RoyC46

[RoyC46]

Hi guy' s I' m new to the site, and new to Owning a 79xs11sf. Having difficulty getting her to run properly. I Live in the South Philadelphia suburbs. I don't know anything about the previous owner Bought her on Craigslist from a kid. she has had the pickup coil wire repair new fuse block and new ignition coil I put her in the shop Here at rullo to get the carburetors rebuilt they also diagnosed that I needed a vacuum advance and she still stumbles from idle to 3000 is there anyone close by that could give me directions

[BowlingSS]

Did the shop clean the carbs or just did a diag?

Welcome to the site.
Bill

[bikerphil]

One thing that comes to mind about the stumble from idle to 3K rpm. If the shop that rebuilt the carbs used carb kits and changed out the pilot jets, they may be the inferior type that have caused so many people problems. Hard to say without actually looking at them.

[TopCatGr58]

Hey Guys,

Here's the email I sent to Roy with his membership confirmation since he asked for some advice with his membership request....and I just wanted to show that I "do" do some work around here. Also wanted to show what I had told him to save others from saying the same things.

Regrettably the first mistake you made was putting it IN THE SHOP! Bike shops and most of the mechanics are younger than these bikes, don't know how to work on or TUNE carbs...they mostly know Fuel Injection and computers!

We have lots of ideas, but we can provide more accurate help if we know more about what was done to the bike, and photos showing the bike, engine, carbs, so that we can be sure they are 79 series carbs....lots of previous owners (POs) will get different year/model carbs and put on their bikes. There are considerable differences between carbs for the 78-79 and the 80-81 series of XS11's, as well as specials vs. standards.

Okay, problems with idle to 3000 rpms is mostly the PILOT circuit. We have found that CARB KITS...usually K&L brand use generic jets.....and they are sized WRONG compared to OEM Mikuni jets. They are way larger/richer than the same sized Mikuni jets, so they cause stumbling, bogging, and the plugs end up looking like black sooty messes!!!

SO....the first advice we would give you is to order GENUINE Mikuni Pilot Jets from JetsRUs or Dennis Kirk type sites.

Next, we can only hope that they truly disassembled the carbs completely to clean them? The 79 carbs and pilot circuit gets easily clogged with old varnish/gum from fuel sitting in them for years, and unless they are totally disassembled, cleaned, and the passages cleared, then they won't work right no matter what jets are in them.

The pilot SCREWS on the top front of the carbs have very fine tips, and IF one isn't careful when first "Gently" seating them in place before turning them out to the 1.5 turns beginning setting....the tips can get lodged into the carb bodies, and then break off when the screws are backed out. Then the screws become useless because the port is now totally clogged with the screw tip!

There are a bunch of other things that can cause poor low rpm throttle response, and it's not all carbs.
You say you had your vac. adv. repaired....I'm assuming that you had the vac. adv. pot replaced because they really can't be repaired...when they go bad it's usually the vac. diaphragm that gets holes in it and won't pull/hold a vac.. But the Vac. Adv. unit isn't really for POWER! It's designed to kick in under very low throttle mid rpm range input like when CRUISING holding a steady speed....it then increases the timing way up to ~52 degrees to allow it more time to burn ALL of the fuel to improve/increase mpgs/fuel economy....but when you crank the throttle, vac. drops, and the vac. adv. unit releases allowing the timing to retard back to the max ~35 degrees timing adv. point for the MOST POWER setting for acceleration.

SO....the vac. adv. really doesn't provide much input with regards to low speed/rpm throttle response or acceleration.
You can actually plug it, cap off the #2 carb port(where it's supposed to be connected....not to the Intake BOOT port), and the bike will run with essentially all of the regular power that it can provide, it will just use more gas when maintaining a cruising speed.

OTher ignition things...the Pick Up Coil wires are known to fail due to continuous flexing, which will then drop out a pair of cylinders.....so while running spritz the headers with water to ensure that all four cylinders are firing.

The Ignition coils are 30+ years old....the plug caps, wires can fail...corrosion between the wire/cap, the internal resistor in the cap can corrode/fail. They run on less voltage due to the ballast resistor, but at lower rpms the charging system is putting out very little power...doesn't reach full capacity until around 2500 rpms....and with any corrosion in the harness that feeds the coils...the voltages can drop lower than the ~9 volts they run with the ballast resistor....and too low voltages can cause even weaker spark...the coils fire 2 plugs at the same time, but it has to flow from coil to 1 plug, thru the engine and then back up the other plug back to the coil for a complete circuit....but with too low voltage it can fire only 1 plug causing a low rpm stumble.

So....I hope with this preview, you'll document about the bike, how you got it, how long has it sat, how many miles on the engine, did it run when you got it, any history from the PO as to why it was parked/stored, and of course what work has been done to it, by whom, etc....the more we know the more we can better guide you to fixing it and getting it running right without blowing hundreds of $$$$ at a dealer/bike shop!

T.C./ADMIN

[Rasputin]

While I do appreciate what TC does here, I would have to say the trying to answer new members questions, in an introductory message is uncool!
I think there should be a standard message, as this is a bulletin board after all, and let the members give the advice needed.
Not much sense to me to try to answer all the applicants questions when they apply? I dunno maybe it is just me?

[TopCatGr58]

Hey Ras,

In my defense I rarely do this. Most of the time, they just request membership, I register them, send them the confirmation, along with the links to Bug's webpage for manuals and that's that. But sometimes they also request assistance in the email, and so I will try to provide a little bit of info, but also inform them that there are many members on our site with much more knowledge and experience than I, and that they will have much better chances of getting answers that they can use, as well as things that I surely didn't cover/provide.

And sometimes I'm just bored....kinda like Scott/3Phase!

T.C.

[3Phase]

And sometimes I'm just bored....kinda like Scott/3Phase!

T.C.

I'm just trying to keep my mind from going all, "Flowers for Algernon," so you go right ahead and answer as many questions as you can handle without bouncing away down the road!

.