so today i finally got a chance to mess with the fuel screws on my 79. first i turned them in to see how far out they were and they were about 6 turns out from the seat. i know that is way to far. but i turned it out another turn and the flat spot off of idle went away. so then i took the carbs off and took the top plate off to find out my snap ring pliers are not long enough to go into the slide any way. so now i have to wait until funds allow me to buy a couple main jets and a pilot jet or two and get a new pair of snap ring pliers. what a day. how far up should i go on the pilots and mains?
-
Enjoy XS650.com? Consider making a donation to help support the site.
XS650.com receives a small share of sales from some links on this page, but direct donations have a much greater impact on keeping this site going.
carb tuning
- Thread starter spanks
- Start date
-
- Tags
- carburetors
Sundie
Jabroni
Why would you?
littlebill31
Smells of Raw Fuel
You really need to read this http://www.amckayltd.com/carbguide.pdf
The mix screw on that year carb is 2 1/4 out, not 6. I really suggest studying the carb guide...a lot. There are more to these than just switching jets and shit.
The idle hanging means it's too lean, pilot circuit, too much air.
The mix screw on that year carb is 2 1/4 out, not 6. I really suggest studying the carb guide...a lot. There are more to these than just switching jets and shit.
The idle hanging means it's too lean, pilot circuit, too much air.
Six turns out on the mix screws is way outta line for any carb on any bike. Stock spec for your '79 carbs is 2 1/4 turns out and they usually dial in somewhere between 2 and 2 3/4. Your idle circuit may be partially blocked and need a cleaning.
The '78-'79 carb set came with the largest mains ever put in a 650 (#135) so you shouldn't need to go up much, maybe one to three sizes depending on your mods. That large stock main put the upper midrange right on the verge of being too rich so any main jet size increase, even one step, will probably require lowering the needle a step. When you do that, it usually creates a flat spot just off idle so a size up on the pilots will be needed, maybe even 2. Mikuni now makes a 32.5 VM22/210 pilot size but you can't get it from Mike's. He only sells 30s and 35s. The 35 is actually 3 sizes over stock and is usually too much.
The '78-'79 carb set came with the largest mains ever put in a 650 (#135) so you shouldn't need to go up much, maybe one to three sizes depending on your mods. That large stock main put the upper midrange right on the verge of being too rich so any main jet size increase, even one step, will probably require lowering the needle a step. When you do that, it usually creates a flat spot just off idle so a size up on the pilots will be needed, maybe even 2. Mikuni now makes a 32.5 VM22/210 pilot size but you can't get it from Mike's. He only sells 30s and 35s. The 35 is actually 3 sizes over stock and is usually too much.
i read the carb guide i tried 2 and a 1/4 turns out and it wouldnt run at all. as i turned it out the idle went up and up until about where the previous owner had it set at six/7 turns out then it ran ok and the flat spot went away. so i need to rejet...
bluebikerblan
Geezer
I don't understand why you would choose to ignore this probability & remedy to pursue
a rejetting offset instead? Maybe reconsider the advice? Seems pretty sound to me as well.
Blue
Classic
rackin' up the miles
That's wild... I think BS38 mix screws at 6 turns would be on the brink of falling right out and leaning out a cylinder...
I have several snap ring pliers from my days of turbo rebuilding and they don't fit so I just used a couple of very small phillips head screw drivers. If you don't rev the shit out of your bike bringing up the needle one notch will probably suit your mods fine. If it's still spittin' you can go up another notch and bring in your idle mix screws to about 2 turns out from seated.
Read the carb guide.... thoroughly.
I have several snap ring pliers from my days of turbo rebuilding and they don't fit so I just used a couple of very small phillips head screw drivers. If you don't rev the shit out of your bike bringing up the needle one notch will probably suit your mods fine. If it's still spittin' you can go up another notch and bring in your idle mix screws to about 2 turns out from seated.
Read the carb guide.... thoroughly.
Last edited:
To remove the snap ring in those I bought a $2 pair of needle nose and ground them down.
5twins if that particular mix screw has the o-ring missing or wrong size wouldn't that be a possibilty? Having to run it out to counter the air leak?
5twins if that particular mix screw has the o-ring missing or wrong size wouldn't that be a possibilty? Having to run it out to counter the air leak?
Yes, the '78-'79 mix screws do use an o-ring. If it's bad or missing, maybe that's the problem. Also, you said you cleaned them but did you do a thorough and proper job? Did you use compressed air to blow carb cleaner through from the pilot jet inlet feed on the bottom of the carb body and make sure it came out the 4 little holes in the main bore? And did you have the mix screw removed during this process (you really need to)?
Similar threads
