1978 GS550e air leak?

[tomservo]

Guys, I've got a 1978 GS550e that runs well initially but after the engine gets good and warm it won't hold it's idle. It will slowly drop a bit.. then pick up a little, but eventually it will drop to the point it quits running. This happens after running on the highway for instance for about 15 minutes and then getting to a traffic light or other stop. what's strange is after a few minutes of stop and go traffic on secondary roads it will go back to idling fine. I've also had this happen in cases where you're tooling around slowly in a parking lot (in a riding class for instance) and after 20 minutes or so it will start doing this again.

It sounds to me like there is an air leak that's occurring once things get good and hot. I tried just starting it up and spraying some brake cleaner around the intake boots to see if I could get the engine to rise a bit but admittedly when i tried it the engine wasn't doing this thing at the time I tried.

Any thoughts on where in particular I should be looking? Is there a known issue that causes this behavior?

Thanks,

Brandon

[MisterCinders]

Do you need choke to start it? If it's bogging down when warm, I'd think it was running rich instead of lean.

Any mods on the bike (pods/pipes)?

Have you done all the maintenance stuff (valve clearances, carbs cleaned thoroughly, etc.)?

[tomservo]

carbs have been gone through both by me and a pro friend of mine . It needs choke to start and in fact when it is having this issue it will take choke to get it to restart which leads me to believe that it is getting air from somewhere it shouldn't be. Carbs have been sync'd and no mods have been done. I've tried to keep it as close to original setup as possible.

[BassCliff]

Greetings and Salutations!!

Hi Mr. tomservo,

Sometimes squirting stuff around the carb boots just doesn't cut it. Have a look at the Air Intake Repair guide. What other maintenance have you done? Have a look at the required maintenance lists in the "mega-welcome". Oh, pardon me. It seems I'm very late with your "mega-welcome". Here you go.

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Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. This is what NOT to do: Top 10 Newbie Mistakes. Now let me roll out the welcome mat for you...



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[hampshirehog]

Leaky intake boot or o rings would be my first look. 2nd would be busted off fuel screws that has been compensated by a dodgy carb synch ( I had exactly the same issues as you describe on a 550 and it was a busted fuel screw).

[tomservo]

Yes, after reading through the info presented above the problem is sounding very much like the intake O-Rings. I'll be taking a look in there tonight to confirm. The rest of the carbs I went through myself and put in rebuild kits. Then I had my genius mechanic friend tune it and it did run spot on when he did it. It has been doing this crap intermittently though and the O-Ring issue is something I know we haven't looked at yet. ( I didn't even realize they were there). I'll be keeping my fingers crossed as this would be an easy and cheap fix.

[tomservo]

Awesome info by the way guys. I'm just now starting to get a second to absorb all the other info! Thanks for the excellent resource.

[tomservo]

Yep, the o-rings were toast, literally. Got new ones on the way.

[Suzuki_Don]

Yep, the o-rings were toast, literally. Got new ones on the way.

Tom you will notice a huge difference when you have fitted them. While the carbs are off check the fuel screws, but count the number of turns out they each are from fully bottomed.