SOHC.co.uk Forums > CB750
What are these plugs telling me?… and other questions!
Craizeehair:
I’m hoping some of you clever kids might be able to help a novice spannerer out?
I bought this bike a couple of months ago, with a view to get more hands on and really get to grips with my own maintenance and repairs, I’ve ridden on and off for most of the last 36 years since my first Honda XL125 as a teenager, what I never did was any meaningful maintenance or repairs, usually paying someone else to do it for me. I am happy with oil changes, brakes, cables etc, but engine work, carbs and the like are a mystery to me.
The bike hadn’t been a regular rider for a number of years since a restoration but had a wee run out every year to keep the juices flowing. So it was always going to need some TLC, only I was hoping to do that through the winter in my (hopefully) new workshop / shed I’m panning to build. The bike had a pronounced flat spot from take off and low revs, from throttle off to throttle on. I’m pretty convinced that it has got worse but that could just be my imagination?
I have only managed to put a couple of hundred miles on the clock so far and today I decided to go for a bit of a blast, about 50 miles in total, with a good proportion of dual carriageway to blow away any cobwebs.
All was going well, when about 3 miles from home and now on smaller country roads, I noticed a noise. It was a bit faint to start with, almost like a wheel rubbing or something catching but only when the bike was moving and not stationary, however I convinced myself that it was more likely coming from inside the engine rather than from something outside. I nursed the bike back home, turned the engine off immediately and had a little panic to myself! I checked both wheels and they seem to be turning freely with no noise when raised off the ground with no play.
I have read plenty on here about how everything needs to be set up right or these bikes can sound very ropey. So I have adjusted the cam chain tensioner (not sure if that did anything as there was no discernible happening to indicate any change) and I also set the valve clearances, some of which were very tight. Tomorrow I will checks the points and static timing. I have no doubt the carbs will need attention too.
So, to the question in the title… after another question. Would it be possible that a combination of these things being incorrect could produce such a noise?
These are the plugs that I removed tonight, 1-4 from left to right. Any advice as to what they are telling me? Too rich? Big Trouble? Carb issues? Run away?
Worth noting that they aren’t all the same plug either, I presume a new matching set of the correct type would be in order.
I have a feeling that I will need to tackle the carbs, which is something that strikes the fear into me, I will need to purchase the appropriate necessities for that, as it is something WAY beyond my comfort zone! Would you recommend vacuum gauges or something like the Morgan carbtune pro?
Apologies for the waffle and the Tommy Tippee beginner questions but I guess I have to start somewhere and you kind souls seem just the type to help me on my way. Thanks in advance
Sent from my iPad using Tapatalk
Trigger:
Why do you have a mixture of plugs and are they resistance plugs ? They should not be resistance ;)
Craizeehair:
--- Quote from: Trigger on August 19, 2023, 11:42:51 PM ---Why do you have a mixture of plugs and are they resistance plugs ? They should not be resistance ;)
--- End quote ---
No idea? They were in the bike already, I took them out tonight to check them and they are what I found in there. I know I need a new set but that’s a good point about the resistance plugs, which leads me to my next question, how do I know if I have resistance caps or doesn’t that matter and any suggestions for best plugs for these bikes?
Trigger:
Most caps are resistance these days. The plugs you need for a 750 are X24ES-U ;)
Trigger:
Sound like the bike needs a good service and i would change the plug caps .
Spark plugs >>> https://www.gsparkplug.com/1x-denso-standard-spark-plugs-x24es-u-x24esu-067800-1700-0678004130-4099.html
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