Ignition Timing jumping around

[johno270583]

Also should probably mention the title of this thread!

After adjusting idle mix, rechecked timing and idle speed. Timing about 7 btdc, was originally set at 8 (there is actually only 1 arrow to set timing to, so just a guess at 7.)

When running normally, timing still jumping about, but I guess that is ok?

Didnt check when boat moving, but will do that next time. See if timing advances, as it should.

Everything ran well as mentioned, great pickup and speed, so would seem like it is running as it should.

[ss3964spd]

Didnt check when boat moving, but will do that next time. See if timing advances, as it should.

Don't need to check it with the boat moving John, the ignition system doesn't know if the boat is moving or if the engine is under load.

Dan

[johno270583]

Checked the mainfold pressure today. Was sitting at 16. Sound about right?

[ss3964spd]

Manifold pressure - AKA, vacume? If so then 16 inches of vacume at hot (fully warmed up) idle sounds like it's in the ball park - maybe a little low, but I don't know what the specification is for your particular engine.

And oh - was the 16" of vac nice and steady? Meaning, was the needle steady or was it fluctuating? From what port was the reading taken?

[seapuppy]

16 at idle is good...should be between 12-19 in/hq.....16 is good ....
as long as it's steady....bouncing around means weak valve springs or late timing....or too advanced...


SP

[johno270583]

Vaccuum was checked off the bottom of the carb, where the rocker cover vent hoses connect to.

There was a very slight, fast movement of the needle on the gauge, barely noticeable, but definitely some movement.

I have done a bit of searching, but couldnt really find what this might relate to.

[ss3964spd]

John,

That port on the carb is exposed to full manifold vacuum so, well done.

If the needle is fluctuating rapidly but only moving slightly I think you're in good shape. The rapid movement probably coincides with each cylinder firing.

If the movement was slower and more pronounced it could indicate a number of things; a vacuum leak affecting just one cylinder, a misfire, a valve out of adjustment or a questionable lifter, idle mixture screws not correctly adjusted. So, as long as the needle isn't dancing around - showing a variation of 1 in/Hg or more of difference, I'd say it's good. Would still like to know what the idle vacuum specification should be for that engine. Most carb'd engines with mild camshafts will normally make vacuum approaching 20 in/Hg. That said, camshafts in marine engines are a bit different than those found in the same size automobile engine so 16" may be right on.

Dan

[seapuppy]

ditto what dan said.....sounds like you have a good solid engine....



SP

[johno270583]

Thanks for the feedback. Glad to see and hear that everything is ok internally. Costs me enough without more problems!

I would also like to know the reccommended manifold pressure/vaccuum, I'll have to do some more research.

If a little low, I would still be leaning towards the intake manifold leaking. I haven't done the soapy water test as yet, but will do next time I run the boat.

I have had it in for a service this week. I hate that time of year! Work on the trailer, a burnt out bilge pump from the last time I took it out, a new power steering pump, new impeller, general work, etc. grand total........$1600

Gotta love expensive Australia!

[seapuppy]

Boat = break out another thousand!!!....



SP