and it will not change the top speed. Of course it will be a little harder getting there if the mixture is shut off but only until you get up above about 3000 rpm or so.
Or just read a few articles about carb theory. Not posts on some forum, but published articles
Most of the 50cc scoots I have had contact with have been jetted way lean. You can open the mixture screw up as much as you want, and those bikes will still be to lean. He only way you cand get an engine to run right at 7000 rpm is changing the main jet
|
|
ratdog
Scoot Enthusiast
Posts: 342
|
Post by ratdog on Aug 10, 2018 22:54:22 GMT -5
You know, I though of another way to prove this to you. As you are the world class mixture screw adjuster you are, I’m sure you know how to adjust it.
After warming up the bike, the first thing you do is adjust the stop screw to give as low an idle as you can. Then you adjust the mixture screw to get the highest rpm. Right? So why do you adjust the stop screw first. Simple, the stop screw controls how close to closed the butterfly is to being closed. If you have he stop screw set to “open”, you will get no difference in speed by adjusting the mixture screw. If you have the stop screw set ugh enough, like 2500 rpm of so, you can turn the mixture screw all the way in or 5 turns out and it has no effect. Why? Because the mixture screw is is now being bypassed because the air has an easier path. So if the mixture screw has no effect at 2500 rpm, how could it have any effect at 7000 rpm?
|
|
ratdog
Scoot Enthusiast
Posts: 342
|
Post by ratdog on Aug 11, 2018 11:16:34 GMT -5
If your mixture screw changes your idle at above 2000 rpm, you have the only carb ever made that does so
And btw, when I was racing karts, I was the one building engines or other people, and I kept a couple E100 modded carb in stock to sell to other people
So we should belive your claims over about ever published or on cab theory
BTW, on the diaphragm carbs we used in the old days on our karts, they actually had a “low speed mixture” screw and a “high speed mixture” screw. But a diaphragm carb on a 15,000 rpm two stroke is a totally different animal from the CV carb found on these little guys.
|
|