Carburetor problem

[robbo]

My SF seems to be running lean below 3000 rpm, the PO fitted a 4-1 pipe with a megaphone silencer, he told me that he had dropped the clip on the needles one notch which had helped improve things, but did not completely solve the problem. My question is, is it just the pilot circuit controlling the air/fuel mixture below 3000 rpm or has the main jet come into play by then? Sorry if this seems a dumb question but I naturally want to try and cure the problem as simply as possible, without having to pull the carbs apart to many times.

[DiverRay]

You are running the pilot below 3K. probably need one size up on the pilot, one size up on the main, and put the clip back in the middle. The other thing you can try is adjust the idle mixtures. You will need to be about 2 turns out to begin with, and if you get over 3 turns out you DO need a bigger pilot jet.

[robbo]

Many thanks Ray for that info

[Bonz]

What is the symptom making it seem lean? How many turns out are your pilot screws? You may be able to work with that adjustment if they are turned in too far and not need more pilot size.

Here are my thoughts... If you don't remedy the issue by adjusting the screws, stay with the pilots you have, go up a size in mains and leave the needles where they are because the needles seem to be ok from what you have said. A small increase in main allows incrementally more fuel in at any needle height, even at lower rpm where it isn't lifted much, and you may get a bit more in the mid range as a bonus, then onto a great top end pull.

Float height isn't known either, and too high of a float level (low fuel level in bowls) will cause a slight lean stumble when getting on the throttle at lower rpm.

Ultimately, you tune for the correct main size first, then needle height and lastly fine tune with the pilots. Try going up a size in the mains.

[robbo]

Thank you Bonz for your reply. The screws are out three turns. Several times i've pulled out the choke a small way when riding at between 2000-3000 rpm and this seems to help, so that is why i'm thinking its running lean. Once I get above 3000 rpm the bike pulls well.

[mack]

Hi

I believe Bonz was actually refering to idle mixture screws. If you have the original early carbs, your mixture screws came out of the factory at 1 1/4 turns out from lightly seated. 3 turns would make it idle very rich.
If you have the later carbs, 3 turns would be right in the ball park.
HOW WELL DID YOU CLEAN THE PILOT TOWER PASSAGES? The other thing you may want to check are the small holes in the top of the intake (opposite of the bell) above the butterfly. To clean these you need to pull the enrichement plunger back and expose the hole slightly offset from the diaphram chamber and spray cleaner into that hole. Let it sit for a bit then close the plunger. Now spray compressed air up through the pilot tower keeping the enrichement plunger closed(the compressed air will try to force it open. You should see carb clean coming out the 3 little holes and if you put your finger under the holes you should get a good blast of air. If not, repeat as required until you do for each carb. Never stick any sharp pointy objects in any of those holes.

[skids]

You are running the pilot below 3K. probably need one size up on the pilot, one size up on the main, and put the clip back in the middle. The other thing you can try is adjust the idle mixtures. You will need to be about 2 turns out to begin with, and if you get over 3 turns out you DO need a bigger pilot jet.

In addition to that, you can consider raising the float levels a tad. Always check the vacuum synch.

[Bonz]

Thanks for the extra info, robbo. That was helpful.

I was meaning what Mack said with reference to pilot screws, hope it didn't confuse anyone. I use pilot screw, fuel screw, idle adj screw interchangeably.

Mack's idea is a good one, dbl check the cleanliness of the pilot system and the small holes.

[TopCatGr58]

Hey Robbo,

You might find this thread informative with regards to the little fuel/air passages in our carbs! There are several pages of photos, and you can click on a photo to enlarge it to see better details!

http://www.xs11.com/forum/showthread...t=carb+anatomy

example:


T.C.

[Boneswig]

Don't know if this has been resolved but I had this on my previous XS. The PO was nice enough to turn the screws in to deep and broke off the pins in the carbs. Take out the screws and check if you don't have the same problem I had. I never got them out and eventually had to replace the carbs.

[mack]

Carbs

Bones: what did you do with the carbs with the needles broke off. If you still have them, send them up to me and I'll get the tips out.

[robbo]

Pilot jets for SF

I need to up the size of the pilot jets on my SF, I've found a site selling them but just want to check they are the correct ones as I understand they differ between models. The ones on the site that they say are for an SF have 6 holes, are these the right ones ?

[robbo]

Pilot jets for SF

I need to up the size of the pilot jets on my SF, I've found a site selling them but just want to check they are the correct ones as I understand they differ between models. The ones on the site that they say are for an SF have 6 holes, are these the right ones ?

[dbeardslee]

I've got a set 42.5's in my hand that came out of my "F" model. They've got six holes. You're looking at 45's, right?

[DiverRay]

#1 question is ARE THEY MIKUNI?!?! if no, just walk away quickly. K&L jets have been the bane of many on this site. Just make SURE you are buying genuine Mikuni jets ONLY for the carbs. If they are Mikuni, they will work. IF they are K&L, or another off brand, they will NOT work.