Need help from my compadres - jetting at partial throttle

[11Rider]

Hi guys, I did a search and read throught the stickies in the carb section, but I still don't have a perfect understanding of the low speed/partial throttle circuit. I have a '79 SF with 7500 miles on it. It's in great shape and starts and idles perfectly with the choke on. It also runs great once warmed up with a good amount of throttle and once it gets past 3k rpms. However, throttle response is very soft and there's a lot of hesitation below 3k, so much so that you have to rev it higher and then work the clutch to take off.

From what I've read here it looks like it's the pilot jet circuit. I believe the brass screws in the front of the carbs (engine side) are the pilot jet adjustment screws, am I right? It seems as though these have little effect on the throttle response. Would that mean that I would likely need larger pilot jets? If so, do the carbs have to come out to do that? What size would you recommend and where would you buy them from?

Thank you for any help

[wingnut]

The brass screws in the front are the idle mixture adjustments. Those have the most effect under 1k rpm. The pilots jets are in the bowl just to the side of the mains. Your 79 carbs have a rubber plug covering them up. If you remove the plug you should be able to see them. What should have you scratching you head is with stock pilots, air box with filter installed and stock exhaust the condition you are seeing should not be happening. First is the bike stock? Need to know if its got pod filters or stock air box. Stock exhaust? And now the big question, have you had them (the carbs) off and cleaned them by removing all the jets and needle valves and assured yourself that every passage is absolutely clean? Checked for air leaks around the boots? Post any aftermarket parts installed in your profile and the guys here will be glad to help you work thru the problem. My bet, dirty pilot jet circuit.

[11Rider]

Thank you Wingnut. My bike is all stock to my knowledge with the exception of a K&N air filter. The PO is a member here in good standing and seems to be an honest person. He told me that he had the carbs sent to a guy who is the "guru" so to speak of XS1100 carbs and that they were cleaned and jetted properly (that was about a year and a half ago). But as I'm typing this, I'm realizing that all this is a big variable and unkown. I guess I should just bite the bullet and pull the carbs and see what jets are in there anc how clean everything is huh?

[natemoen]

'79 carbs should have the screw over the pilots, it is the '80's that have the rubber plug.

Otherwise wingnut has it for starters.

I woild add though, it could be broken tips on the needles. Unscrew the needles and see if the tips are nice amd sharp or broken off and blunt.

[11Rider]

OK thank you.

[DGXSER]

IF a fellow member here did the carbs, I can probably guess between two who that might have been. And in either case I would expect them to be right on the money for the bikes set up.

Did the bike run fine a year ago? Did it sit with gas in the carbs over the winter and no fuel additive?

It definitely sounds like your running lean on the idle circuit.

[Rasputin]

Here are a couple of links that helped me to understand more about the carbs. They are not nearly as intimidating as I once believed. Check em out.

http://www.factorypro.com/tech/carbt...m_engines.html
http://www.iwt.com.au/mikunicarb.htm
http://oldmanhonda.com/MC/Rcarbs.html
http://www.youtube.com/watch?v=Hr6_Q...eature=related

[11Rider]

IF a fellow member here did the carbs, I can probably guess between two who that might have been. And in either case I would expect them to be right on the money for the bikes set up.

Did the bike run fine a year ago? Did it sit with gas in the carbs over the winter and no fuel additive?

It definitely sounds like your running lean on the idle circuit.

Yes, it ran good a year ago, but a little cold blooded like they were originally in that year due to the emissions. However, I had a bad back operation last fall and didn't have a chance to winterize my machinery like I always do. This year it's much worse. Probably plugged jetting circuit as you guys seem to think. I was hoping for some kind of amazing tip that would allow me to skip taking the carbs out/apart, but I guess there's no shortcut. That's OK though.

[bikerphil]

Try some Seafoam in the tank. Run it a bit with the Seafoam and let it sit overnite to let it "soak' in real well then see if it improves the next day. Worst case, the Seafoam will make the carbs sooo much easier to clean if they do need to be disassembled.

[DGXSER]

Phil is a smart guy!!! If it runs but not so well at partial throttle, try the Sea Foam. About a 60-70% chance it will clear things up for you. Sounds like the gas gooed up a bit in the small passages.

[11Rider]

Thank you all for your help. I did try the Seafoam - a pretty strong concentration too. I'll be taking the carbs out and it's not all bad. I'm curious what jets are in there. Thanks again!