NSF4/5/6 timing

[km1125]

I have a NSF4A motor but the manual for a NSF5. Thought these motors were virtually identical but when I went to check the timing on the NSF4A, I get a constant 25 degrees. My manual states that the timing should be at 5 dBTDC at idle and climb to 25 dBTDC above 3500 RPM, as shown on the diagram below (from the manual)

Did the earlier NSF 4/5/6 models have static timing at 25 dBTDC, or could this indicate a problem with my CD?

 

[pvanv]

The CD is supposed to control the advance, so if you are having over-advanced issues (such as coughing) at slower speeds I would consider trying a different CD. If it is running OK, I would leave it alone. Both the 4/5/6A and the 4/5/6A2 use the same CD (might be labeled CU2568). The 4/5/6B models had a running change to an ignitor (combining the coil and CD, and eliminating the exciter and pulser). What kind of timing light are you using?

 

[km1125]

I was using an old in-circuit neon timing light, so it's very accurate (no issues with a pickup or sensor). I didn't see the timing vary at all from idle to ~4500... just stayed at 25dBTDC. I just looked up a service manual for the MFS 4/5/6B's and it shows a spec of 0 dBTDC at idle and 25 dBTDC

The CD is a CU2568. It also has a 9F29... is that a date code?

I was just checking everything over, as this motor is fairly new to me. This is a longshaft and I put a 5HP carb on it but it still seems a bit anemic compared to the 6HP shortshaft I have, even considering the 20% HP difference . Lots of variables though and I might play with props the next time I get it in the water.

Does seem to start and run consistent though. Not seeing coughing, but there is a little bit of a stumble in the 1500 rpm range.

 

[km1125]

Ok.. so an update.
I finally got around to checking my other motor. It is a NSF6A with a CD CU2568 but with 0L11 code (date code?). This unit also seems to be fixed at 25 degrees BTDC.

Were earlier versions of these motors fixed timing and different than what my manual shows?

Has anyone actually tested the advance on these motors and saw a 5 dBTDC at 1500 RPM?

Why am I concerned? Normally on IC engines, I'd think 25 would be WAY too much at the lower RPMs especially under WOT conditions. If not propped exactly right, this would be even more of an issue as the engine would never get over it's midrange RPM to get to the right cruise RPM. I also run premium fuel so the problem would be worse if I was running an economy fuel (87 octane)

 

[km1125]

I asked the same question in a email to nissanmarine. I got responses back today. While the first email said it should vary from 5 to 25, a followup email corrected that and said "however, some of the NSF5A2 models had a set timing of 25 degrees BTDC.".

Great customer service!!!

Doing a bit more research though... if the engine gets over about 2000 RPM than 25 degrees shouldn't be a problem.