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How to verify pilot circuit isn't clogged

  • Thread starter Thread starter deanwheeler
  • Start date Start date
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deanwheeler

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I've got a 1980 GS550L, stock airbox, 4-into-1 exhaust. Was running, but was loosing power, loosing top end speed, and had an idle that would hunt (ridiculously high). Found a huge vaccuum leak in 1 carb-to-engine boot, so replaced all 4 and the accompanying gaskets. Since bike wasn't running 100%, and I had the carbs off, I decided to clean them. Did the full dunk and followed the carb cleaning guide here and referenced BikeCliff's guide. Once all gaskets replaced and all put back together, it won't idle at all. It starts hard, and then will run for about 10-15 seconds before it dies. During this 10-15 seconds, the idle is steadily decreasing.

I believe based on what I've read here, that the pilot circuit is still clogged. Is there anyway to verify that it isn't? I didn't see any indication about where to spray cleaner and watch for it to come out to verify those passages are clean. Am I missing something?
 
There is an air passage from the air intake side of the carb to the pilot circuit, an air passage to the enricher circuit, several small passages from the mixture screw to the transition ports in the venturi, several holes in the pilot jet itself, one in the tip and usually several on the sides. I use a jeweler's loop to see the holes in the jets, and a lot of carb cleaner. You can tell when they are clean. Don't have your particular carb right here in front of me to look at, there are slight differences between years and models. Shoot the carb cleaner spray iinto the various places and make sure where the cleaner sprays out and the pattern it sprays out in is identical on all four carbs. You will want to wear safety glasses, trust me. Shoot it into the bore where the mixture screw goes to see the transistion ports are clear. Check the enricher pick up tube and it's tiny holes by spraying cleaner in the small hole in the bottom of the bore the choke plunger screws into. It will come out the pick up tube, both the hole in the tip and the holes in the side, in a nice star pattern, all four carbs should be the same. Also the well in the float bowl itself that the pickup tube sits in, it should be open to the other hole in the bottom of the bowl, it usually gets clogged. Again just compare one carb with all the rest, they may all be clogged but they won't all be clogged exactly the same.

Is your bike having trouble with the choke on or off, or both?
 
1.) "Air passage from air intake side of carb to the pilot circuit" - Clean and verified.
2.) "Air passage to the enricher circuit" - This is clean and appears to be working, will test the "star pattern spray".
3.)" Several small passages from the mixture screw to the transition ports in the venturi" - Will retest, not sure I'm getting anything here
4.)"Pilot jet itself, one in the tip and usually several on the sides" - Clean and verified.
5.) "Shoot it into the bore where the mixture screw goes to see the transistion ports are clear" - Think this is same as #3 above, will retest.
6.)"Well in the float bowl itself that the pickup tube sits in, should be open to the other hole in the bottom of the bowl" - Clean and verified.

Bike starts hard, but will start with choke on. Runs for about 10-15 seconds and RPM's drop the whole time. Seems to starve itself of fuel and then dies. If I start the bike and then use the throttle, can keep the bike alive and running, but have almost no power when trying to ride it. Top speed is about 20MPH.
 
I agree, but am starting to see cross-eyed from trying to figure it out.....

Hopefully the info you provided will help me see if any/all of them are clogged.
 
turn out your pilot screws to 3 turns and start there. Make sure your cables are routed and adjusted properly. Took me an hour to figure the problem on a 700. pilot screws were way off, so start with the base settings and go from there.
V
 
This may be a silly question, but someone will eventually ask it so it might as well be me: have you done a valve clearance adjustment lately? And/or a compression test?
 
Ok, here's an update.
Item #2 "Air passage to the enrricher circuit" - All 4 are clean and working. Shooting spray down sends a spray out all 3 holes. those sprays fan out, am assuming that's what I'm after.

Item #5 "Shoot it into the bore where the mixture screw goes to see the transistion ports are clear" - I think this is done. Shooting in where the mixture screw goes sends it out the small hole into the main body of the carb. So I'm blocking that with my finger and spraying into the screw hole. I believe it's coming out the 3 small holes into the main body of the carb, but not forcefully. Is this ok as the stream loses pressures in the bends of the passageway?

The gaskets do not appear to be covering any fuel passages. And if they were, I would expect it to run once, but never again as that passage would never get gas again.

I've played with the pilot screws from 1 1/2 to 3 turns out. No change. The cables are routed and adjusted.

I have not done a valve clearance adjustment nor a compression test yet. It was running when I pulled it into the garage, so I expected it to be able to run to leave the garage. I was hoping for a quick fix so I could end the summer riding it, not working on it.
 
If you're running rich and fouling plugs I'd look into a restrictive air filter.
 
That's really the trouble, it isn't running. It will only idle for about 10-15 seconds and slowly the idle drops til it dies. It seems like it's running out of fuel, which is why I suspect the pilot circuit is clogged **open to other suggestions**. Unfortunately no one has been able to provide a concrete way to prove those are open/clear before putting it back in the bike. And I run out of fingers trying to cover the holes, spray cleaner through, hold the butterfly open, and verify it's coming out the 3 tiny holes. So I'm soaking the carbs for the third time now in hopes that will clean them up.
 
Have you verified that the butterflies are synchronized? Are they open enough to allow it to idle properly? What happens if you open the throttle slightly? If it still dies, then you are probably running lean on the pilot circuit. If it improves, then you need to adjust the idle stop position on the throttle shaft.

If lean, check that enough fuel is getting to the float bowls. Are you running an inline filter? These often restrict fuel flow causing starvation throughout the rev range.

And yes, if it was running erratically before you parked it up, check your valve clearances.
 
verify? well,
I Verified I had idle passages clear, by blowing/sucking through them...yes, it's a bit like playing a flute,blocking various passages with fingers etc...With my two carbs, naturally I compared em and that helped, but I know they are NOT smooth as they were from the factory. They work though.
We both have similar cv carbs I think, so,
Might it be a failure of little rubber plugs inside the bowl that isolate the idle circuit? If they suck gas directly from the bowl, that is very hard to tune out...?
and, the airbox gasket can easily cover the idle circuit's air intake hole as hjfisk was hinting?
When the throttle plates are closed completely, the idle passage's intake ideally would be the only air/fuel available. The enricher(choke) would just add gas to it.
and, throttle completely closed, the throttle slides would not be opened by engine's vacuum (because the other side of the vacuum diaphragm is at atmospheric pressure-again, check the airbox boots to not clog THESE oval air ports)....so no gas from the throttle needle.
Ok, Assuming the bike can't be made to run with plates totally closed, Open the throttle plates and the vacuum of moving air raises these...and allows gas up the needle ...(Ruuum!) therefore, any chance the diaphragms for these are leaking or the slides are sticking and the throttle needle is NOT rising when you open the throttle? It's easy to get the diaphragms in wrong on a reassembly. You can verify operation by raising the slides with your fingers and plugging these oval "atmospheric" ports...slides stay up.

I assume you did of course completely clean the brass main jets and their teeny tiny little holes..)
 
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