1978 GS550 start/running problems

[Anonymous]

Hi, I'm a newbie to this scene but have just bought a 1978 GS550. I was wondering if anyone had the same problem as me when starting. The bike ran as lumpy as a bag of spanners from when I got it so I've cleaned the carbs, only setting the float levels and the mixture to 2 turns out (as in the book) I've left the jets alone. I put the fuel cock on prime and full choke and bingo! sweet music the engine fired first time and responded to the throttle like a racer. After about a minute the revs started to creep up and whitish grey smoke started from the exhaust. Now she will start on prime still but smokes and misfires or she will start using on/res but will fade and stall after a few seconds running. Could it be a fault in the fueltap either flooding or starving the carbs or should I look somewhere else for the fix.

cheers
dave

[Anonymous]

Hi Dave

Welcome to "THE CLUB"

I have a 1977 GS550. When you put the fuel valve( I know the proper name, just trying to appease some of the sensitive members) on PRIME the fuel flows continuously and probably IS flooding the carbs. On ON or RES the valve needs vacuum from the engine to operate. Sounds like the valve isn't opening.
I'd first check the vacuum line-it should be the smaller of the 2 connected to the fuel valve. If that is okay you probably need to rebuild or replace the fuel valve.
Hope this is of help.
Good luck!

Scott

[SqDancerLynn1]

Yes check the fuel valve it is common for them not to work after 20 years
They can be rebuilt if it is in good condition and the metal is not coroded Parts can be had from local cycle supply don't ask dealer they will want to sell you a new one. Also put a fuel filter on. Most of our older bikes have rust in the tank. Even cleaning the carbs will not do any good if the tank is full of rust. All of your work will be for nothing if the fuel has rust in it. Also check vents between carbs 1&2 and 3&4 if there is any fuel coming out of them you need to recheck the floats and needle valve

[Anonymous]

many thanks for the info and letting me know I'm on the right track. This bike is just itching to go but needs a little TLC. Fingers crossed.

Thanks
Dave

[Anonymous]

carb clean-up

Hi

It would be worthwhile to take a look at the Carb Clean-up article (see near the bottom of the home-page) if you are new to working on your own bike. They must be very clean to operate well.

I would check the fuel tank for rust and clean this up if necessary then add an in-line fuel filter as SqDancerLynn1 suggested.

You can check back on 'Old' Technical Q&A for advice on cleaning the gas tank. The Old Q&A section contains a lot of valuable information.

Hope this helps.


Patrick