Cylinders 1 and 4 not firing

[Flynride]

Ok, so i'm new here and here is how the story goes with my bike. I got a 1978 Suzuki GS550 from a friend for pretty cheap. I saw the bike when it was running and it ran fine then. He let it sit all summer and then when he tried starting it up it would just idle and not rev up at all. We cleaned the carbs out briefly and i got it to be able to rev up without dying but couldn't shift into any gear without it dying.

Cylinders 1 and 4 weren't haven't any heat in the cylinder so i figured it was an ignition coil out because I wasn't getting any real spark. I bought a used on off of ebay (maybe not the greatest choice) but did anyhow. Now, I just rebuilt the carbs cause they were all gunked up and nasty and i put the carbs back on the bike and it runs 100% better than it did, starts right up and what not.

Ok, at first the cylinders i believe are firing as the exhaust get hot to the touch, however about 5 minutes into the drive they cool off like they aren't firing any more.
Also when I remove the ignition leads to 1 or 4 the engine's RPM's don't change at all, however, with 2 or 3 the engine just about dies or does. Me in my bright mind and being fairly cheep, I wanted to compare the "shock" difference between the cylinders at the spark plugs via holding it and sticking a metal screwdriver to the contact point and feeling the shock. (judge me as you wish) Anyhow while holding 1 and 4 i felt not shock at all unless i touched the bike's metal somewhere else with my hand and then there was a great shock, however with 2 and 3 i got the shock without touching any other part of the bike. So I'm not figuring I have either a bad ground somewhere or my contacts are dirty in the timing part the bike. (I already cleaned and re-attached the universal ground under the seat, but haven't done anything about timing or cleaning the timing contacts.) Any help or insight would be great!

[Octain]

Wow, never heard of this method to test the firing. Sounds like you might fit in just fine around here, lol..
Welcome to the board!
Most just set the connected plug on the head someplace and hit the starter switch and look to see if the plug has fire.
If it were my bike the first thing I would do is clean the carbs and replace all the orings from www.cycleorings.com. It's gonna need done anyway.

http://www.thegsresources.com/garage/docs/vm_carb_rebuild.pdf

Cliff will be along shortly with your welcome page but in the meantime look into doing a proper cleaning to those carbs. You'll be amazed at the difference it'll make.
Also, to aid in helping you with getting your bike running right we need to know if you're running the stock airbox or pods or what? What about the exhaust, stock or aftermarket?

Again, welcome!!

[Flynride]

yup, I just finished with a complete Carb rebuild. Dipped the carbs for greater than 24hrs, new orings, the works. and boy it sounds prettier and starts up great, just running on 2 cylinders. I also just looked at the contacts and they seemed to look fine, but thats about it. It's running a Stock everything, no mods yet. Looking forward to the help!

[Octain]

Swap plug wires and see if it makes any difference.
In other words put 1 and 4 on 2 and 3 and visa versa.

[Big T]

You bikes has points, I assume?

You need new points and condensors then

[Octain]

You bikes has points, I assume?

You need new points and condensors then

Good call!!

[sedelen]

Swap plug wires and see if it makes any difference.
In other words put 1 and 4 on 2 and 3 and visa versa.

I believe if you do that, you'll also have to swap the leads to the coils,
otherwise your timing for all cylinders will be 180 off. I have done this with
my GS1000 for a similar problem.

[tkent02]

You could just look to see if both sets of points are opening and closing correctly.

[sedelen]

You could just look to see if both sets of points are opening and closing correctly.

That would be too easy.

[850 Combat]

I believe if you do that, you'll also have to swap the leads to the coils,
otherwise your timing for all cylinders will be 180 off. I have done this with
my GS1000 for a similar problem.

I like this test. If the same two fire, both coils are good, and the problem is in the points/condensers. If the other two run, its coil/plug wire related.

My guess would be points/condensers, but who knows. A common failure more with points is the points cam wears the plastic rub block until the points don't open enough. This stops firing. If it looks like you see arcing in the points when its running, that is generally the condenser.

[Flynride]

what I've done is i've switched the wiring I.e. i switched ignition coil wiring so that the one on the right that was firing for 2 and 3 was now firing for 1 and 4 and the coil that was firing for 1 and 4 and was then firing for 2 and 3 and routed the plugs as required. so there wouldn't be any bad firing. and 1 and 4 still didn't fire. I did try to just switch the plugs but i got all sorts of mis-firing. Where are the condensers? Is there a picture yall could point me to? I did look at the contact points and they seem looked ok, however I need guidance with learning about them. I learned about magneto's and timing them (i'm an aircraft mechanic, and it looks similar to a mag) but they're kinda magic as well.

so condensers and points yall say?

[koolaid_kid]

The condensors are the two small cylinders right below your points plate. Replace everything at once, do not trust appearances. You can file the old ones down to smooth the contact area and keep them as spares, but you really should change all the parts at the same time.
BoulevardSuzuki is a good source for good prices on OEM parts.

[Flynride]

The condensors are the two small cylinders right below your points plate. Replace everything at once, do not trust appearances. You can file the old ones down to smooth the contact area and keep them as spares, but you really should change all the parts at the same time.
BoulevardSuzuki is a good source for good prices on OEM parts.

awesome, is there a way to test the condenser/points first before I buy new ones?

[tom203]

awesome, is there a way to test the condenser/points first before I buy new ones?

Just buy new ones, cuz the condensers are hard to judge. Way back, you said you got new coil off ebay; Check its primary resistance to make sure it compares to stock ones- probably like 4 to 5 ohms.

[850 Combat]

A common failure mode with points is the points cam wears the plastic rub block until the points don't open enough. This stops firing. If it looks like you see arcing in the points when its running, that is generally the condenser.

Did you check to see if they open? When they open is when the plugs fire. No open, no fire. When they are closed, it creates the high voltage in the coil. When they open it is released to the plugs. This will create a field in the low tension (points) side of the system which can arc at the points, if the condenser is bad. The condenser is supposed to absorb power this to keep the points from arcing, which shuts down the spark. There is an OK chance that your points are not opening due to a worn rub block. OEM points and condensers are kind of high priced. There are aftermarket ones. I have no experience with the aftermarket points, but would be willing to try them.