Air Mixture screw - Location

NorthParkMC

NorthParkMC

XS650 Member
Messages
21
Reaction score
1
Points
1
Location
San Diego, CA
Quick Question. I am looking to make adjustments to the air mixture screw before trying to go up a size on the main and pilot jets. I see a screw at the top of the carbs. Can someone tell me if the air mixture screws are at the top or bottom?
I have an '82 xs650
 
Also I am thinking about buying this from Mikes
Heiden Dyno Tune Needle & Jet Kit for Mikuni BS34 CV carbs

Can anyone tell me if they saw improvement in RPM smoothness using the kit?
 
Each carb has it's own air mixture screw, top, front, on the black body BS34's with handle bar choke that came on the 82 but they are hidden behind small aluminum caps from the factory. If the screw you are speaking of is on the throttle linkage between the carbs it is the synchronizing screw and you should not move it. Hope that didn't insult you but I don't know what you know....

Red ovals in the pic show the idle screw locations.

idle mix screws bs34.jpg
 
We don't know how your bike is set up; air filters, exhaust, engine health, other mods. How much has been done to the carbs? Full overhaul, diaphragms checked, all passages and jets cleared, float valve o-rings replaced? how good are the throttle shaft bores? Do you really know BS34s and all their little "gotchas"?
Without our knowing that how can we give tuning advice?
IF the bike is stock and the carbs are properly cleaned and there is an "off idle" hesitation, the jet needle washer mod often helps a bunch.
 
Thanks. My caps are removed and those are exactly what I thought was the air mixture. I just needed confirmation.
We just did a complete engine overhaul. Had the crank and cam rephased with Hugh. Upgraded to electronic ignition system. Ive got the green monster coils. XS Pod filters, 2-1 pipes with megaphone mufflers.
Just got a new battery.
Im having some hesitation taking off from start until i hit 4000 rpm. Also, when I am cruising on the freeway for about 10 minutes the bike dies on me. it is a slow loss of power almost like im running out of gas. After it rests for a bit it fires back up. the carbs were looked over by a shop and they told me they looked clean. Im not sure any of the jets have been changed from stock. Im hoping maybe just need to go up on the main jets or pilots or both. Worried that it might be electrical. The charging system is weak.
 
We have had lots of member have issues very similar to yours running small pods on BS34 carbs, humor me and try a set of UNI foam filters, see what that does for you?
 
NorthParkMC said:
Thanks. My caps are removed and those are exactly what I thought was the air mixture. I just needed confirmation.
We just did a complete engine overhaul. Had the crank and cam rephased with Hugh. Upgraded to electronic ignition system. Ive got the green monster coils. XS Pod filters, 2-1 pipes with megaphone mufflers.
Just got a new battery.
Im having some hesitation taking off from start until i hit 4000 rpm. Also, when I am cruising on the freeway for about 10 minutes the bike dies on me. it is a slow loss of power almost like im running out of gas. After it rests for a bit it fires back up. the carbs were looked over by a shop and they told me they looked clean. Im not sure any of the jets have been changed from stock. Im hoping maybe just need to go up on the main jets or pilots or both. Worried that it might be electrical. The charging system is weak.
Click to expand...

You need to go to the "Tech" section, and read the Carb Guide. No one can help you if you don't even know what size jets you have.

Engine dies after 10 minutes, then recovers.........................that just might be the gas tank is not venting. As the gas goes down, there is a small hole in the gas cap, which must be clear so that air can enter the tank. If its blocked, you pull a small vacuum inside the tank, and fuel stops flowing.

You bought a bunch of new parts, but none of that will do any good if the charging system is not fully charging the battery:

http://www.xs650.com/forum/showthread.php?t=10561
 
But yeah with a 2 into 1 and megaphone you probably need to go up from stock on the pilots and mains. Idle mix: anything beyond about 3 1/2 turns is fruitless, 3.5 turns allows full flow through the port. do a search here on bs34 jets you will find lots of threads and suggestions.
 
Thanks guys. I just finished reading about the cap venting. Also, since the charging system is barely working, im going to save up and get the PMA. As long as it will get me to work and back for a few weeks i can pull the trigger on the PMA.
Tkurt, as soon as I fix this problem im down to go ride. Im in south Park.
 
Before spending all that cash on the PMA read the charging system guide. With a few easy tests you will find out what's wrong with yours. It may be as simple as a loose wire.
Leo
 

Similar threads

L
Friendly Dissagreement about Mixture Screws
Replies
6
Views
639
gggGary
gggGary
H
Proper Jetting and Fuel/Air Screw Position Mikuni VM-34 on a 1972 Yamaha XS2 (650)
2
Replies
31
Views
1K
Hanniusms
H
johne67
Exhaust Sucking In Air
Replies
13
Views
1K
Slippery
Slippery
J
XS500 carburetor problem.
2
Replies
21
Views
1K
arcticXS
A
fenbrancis
One Cylinder Just a Touch Too Rich
2 3
Replies
40
Views
3K
dps650rider
D
Back
Top