Need opinion on engine please.

[Skyguy]

My 79 CBX with a 81 school motor has been a perfect running machine for the 3 years since I have owed it. The carbs were done by Mr. Nixon a few years back and it starts on the first tick etc. But....The other day I started it up after sitting for just a couple weeks, (Always on the center stand) and it seemed to run fine. Took it for a test ride and around 4100 RPM I detected a slight hesitation and a noticeable crack like back fire sort of sound from the left exhaust. The engine was warm and the issue occurs at about 4100 RPM to about 4500 RPM whenever the throttle is held steady in that regime. It seems to run smooth above 5000 RPM and below about 4000 RPM.

I did a heat gun on the exhaust and the #2 was about 60 degrees colder than the rest. *Sources tell me that that is well within the range. I swapped plugs with the
# 1 # 2 cylinders and no improvement. I have yet to check the OEM paper filter but that is my next step. Now, before I start tearing carbs apart, chasing sparks, etc, is this indicative of any known issue that comes to mind. Please feel free to jump in here if you have any thoughts or remedies or just opinions. anything would be helpful at this point.

Data:
- 79 CBX SS with 81 engine.
-Carbs tuned done to perfection about 2-3 years ago.
-Valves shimmed about the same time carbs done.
-Plugs not changed.
-Using Lucas oil safeguard Ethanol Fuel Conditioner.
-Regular oil changes.
-I ride it about 3 time a month.
-Always on the center stand.
-Glass fuel filter.
-Motobatt battery.
-Tims CBX alternator installed.


Thanks in advance for any help.

Cheers,

Sky


PS: I have been real busy with a high level restoration of a 1975 Suzuki GT750.
Blog is here:
http://www.kettleclinic.co.uk/kcforum/v ... =6&t=12043
-

My CBX:

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

[daves79x]

Sky - it sounds like you have a partly plugged idle or low-speed circuit in #2 carb. I'd try Seafoam and taking it for a good long ride. May clear up. If not, look closely at #5 pipe temp also. If it and 2 are both any cooler, that indicates a spark unit failing. My bet though is the carbs.

Dave

[Skyguy]

Sky - it sounds like you have a partly plugged idle or low-speed circuit in #2 carb. I'd try Seafoam and taking it for a good long ride. May clear up. If not, look closely at #5 pipe temp also. If it and 2 are both any cooler, that indicates a spark unit failing. My bet though is the carbs.

Dave

Thanks Dave, I'll try that a report back what happens.

Cheers,


Sky

[Skyguy]

Well it turned out to be the #2 plug wire....Sheesh! It was somehow not getting all the spark to the spark plug but it humms along perfect now! Funny side note; I did put an oz of Seafoam in the 1 gallon of gas I had and about 1/2 mile from home the engine slowly died as if no gas. Well in fact the Seafoam had somehow clogged the fuel filter. New fuel filter and she runs great!

[steve murdoch icoa #5322]

Can't imagine how Seafoam would affect a fuel filter.
https://www.instructables.com/id/Homema ... -Knockoff/
I would be looking at crap in the bottom of the tank.

[tevan]

Can't imagine how Seafoam would affect a fuel filter.
https://www.instructables.com/id/Homema ... -Knockoff/
I would be looking at crap in the bottom of the tank.

I am with Steve on this one the sea foam did not clog your filter. You might think about flushing your tank out and go from there.

[NobleHops]

Seafoam could have dissolved varnish in the tank, putting it into solution, that the filter then caught. That to me is a warning shot across your bow and a good tank clean-out ought to be in your future. I have mixed feelings about Seafoam; it's become a running joke that it is some miracle cure and it gets misused with too-high concentrations. Seafoam will swell buna rubber parts if that's what's still in your carburetors, and IMO is best used not as a fuel conditioner, but as a fuel system cleaner, and (once again IMO) it ought to be used when it can be run through, eg used up. I personally do not like to leave it or similar sitting in carburetors.

Glad you got the main running issue sorted out!