Topic: CB550 started running like crap

[rollypoli]

Just rebuilt my engine. I have been doing some finishing touches on the bike but I’ve been trying to get some miles on the engine. No large leaks have formed only a small drip out of the shift cover area which I plan to diagnose this week. I’m about 35 miles on this engine. Fully stock. And I went out tonight. Stopped for a bit. Got back on did a good pull and I think it changed tone a bit and now wants to die when trying to get going in 1st gear and any low rpm it has terrible response and takes feathering to get going. I’m going to pull the valve cover and peek at how it looks this week. I just don’t want to have blown my bike so soon :/ if so I’m gonna get crazy good at rebuilding these. Here’s a video of it running now. (4into1 exhaust). Lmk if you have any ideas what’s going on.
https://youtube.com/shorts/CnVZUhSdf78?feature=share

[Nurse Julie]

It's not running on all 4 cylinders, you just need to find out why.

[TwoTired]

Whenever my bikes suddenly change behavior, I check the spark plug deposits, and if that doesn’t tell me something, I repeat the whole routine tune up procedure, which if it doesn’t fix it, at least I know that a correct fix will not need a repeat tune up.

[Shtonecb500]

I would start with fuel and carbs first make sure your jets are still clear, does it idle ok before you take off into a poor running first gear and struggling second? It's a brand new build and you just took it out so check all your electrical connections/grounds make sure something didnt come loose hitting bumps/potholes.

[Tracksnblades1]

Sounds like only two are hitting….

Check for dead cylinder(s) by finding the considerably cooler exhaust pipes near the exhaust ports and concentrate your efforts on that (those) cylinder(s).

If you have a pair of cylinders not running and they’re a (ignition) running pair (same coil), I’d verify your spark(s) are discharging first. Carbs usually don’t instantaneously change like Ignitions and sparkplugs can.

You’ll find it. It’s not trying to pick it back up when your revving it up..

[Deltarider]

It's not running on all 4 cylinders, you just need to find out why.

This ^. First check there is any arching taking place between plugcaps/HT wires and the head. Step 2. Pull plugs for inspection.

[rollypoli]

Thank you all I thought I was down a cylinder.
I tried to start my bike this morning but it just wasn’t having it. I felt the exhaust and I could feel warmth in 1&2. 3 was cooler but it was hard to tell and 4 was cold. I took out the 4th spark cap checked if the plug wires were on good then popped it back on and the bike fired right up. I have new spark plug caps that just came in. I’m gonna thanks the plugs out and see how they’re looking so far and pop on new caps after. I have a steel dragon breadbox coming but rn it’s just has pods so I can run it and diagnose issues So I doubt the tune is perfect

[willbird]

I had checked pilot jets in my cb750k2 then went for a ride. About 50 miles in it started running like crap. A pilot jet I obvious didn’t tighten enough had unscrewed and was laying in the float bowl :-).

[Tracksnblades1]

Thank you all I thought I was down a cylinder.
I tried to start my bike this morning but it just wasn’t having it. I felt the exhaust and I could feel warmth in 1&2. 3 was cooler but it was hard to tell and 4 was cold. I took out the 4th spark cap checked if the plug wires were on good then popped it back on and the bike fired right up. I have new spark plug caps that just came in. I’m gonna thanks the plugs out and see how they’re looking so far and pop on new caps after. I have a steel dragon breadbox coming but rn it’s just has pods so I can run it and diagnose issues So I doubt the tune is perfect

Crosswinds on breadbox equipped cb750s can cause some challenging tuning…not sure if they affect 550s..
Stainless steel shim stock installed on the outside edges of both side of the breadbox was the quick fix on the 750s. It looked like it was part of the breadbox if installed under the perforated metal ..

[rollypoli]

Crosswinds on breadbox equipped cb750s can cause some challenging tuning…not sure if they affect 550s..
Stainless steel shim stock installed on the outside edges of both side of the breadbox was the quick fix on the 750s. It looked like it was part of the breadbox if installed under the perforated metal ..

Ooo interesting do you have a photo of the shim installed? Or a point to the thread I could find this in

[Tracksnblades1]

Crosswinds on breadbox equipped cb750s can cause some challenging tuning…not sure if they affect 550s..
Stainless steel shim stock installed on the outside edges of both side of the breadbox was the quick fix on the 750s. It looked like it was part of the breadbox if installed under the perforated metal ..

Ooo interesting do you have a photo of the shim installed? Or a point to the thread I could find this in

No, but it’s not rocket science..

Look at picture. The stainless steel shim would be placed  between the outside perforated steel (little holes all over it) and the green filter media. Cut to fit. The shim stock come in inch width like 2,4,6 etc wide. Get the width that the box will trap between the lids. Some guys would just pop rivet them on the outside but it looked like it. I like them on the inside so it didn’t look cobbled.

With set back pegs you may not need them since your thighs will do the same…
I’d try it without it first. If it doesn’t misfire and mis carburete in a stiff cross wind you won’t  need the little shields on the outside ends.

[rollypoli]

Another thing is I believe the steel dragon breadbox is individually filtered

[rollypoli]

Update. I got it running great. The breadbox is amazing. And have put about 400 miles on the last two months. But I have been hearing a tapping noise off throttle in neutral. And I think it’s still there in first with the clutch in. Is it primary chain slap? Something else? I’d love help figuring it out as it makes me not want to ride as much. Otherwise it’s been perfect.
Video of the sound:
https://youtube.com/shorts/CnVZUhSdf78?si=ZpblrnOsfktVja7s

[calj737]

Check for an exhaust leak at the head. Pretty common after a few heat cycles for the nuts to no longer be tight.

[rollypoli]

An exhaust leak would cause that pinging?

[calj737]

I didn’t listen to your audio/video when making that comment. But an exhaust leak often creates a “ticking” sound and after a rebuild, it is not uncommon to need to retighten the exhaust bolts just a smidge.

Now that I’ve watched the video, I’m no closer to diagnosing it because the audio is not great. It could be that your carbs need synching, it could be many things. I didn’t detect from the video the bike dying due to anything as it looped back.

[Scott S]

 It could be the rocker shafts in the valve cover. They get worn/ovaled out and cause a tapping.
 Out of sync carbs can make the bottom end sound like a rod knock.