hello and carb questions

[ezemm]

greetings xs, i recently bought a 1979 xs 650 special SG that had been sitting garaged and unused since 1982, with 2500 miles on the clock. predictably, the big challenge in bringing the bike back to life has been fuel related, as bike was put away wet. it seems to have been spared any stuck valves. i've been reading a lot of the threads on carbs here, and finding them most helpful. however, i jumped right into working on the bike before i discovered this community and wealth of experience, and soaked my carbs in a gallon of old carb cleaner before learning that is not recommended. my first question is, what might i have damaged by doing so? the carbs came out clean, came apart without incident and are now on the bike, which is mostly running ok. my most irritating problem is that on cold starts, only the right cylinder will fire until engine speed gets up to around 3k rpms. then the left cylinder kicks in, with a lot of popping. i'm able to ride away within a few minutes, still with backfiring and poor left cylinder performance in low rpm, but within 5 minutes or less of stop and go in town riding, i have full power in both cylinders, and backfiring is reduced 90%, idling nicely. bike seems to retain a bit of that backfiring on deceleration no matter how warmed up it is. i am unable to detect any exhaust leak anywhere, but did obtain some new gaskets just in case. from what i have read here, i suspect the pilot and /or enricher circuits are not fully cleaned, and i plan on going through cleaning again in a week or so. greatly appreciate any experience anyone has to share that speaks to this problem. lastly, how sturdy and reliable can i expect this bike to be, once i've got this kink worked out? do these bikes require more than average maintenance for their age? my first bike back in the early 80's was a '75 RD250, ridden moderately for 6 months a year and stored under a tarp for the other 6, and it seemed to need very little attention. after that it was old triumphs for years, very much attention required. wondering how the xs fares?
emmet.

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[warrenlevihursh]

Did you take everything apart before soaking? You didn't soak the diaphragm did you? On top attached to the needle? The only other thing on the BS38s I can think of that shouldn't be submerged should be the plastic floats and an o-ring that is on the main jet I believe. I've read these o-rings are very important to be in good shape. Did you check float levels when you put it back together?

 

[ezemm]

hi warren,

i got the slides loose and diaphragms out before soaking, otherwise the whole carb went in the drink. floats were brass, and stress cracked with age, so i replaced with new. rebuild kit i used was vey complete, and i believe all jets and o-rings are new. i've only done an eyeball check on float levels, haven't checked fuel level in the bowl using a clear tube. for the record, these are 34's, not 38's...

 

[warrenlevihursh]

hmm, ok, The 1979 use BS-38s normally, and if they had brass floats, they aren't BS-34s, they only had plastic unless I'm mistaking. Someone please correct me if I am wrong. Maybe you ordered the wrong jet kit, because the pilots are different. They will both fit, but it wont run right. Verify the carb type first, but the BS34 use BS-30/96 pilot jets and the BS-38s use the VM 22/210 jets. The wrong pilots could cause what you are describing.

 

[5twins]

A '79 would have had BS38s stock. Either your carbs were swapped or you actually have a 1980 model. On the BS34s, the float needle tip is rubber and the float needle seat seals into the carb body using an o-ring. Both or either could have suffered damage from soaking in carb cleaner. But a rebuild kit should have had replacements. There are rubber seals on each end of the throttle butterfly shafts. Soaking could hurt them. There are also small o-rings on the bottoms of the mix screws.

When you cleaned the carbs, did you just soak them or use compressed air to blow through the various passageways? Just soaking usually isn't enough, especially where the pilot circuit is concerned. Also, the mix screw was capped over with a brass plug on the BS34s. You have to remove that plug (drill it out) and the mix screw to do a proper cleaning of the pilot circuit.

 

[warrenlevihursh]

You prob actually have a 1980. I stand corrected, the 1980s Bs34s did have a brass float. How does your choke work? If it has a knob that pulls out, they are BS34s.

 

[Brassneck]

SG's are '80... likely have 34's.

Sounds like the left carb is running lean...idle mixture adjustment would be my next move.

 

[XSLeo]

www.amckayltd.com/carbguide/pdf is our carb bible. Read it, print it out and read it. Read it till things start to make sense. Once you get that far use it to tear down, clean, inspect, repair, adjust as you reassemble, reinstall, test and adjust as needed.
Leo

 

[ezemm]

manufacture date is in 1979, maybe june, i have to look at sticker. the bike had no registration or title when i bought it. ignition seems to be factory TCI, from what i am learning, so probably an 80 model. pull out choke knob, these are definitely 34's. kit had replacement float needle seat and o rings, cleaning was done with soak, spray and compressed air, as well as a poke here and there with fine wire. i have been reading posts and carb guide, which informed me of the no-soak recommendation. pulled the cover plug from mix screws and replaced o rings, bench sync only on carbs, some adjustment on mix screws, but i have yet to get into the more accurate techniques. also, not knowing any better, i ran the engine just a bit with plug wire disconnected, for maybe 10-20 seconds several times. could i have damaged my coil in so short a time? and if so, would it weaken spark in both cylinders, or just the one?

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[5twins]

If you hurt the coil, it should effect both cylinders, not just one. That single coil fires both cylinders at the same time, even though only one is at TDC on the compression stroke. The other gets a spark anyway, what's called a "waste" spark.