OMG. I had forgotten....

[Incubus]

So the last time I rode Succubus, my original '79 XS11, I remembered her as being quite lively over 3000 rpm and a dog below that. I didn't really have anything to compare it to, though, since she was the only XS11 I had ever ridden.

Succubus is not stock. When I got her the top end was a frozen lump of rust and it took literally weeks before I could pry the head and barrels off. Then I could not readily find another '79 top end, so I ended up getting an XJ top end from another member (thanks, Mike) and installing it - after plugging up the YICS with set screws. So Succubus has the pistons from an XS11F, the cam from an XS11F and the barrels and head from an XJ with the larger valves.

I rode Succubus a few minutes ago for the first time in probably two years. Maybe longer. All I can say is... holy ****. This bike stumbled badly under three grand and then... wow. It is so much faster than my stock and exceptionally well running other '79XSF that it almost seems like another class of bike. Scary.

I still have to solve that awful low rpm stumble. I was watching the thread from Planedick hoping for inspiration. When he decided it was the butterfly seals he lost me. I tried butterfly seals. Tried it three years ago. And now? Ain't gonna happen. No way. After years of intensive therapy I no longer have an overwhelming urge to hide in the septic tank when the annual Monarch migration comes through, but even typing the words "change the butterfly seals" has caused me to break out in a cold sweat.

The bike starts easily and idles on all four. Right now it is idling at about 1500, but I haven't tried to turn it down. I just wanted to see if it would run. Has anyone had any success solving the stumble by changing slow jet size? I don't want to start buying stuff unless I have some idea of the expected outcome.

Patrick

[DiverRay]

Patrick,
Take it out for a ride with NEW spark plugs. Keep it under the 3,000RPM "stumble" range, and do a chop test. Just pull in the clutch and kill the engine someplace you can pull out of harms way, and remove and inspect the plugs. If you can, try to get pictures so we can try and help.
If the plugs are still white, you are lean, and that is probably the stumble. If they are black, it's rich, and you may need to adjust the float height, 1mm ONLY. That is what I would do for the carbs. The other thing to think about is the valve lash. The XJ had the valves set a little tighter than the '79 XS. If the clearance is too tight, the bike will NOT run properly at low RPM's.

[planedick]

Solved

I had the extreme luckof being given a complete set of carbs and after installation the low end stumble is gone, but they're the later carbs and have 110 mains all across and are really lean at WOT, so I want to get my original carbs rebuilt. I have taken two of the carb butterflies off, not a real problem, and I've ordered new seals for the butterfly shafts as these are dry and shrunken to the point where they leak badly. It looks like the seals (not "O" rings) are 8 X 12 mm. When they get here I'll post the results.

[phlips308]

bigger valves!!!!

so the xj's have bigger valves?are do the ports support more cfm's?i am scouting for parts for my new project(1980 xs1100 g that was given to me by a neighbor looking to scrap it).ive diagnosed the #3 cylinder with blow by and 62#s of compression.i was thinking of getting another head just in case.maybe a little port cleaning.im a power freak,and like tinkering with power.the head on the bike seems sound for now,except cosmetic broken fins from probably falling over.i know it will have more power with fresh rings.im going to try the hasting rings mentioned on another thread.i found some for $30.00 from perfect engine.it looks like one of the oversized sets will work,if the id of the fitted and compressed ring is right.i can modify the ring groove on a cnc lathe where i work,maybe even if the rings need to be modified.i make alot of old car parts at work and have modified rings id before.if it works maybe i can be as much help as the cool people on this forum have been already.thanks guys.but short story long.the xj head sounds interesting.

[phlips308]

so the xj's have bigger valves?are do the ports support more cfm's?i am scouting for parts for my new project(1980 xs1100 g that was given to me by a neighbor looking to scrap it).ive diagnosed the #3 cylinder with blow by and 62#s of compression.i was thinking of getting another head just in case.maybe a little port cleaning.im a power freak,and like tinkering with power.the head on the bike seems sound for now,except cosmetic broken fins from probably falling over.i know it will have more power with fresh rings.im going to try the hasting rings mentioned on another thread.i found some for $30.00 from perfect engine.it looks like one of the oversized sets will work,if the id of the fitted and compressed ring is right.i can modify the ring groove on a cnc lathe where i work,maybe even if the rings need to be modified.i make alot of old car parts at work and have modified rings id before.if it works maybe i can be as much help as the cool people on this forum have been already.thanks guys.but short story long.the xj head sounds interesting.

carbs on carbs off!!!

[XS1100_OEM4ME]

exaust

So the last time I rode Succubus, my original '79 XS11, I remembered her as being quite lively over 3000 rpm and a dog below that. I didn't really have anything to compare it to, though, since she was the only XS11 I had ever ridden.

Succubus is not stock. When I got her the top end was a frozen lump of rust and it took literally weeks before I could pry the head and barrels off. Then I could not readily find another '79 top end, so I ended up getting an XJ top end from another member (thanks, Mike) and installing it - after plugging up the YICS with set screws. So Succubus has the pistons from an XS11F, the cam from an XS11F and the barrels and head from an XJ with the larger valves.

I rode Succubus a few minutes ago for the first time in probably two years. Maybe longer. All I can say is... holy ****. This bike stumbled badly under three grand and then... wow. It is so much faster than my stock and exceptionally well running other '79XSF that it almost seems like another class of bike. Scary.

I still have to solve that awful low rpm stumble. I was watching the thread from Planedick hoping for inspiration. When he decided it was the butterfly seals he lost me. I tried butterfly seals. Tried it three years ago. And now? Ain't gonna happen. No way. After years of intensive therapy I no longer have an overwhelming urge to hide in the septic tank when the annual Monarch migration comes through, but even typing the words "change the butterfly seals" has caused me to break out in a cold sweat.

The bike starts easily and idles on all four. Right now it is idling at about 1500, but I haven't tried to turn it down. I just wanted to see if it would run. Has anyone had any success solving the stumble by changing slow jet size? I don't want to start buying stuff unless I have some idea of the expected outcome.

Patrick

What exaust are you running? Low back pressure can cause these bikes to lose power and stumble below 3500 rpm

[Incubus]

It is time for an update. Since the original post I regapped the valves. I discovered that when I gapped these valves the last time I was either drunk or an idiot. Sadly, I don't drink.

I gapped the valves a bit wide. Actually, Palo Duro Canyon is a bit wide. My valves had never really been close enough to my cam to actually become acquainted. After I did the valves the bike now idles and runs well. It has a slight low end hesitation (like from idle to about 2000) but that is pretty much like my Stock F. This bike is very quick and pulls very strong through the midrange, noticeably better than my stock bike. I haven't really explored the top end, say above 7000 rpm, because the rings are new and probably have less than 200 miles on them.

So far, so good. But Succubus has disappointed me before, so I'm still waiting for the other shoe to drop.

If Succubus had run like this two years ago I likely would not have gotten my second XS because I already would have had one. Either that or I would have three or four XSes in the garage right now.

Oh, and I am running a 4-1 of unknown make or model on Succubus. It used to have a 4-2 Jardine on it, but I think along with the valve problem I had some blockage in the left side pipes. That, however, is a much longer story.

Patrick