The International CBX Owners Association

My 79 CBX has a higher RPM issue. I am assuming, (Good chance of being wrong) that it is electrical. The carbs were rebuilt by the famous Mike Nixon 4-5 years ago. It has always ran great until now. It started to have a "Pop" or a crackle" on throttle close; more than usual, (I have Pipemaster pipes for 5 years now) and now there is a higher RPM issue.

It runs fine and revs very well in neutral until about 6000 RPM then it has a definite "Misfire" type of sound. It also occurs when I'm riding it under load about 5000 RPM. When I close the throttle it has that "Cackle/pop" sound more than usual. I don't suspect a fuel issue, the clear fuel filter shows good draw and the choke cable is intact and working fine.

I did gap and replace all 6 plugs and didn't notice any unusual burn pattern, (Lean or rich) on the old plugs. Still has the issue with new plugs.
I checked the spark plug wires and they seem ok and plugged in properly.

I did a valve adjustment job about 3 years ago and it has always ran fine after.

I am doing research but my expertise is in the area of 2 strokes.


Any ideas or thoughts are highly appreciated.


Thanks in advance,


Sky


*This is my bike video on the exhaust sound done 11 months ago.


https://www.youtube.com/watch?v=vWOPwHJxIf0

Ha, a number of the views of your Youtube video are from me.
The smart guys will be along but an air leak can cause a "pop" and "crackle".
Check the carb insulators.
Are you using the stock airbox and filter?

A spark unit that's starting to go will cause this. They sometimes work and sometimes not until they fail completely. If you have access to a different spark unit, plug it in and see what happens.

Dave

I thought I'd eliminate it being a fuel issue. I removed the gas cap and ran it with the same results; possibly expecting a gas cap vent issue. Also ran it on reserve and in both cases, the clear fuel filter showed ample gas going through the lines and it ran fine until 4500 RPM.

Hummm. I was thinking of checking carb boots for air leaks using starting fluid or carb cleaner but it simply seems like an ignition issue. It runs great and I mean great until about 4500 RPM and then it cuts out like it's being choked, (I did have the gas tank off and checked the choke cable operation, all good.)

So, not wanting to simply guess and throw $ at the problem, I have considered getting a Dyna-S ignition system. Although a thorough inspection of the coil wires, spark plug wires, caps is warranted, it is a mystery to me that it runs perfect to 4500 RPM and a Dyna-S might solve it. Not too interested in keeping it OEM.

Thoughts, opinions?

Sky

Edit: After doing some more research, my confidence level is high that it is a pulser(s) going bad. It cuts out at 4500-5000 RPM exactly.

Thoughts?

Not having looked at the Dyna ignition, does the Dyna ignition eliminate the pulsers?

Sky

Yes, the Dyna kit gets rid of the pullers.

So thinking the problem was the pulsers, I bought a used set and installed them. Same problem. The chances that 2 sets of pulsers are bad is minimal but not "Out of the question." (*The replacement set was used on e-bay.) So the question begs, "What's wrong." It still misfires above 4500-5000 RPM.

I put a timing light on the pulser rotor and ran RPM's to the problem point of 5000 RPM. I noticed it was missing a beat and the strobe light would reflect a break in the continuous strobe. Sidebar: The carbs were done by Mike Nixon about 4-5 years ago and not suspect at this time, but always a possibility.

The only other possible faults are the spark units, (No real reliable way to test these and according to Mike N, just "Test around them." ) and the coils themselves. *The spark plug wires are aftermarket one piece and look solid but unknown if they are of the resistor type, (The bike ran with the same plug wires and clean spark plugs and ran great until the problem started.)

Will test the coils today for proper spark using the Mike N. method of grounding the lead on the coil with a plug grounded on the outside of the engine to test for spark. Not confident this will prove much because the bike starts right up and runs great until 4500-5000 RPM.

I checked the fuel supply. It's all good including the venting of the cap. I really don't want to invest in the Dyna-S from Tim's CBX if the problem can be solved using OEM parts.

*Cleaned all the spark plug wires and got all the connections bright again and cleaned with spay electrical connector stuff and then used dielectric grease on the connections. Same issue, no improvement.

*I had to buy a new multimeter as mine was giving wrong readings on the OHM settings. Go figure!

I really do not want to touch the carbs.....


Any new ideas to check?