Topic: '76 550K running on 2 or 3 cyl.

[tfrasca]

I couldn't get my '76 550 to idle today after putting the freshly cleaned/rebuilt carbs (with stock 38/100 jets) back on. Cylinder 3 and 4 headers were both cold after trying to run it a bit. After a few more attempts, cylinder 3 would intermittently heat up, but definitely not as hot as cylinders 1 and 2.

Since the issue was with two adjacent cylinders, I first ruled out coils, and suspected the two right carbs. Maybe they weren't getting fuel by virtue of a stuck float needle or something. I loosened both drain screws, and fuel dumped out, so that's not it. All the floats were set to 22mm, brand new jets and float needles were also installed.

I pulled the plugs and checked for spark. Nothing on plug 4. I was able to get what seemed like a faint spark out of plug 3, but my starter is not wired up and I'm kicking the bike over while simultaneously checking for spark, so I'm not 110% confident on this. But I'm fairly certain that plug 4 never sparked, and plug 3 kind of did.

Back to the carbs: I looked inside cylinders 3 and 4 and saw what looked like moisture on the top of the piston, which I'm assuming is unburnt fuel. Which would tell me that the carbs are at least getting fuel to the combustion chambers.

Can someone tell me if I'm right in blaming something electrical here? I just think it's odd that 1 and 2 are firing away just fine, but 3 and 4 are struggling, when they're each coming from a different coil.

One more piece of information regarding electric stuff: right now my starter and headlight will not work because the grounds inside the headlight bucket are not connected. I traced these grounds and they should only affect the previously mentioned items, and everything works. The black/white wire to the coils is getting voltage with the ignition switch on. Electronically, it should run as it is now.

Thoughts?

Thanks,

TF

[iron_worker]

You're right to rule out coils if the problem is on #3 and #4.

Have you checked your spark plug gaps? Plug cap resistance? Clipped the ends off the wire to ensure you getting a good connection from wire to plug cap? Also verify that you have your plug leads going to the correct cylinders (I would assume it wouldn't run if you didn't but check anyway).

Did you mess with the valve lash? If your valve lash was too tight your valves could be hanging open and bleeding off compression. I would think you might hear some back firing if that happened though but that's an easy one to check anyway. Have you checked compression?

Is 22mm correct for your bike's carbs? Maybe someone can double check that. I thought it was 14mm but I could be wrong. What are your IMS screws set at?

Is your tank clean? If it's full of rust/crap then there is no point cleaning carbs because they will quickly become clogged up with crap flowing down from the tank.

Those are the things I could think of.

IW

[TwoTired]

You did connect one coil to 1&4 spark plugs and the other to 2&3, right?

[tfrasca]

Yup, I checked the plug wire configuration several times, mostly hoping it was a dumb error on my part. No such luck. one coil powers 1 and 3, the other powers 2 and 4.

Float height should be 22mm according to the Clymer manual. Tank is pretty clean. some surface rust, but nothing floating, and the petcock and filter are brand new. Fuel flows evenly out each petcock outlet with the hoses disconnected.

Plugs are new NGK D7EA, gapped to the specs in the Clymer manual. I also tried to replace the resistor caps, but the kit they sent me had two 90 degrees and 2 130 deg. the 130's didn't fit, so I still have two of the old caps on the bike. They are all 5K, and even the old ones are relatively new. Just to be sure, I just switched the caps from cylinder 1 and 4, but the problem didn't follow the old cap. New cap on cylinder 4 still won't fire. I will order two more 90 degree 5k caps, but I don't think that's my issue right now.

I haven't messed with the tappet clearance, and it ran on all 4 when I bought the bike.

There's nothing that could only slightly affect each coil enough to send only one spark, right? Maybe the whole system is not grounded sufficiently, so the coils can each only spit out enough spark for one cylinder? Unlikely, huh?

[tfrasca]

Well this is interesting.

A few weeks ago when I first got the bike, I bought a new battery for it. They charged it up for me, I brought it home, and my buddy and I messed around with the bike trying to get it running better. One of us left the key on and the battery died. He took it home and charged it on his charger for me. Put it back in after some more tinkering, and it worked. Headlight, starter, etc.

Since then, it has been under some stress because I've been wiring things up and trying to to get it started, so I got my own charger. I just topped it off before I posted earlier, and now it's resting at 11.55 volts. Come to think of it, I don't know if I've ever seen much more than 12.00 out of it. Right now, with the battery in the bike and hooked up, I see 11.55 at the terminals when the key is off. It drops to 10.50 with the key on. Normal? Or is my battery toast. If it is toast, would that cause my starter/headlight issues, as well as affect my coil output?

[calj737]

Yup, I checked the plug wire configuration several times, mostly hoping it was a dumb error on my part. No such luck. one coil powers 1 and 3, the other powers 2 and 4.

This is still not correct. left side coil should be wired to cylinder #1, the right side coil serves #2.

[tfrasca]

Cal, I guess that's what I meant. I just looked again, and that's how they're wired. Left side powers the outer plugs, right side powers the inner two.

[tomk1960]

Check your point gaps ad then statically time it. It could be that your timing is slightly off enough.  My son's 550 did something similar. Once we sorted out the timing, all the cylinders lit up.

[iron_worker]

A known good battery should hold 12.6 - 12.8v while fully charged. Anything under 12v is dead dead dead. I think you've found at least one of your problems.

To test ... charge your battery, let it sit for 3hr, measure the voltage ... it should be at least 12.6V. To be extra sure, check again in another 24 hours ... it should still be over 12.6V.

IW

[tfrasca]

Alright, so I confirmed that the battery I have is indeed dead. It won't stay above 12v for more than an hour. Kind of lame, considering it's brand new.

I suspect a low battery is some, if not all of my issue. I tested for spark again with the battery connected to the charger, and I had it on all 4 plugs. Baby steps. The spark seemed weak, but I'm not familiar with bikes and was expecting a fatter spark like that of a 12v car system. I got a little blue spark, and it wasn't very bright. Normal?

For now, I'm waiting on a cleaner wiring harness and looking at AGM sealed batteries. Any recommendations, other than Scorpion? That's what my research has led me to, but I wanted to double check with you guys before adding to the ever-mounting moto bill.

Thanks again for being a great resource!

TF

[goldarrow]

Don't overlook the condition of the spark plug wires.  They can be broken internally. 

[tfrasca]

Any way to test the wires themselves for proper continuity? All 4 caps are brand new, as are the plugs. The wires are permanently affixed to the coils, so I'm not sure how to test these...

[TwoTired]

I suspect a low battery is some, if not all of my issue. I tested for spark again with the battery connected to the charger, and I had it on all 4 plugs. Baby steps. The spark seemed weak, but I'm not familiar with bikes and was expecting a fatter spark like that of a 12v car system. I got a little blue spark, and it wasn't very bright. Normal?

Yes, normal.  Modern cars have high energy ignition, so they can run big spark gaps and reliably fire worn spark plugs with 100,000 miles on them.

The coils are just wire, as are the leads.  Measure resistance end to end with the caps off.  S/B ~ 15,000Ω.  An open/broken lead will show infinity.

[tfrasca]

Ok, that makes sense about the ignition on cars vs. moto.

So, to test coils/leads, measure from end of lead without cap, to the ground on the coil?

[TwoTired]

Ok, that makes sense about the ignition on cars vs. moto.

So, to test coils/leads, measure from end of lead without cap, to the ground on the coil?

..if you want to check for grounds. The internal wires are not connected to any ground.  In fact, the coils need no ground to operate.  Measure from lead to lead.
There is a FAQ entry about this. FYI

[KiefRichards]

Alright, so I confirmed that the battery I have is indeed dead. It won't stay above 12v for more than an hour. Kind of lame, considering it's brand new.

FWIW, I never charge my motorcycle batteries over 2A. It's easy to damage a small bike battery with a full-size car battery charger.