My test ride wasn't great, can anyone spot the fault?

[Wes51st]

I took my 79 GS550e, for its first run in months after giving it a thorough renewal after I bought it. It's taken a lot of work, but now everything is running as it should- or so I thought.

After about 20 minutes of riding while stuck in traffic, the engine just died. It wouldn't restart until I took it to the side of the road and waited a few minutes. I put the choke back on then off as it seemed like it wanted to fire but just couldn't.

Eventually when I was able to restart the bike it seemed not to have the power to rev and keep idle, instead it bogged out when I rev'd it. After a minute of playing with the choke (mainly putting it on) it would hold revs and I could continue my journey until it occurred again. This happened again another 3 times along my journey about 15 minutes apart.

Does anyone know why this might be happening? Your advice would be a huge help!

*Just in case this info helps. Carbs have been really thoroughly cleaned, it has a new battery and the spark plugs are a little sooty, but not heavily fouled, and it has a full tank.

[GS1150Pilot]

Air leak somewhere? Plugged pilot, maybe?

[chuck hahn]

Plugged pilots as was mentioned. And possibly the petcock isnt working right. Be sure the vacuum line to the petcock isnt pinched or folded onto itself also..the fuel line too. Had you taken the petcock off to see that the in tank filter wasnt plugged up???

[TxGSrider]

Maybe your vent is plugged. Maybe your filter is dirty. Unhook your fuel hose and let it drain into a container and check for good steady flow.

[chuck hahn]

Doesnt matter if they were thouroughly cleaned or not. Just one spec of scale breaking off the carb body or from the bowl can get sucked up and replug jets.

[bobgroger]

Open the gas cap after riding for a bit and see if you get a "whoosh" sound. If so the vent in the gas cap is plugged. Happened to me on my 850, took a while to figure it out. There are 2 steel balls and other small parts under the cover on the gas cap, so take it apart carefully and note where everything goes.

[Wes51st]

Thank you guys, this is really helpful.

I have previously taken the petcock off and cleaned it, it was in perfect condition. Now I might have to confess that this problem could be of my own doing. When I got the bike I noticed that the fuel cap was a bit loose. I guessed being an old bike it had just worn out rubbers, so I fitted a cork washer to create a tighter fit. I bet you're right with the air venting and that is it, it's stopping the vacuum from working!

I'll check today and let you all know what happens. With that can anyone tell me if there are vents or anything like that which should be kept clear for the air to circulate in the tank, not sure I've ever seen holes or vents?

[chuck hahn]

The venting is via a molded in channel under the chrome cap cover itself. Bugs and stuff can get in there and plug the passage. The seal should be snug so gas dosent splash past the seal and get on the tank. Throw it in a can full of vinegar overnight and spray it down with lots of compressed air to dry the lock cylinder and such if your concerned its a venting situation.

[JTGS850GL]

Did it die suddenly or sputter and die gradually? If it was sudden it may be igniter related. The GS550's were known to have issues with their igniter. If it dies, quickly check for spark. Take a spare plug with you and when it dies put that plug on one of the plug wires and place the body of the plug on top of the head. Crank the engine and see if you have spark. If no spark then I'd suspect the igniter. If you do have spark and the spark is nice and blue, then carbs or fuel related issues are suspect.

[Wes51st]

I've taken on everyone's kind advice and sadly I'm still struggling.It's running really badly today, worse than yesterday.

Here's what I did today:

I looked but couldn't seen the channels for the air vents in by the fuel cap, so I tried running with the cap on, cap off. Nothing changed.

I could get it running with the choke on full and in prime on the petcock. But there seemed to be a high pitched piston whoosh sound every 5 seconds.

At the end of hours adjusting the idle and doing all the fault checking I can with spark plugs etc, the whoosh sound had gone and I was left with the bike being able to idle with the choke fully on. However when I slide the choke gradually down to off the engine would rise to 4-5k revs, before coming to a slow then spluttering stop as I closed the choke.

Please any advice is welcome, I'm can't spend anymore time in the cold!

Extra info on the carbs: I've set the fuel screw to 3/4 turns out and air screw 2 turns out.

[GS1150Pilot]

I still vote plugged pilot passage.

[chuck hahn]

Turn the pilot screws to 7/8 and the side ir screws to 1 1/2. this will richen the pilot and main circuits a bit and may help. What do the plugs look like?? Black and sooty means too rich. White and ashy means its too lean.

[Wes51st]

Turn the pilot screws to 7/8 and the side ir screws to 1 1/2. this will richen the pilot and main circuits a bit and may help. What do the plugs look like?? Black and sooty means too rich. White and ashy means its too lean.

I'll try this. It does have fairly sooty plugs, but because the bike runs better with the choke on, it would seem its running too lean? But what do I know, clearly something is wrong and I'm at breaking point with no other ideas.

[Wes51st]

I still vote plugged pilot passage.

Speaking of ideas I will check for this. Am I looking for dirt in the air screw passage? Sorry but I don't really know what to look for.

[chuck hahn]

Take a look at the carb rebuild tutorial here. Youre comment about not knowing what to look for is very telling. Im now suspecting you need to do a 100% full tear down and rebuild from top to bottom.

If you have problems with the rebuild you can PM me your number nd I can call and walk you through things. Its not as daunting as you may be thinking.

VM tutorial on right side here..

http://members.dslextreme.com/users/bikecliff/