More Carb Questions

bigfozz · Posted: August 4, 2009, 3:27 am Post subject: More Carb Questions

Hey all.
So- due to having the incorrect manifolds i am now stuck with pod filters (story is too long to bother with). I therefore need to adjust my jetting.
I bought some Carb rebuild kits from mikes xs which had much richer jets than the factory settings (1976 model)
main jet size 135 instead of 122.5
pilot jet 27.5 instead of 25.
needle was the same and needle jet didnt come in kit.

Why is balancing carbs so talked about if you can just do it visually,
Or by disconnecting one spark plug at a time and adjusting by the rpm?
(I dont know what im doing and i still figured out that one by myself)
I have both mixture screws out about 1 and 3/4 turns..
There is a slight flat spot and hesitation at about 3000rmp (is this too rich? too lean? badly balanced? bad stator?)
one carb is still running rich
the other is lean i think. (due to spark plug evidence)
the only solution i can think of is having different size jets in each carb..
is this a NO-GO zone?

too many questions.. not enough sense..
feel free to rip shreds out of me.

schtipp · Posted: August 4, 2009, 9:38 am Post subject: Re: More Carb Questions

does it sound like a rasberry being blown at you or like it's an rpm monster? the rasberry is rich. if you know that one side is lean and the other rich, adjust it. i'm sure that you got the sync close with your method. but mixture will also affect the rpm on each cylander. you want to sync them using vacuum so that when you open those butterflies they are the same amount open. do a search for u- tube manometer. the one retired gent. uses works awesome, is highly accurate and dirt cheap to make. is the bike hard to start. or does it fire right up with no choke?

schtipp · Posted: August 4, 2009, 9:39 am Post subject: Re: More Carb Questions

does it sound like a rasberry being blown at you or like it's an rpm monster? the rasberry is rich. if you know that one side is lean and the other rich, adjust it. i'm sure that you got the sync close with your method. but mixture will also affect the rpm on each cylander. you want to sync them using vacuum so that when you open those butterflies they are the same amount open. do a search for u- tube manometer. the one retired gent. uses works awesome, is highly accurate and dirt cheap to make. is the bike hard to start. or does it fire right up with no choke?

jayel · Posted: August 4, 2009, 10:52 am Post subject: Re: More Carb Questions

bigfozz wrote:

Hey all.

Why is balancing carbs so talked about if you can just do it visually,
Or by disconnecting one spark plug at a time and adjusting by the rpm?
(I dont know what im doing and i still figured out that one by myself)
I have both mixture screws out about 1 and 3/4 turns..
too many questions.. not enough sense..
feel free to rip shreds out of me.

there is a difference between getting the carbs adjust so they are running the same air/fuel mix (both cylinders doing their share of the work) and getting both carbs to open the same amount (again both cylinders doing their share of the work) if both sides aren't running close to the same ideal mix and opening it would be like having a 250cc piston on one side and a 500cc on the other, engine would be un-balanced and fighting against its self

bigfozz · Posted: August 6, 2009, 5:17 am Post subject: Re: More Carb Questions

re adjusting the rich/lean sides-im not sure at what point it is lean/rich. therefore im not sure what to adjust. pilot screw. pilot jet. jet needle. main jet. actually im quite sure its not the main jet because i rarely reach anywhere near full throttle on my little rides(charging system is ka-put) .. oh man.. i give up. im taking it to a mechanic!
you guys really sound like you know what you are talking about. thanks for your help and patience.

Joseph · Full Member Joined: May 22, 2007 Posts: 767 Location: NY

Do you have a manual, you can adjust lean and rich conditions with the mixture screw and float height, also air leaks can cause problems.

Retiredgentleman · Posted: August 6, 2009, 10:26 am Post subject: Re: More Carb Questions

bigfozz;
Read through the "carb guide" for CV carbs. You need to increase your knowledge on how these carbs work. Also read previous posts in the "Fuel" section.
xs650temp.proboards.co...read=10538

bigfozz · Posted: August 7, 2009, 1:27 am Post subject: Re: More Carb Questions

I have adjusted the floats previously.. when i rebuilt the carbs. But i am one of those "did i leave the stove on?" type people. so ill check it again.. and change some things to allow for the fact that they are drooping slightly due to the imperfect manifolds.
i have tried many different adjustments with the mixture screws.. guess ill keep trying that too.

air leaks i havent considered.. ill try spraying some starter around the manifolds now.
thanks

bigfozz · Posted: August 7, 2009, 3:53 am Post subject: Re: More Carb Questions

Checked for air leaks and it seems all good in that department.
Took the carbs off again and checked float heights. they were 25mm from gasket height... so it was far too lean. right?
ok also found some small splits in the slide diaphragm of the right hand side carb.. very small. but enough to annoy me. ive read that this can be fixed with some surgical glove and glue.. is this right? or should i just buy two new ones?

so.. if i have to order new parts its gonna be another week until i can check any improvements.
i started reading the "carb guide" pdf. thanks for that one!

borjawil · Posted: August 7, 2009, 1:29 pm Post subject: Re: More Carb Questions

sorry to interrupt just wondering why my rpms get pretty high when i pull my choke all the way out.

im runninmg 34's on a 81 xs650.

Xumi · Posted: August 7, 2009, 2:30 pm Post subject: Re: More Carb Questions

As far as the diaphragm repairs.. that's not easy. You *can* but you have to make the repairs airtight while at the same time keep them very pliable.

I've had success with simply using clear packing tape.

bigfozz · Posted: August 7, 2009, 5:38 pm Post subject: Re: More Carb Questions

i thought about the tape option.
is there any substance you can use to clean the rubber before putting the tape on that wont damage it?
the surface will need to be free of residue for the tape to stick.
metho?

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