CB400F2 Dynamic Timing Question.

[McCabe-Thiele (Ted)]

As I initially set the timing statically I thought I would do a check of it dynamically as it takes quite a bit of cranking from first start when cold to run. Once it has run it starts pretty easily - it could of course just be a fuelling issue or compression related but I'm thinking the timing might be a tad retarded.
I checked Cylinders 1 & 4 first I had to guess the engine RPM as the rev counter is not connected at the moment, on what sounded like around 1200 rpm the F 1.4 mark aligned nicely. When I tried the 2 & 3 moving the connector onto plug 2 the marks were pretty much out of view.

The Dynatek instructions state:- "The engine can also be timed dynamically using a strobe light in the normal manner.
Use the advance marks and an engine speed of about 2500 RPM (full advance)."

When I tried this again guessing the RMP as 2500 - roughly double the engine idle speed. The 1 & 4 marks lined up to the right of the F marks were there are two close together marks.

Am I right that the 2 & 3 timing must be out as it should be showing as per 1 & 4 except showing 2 & 3 marks with the strobe?
Reading my Haynes Manual is more confusing as it talks about "The two advance marks are on either side of the static mark"?

Suggestions are welcome please. Ted

[Erny]

if I understand you correct, yes, 2-3 timing is out

When checking 1-4 you connect to cable/plug 1 or 4
when checking 2-3 you connect to cable/plug 2 or 3

Do it first for idle - F mark
Then check with 2500, you should see it ideally in the middle of double mark. If you have first set F at idle for both 1-4 and 2-3, then it must be the same for 2500 RPM for both, as this is managed by advancer (springs). It cannot be be different, unless there is some issue in strobe pickup in higher RPMs.

[McCabe-Thiele (Ted)]

if I understand you correct, yes, 2-3 timing is out

When checking 1-4 you connect to cable/plug 1 or 4
when checking 2-3 you connect to cable/plug 2 or 3

Do it first for idle - F mark
Then check with 2500, you should see it ideally in the middle of double mark. If you have first set F at idle for both 1-4 and 2-3, then it must be the same for 2500 RPM for both, as this is managed by advancer (springs). It cannot be be different, unless there is some issue in strobe pickup in higher RPMs.

I re-checked the static timing again on both 1-4 then 2-3 they are spot on by my eye / lamp co-ordination.

Then I realised that I had been connecting the plug lead clip to number 2 rather than number 3 cylinder (does that matter?)- the dynamic timing marks were spot on for both 1-4 & 2-3. I'm thinking it's either my strobe or possibly an issue with the coil connection at number 3 lead or its the idiot at the end of the timing light. (me)

As the Carbs have not been synchronised or the air screws altered since I did the bench build on the carbs I will do a compression test in the morning just for peace of mind. I saw no point in spending time on the carb balancing etc as it's going to be stripped down soonish anyway.

[K2-K6]

"Then I realised that I had been connecting the plug lead clip to number 2 rather than number 3 cylinder (does that matter?)- the dynamic timing marks were spot on for both 1-4 & 2-3. I'm thinking it's either my strobe or possibly an issue with the coil connection at number 3 lead or its the idiot at the end of the timing light. (me)"

It's ok to use either 2 or3 to check that timing point as they are both fired from one coil,  and hence the single set of points. It'll look the same whichever of the two you use from that coil.

One time that "may" be a wrong statement is if you use an inductive pickup for HT sensing,  they can be sensitive to polarity and with these coil pairs one lead comes from one end with the other effectively opposite as they travel to the two plugs from that coil.  This can prevent some strobe from picking up the signal and show as no response.

[Bryanj]

Yup strobes are designed for cars and dont like the elektrikery running the oposite way

[McCabe-Thiele (Ted)]

That might explain my timing light giving odd results, I was surprised to find that the induction clip had an arrow for direction of current flow presumably.

[Bryanj]

Correct but that is for cars, one of the Japanese big 4 (Suzuki i think) recomend swaping the plugs on service (1to4 and 4 to1 etc) as one plug sparks from centre tip to side electrode and the other opposite