1980 GS 550 ran great when I bought it and now won't start

[Al1208]

Hello fellow GS enthusiasts, I have an ongoing dilemma. Right when the pandemic started, I bought a 1980 Suzuki GS 550 from an honest dude on Craigslist and it was a running motorcycle. I rode it around for about a month; took it on the freeway a few times and it ran strong. At a certain point it started showing signs that it needed a carb cleaning: took longer to turn over and sometimes bogged in low gears. With the help of another member of the forum Ed, who lives a few cities over from meI removed the carbs, cleaned them thoroughly, replaced some mismatched jets, replaced the intake boots (one of them had a tear in it) and reinstalled the carbs. Ever since I made this repair the bike has not started. I have checked the vacuum fuel tap for leaks and something else I noticed is it's only getting spark on one plug. I don't think it's taking in gas from the tank because the float bowls are dry when I check them after I try to start it. What should I do next? I am not afraid to get my hands dirty and I have some tools. I am far from a mechanic but I have taken apart two stroke engines and worked on those before. I have yet to check the valves so that is definitely at the top of the list. But what about the spark or lack thereof? I took a bunch of pics so I could post them but it's telling me I can only post one file(that sucks) but if anybody can help me I will be forever grateful. Thank you for reading, Alex in Hermosa Beach, CA

 

[tom203]

No fuel in carb bowls likely means petcock ain’t passing fuel…..might be defective or you might not understand how the famous 1980 petcock is supposed to work.
How are you determining that only “getting spark on one plug” ? Note that the ignition coil fires two plugs simultaneously….spark travels down plug, thru head, and thru second plug and back to coil….it’s easy to reach a false conclusion. But it might be a failed ignitor, as the stock 550 ignitor seemed unreliable over time.
I’m sure Ed stressed the importance of valve checking…so do this soon as you get this critter running again.
if your fuel is over 6 months old , dump in in your fuel injected vehicle and get new.

 

[Al1208]

Thanks Tom for the useful response! I am gonna be spending a good portion of the day working on my bike. Definitely going to follow Basscliff's guide to checking valve clearances so I can check that one off the list. The reason it looks like it's only getting spark on one plug is because months ago I changed the plugs out and since then I have been able to get the bike running for maybe 30 seconds and then it dies. When I check the plugs afterwards, three out of four look brand new, still to this day. One plug has light gray soot from the gas, spark and air mixture (and it is the plug on the outer left side when you are sitting on the bike facing forward). Not sure if that means anything but the gas in the tank is about 9 months old so I am changing it out today. I'm wondering if the carbs need to be cleaned again since the bike has been sitting for months and months at a time. And unfortunately my previous residence didn't have a garage so the bike was stored outside in a carport, covered of course.

 

[Nessism]

Hi Alex,
If you bring the carbs over to my house I'll check them over for you. Also, bring the gas tank, so we can check the petcock. Those petcocks have a check valve that often fails, and when it does the prime feature doesn't work. It makes filling the float bowls really difficult.