Warped head/bad gasket?

[RJ CB650]

So, going to run this passed you guys. This weekend I will first re-do the timing and re-inspect the plugs for mixture. Barring that, it does make me think head warpage or gasket. Will also have to re-inspect oil and airbox for fouling.

Symptoms:
After warming up, and a couple minutes of riding, dead spots when giving throttle (not WOT, but just general acceleration) it gets a bit rough or hesitation at low speeds. Sometimes near stall.

Once she gets nice and warm, is almost like a switch. Real smooth, and little to no low end hesitation.

Causes?: Main one I can think of is that issue with the plugs. During testing, non firing cylinder could have caused inconsistent heat build up or possibly being ridden previously without proper 6 cylinder operation.

[herdygerdy]

If it was head gasket, I think you would find oil seepage somewhere and the engine poor running symptoms would be consistent hot or cold.

Dare I say it, but IMHO it sounds like it may be ignition related. Measure voltage across the battery then compare that to what you get when measuring across the black/white wire at the coils to earth with ignition and kill switch on. There may be voltage drop happening, but could also be your ignitors under the battery box playing up.

[RJ CB650]

Will check both. I have been suspecting an issue with number 3's ignition.

[daves79x]

Sorry, but it's still the carbs. These things are pretty lean, but if you get all the slow-speed passages open, they warm up pretty seamlessly. Your key is that it runs great good and hot. I can't remember where all we've been with your bike, or what you've done so far, but if your carbs are pretty close to perfect, I'll bet it runs fine.

Try a little choke when it's stumbling as it warms up. If it clears right up, then it's still the carbs.

Many an electrical problem has been solved by cleaning the carbs

Dave

[Larry Zimmer]

I'm no expert; but, gotta agree with Dave. The only ignition problem source I can think it could be, based upon the symptoms described, is dirty secondary ignition wires/terminals/plugs(outside) or cracked coil case, or wires, with moisture accumulated that is causing some shorting until things get hot and dry. That one is a long shot, though; unless, it is being kept outside uncovered.

[RJ CB650]

Sorry, but it's still the carbs. These things are pretty lean, but if you get all the slow-speed passages open, they warm up pretty seamlessly. Your key is that it runs great good and hot. I can't remember where all we've been with your bike, or what you've done so far, but if your carbs are pretty close to perfect, I'll bet it runs fine.

Try a little choke when it's stumbling as it warms up. If it clears right up, then it's still the carbs.

Many an electrical problem has been solved by cleaning the carbs

Dave

Darn carbs XD. The slime filled nighthawk carbs had less trouble with! There are two issues I am planning to address and one will require carb removal here.

1. That air cut off valve. New one ordered, waiting for it to come in.

2. Accelerator pump, had water on top of diaphragm at some point.

I am certain there is a vac leak somewhere. I am betting it is in the air passages. Some o-ring is failed. Rabble rabble ^.^

Electrical has been iffy on it so will still start with there. One coil wire was loose when I did my inspection, maybe is some corrosion somewhere else. Been a few corroded connections on it.