GS750 1977 not starting

[haxorb]

Dear GSforum,
My Name is Toon and i've been working on a motorcycle with my dad, which he had (covered) in his front yard for 8 years. After taking the engine apart and changing the head gasket and putting everything back together, the motorcycle wouldn't start. We've got spark, We've got gas, but no explosion. The battery is full and was recently replaced with a new one. Anyone know where i should look at to fix this problem? Any suggestion is welcome !
Greetings,
Toon

 

[sam000lee]

You didn't mention anything about cleaning the carbs so I would start there. After sitting for that amount of time you'll need to do a full teardown and soak, replacing the likely dried out O-rings.

While they are off, I would seriously consider replacing the intake boots and airbox boots if they are original. Definitely replace the O-rings between the intake boots and the head.

Sounds fun and good luck!

 

[haxorb]

The motorcycle has run (with some issues)before, but the head gasket was leaking. Thanks for the quick reply!

 

[Boriqua]

Just because there is gas in the tank doesn't mean there is gas getting to the combustion chamber. I like to start things at the top (gas tank) and go forward so be sure that the fuel isnt clogged. When I picked up my bike it had been sitting for 2 years and the petcock screen was rotted out and the tank was filled with floating rust. There was floating rust in the line.

Keep going forward until you hit the cylinder head.

After you are sure gas is flowing freely to the carbs you will have to make sure the carbs are lickity split clean. Only way to insure that is to clean them yourself. There are a couple of great carb clean tutorials on this forum and here is a link to one and lots mots more info

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

My local auto place has berryman chem dip in a gallon container for just under $30. Start there. Also pick up a can of the spray carb cleaner and a can of compressed air if you dont have a compressor.

My jets were completely clogged with varnish and whatever the previous owner used for gas stabilizing. Left sitting a long time and the crud hardens in the tiny openings.

Forward of that is the connection of the carbs to the cylinder head .. depending on your model it will be boots or boots and O rings. The orings can be had cheap.

At this point you can eliminate gas getting to where it needs to be. If you have spark it should start ... In my case I just needed it to start so that I could continue to investigate and remedy a bunch of other issues but ya gotta start somewhere.
alex

 

[tom203]

Since you had engine apart...doublecheck camshaft to crankshaft timing - there are marks on both shafts