Ran great, now suddenly like crap (78 GS750)

[Octain]

points long gone (dyna s). plugs are new (3 months) and look ok. now i did have a dyna s module go bad about 6 7 years ago that caused it to run on 2 cylinders (just like a set a broken points). but if that was the case, I shouldn't be getting good spark at all 4 cylinders -and I am.

Replace the plugs.. 3 mos old? Replace em anyway, they're 2 bux.
Still dont do it, remove em and put a few drops of fuel in the cylinders. Place the plugs and fire it up.
Post the outcome..
If you have fire and compression all ya need is fuel to make it run. If it runs good for a few seconds your carbs need work.

Been there done that.

[Octain]

charge the battery for several hours and make sure its hot, make sure no one has played with the firing order by swapping wires on you as I have seen this done. replace all plugs because compression fouled plugs can spark fine outside the cylinder but once installed they do not. if this doesn't help, pull the carbs, remove the main and idle jets, pull one bristle from a typical 8-10 inch wire brush and slide it completely through each jet and spin the jet on the wire a few times to completely clean all sides of the inside of the jet and to insure a crud free perfectly round hole. then spray through each jet with carb cleaner such as b12 chemtool and then blow through them all with compressed air . hold each jet up and verify that you can see day light through them all and reinstall. withe the entire rack of carbs standing on their sides (so no weight is put on the needle and seat from the floats)re set all floats to where they are level with the flat bowl gasket area of the body of the carb and all look the same then reinstall the bowls and carbs and try again. I have removed carbs to find a main jet laying in the bottom of the bowl. that sure makes a motor run funny if it still misses I would probably do a compression check. if that's good your dyna ignition is suspect and swapping a points plate back in for testing would be my next step.

Wouldnt it make more sense the check the compression first?
Do the simple stuff first..

[Speedo]

Thanks for all the advice folks. I will be a busy guy over next few days and will def post my results. Couple thoughts /notes to now:

* bought comp tester today to do test
* no way are plug wires hooked up wrong (confirmed)
* battery is brand new (1 month) and fully charged now. starter spins fast and healthy
* Dyna S module possible but highly unlikely as there is all around. When I pull wires off plugs one at a time, every one of them starts jumping spark to top of plug like crazy if I get within 2 inches. I still need to pull plugs and run test with plug against cylinder to make sure actual spark is fat/blue.
* no EGT (ex gas temp) tester. Is there a cheapo workaround? If not, I'll do the water spray test
* no gas spilling out of carbs. no fuel in airbox since no airbox(K&Ns)
* will try few drops of fuel in cylinders test and post results
* If everything points (no pun intended...well maybe) to carbs I will give my best college try at cleaning carbs.

I think that summarized all the advice / my "to do" list.... Thanks again.

[supersonictoys]

Wouldnt it make more sense the check the compression first?
Do the simple stuff first..

basic tune up is the simple stuff and the most sensible approach in my humble opinion. if the bike ran fine when parked and then when restarted ran like crap, I doubt it scored a cylinder or bent a valve from storage. make sure you have the basics that "can" change from sitting. a hot battery, good spark, clean new plugs and a clean proper functioning fuel system.

[Speedo]

Healed itself - how? Miracle?

Again, thanks for everyone's help.

The good news: Suz (my 78 gs750e) runs great again!
The bad news: I did NOTHING to it! Nothing. I was getting ready to pull the plugs, etc and I decided to fire it up one more time just to warm her up a little.

A "miracle"? What the?

Review: ran great to my buddy's house 15miles. 5 hrs later, battery dead and wouldn't turn it over. I bump started and ran terrible but got me home. Next day, with fully charged batt (new, 2months old), turns over fine and evenly (WV compression check) and fires right up but continues to run terrible (like on 2 or 3 cylinders).

Then I post to you guys. Then I'm busy until today to try all this stuff you all recommended, fires right up, ran perferct, just returned from a 10mile ride. Perfect.

Theories anyone? Stuck slide or float bowl that magically unstuck? I'm 99% sure that, not having touched the Dyna, coils, or plugs that I can rule out that it was a spark issue.

[chef1366]

Fix the charging system and do the coil mod.

[Speedo]

chef-
What charging sys fix? What coil mod (they are dyna coils)? Are there prior posts I can read regarding this or can you be a little more specific in pointing me right way?

[chef1366]

Coil mod supplies direct 12V from the battery to the Dyna S and the coils. You can find the tutorial on Basscliff's site.
Check out the Stator Papers off the main page of this forum. http://www.thegsresources.com/gs_garage.htm

[Speedo]

Ok thanks. I'm on it. Much appreciated...