Topic: Cb550 running rough after rebuild.

[Jesse Str cb550]

For the last 7 month’s I have been doing a complete rebuild on my 1978 cb550. As I’m 20 years old I’m still lacking some knowledge here and there, I am hoping you guys can help me.
It’s got the 572cc dynoman pistons with a 10.5-1 compression ratio

[newday777]

Welcome aboard Jesse
I don't know the 550s very well but the running rough, has to be attributed to poor fuel delivery, poor air delivery or poor spark delivery, so you will need to supply more Information, so much you have left out about your build  for anyone to help you diagnose it from a distance.
Did you do the work/rebuild yourself or have someone else to do it? Are you running a high profile cam and has it been dialed in? How are the condition of the valves?
Have the carbs been rebuilt, properly fully cleaned and jetted properly for the motor? Has the bike been on a duno for tuning? The 78 carbs on the 550 are very finicky on stock bike, are you running the stock carbs or what carbs are on it?
Are you running pod filters or stock airbox?
Have the coils and plug caps been tested with a meter for output?

[Jesse Str cb550]

Sorry!! It deleted half of my paragraph,
So basically done the rebuild myself, it’s got the 572 dynoman kit which is compatible with stock internals. Lapped the valves in, got all seals, timing chain, tensioner and primary chain swapped for new ones. Running the stock carbs with uni foam pods on stock pilot’s and 110 main jets. It has a 4 into 1 exhaust with a highflow muffler. It also has a electronic ignition fitted. So basically I rode it for 100km after the rebuild was done and it was running ok it just had a rough time starting and would also have a power hole during acceleration and would backfire or “crackle” during deceleration. That made me think that it was running lean so I changed the needle position from the 2nd notch from the top to the 4th notch from the top. I also did a bench carb synch. Then after trying to start the bike it fired right up but would only run on 3 cylinders. After troubleshooting and checking compression, spark, fuel I still haven’t found the issue. I even cleaned the carby jets again to rule out a blocked jet. It has a really rough time idling and it also backfires a lot and makes popping noises. Swapped the spark plugs and leads around but still the same cylinder that isn’t firing.

[Jesse Str cb550]

The spark plugs also looked quite rich and were a little wet, but the weird thing is the bike only really wants to run with full choke. Could it be that I might not have spark once the spark plug is turned into the head? If there’s any more information that might help please let me know!
Thank you so much for your help Newday!!

[Scott S]

 Have you tried new plugs? Or, at least cleaning the ones you have? Carbon or fuel fouled plugs can cause a cylinder to miss or not fire.

 The hard starts, popping and flat spot are all because of the pods.
http://forums.sohc4.net/index.php/topic,182280.0.html

[newday777]

"Swapped the spark plugs and leads around but still the same cylinder that isn’t firing."

That tells its lack of or low fuel in that cylinder.
How did you clean the carbs? Just cleaning the jets doesn't unclog the internal ports. PD carbs need full strip down and boil clean or heated ultrasonic cleaning to get any hardened gas deposits in the ports, especially the choke circuit on PD carbs(probably the hard starting problem).

[bryanj]

If you have PD carbs with all the changes from standard you have i think you will be forever chasing problems, as you have no airbox fit the earlier 500 carbs with inlet manifolds, parts are easier to get and change plus easier to get clean and tune

[Stev-o]

Sounds as if you may have multiple issues that are contributing to it's running issues.

Hard enough to get a stock motor running properly for a newby, and with the changes you have made, it will take a person with experience to dial in this motor to be running great at all RPM.

[Jesse Str cb550]

Thanks guys for all your good info! I cleaned the carbs with only carby cleaner and air as they were only off the bike for like one week since it ran, I might try and re set the needles to the original position to when it ran. Because I have a higher compression ratio does that mean I have to get new spark plugs that have a higher temperature rate? Right now I’m running the stock ones which are 7ea should I be using 8ea?

[Scott S]

 IMO, you're overlooking a lot of info here.
 The '77-78 550's came with lean jetted carbs to meet EPA requirements. You've increased displacement, changed the induction system and opened up the exhaust.

 Read the sticky about pods at the top of the forum. There is no simple answer. You're going to have to experiment, do plug chops, etc. OR....invest in dyno time.

 Install a NEW set of plugs and let it idle. What do they look like. Then, install a NEW set of plugs and do a plug chop: ride it, get it at upper RPM's, then hit the kill switch and coast to a stop. What do THOSE plugs look like at, say 5,000 or 6,000 RPM? That will tell you what you need to change.

 Don't do any of this until you've adjusted the valves, cam chain and verified timing.

[dave500]

make sure the spark plug caps are good.

[exponent]

Being like you with similar ideas minus in the US, I gotta say this is all good advice, getting a stock box or plenum to a single pod would decrease a lot of the popping. The carbs are made for having a single intake from atmosphere flow, with individual or single uni pod you deviate from smooth airflow. Having pods creates turbulence in any cylinder at any times so very far from ideal. After that you can move to timing and other tuning which is where the real reading comes in.