sdew99
CB750 Enthusiast
Ok thanks for the help. Going to make sure that cylinder isn't running rich still and go from there
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Cylinder 4 plug carbon fouling
- Thread starter sdew99
- Start date
sdew99
CB750 Enthusiast
Update.. ran the bike today with the new plugs, and within 5 minutes this what the plug looked like.
How is this possible? Lol. All other plugs look perfect.
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sdew99
CB750 Enthusiast
Checked the valves clearances and they were between 4 and 6 thou.
sdew99
CB750 Enthusiast
Shouldn't the plug be somewhat wet if it's oil?
Unless it burned during combustion. Leaving a black residue behind. If it dumped oil, I would say yes.
5 minutes is a very short time for the plug to turn THAT black from a rich mixture. If you have stock jets, then either your float height is way too high or you're burning something else. My two cents, of course.
sdew99
CB750 Enthusiast
Ok thanks. Jets are indeed stock, float height in that carb is 15.5mm.
I really hope this is a stupid question, but these are supposed to have ngk dr8ea not d8ea plugs right?
I really hope this is a stupid question, but these are supposed to have ngk dr8ea not d8ea plugs right?
sdew99
CB750 Enthusiast
Ok.. I am mindboggled. Canada calls for resistor type plug but other places don't?
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sdew99
CB750 Enthusiast
Changed my plugs from dr8ea to d8ea for the hell of it and there was no change..
It's hard to tell what the plug smells like.. kind of leaning towards oil. Compression was 130 when I tested it.
It's hard to tell what the plug smells like.. kind of leaning towards oil. Compression was 130 when I tested it.
Just for fun, pull the plug wire off that cylinder while it's running and see if it spits raw fuel out the pipe. Even though the float is set right that doesn't mean it's all good. Maybe the needle is bad, or the seat is bad, or there could be a piece of something stuck in the seat. Also check to make sure you don't have the primary and secondary jets mixed up. I have seen that happen.
sdew99
CB750 Enthusiast
Will try later tonight and keep you updated.
ninjalips
CB750 Member
Any updates?
I am having the same problem on my 82 750k. Just did a full service and re did the carbs like under a year ago. Not only am I having the same fouling problem but as of two days ago cylinders 1&4 only fire one the bike gets hot. I'm at a loss
I am having the same problem on my 82 750k. Just did a full service and re did the carbs like under a year ago. Not only am I having the same fouling problem but as of two days ago cylinders 1&4 only fire one the bike gets hot. I'm at a loss
What was all done during the service? So the bike only runs on cylinders 2&3 till it warms up? Could be a number of things, low compression, valve adjustment, 1&4 flooding? Don't rule out the carbs just because they were worked on in the past. You might want to start your own thread on the subject.
sdew99
CB750 Enthusiast
Not yet. Hoping to get to it tonight.. I was having the same problem and I think my plugs were so carboned up they wouldn't spark.
Put new ones in and it was day and night... except for cylinder 4 that fouls instantly.
ninjalips
CB750 Member
I did oil plus filters. New cdi units and new spark plugs. Day of the service she ran like a dream then I did a 30km ride and the next day this cylinder issue started.
ninjalips
CB750 Member
Have you tried to keep her running? I only found out about the temp Parr once she was running got a bit and I could hear 1&4 start to fire here and there. Then a huge backfire shat Myself and she was running fine
ninjalips
CB750 Member
I'm going to pull the carbs this weekend and do a full cleaning and rebuild. Also might be my float level she smells like she is running a little rich
What was the problem that time? What brand of parts did you use?