Starts, runs, then won't start

[joeninpo]

Ok...so, I've searched through the threads here, but I'm a noob to the site. If a similar posting is already on here, I apologize and ask that you send me to the appropriate link.

I have a problem and I'm pulling my hair out at this point. I have an 80 model GS550L that is basically stock. Aside from routine maintenance (carbs being rebuilt, oil changes, ect), all of the parts that have been replaced have been with OEM parts. I just bought it a few days ago from a fairly competent guy who took resonably decent care of it. We're just coming out of a harsh winter and the bike hadn't been ridden for the past few months, but again, it was pretty well maintained. It has the stupidly designed 1980 550 petcock, but from what I can tell, it's set right. I could be wrong, but I'll do more research on that just to be sure. It does idle kinda low (around 500 rpm), but I'll figure out how to adjust that as I go through the manuals. That's about everything that I know about the bike for now.

Now, here's the problem that I'm having. It will start up just fine, warm up just fine, and ride just fine for about 15 minutes. After that, if I stop it or it stalls out for any reason, it will not start back up again. I have to let it sit for a few hours and then it will do the same thing. I've spent more time pushing it home than I have riding it, so I would appreciate any help that you can give me!


Thanks!
Eddie

[1_v8_merc]

Do you mean it won't crank at all, like the starter button won't work.

Or do you mean, it keeps cranking but wont actually fire up?

[SqDancerLynn1]

I would start with the fuel system, make sure the petcock is working. Go for a ride, (take an extra spark plug), when the bike quits ? pull a plug wire and attach to the spare plug and ground to the engine and crank it over, checking for spark

[jwhelan65]

How old is the battery?

[chuck hahn]

find the curb idle adjustment and turn it up till your aropund 1.000 rpm...your idle is way too low for the bike to generate proper vacuum to keep running.. it simply wont run that low..look down around the carbs for a roundish looking nob sticking in between the carbs somewhere..turn it in a turn or so then see how she performs. Engine rpm provides the intake vacuum so the engine actually is pulling sufficient fuel in to the cylinders to keep it running and it supplies the vaccum needed to keep the fuel cock open in the case of a vacuum actuated petcock..RPMs too low= engine not drinking in gas=it stalls if you let off the throttle..And then you will have to twist the throttle a little as your cranking to get it to start again.

[chuck hahn]

And i agree with the potential petcock issue. If it will start again and be fine for another 15 minutes then maybe the petcock isnt working properly and you burn the gas out of the carbs and then it is starving for fuel at that point. After setting a while the bowls get a chance to fill up again and its ok then ...for another 15 minutes at least!!

[derwood]

open the gas cap

[chuck hahn]

if he has the stock gas cap,it should already be self venting..sounds more like a petcock malfunction causing fuel starvation... he will have many things to check and hope he post what he discovers.. always need the info for future reference..

[joeninpo]

Hi All! Thanks for all of the great advice. I have some good news and not great news. The good news is that I adjusted the idle to just under 1,000 rpm and that made a pretty decent difference in how it runs. The not so good news is that it's been raining here in DC off and on all day, so I haven't been able to ride it around to see if I could replicate the problem. More to follow tomorrow....

And just to clarify a few points and to help people out in the future who may have similar problems, the battery is quite strong and the bike has no problems turning over after the problem starts. I've worked on old British cars for the past 15 years or so and I've heard similar sounding engines that I've worked on before. I know it sounds weird to say that, but it sounds like the engine is fuel starved once it shuts down. I'm going to see tomorrow if the idle adjustment worked and then we'll go from there. The next suspect on my culprit list is the petcock, but I don't know if it's because it could be a problem or just because I think it's a stupid design and I want to replace it with something that makes more sense on a bike. Must be part of my oldtimer cantakerous disease :-)

Again, thanks for all of the help!
Eddie

[Colorado85gs550]

my '85 GS550ESF is doing the EXACT same thing.........I'm rebuilding the petcock tomorrow. We'll see if it's the problem!

[thombre]

Eddie,Test charging circuit.
Test battery voltage,charge to 12 VDC.
Check each cell with hydrometer,add distilled water
Test stator leads for continuity to ground,there should be no reading.
Check rectifier to see if any wires are burned.

Drain fuel put 1 gallon fresh fuel in tank
Start engine,take DC voltage test at battery terminals,you should read 14VDC at 2500 rpm,any less will cause battery to drain when riding.

[Colorado85gs550]

rebuild your petcock!!! I went ahead and just put my rebuild kit into mine and tested at idle for 20 minutes and mine NEVER died!! I ran it with the fuel cap on the whole time...........

I was under the impression there was a vent that went to the bottom of the tank, not through the cap........

I noticed 10 times the fuel flow as I reinstalled my petcock after the rebuild

I got my rebuild kit from Z1 Enterprises and it took 2 days via Priority Mail.

[BassCliff]

Hi,

These are the proven, tried and true, guaranteed steps to GS happiness. I quote from the venerable Mr. bwringer...

(This is part of your "mega-we.come".)

***********Quoted from Mr. bwringer************
Every GS850 [and most other models] has (or had) a set of well-known issues that MUST be addressed before you have a solid baseline for further troubleshooting. It's a vintage bike, and it's quite common (as in, every single GS850 I have had contact with) that there are multiple problems that have crept up and slowly gotten worse over the years. It's not like a newer vehicle, where there's generally one problem at a time.

These common issues are:

1. Intake O-rings (install NEW OEM or Viton only - common nitrile O-rings will quickly deteriorate from heat)
2. Intake Boots (install NEW -- these cannot be repaired)
3. Valve clearances (more important than most people think)
4. Carb/airbox boots
5. Airbox sealing
6. Air filter sealing
7. Petcock (install a NEW one)
8. On '79 models, install new points or Dyna electronic ignition (or at least verify that the old points are working correctly)
9. On all models, it's fairly common to have problems with the spark plug caps. These are $3 or $4 each, and often worth replacing if you're keeping the stock coils/wires.
10. Stock exhaust with NO leaks or holes -- good seals at the head and at the junctions underneath.

What I have noticed at the rallies is that very, very few 850Gs are actually running right. Make VERY sure it's actually running the way it's supposed to before busting out the modifications.

Brian's E-Z and fun plan for GS850 happiness:

1) Seal the airbox and air filter with weatherstripping.

2) Ensure no intake leaks. Spraying WD-40 or water doesn't tell you much, since very small air leaks can cause problems even though they won't suck in enough WD-40 to make a difference. Replace your intake boot o-rings and boots if needed, and seriously consider spending the lousy $28 for new airbox/carb boots.

3) Ensure clean carbs with correct settings, new o-rings, and original OEM jets. No, not just squirted with something. I mean completely disassembled.

4) Check/adjust valve clearances (Manual calls for every 4,000 miles. This is not optional.)

5) Ensure healthy electrical system.

6) Seriously consider upgrading coils and plug wires.

7) Install new, stock NGK B8-ES plugs gapped to .031".

8 ) Fine-tune float height and idle mixture screw to ensure best off-idle transition.

9) Clean air filter and reinstall with only the lightest oil mist -- over-oiling and/or letting the filter get dirty is a common and critical mistake, and will make the bike run funny at low speeds and run rich. This may take a few tries.

10) Make sure the exhaust seals are sealing.

11) Ooh, much better now, huh? You're gonna need upgraded suspension - Progressive or better fork springs and shocks. Set suspension sag appropriately.

12) Upgrade brakes with new pads and stainless lines to deal with all that extra speed.

13) Install new petcock, since I'm going to head to the roof with a rifle if I have to read about yet another #2 plug fouling and failed hillbilly attempts to rebuild the petcock and/or deny there's a problem.

14) Oh yeah -- check compression somewhere in there to ensure the valves and rings are reasonably healthy.

15) You'll probably need new OEM clutch springs -- the clutches last forever, but the springs get tired after 20 years or so under pressure. E-Z and cheap.

Carburetor maintenance:

Replace the intake boot o-rings, and possibly the intake boots. Here's the procedure:

http://bwringer.com/gs/intakeorings.html

Here's an overview of what happens with this particular problem:

http://cycleorings.com/intake.html

You'll also want to examine the boots between the carbs and the airbox. There's a good chance these are OK, but check them over.
And finally, if things still aren't exactly right, you'll want to order a set of o-rings for BS carbs from the GS owner's best friend, Robert Barr:
http://cycleorings.com
Once you receive these rare rings of delight, then you'll want to thoroughly clean and rebuild your carburetors. Here are step-by-step instructions that make this simple:
http://thegsresources.com/gs_carbrebuild.htm
****************End Quote********************


Do these things and you will enjoy GS bliss. Sometimes there just are no short cuts. If I may say, I have a bike that starts with the merest flick of its start button. It idles steadily, warms up quickly, runs like a scalded cat, and stops on a dime. Sure, it takes some time, some parts, some reading, some study, some learning, some wrenching, but it's worth it. Keep us informed.


Thank you for your indulgence,


BassCliff

[chef1366]

When it doesnt start check for spark and fuel in the bowls.

[Colorado85gs550]

WHEN it dies, spray starter fluid into the carbs and see if it fires up! If it does, it will mean it is the EXACT thing I just faught and figured out. If not, then check for spark, then check for fuel in the bowls.........

I'll bet you a day's wage that it's your petcock...............