Need help with carbs, PMS

[Lee Spoken]

Hi, I need help setting up my carbs.
Carbs were disassembled, cleaned ultrasonically, float height set, and reassembled.
The issue I am having is setting the pilot mixture screw.
I have searched for info and haven't found the info I need.
Most threads say to screw the mixture screw to a gentle seat and then turn out the prescribed number of turns before fine tuning.
My mixture screws have a large external spring and it is diffucult to tell when I am at a 'gentle seat'. Just wondering if anyone can walk me through this.
Here are a few pics to try and help explain the issue.



The bike is a 1977 xs400b. I really want to ride this thing, thanks for the help!!!

 

[xschris]

Welcome to the forum. First off you need to make sure the air barbs on your intake manifolds are hooked up proper. The left one needs to have a air hose from it to the back of the petcock. This will turn on the fuel flow with the bike running and turn off the flow with it off. The left barb gets a cap on it so air don't get in. As for the mix screws mark one side of the screw with a black marker so you can tell when you have a full revolution. You will need to take off the tank in order to turn them safely. I would put a drop of oil on each one so they turn smoothly as possible. Another thing to make sure is the needles are not worn at the tips. They should not have any notches or wear marks on them. If they do you are at more risk of them breaking off in the bodies. If they are good, turn the clockwise slowly till they start to feel resistance then STOP. Turn them back out 2-3 full turns. This is a starting point for tuning. If the bike is stock and the exhaust and air filters are also you should be good. If you have already checked the timing, points and valves all that is left to do is sync the carbs with a manometer.

 

[Lou Ranger]

Need help with carbs, PMS

And this should take care of your second issue:

 

[xschris]

Good one.

 

[Lee Spoken]

HAHA that makes my day. Thx for the quick reply xschris...good eye on the air lines, yes I make sure i have them connected, I just had the carbs off and the tank. When I cleaned the carb, I inspected the needles and they looked good. The part where I get confused is where the resistance part starts...not sure if I need new springs, but when the springs are compressed to the point where they are visibly still straight and touching ,ie. no spring left, then the needle is at the point where it has entered through the wall of the carb housing (ventury area). Probably about a millimeter. Thanks again for the info. Much Appreciated

 

[levdir]

I'll let Chris handle the technical advice, he knows basically everything there is to know about these bikes. I just wanted to say hi from Edmonton

 

[Lee Spoken]

Hi from Sherwood Park. Have you joined the Distinguished gentlemen's ride for prostate cancer in Edmonton on Sept 27? Trying to get the bike ready for that. Yes Chris seems like a great guy to have in your corner for this stuff. Thx again Chris!

 

[lazydays]

To seat them just tighten them finger tight - alternatively if you remove the carbs again you should just be able to see the tip of the needle through the hole on the inlet side of the carb when they are 'seated'

 

[lduberti]

I have a question, both mixture screw in each carburetor are configured the same, with the same numbers of turns???? I ám from Argentina and my english is to bad, sorry, therefore I find it hard to understand.....
I have same carbs, same mixture screws, so I can understand what you say, the mixture screw must be fully closed to get started tuning (2-3 full turns on=open screw!!!!) It is well ??? until a spark plug brown color??? is that correct ???