How far out should the high and low speed needle adjustment screws be out on the carb be out? The red and white caps have come off , and doesn't want to start. Thanks

Some carbs have obvious adjustments ("H" for high speed, "L" for low speed or idle. )

Some however are hidden. Heres a video showing how to find theses hidden adjustments.

https://youtu.be/tlsVcCdzaoA

http://www.aerocorsair.com/id150.htm

Look down this website until you come to teh Carb Tuning section.

The carb screws have anti tamper sleeves on ( one red one white ) to adjust the screws you need to draw the caps back, you can do this with a small self tapping screw, screw it into the centre of the cap, when it hits the adjuster underneath the cap will draw back as you carry on screwing it in, only pull the cap back far enough ( approx half way ) you can then remove the screw and insert a 2mm flat blade screw driver through the centre of the cap, the adjuster underneath will now turn, the reason not to take the can right off is because the screws are only 2mm across, and it is near impossible to adjust the saw whilst it is running.

After seating the screws back them out 1 1/2 turns. This should be close enough to get it started. Let the motor warm up a little then, with it idling, turn the low screw in until it starts having a hard time running then back it out until it idles smoothly. Prop up the Mantis so it can run at full speed safely while you adjust the high side. With the throttle wide open, again turn the high screw in until it starts running roughly and back it out until the motor is running smooth. Some say to turn the screws out until the motor starts having a hard time running and then turn it back in half way to where it was running bad at the other end. This doesn't work as some engines don't care how far open the screws are.

Hi allenplum,
There are 2 mixture screws, 1) the idle speed screw, 2) is the idle speed mixture screw. The idle speed screw is located on the carburetor, nar the throttle arm where your throttle cable is connected. There is a screw that you will find there that you screw in or out to speed up, or slow down the engine idle. The idle speed mixture screw is located lower down on carb and has a spring on it. There should be 2 screws side by side, one is the idle speed and the other is the high speed mixture screw. They are marked on the carb body, with the letter H or L . To adjust, remember the screw position before you do any adjustments. Start by turning the screw in (clockwise) all the way in until lightly seated, so no damage is done to the seat or needle. Turn out (counterclockwise) 11/4 inch, this should be OK to start the engine. Along with the idle speed screw, you should be able to get the correct idle required. With all the modernization happening, there might not be a high or low adjust as they are ported inside the carb. You might get just the high or just the low adjust needles. I hope this is helpful to you. All the best and good luck. Denis.

Hi Roseann, newer 2 stroke engines for the past 6 or 7 years have changed to newer carburetors, and some of them don't have any adjustment needles at all, or just 1 adjustment needle adjust. Without knowing how old your Homelite is or what type of carb you have, I will assume you have adjustments. If you look carefully at your carb, next to each needle you will find the letters F or H, F is the fast speed adjust needle and L is the low one. In general the L or low speed needle is the one closest to the motor. To adjust them you turn both the H and L needles in (clockwise) until lightly seated (so no damage is done to the needle or the seat), now you turn them both out (counterclockwise) 1 turn. You should be able to start your vac with these settings. Only minor adjustments should be required if any at all. To adjust the low one with your engine running at idle, turn in just a little and notice if any difference, if not turn a little bit more until it starts to run rough, now bring back to the position you started with and now turn it out (counterclockwise) in small turns at a time until it starts to run rough. When you do this remember the position of the needle (how far in and how far out) and adjust to the needle to the middle of those 2 positions. Do the same with the H or high needle. At the top of the carb where the throttle cable hooks to the carb you will find a screw that is to adjust the idle speed by adjusting the throttle position. You can adjust that screw at any time to get the idle speed you want.
I hope this is a bit helpful to you. All the best and good luck. Any questions welcome.

Hi Jack, I will try to help you out. As far as the high/low screws go turn them in (clockwise) until lightly seated so no damage is done to the needles or the seats. Now turn them both out 1 turn but also remember the position so you can go back to it if you have to. That is the suggested basic adjustment. The saw should run at this setting and sometimes is bang on. If everything is OK with the carb only minor adjustments should do it. When adjusting go 1/8 turn at a time. Because of idle problems start with the low speed mixture needle. Turn out (counterclockwise) 1/8 turn and try running your saw. Do that 5 or 6 times, if no good results go back to starting position. You might try the high speed mixture needle the same way to see what happens. ( Always remember the starting position of the adjusting screw) The one thing to be careful of when adjusting the carb is not to adjust the high speed needle less than 1 turn out (counterclockwise) from a lightly seated position. The reason is you don't want to run it too lean (less gas more air) which could damage the engine because it could overheat. The gas and air mixture also helps with cooling. Try any adjustments as long as you don't go too lean.
Inside these types of carburetors there is a mesh type filter which is very, very fine, so if anything even dust gets in, this mesh will stop it, so it is something to check out, it is a common problem. You say you took the cap off the bottom, that is usually the metering side. It is critical that the diaphragms (membrane as you call it) be installed very accurately.
From what you describe you did a very good job of checking everything out, so what could be needed is a carburetor overhaul, unless it is something that is intermittent, which is a pain. I hope I have helped you out even a little. All the best and good luck.

Try by tightening both setting screws (not too tight as this will damage them) ...just enough to the home position...then backing off 1-1/2 turns on each. Try to start, if does not start, then then back off another 1/4 turn, continue till you can start then once started regulate adjust screws slowly to find a smooth idle.

The standard setting on needles is to screw them in all the way and then back them out 1 and a half turns.

You need to set the mixtures for the carburetor. You will find a Low and High adjustment screw. turn the low adjustment screw out. You will notice that the rpms should start increasing. keep turning it out until the rpms start to drop then turn it back in a quarter of a turn. You may need to readjust the idle speed so the chain doesn't turn during idle. Do the same for the high adjustment screw.

turning Hi & Lo mixture screws in leans the mixture,out rich-ens it.turn the T screw in to increase idle speed the chain should slowly come to a stop at idle [chain brake off] adjust Low needle first until it accelerates smoothly then Hi needle for best 'revs'.then Lo again if necessary if you don't know where they were set before,start w/ screws 3/4 to 1 turn out from a lightly seated position