1980 xs1100 special surges, what to do....

[mmarquis]

I'm a new member , I recently bought an 80 special off of craigs list for 400 bucks, it has a little over 24k miles on it. It needs cleaning up and minor repairs here and there , but the thing i need info on is this surging that begins at about 2500-3000 rpms and will go up to 5000-6000 rpms ,and will no come down till i switch the ignition off so ,whats up with it ? In the past I've owned a 76 honda 750 supersport (extremely reliable), a 1972 honda 500-4, and a 1978 suzuki 1000. Can anyone tell me what the probable malfunction is . I am in Flagstaff ,AZ and the elevation is 7000 ft ( yes the bike runs rich).

[jwhughes3]

vacuum leaks and gummy carbs

No I don't mean small German candy carbs - I mean your carbs are likely varnished and have sticky float valves if you bought it for $400 (nice deal BTW) it was likely neglected - the other raging idle culprit (and I am not the best guru around here - but have been listening) is vacuum leaks or cracking in the carb manifold boots or one of the hoses - mine has been sealed with black Plastidip - but takes a little teardown.

Best of luck! Got pics?

John in San Antonio

[DGXSER]

Hanging idle like that is typically as JWHughes suggested, vacuumn leak which you can check by putting an unlit propane torch with gas on around the carb boots and the butterfly valves of the carbs with the bike running. If the revs go up, that is the source of your leak.

Another common source is running lean, but you say they are running rich. The carbs have sort of three different ranges, idle to low revs under 3k which relies on the pilot jet circuit, the middle or 3-5k range which bring sin the needle valve that is on the slide (not the float needle valve), and then finally above 5k which is all main jets (primarily). Here is a good link to tuning these CV carbs.

The third source is synchronizing the carbs. If they are out of synch then one will hang a little high and pull the others along with it which makes that one go higher and so on and so on and so on. So synch the carbs for sure.

[TomRodgers]

Thanks to the folks here at Channel 11, i can say this for sure....

Black Sunshine had the same issues. After pulling the carbs apart, cleaning them thoroughly, lubricating the springs and such, i put the beast back together.

i still couldnt get a decent idle out of it. fluctuated like CRAZY!!! I ended up purchasing a COLORTUNE plug, and d!cked around with it. Colortune is used to set your idle mix and to check mixture up TO but not including WOT. EACH cyclider i played with changed the idle. #1 was so lean....after setting #1 properly, my idle went from 1100 rpms to 1600. i backed it down, and started on #2. Idle went from 1100 again up to almost 2000 rpms. turned it down again and started on #3. 3 was RICH. backed it down and idle fell to just over 500 rpms...barely running. raised the idle ...and started on #4. 4 was relatively close.... after doing this i sync'd the carbs, checked the colortune again, and one more time the sync. B!tch runs like a raped ape now, idle response is quick, and returns to idle nicely!!!! no more fluctuation.

So... check for leaks on your carb holders (unlit propane method), and do yourself a favor....pull the carbs and dive in. I was scared sh!tless about mine, but several of the Guru's here helped me. wasnt that bad. now i have 2 running bikes. (they run, but one wont stop..hehehehehe no brakes yet!!).

Good luck and ask!!!!!

[Ivan]

Thinking about a surge from 2500 to 6000, that's the range the slides and needles control. I would pull the airbox and make sure all the slides move freely. Then block off the lima bean shaped opening on the carb inlet side, push up the slide and make sure it stays up or drops very slowly.

If the slides are sticking it would definately screw with the mix in the 2500-6000 range. below that is idle jets and pilot air jets and mix screws, and above that is main jets.

If this is the case, then clean them up with some carb cleaner and get them moving freely.

After that, take all the other guys advice as well. If it has been sitting, it probably has all those troubles to boot, since they are pretty common on a neglected scoot.

[Athedra]

Agree with Ivan, and also going on that you said she runs rich.

Check the needle pistons. If the are loose, make sure your diaphragms at the top are not worn. While you have the tops open, check your springs. Friend of mine on his GPZ600 had a case where the spring wasn't put back properly, and it twisted inside the top. Opened it up, put it back in correctly, and still running perfectly today.

If the diaphragms has holes or tears in it, patch it with a dab of silicone on both sides, let them dry up and off you go.

Noticed you speak very highly of your other bikes. I have three bikes (XS, KTM250, GPZ550), and love my XS so much that lately it's the only one I use. So bad that the other two hasn't smelled tar for three months. Considering selling the other two and spend the money on my XS making it a tourer. As I mentioned in another thread, theses are still the kings on the road, and trust me, after you started fixing her up, you will get offers for her daily. I been using my XS daily for the past three months, and have at least 2 offers for her per day.