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Bike has no umph

  • Thread starter Thread starter Benjisus
  • Start date Start date
B

Benjisus

Guest
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
 
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.
 
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!
 
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.
 
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?
 
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.
 
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?
 
Valves clearances first, then rebuild the carbs and sync them.
 
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!
 
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
 
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.
 
If the charging system isnt working and the battery drops below 10 volts the bike will not start as the coils wont fire at such a low voltage. All the above as far as doing a PROPER carb rebuild and adjustment of the valves are valid points, but first thing I would do is out the battery on a charger till at 100%. See it on DC VOLTS if it fires and if it does set a multimeter on DC VOLTS and read the voltage at the battery at idle..write that down.

Next, keep the probes on the battery and run the RPMs up to about 4000 and watch the meter as you rev. you should see the voltage increase to at least 13. to 14.2 volts. If there isnt any increase in RPMs then thats probably your main reason it wont start...its not charging and the battery gets too low to fire the coils. If the RPMS do rise write down whre they settle in at.

service manual..... http://zeus.mtsac.edu/~cliff/storage/gs/GS750_Service_Manual_early8valve.pdf
 
AND VERY IMPORTANT.....you can jump a bike off a car BUT UNDER NO CIRCUMSTANCES ARE YOU TO HAVE THE VEHICLE RUNNING!!!!!!!!!!!!!
 
I have had a motorcycle solenoid fail on two occasions when it was jumped by a car. Once on a CBX on a ride home to Fairbanks from Anchorage. At a gas stop in Talkeetna, Ak the volt meter showed that my bike wasn't charging. I pulled the headlight fuse and made it to the next place I needed gas, Nenanna, AK. I jumped it off of a pickup and made it home to Fairbanks. Solenoid never worked again. It was a worn out brush on the alternator that stopped the CBX from charging. Similar thing happened with my 1000G in Maine.

I see no engineering reason why this should happen. It has happened twice though, so coincidence seems likely than it did when it had only happened once.
 
Thank you all so much for the information!!

I am hoping to get to the bike this weekend to figure out exactly where the issue is.
 
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