bad ignition advance?

[kevxs]

hey guys, i've been told by a shop that my ignition advance was on the fritz, i could usually get it to work ok by cleverly working the throttle but it feels now like its stuck in the advance mode. if i can manage to get the revs up to 4000 it takes right off but runs like crap below that. also there is a ticking noise coming from that area.

can anyone tell me how to confirm the problem and how hard of a job it is to replace the unit?

thanks in 'advance'

[cywelchjr]

Sounds to me like the vacuum advance is connected to the wrong port. It goes to the vacuum port on #2 carb, NOT to the carb boot. Hooked to the carb boot WILL give you a clicking noise and often cause problems at lower RPM's because the timing is too advanced. And since the XS11 is pretty unique in having a vacuum advance, it's not likely that any shops would understand enough of how it works to even know if it's working right or not, and they wouldn't know even where to hook it up to.

[kevxs]

yeah looks like your right cywelch, the octupus is hooked up to carb 2 and the advance is hooked to the carb boot, i guess i need to switch those? it has probably been hooked up like this since i got it but it didn't really start acting up until yesterday, hope i didn't wreck the advance somehow . . .

[Larrym]

Good Reflexes....

kevxs,

Cool! You dodged the repair shop's bullet this time.

Just a thought, if the unit ever does stop working altogether and the shop tells you that it has to be replaced ...

Try testing or replacing the vacuum line/hose before springing for the "shop-time" and "replacement" of the entire assembly.

Just saying that some(???) shops aren't that oriented towards comprehensive evaluation and/or diagnosis as much as most folks think. The emphasis is towards DOING SOMETHING even if it's the wrong thing to do. Especially when it comes to having the owner buy parts that may/may not be the true problem. They get paid for "trying"....

Not to be taken as a blanket indictment of all repair facilities or those working there.

JMHO...

[kevxs]

yeah i've learned my lesson with shops, thats why i ask my questions here, so just to confirm, the octupus should be hooked to the carb boot?

[DiverRay]

YES, the Octy should be on the #2 carb BOOT, and the advance is on the #2 carb BODY.
You may want to pull the cover, and spray some silicon lube into the advance mechanism on the crank as well. I found a LOT of rust in more than one advance unit.

[kevxs]

well changing those vac lines around made an improvement, i also sprayed some silcone lube in around the advance although i didn't see any rust.

the advance dosen't feel stuck anymore when i'm driving. if im easy on the throttle i can get the bike to accelerate well until about 3500 -4000 rpm then it bogs down. if i pull in the clutch lever in, it still won't rev very well at this point but as soon as i put it in neutral, the thing revs great again. if i'm not easy on the throttle i will bog down almost immediatly.

i don't yet have a vacuum tester but would a vac leak be the likely suspect in this situation?

[cywelchjr]

At this point it sounds more like a carb issue, and unlikely to be a vacuum leak which would generally affect lower RPM's more than higher. Bogging issues are often rich mixture, although it can be lean mixture as well. I have also seen this type of thing from the slides not moving up as they should, either from springs that are too tight, or hole in the diaphragms. This is the region that both the slides are kicking in at, and as a result the mains are taking over from the idle circuit (which is the primary mover up to about 3500 RPM) and as such the first thing I would check is that the slides move freely, that the carb floats are at the right height, and that the main jets are clean and clear.

[Bonz]

This thread is the closest to describing what I have going on w/ my 80 SG Special.

Since the day I bought it and rode it home, 2 1/2 years ago, when its warming up and otherwise cruising fine at light throttle, it will simply go flat and not accelerate, but not slow down either. Just a "blaaaaaaaaaaaaaah" sound no matter how much throttle I give it while in gear, if I roll out and roll back on,while in gear, it does not go away.

But, I get off the throttle, pull the clutch in and re-engage the clutch, it usually goes fine, occasionaly it will go flat again. Once warmed up (I mean, really up to operating temp after miles of riding) it is more or less fine. Then, when I get to half a tank, no matter what I do, it continually wants to go flat again if the petcock is "on" and I'm at low speed, light throttle. I can switch to reserve and it goes another 20 or so miles (still plenty of gas in the tank, just under half full now) before it begins going flat at low speeds continually. It will begin to feel like it's starving out at higher speeds as well by this point. So I just fill the tank and call it good. But I'd like to get more than 70 miles or so before having to do this ritual. I.E., I'd like to run a normal tank through it!

When I got the bike it would do a full tank (still had to low speed flatness issue, but would otherwise swallow a whole tank without having to go to reserve until it actually needed to), but has degraded to this point and stayed here for a year. Running on prime makes no difference, and I thoroughly took apart the carbs, cleaned them thoroughly, etc last fall. Because the flatness issue was there before and after the carb job, I tend to think I have a fuel supply issue (Octy) vs. a fueling issue from the carbs themselves.

As well, when it's really hot outside, and the engine is very hot as well (such as yesterday when going through Denver, 97 degrees outside air temp, slow speed through construction zone on I-25) it will continually need constant throttle and clutch tap dancing to get it to pull away cleanly from a stop or crawling speed. Otherwise it wants to be herky jerky, and sometimes if I don't do it just right, it'll just quit. Starts back up with a little work on the throttle, but this bike absolutely hates the hot air temps and low speed, no matter the fuel level in the tank. Cooler days (70's) and it runs like it never had a problem in it's life, and yesterday, or any day, at any speed above a crawl, it runs flawless despite the crazy heat. Make sense?

My mind has a lot of things going through it...

First, I have new fuel line and such to eliminate the Octy, and will do that tonight I hope. Start there and maybe that will be the end of my problems.

Second, I am going to pull off the fuel cap and makes sure it's venting. I can hear a hiss when I park it after riding, so that tells me something is venting, but is that also an indication the vent could be plugged/partially plugged and my hot day blues come from not enough air coming into the tank to replace the fuel that leaves?

Third, could my carb diaphragm slide springs be too tight/stiff and causing the issue of the flatness until it's warmed up? All it takes to set it right is to pull the clutch in and re-apply throttle to usually clear it up... Until I get to a half tank, then it wants to go flat all the time at light throttle regardless of how hot it is outside/how hot the engine is.

Fourth and last on my list, is an issue with the vacuum advance or pick up wire. YES the vac advance is hooked to the carb body, and the octy to the carb boot, so that is in order.

OK, that about covers it all, so have at it boys, love to hear if I'm thinking the right stuff...


Thanks much!

[DGXSER]

Sure sound slike a fuel starvation issue to me from what you describe. I also wonder if the bike ever sat for a long time. Perhaps you got crud in the fuel filters in the tank on the petcocks and it needs the extra pressure of the higher fuel level to push the fuel through there?

You say Prime makes no difference, so the octy has already been eliminated, as the PRIME setting takes it out of the equation if its piped correctly.

The vent item has some merit, but it would not change with fuel height or temps, not that drastically anyway.

One mor eitem that comes to mind, is a bad or partly bad coil. Typically they go completely or not at all, but I have had one that would let the egnine run, just barely but never give good power or let me give much throttle. Always had to feather the throttle very lightly. Just another SWAG.

[Larrym]

Food/Fuel for Thought

hbonser,

Gawd! That sounds like it would be more than just a little annoying. Amazing that you have the patience to put up with that.

I dunno...."Lean?" Too much air and not enough fuel? "Rich?" Too much fuel and not enough air? It's all relative to the AFR that's s'posed to be happening. Off is just "Off" IMO.

I'd weigh in on the side of the mixture being too rich (comparatively...). Runs good cold and then gets progressively worse as the engine and temps get higher/hotter.

Spark plug color and condition?? That'd be where I'd start. Also, I'd suggest that you warm up the bike with a good run and then STOP. (No..not a throttle chop.) I mean stop the bike and have the wind at your back. Use your nose and see if you smell GAS fumes like all the fuel isn't burning completely. (As in running way Rich due to lack of enough air flow for the correct amount of fuel or due to too much fuel being added to the correct amount of air flow or even one cylinder firing/misfiring due to an intermittent spark...)

Having the bike "stock" with the OEM exhaust is a good clue here. If you had another exhaust with less back pressure or no baffles or something like that it would sorta explain the symptoms you describe.

Stock main and Idle jets to go with the stock exhaust? You should be golden as far as the carbs if that's truly the case.

"Rich" mixture is the hardest to ignite with a spark too. Hit-and-Miss under the right(WRONG) AFR. Ensure that the coils/spark are rock solid before spending days/weeks chasing a "carb" problem. One cylinder "hitting-missing" is enough to ruin that perfect take off from a standing stop.

HTH

[Bonz]

LARRYM,

I appreciate your thoughts on the A/F and the carbs. No issue there. The plugs are a nice light tan on the center insulator, and the bike is truly stock other than the K&N filter. I run 2 turns out on the airscrews, and it needs a bit of the enricher to fire up, and acts exactly the same as it does at 3 turns out (current setting) and needs 1/2 setting on the enricher to fire up most mornings. I do not suspect anything rich or lean is going on, per se, that is contributing. I'm going to work on the fuel supply/petcokc screens/tank vent side of things, I believe the answers lie there.

[Bonz]

Thanks DGXSER!

I think the main issue is going to be the fuel screens in the tank as it relates to the poor running at half fuel load. The bike sat for many years in a shed, with that said, it's in immaculate condition, and the tank is pristine inside. But it sat with a low fuel level in the tank, so the screens could have been exposed in the tank and rusted themselves, old fuel/debris could have clogged the screens up since I bought the bike and started running it regularly, etc. I did have good performance for a full tank when I first bought the bike, so after running it for a while, the screens could just be doing there job and are now filled with whatever debris was in the tank, despite the tank being pristine and shiny inside. I attribute that to the low humidity here in Colorado where the bike was stored in that shed.

As well, I think there is a fuel venting issue when the bike gets HOT, as in riding on 85+ degree days (97 degrees yesterday going thru Denver like I said) and that is contributing to the low speed fuel issue. I believe the two issues are independent of each other, yet existing at the same time. Make sense?

So, I have two things I'll be doing. Cleaning the fuel screens and making sure the tank vent is not clogged/partially clogged, which I believe it is.

[b.walker5]

.. so the screens could have been exposed in the tank and rusted themselves, old fuel/debris could have clogged the screens up since I bought the bike and started running it regularly, etc.

The screens are plastic and covered with a nylon type mesh. No rust from the screens, but could certianly be blocked with fuel varnish and rust and debri from the tank.

[Bonz]

Well, that's a huge bonus in terms of them being plastic w/nylon covering... No rusty junk to look forward to in terms of the screens themselves. Gotta believe even though the tank is shiny and clean that sitting for all those years probably got some junk in there for sure. Thanks much!