Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Ken4004 on August 08, 2026, 05:30:12 PM
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Afternoon all, I have a question about timing .
What is the difference between setting up ignition timing using a light (static timing) and setting timing using a timing gun in terms of accuracy.
Now what I am trying to say is do you think just carrying out static timing is good enough or do you really need to do dynamic timing afterwards ?, for instance you may only have a test light to set your timing is this accurate enough ?.
I do appreciate that only having a test light you cannot check that the advance retard mechanism is working correctly.
The reason I am asking this question is because the timing light I am using is fairly old and I am not sure how accurate it is ( I am using a Gunsons light used to use on my car years ago see photo attached) I would have thought if you set up the timing using a timing light only it should be close enough and if it isn’t what’s the point in doing a static and dynamic timing why not just do the dynamic timing.
Look forward to your comments thanks
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My stance is that static timing is to get the engine running.
Dynamic timing is to fine tune it for both 1 & 4 and 2 & 3
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I agree, and using the timing light corresponds to Honda's instructions re timing adjustment on page 5 of the CB400F service manual. Your timing light will work fine to check the position of the associated timing marks at 1200 and at 2500 RPM.
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Static timing using a lamp with ignition on or measuring resistance across the points with ignition off has always served me well so long as you're rotating the engine the right direction when approaching the break point.
A timing light is good verification of initial timing and then checking for smooth operation of the advance mechanism up to full advance.
If your timing strobe is like mine where you clip onto a plug lead - don't melt the cable on a hot exhaust!
I did play around with timing once and noticed that mine ran better using about 1-2 Deg advance with the F mark. Also noted on a lot of classic car forums they mention ignition advance by a few degrees for modern E5 fuel because the flame front propagates a little slower than the old leaded stuff. Then you look somewhere else and they are saying not to bother.
Regards Dave.
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The ONLY reason to use a strobe(timing light) is to prove the advacer is working properly. I.E. advancing enough AND not advancing too early.
The static timing, when done properly and with points at correct gap, is all you need for a good running engine IF carbs are good
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Thanks everyone for your input, I believe that I still have a slight issue with my carbs because the bike runs a little erratic below 1500 rpm which means when I am trying to set the timing the mark tends to bounce around a little so not as steady as it should be to set the timing.
I did think it might be my timing light because it’s not one of the clip on type it’s just a spring so you have to remove the HT plug and connect one end of the spring to the spark plug and the other end to the plug cap so it’s just resting between the two which is not ideal( I’ll attach a picture of the spring connector for reference)
I will therefore try and just set the points up statically and then re look at the carbs, I suspect that there is still a slight blockage in the idle circuit so carbs may will need to come off again and will try using guitar strings to ensure the galleries are totally clear.
This is only a slight issue and I believe I am very close to having the bike running spot on , once it idles at 1200 rpm without the occasional splutter I will assume I have cracked it
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It's also worth verifying you are air tight in the induction side, inlets stubs onto the head, rubber bits both side of the carbs.
Sometimes a slight squirt of wd40 around a suspect joint will cause the engine note to change if there's a suction leak.
Also the screws for the vacuum ports, is there a soft washer under them?
Regards
Dave
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It's also worth verifying you are air tight in the induction side, inlets stubs onto the head, rubber bits both side of the carbs.
Sometimes a slight squirt of wd40 around a suspect joint will cause the engine note to change if there's a suction leak.
Also the screws for the vacuum ports, is there a soft washer under them?
Regards
Dave
Thanks Dave that is a very good point, I am using the original joints on air box side and engine side.
They were originally very hard so I soaked them with a mixture of winter green and surgical spirts for a few days which softened them up enough to refit them and I thought they were OK but maybe I should have replaced them all, just trying to save a little cash as the project was getting a little expensive.
This in hindsight was probably a false economy but I was just trying to use a many original parts as possible.
I will there try the WD40 check to see if I indeed have an air leak .
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It's the o rings between the inlet stubs and cylinder head that go rock hard.
Regards
Dave
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It's also worth verifying you are air tight in the induction side, inlets stubs onto the head, rubber bits both side of the carbs.
Sometimes a slight squirt of wd40 around a suspect joint will cause the engine note to change if there's a suction leak.
Also the screws for the vacuum ports, is there a soft washer under them?
Regards
Dave
Actually Dave come to think of it I don’t remember seeing a soft washer under the screws so probably the first place to look, I didn’t think the system was as sensitive as that but it could be drawing in air in this area so a good call.
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It's the o rings between the inlet stubs and cylinder head that go rock hard.
Regards
Dave
Hi Dave , I did change the seals but will take another look at them , hopefully with the WD40 I should be able to isolate the leak so if I get time a job for tomorrow.
Thanks again regards Ken
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Its because of the "stutter" that its not worth checking timing mark with strobe at idle
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1. The erratic running you describe is not a timing issue.
2. Your timing light is functionally as good as one that clamps around the spark plug wire; it's just a bit less convenient to connect. One could argue that it's MORE accurate since there is no delay while the sensor "figures" out there's a signal and sends a message for the light to flash. Of course, since this all that occurs at the speed of light over maybe 1/2 metre, it doesn't matter!!! :)
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I know the words "Dwell Angle" I have difficulty in understanding how it translates in terms of points gap & timing outcome.
In my head I've thought that whilst static timing is the basic set up to get the engine timing as close to correct as possible statically, the reality is that the timing might be slightly different when the engine is running.
This concept is why I've always seen dynamic timing as a a fine tune potential improvement with the added bonus as has been pointed out that you can also check the advancer is working.
I don't mean to Dwell on the issue (pun intended) but I've no understanding of what Dwell Angle really means in terms of spark delivery, I only know it matters.
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I know the words "Dwell Angle" I have difficulty in understanding how it translates in terms of points gap & timing outcome.
In my head I've thought that whilst static timing is the basic set up to get the engine timing as close to correct as possible statically, the reality is that the timing might be slightly different when the engine is running.
This concept is why I've always seen dynamic timing as a a fine tune potential improvement with the added bonus as has been pointed out that you can also check the advancer is working.
I don't mean to Dwell on the issue (pun intended) but I've no understanding of what Dwell Angle really means in terms of spark delivery, I only know it matters.
To put it into more everyday terms, its the time that the coils are taking in energy (with points closed) which of course gives ultimate output.
How it relates to crankshaft and hence "angle" is the degrees that the crankshaft moves while the points are closed, and ceasing at the point of opening.
To extend that, as the crankshaft rises in speed of rotation, then exactly the same angle gives shorter and shorter time in that corresponding angle (which doesn’t change) to give less and less "saturation" of coil energy as revs go up and up.
The coil resistance is set to accommodate both ends of this arrangement, much longer time at lowest rpm, to much shorter at redline. It can't effectively be avoided with singular point sets.
As the information posted above, electronic systems can provide fixed "dwell" by using internal switching that's timed in absolute terms rather than rely apon points opening and closing at variable rpm demand.
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Well a successful morning , I have set up the static timing with the points set to 12 thou as suggested by members of the forum and managed to get the timing marks to line up fairly well for 1-4 and 2-3 .
Decided to run the bike like this and it’s running nicely when warmed up and choke of at 1200 rpm without the stutter, I also checked the rubber joints and vacuum gauge screws with wd40 and no change in rpm so therefore there does not appear to be any air leaks.
I did check the timing with a timing light and it seems fairly close so I think I’ll leave it like this and take it for a spin, so really happy the bike is running smoothly at 1200 rpm which it didn’t do before.
Thank you everyone for your input regards Ken