Lugs and surges with no power till it backfires

[gorgan8]

Ok, my bike is a 78 xs1100 it has a bit of a seep at the front exhaust pipes/ base gasket, I took apart and cleaned the carbs back in February when i posted the float post repair. then i got a new throttle cable. the bike was running well for the past few months ( since my car is out of commission it was my daily driver). recently, i took it for the first long highway ride, it ran great but on the way back i got a misfire in the right side and the bike lost gusto. i got to an exit and stooped at a gas station. after i filled back up it started and ran fine. over the next few days it backfired a few times mostly at start up. the other day i had to ride in a bit of rain and it ran fine but after work, in nicer 50+ degree weather, it had a hesitation it would slowly get up to speed but not go over 50 with the throttle cranked. after a bit of running i got a backfire and the bike ran right. i got home let it sit and it hesitated again. took a test drive and it would surge and crawl, then it backfired again and ran correctly excepts it slowly bogs down and dies if it hits about 1000 rpm. I also noticed a leak at the front 1 and 2 cylinders it looks like oil but i cant tell if its coming out of the exhaust ports or if its from the base gasket.

I looked in the forum and seen a few things like the pick up coil wires, i inspected and cut and replaced them using an old set of meter test leads. started the bike and watched the vac advanced, it seemed to move fine but a bit sluggish to return( i don't know what's normal).
The bike still has the issue. So I looked over the coils, they are bright Orange and have a MADE IN AMERICA stamp so i think thay have been upgraded at some point.

today, i took the bike to the part store got some new fuel line came home to replace the hoses and sync the carbs. while i was there i took out the air box and flow tested the carbs. #2 and #4 began dripping from the port hole on the right of the carb throat and number four came from the jet as well. i rapped the carb a bit and it stopped.. but the bike didn't want to start. when i did get it started with sync tool all carbs were in sync.

I still have the issue! Any ideas? is there anyone In the Milwaukee area that might be able to lend a hand, i am on a budget so its part by part right now.so i just need to know where to go next. at this point i am too tired to try and figure it out.

[XSokieSPECIAL]

Pickup coils......

Text book symptoms.


Check the wires at the plug with a VOM. Each coil should read about 750 ohms


http://www.xs11.com/forum/showthread.php?t=543

[gorgan8]

tested pickup coils?

OK i tested the top (Red and blue) and got 712 ohm and the bottom ( blue and white) at 745 ohms by spec id say the top is too far out od spec but it would jump to 7 33 for a split second, so i slid the test leads into the rubber for a better test and got the 712 repeatedly. so now i'm on the hunt for new coild and i think maybe a new vac advance while i am there?

[SFerinTEXAS]

Did you slowly move the vac advance while testing ? That will expose a bad wire that may be connecting at rest.

[XSokieSPECIAL]

If it's jumping around you've still got a break in there somewhere.Yea, look for a new set be sure they've been tested if the price is up there.


Have you tested the diaphragm in the vac unit to see if it holds vacuum? Even if it does it doesn't hurt to have an extra if you can find it.

I bought a set with the still attached to the breaker plate w/the vacuum unit on it for about $12 the other day on fleabay. Had to repair 1 of the wires in one place but the diaphragm is good in the vac advance unit.

Just gotta keep watching.

[gorgan8]

Here we go again,

SO, i got a full timing advance off Ebay, it had a broken wire, but tested at 738 and 740 ohm so i put them on and and went for a ride it stopped backfiring, but the thing now has no power. at that point i swapped the new vac to it and same deal, it has no power, and and won't even idle. At stops, i put it in gear and crawl across, after a bit its starts to reve higher and gets to go, but it will not go over 45-50 mph, and even then, the rpms start to drop and at full throttle i get maybe 50mph, and to keep that i have to down shift to get it back up. I've been busy with work so i haven't had had any time to tinker, but i have noticed what looks like oil or gas residue coming from the head, i thought it was from the head gasket but its seem to be more from the exhaust port, and #1 exhaust stays cool, and the spark plug is very fouled.

Hears my thoughts/ questions,

when it was running and would backfire, it would run great! but i also noticed that it would idle high( like 2-2.5 gs) then fall back down and want to die. at this point i also noticed that the choke will not stay open, it open it, and it slowly closes, if i hold it the motor revs then slowly dies out.

with these observations, Do i need to get a full pro job on the carbs? could I have bent or burned a valve.

I'm too frustrated to keep fighing it, i just want to go for a ride!

[prometheus578]

You have a carb issue

while i was there i took out the air box and flow tested the carbs. #2 and #4 began dripping from the port hole on the right of the carb throat and number four came from the jet as well. i rapped the carb a bit and it stopped.

Firstly... rappin' on carbs doesn't do anything. Where this idea comes from I don't know.
I've often read:
"The float must have been sticking, I rapped on the carbs and 'fixed' it"
Nothing is fixed until you address whatever caused the problem in the first place.

...but i have noticed what looks like oil or gas residue coming from the head, i thought it was from the head gasket but its seem to be more from the exhaust port, and #1 exhaust stays cool, and the spark plug is very fouled.

You're running on only three cylinders and have probably been doing that for months. These engines will sometimes run remarkably smooth on only three cylinders. Some people can hear the difference, some people can't. The clue is what you mentioned... #1 exhaust stays cool.

#1 exhaust stays cool because the spark plug is fouled and not firing.

"I should just put in new plugs, then?"

No... remember, nothing is fixed until you address whatever caused the problem in the first place. The plugs are fouling because the carbs are flooding.

...flow tested the carbs. #2 and #4 began dripping from the port hole on the right of the carb throat and number four came from the jet as well.

You need to pull the carbs and go through them again. Probably need new float needles, as worn ones are the main reason for flooding and plug fouling.

[3Phase]

Gorgan, was the fouled spark plug new or cleaned before you changed the pickup coils?

Clean or replace the fouled spark plug then double-check the 'new' pickup coil air gap, the connections and the ignition timing.

The air gap should be checked with a brass feeler guage: 0.7mm/0.0275".

Set the static timing at the 'F' mark/10 degrees BTDC.

Dynamic timing is tested with the vacuum advance disconnected and should show 36 degrees of advance BTDC at 5200RPM. The reluctor should advance and return smoothly and completely when turned by hand with no sticking or notchy feeling.

Test the vacuum advance and make sure it adds 16 degrees total advance at 150 mmHg/6 inHg.

[cywelchjr]

Firstly... rappin' on carbs doesn't do anything. Where this idea comes from I don't know.
I've often read:
"The float must have been sticking, I rapped on the carbs and 'fixed' it"
Nothing is fixed until you address whatever caused the problem in the first place.

While true, if it's just that it hung up on the gasket, then it will fix it until the bowl is empty again. I've also had them get a little crooked in there from the install process, and the rapping does fix that, and it often stays fixed afterwards. But for the most part I agree that it doesn't fix the problem. However, even if it doesn't fix it, it does tell you a bit about what may be happening in there if it makes it stop leaking.

You're running on only three cylinders and have probably been doing that for months. These engines will sometimes run remarkably smooth on only three cylinders. Some people can hear the difference, some people can't. The clue is what you mentioned... #1 exhaust stays cool.

That's right on point there. It's amazing how easy it is to tune these things to appear to run pretty well on 3. For that matter, I found about 18 years ago, that my XS400 actually ran pretty well on 1 cylinder. Didn't have a lot of power, but it wasn't really that rough, just low on power (and dripping raw gas out one pipe.

#1 exhaust stays cool because the spark plug is fouled and not firing.

"I should just put in new plugs, then?"

No... remember, nothing is fixed until you address whatever caused the problem in the first place. The plugs are fouling because the carbs are flooding.


You need to pull the carbs and go through them again. Probably need new float needles, as worn ones are the main reason for flooding and plug fouling.

Yes, that too, although depending on the year, the later carbs can be leaking around the o-ring that seals the seats in their hole, new needles without fixing the o-ring problem doesn't help. I fought that on my 400 (same exact carbs on the 80+ models) for quite a while, and many of the kits I got didn't have replacement seats OR o-rings.

[natemoen]

SO, i got a full timing advance off Ebay, it had a broken wire, but tested at 738 and 740 ohm so i put them on and and went for a ride it stopped backfiring, but the thing now has no power. at that point i swapped the new vac to it and same deal, it has no power, and and won't even idle. At stops, i put it in gear and crawl across, after a bit its starts to reve higher and gets to go, but it will not go over 45-50 mph, and even then, the rpms start to drop and at full throttle i get maybe 50mph, and to keep that i have to down shift to get it back up. I've been busy with work so i haven't had had any time to tinker, but i have noticed what looks like oil or gas residue coming from the head, i thought it was from the head gasket but its seem to be more from the exhaust port, and #1 exhaust stays cool, and the spark plug is very fouled.

Hears my thoughts/ questions,

when it was running and would backfire, it would run great! but i also noticed that it would idle high( like 2-2.5 gs) then fall back down and want to die. at this point i also noticed that the choke will not stay open, it open it, and it slowly closes, if i hold it the motor revs then slowly dies out.

with these observations, Do i need to get a full pro job on the carbs? could I have bent or burned a valve.

I'm too frustrated to keep fighing it, i just want to go for a ride!

First you say that the pickups you got off eBay had a broken wire but you put them on anyways. Did you fix that wire before you put them on? If not you gotta do that before you go farther because electrical problems sometimes manifest themselves as problems that look like carbs.

Second. You said you pulled the carbs apart and cleaned them. Did you take out every piece and completely disassemble the rack to clean it? There are all those little holes in the emulsion tube and the pilot jet that can get clogged and then it will not flow gas properly. There are also 4 little tiny holes in the top side on the intake side of the carb right by the butterfly that need to be clear otherwise the bike most likely will not idle let alone run well. Also what size jet did it have in it when you pulled it apart? Where are the floats set? You dont need a pro to do the carbs. They are pretty simple but sometimes it just takes some time to get it figured out.

Third. What does the fouled plug look like? Black and dry, black and wet, white? What do the other three plugs look like? If they get fouled clean then off otherwise it wont work. A propane torch works good for cleaning then. Heat the plug up and just give it a scraping with a wire brush.

Gotta do a compression test if you really want to see if you have a bad valve, leakdown test would be good as well. Send me a PM if you want some help and I can see what I can do (I am that guy that you met at the gas station today).