Problem with friends 1978 GS550, Any suggestions appreciated

[Mastiff]

I have a friend with a 78 GS550 who can't get it to run right. I haven't seen the bike, she is up in Milwaukee.
The bike takes 15 to 20 minutes running before you can take the choke off. She builds up speed on the choke, and when the bike starts slowing down for a given throttle position, she backs off on the choke a bit and the bike speeds up. When starting out in 1st she has to really up the revs to keep the bike from bogging out, even after she can ride without the choke. It will also bog when accelerating in 2nd, although not as consistently. It doesn't bog down in the higher gears. She does get some backfiring while on the choke.
She has rebuilt her carbs twice. She has replaced the points and condensers. She did not replace the carb intake boot O-rings. She has a 4 into 1 exhaust but she is running with the stock airbox.
I told her to replace the O-rings (since it is a cheap fix), and told her the stock airbox with a 4 into 1 exhaust is not an effective combination. I told her she'd need to either get a stock exhaust or go to pods.
Does anyone else here have any other suggestions for her? She loves the bike, but isn't riding it anymore because of these problems.

[rgierer]

a couple of things.

I have a 78 GS550 at home with stock airbox and 4 in 1 exhaust, and although it may not be the most effricient it seems to do just fine without jetting. It is a well muffled 4 in 1.

The kind of performance you describe could easil;y be boots or O-rings. Get out the WD 40 and check. I used white grease in a spray can to check mine and it was clearly the culprit. The other thing is checkout settings on carbs. When I did my carbs I must have pulled them out 9 times before I I got it right.

hang in there!

rg

[Anonymous]

did you tell her to spray some carb cleaner on the intake boots to see if the engine revs up??? that will tell her if she has o-ring problems or even bad intake boots.....

[Mastiff]

Yes, I told her about spraying WD40 on the intake boots and seeing if the engine revs higher. She is also planning to do a quick trial with the air filter removed from the air box, but with a screen in the box in front of the carb intakes. She figures if the increased airflow improves the bikes performance, it would mean she should switch to pods.
Thanks for the help, folks.