Bike has no umph

[Benjisus]

Hey everyone!

I have run into an issue with my bike.. I have a 1978 GS750, and I just put on a MAC 4-1 exhaust. Once I put on the new exhaust.. the bike is not starting, but I have a feeling it might not be the exhaust.

I recently replaced the battery of the motorcycle because when I first bought the bike the owner told me "Hook the bike up to a battery for a few minutes"... Well a new battery would fix that.. I thought.
Anyway, so this is what has happened, the motorcycle when I first turned it on with a new battery the headlight shined brighter then my future, now it barely produces any light when i turn the key. Also, when I used the push start it attempted to start the bike, and now there is nothing. And lastly when I try to kick start, there is no resistance at all.

I had the bike running not 2 days ago with the new battery. Can anyone help me!? Please!?

- Ben

[gordinho80]

I'm in no place to diagnose the electrical aspects of your problems... but I will say, going from stock exhaust to a 4-1 shouldn't impact the starting, but it could/and likely would, impact the engine's performance without a carb re-jet and a carb sync.

As far as starting, can you do a compression test? All fuses in good shape? Electrical contacts all clean and tight? Especially grounds? Hook up the bike to a car with a good batter, don't run the car, just hook it up... see if the starter spins.

[Benjisus]

Im not really sure how to perform a compression test.. What do I need to do for that?

I will run out and check the grounds and try the car! Thank you!

[gordinho80]

Go to your local parts place, most have a tool rental. Ask them for a compression test kit and search on here for how to test. It involves removing spark plugs.

[Benjisus]

Ok, I will do that once I have the time!

I did hook the bike up to a car battery, and the starter did work. It would turn over a few times then stop. I was able to build up some more compression with the kick start and it would continue to do the same thing, attempt to start, loose its umph. I was eventually able to start the bike with the kick and it was blowing some serious smoke out of the exhaust...

I also checked all of the grounds and sanded them all down. A few definitely needed it.

What would you recommend next? The compression test?

[Nessism]

You might want to check the Newbie Mistakes thread linked in my signature to see if you missed anything.

I would not bother with a compression test unless you have adjusted the valves and have done all the bikes maintenance in general.

What you describe could be as simple as the bike running on 3 cylinders.

[Benjisus]

I was planning on rebuilding the carbs since I wasnt sure the condition after the previous owner. So would you just recommend doing that before I look into any other issues?

[gordinho80]

Valves clearances first, then rebuild the carbs and sync them.

[Benjisus]

I remember seeing something a while ago that was like a valve graph? Showing what adjustments need to be done.. You wouldnt by chance have this? I cant seem to find it now!

[gordinho80]

Contact member "Steve" on here. He has a handy spreadsheet that I just used to do mine. Get your clearances measured then order shims from the Shim Club (http://www.thegsresources.com/_forum...ight=shim+club)

[cowboyup3371]

Valve adjustment and a carb cleaning can and should be done at the same time.

[Big T]

Does your bike still have the points ignition?

[Benjisus]

Does your bike still have the points ignition?

Yeah, it looks like it still has the points ignition.

[Big T]

you probably went from go to no ump because 1 or 2 cylinders aren't firing

Take the cover off rotate the crank clockwise and see if the points open and close. My guess is one set closed up , or bad condensor

If you've never changed your points/condensors, that's where I'd start. Then, order a Dyna S and never worry about points ever again

[850 Combat]

It is free to adjust points. New OEM points and condensers cost nearly as much as an aftermarket electronic ignition. Aftermarket ones are considerably less expensive.