SX22 vibration

[swordfishman]

Well after 4 years of drought and my lake dropping to 3% capacity I am finally back to a usable lake as my front yard.  I had a serious tubing adventure yesterday and all went well with the boat.  Today I tried to go for a leisurely cruise and I have a pronounced vibration around 4000 RPM.  It also seems to be exacerbated by left turns.
I have read the posts about regular gas causing vibration and I will do this experiment.  I intend to attempt the shaft/prop alignment testing tomorrow. 
I have no water dripping at my packing where the driveshaft exits the hull.
runs nice and smooth until the 4k-ish RPM

The only thing I did in the interim was attempt to lift the boat with an undersized lift that put too much pressure on the forward fin.  the prop and shaft were well clear of any structure.  I don't believe this is relevant but I wanted to disclose it in case it could have unpredictable side effects.

Any sage advice or alternatives tests are appreciated.

Cheers,
Benjamin

[toyotafreak]

Prop dings, etc.?

[swordfishman]

I never felt anything.  Was cruising at about 4k without the vibration and then it suddenly started.  I throttled down and retraced my track looking for anything I may have  hit but found nothing.
The blades have a few small dings (from the previous owner) I intend to get motivated to check the driveshaft, and prop fins today.

[blindside]

A bad spark plug will cause vibration like this also. The engine is not firing on all cylinders and is thus out of balance. I've had this happen several times.

[breakawaydaze]

Well, I hate to say it...but its probably the spark plugs.  Actually, its probably just one of them.  There is an easy process to figure which one, but its just easier to replace them all.  Now your big question is, Ford Plugs, Denso Plugs, Iridium plugs and so on and so forth. 

I am a big fan of get the best and don't worry about it, but because of a lack of time and availability, I put in the Ford Plugs and noticed no difference in performance at all.  I have over 125 hours on them, inspect them every spring and they are running clean with no deposits or sign of failure.   Autolight 3923  you can find them anywhere.

Lots of discussion in forum on this topic, you can start here:  http://www.epicmarine.com/forum4/index.php?topic=2490.0

[swordfishman]

I took it out today and it seemed much better.  I was the only person in the boat and I am only 150lbs while the other day I had 6 people in the boat.
There was still some minor vibration and it still was exacerbated by turning to the left.

I will pick up a set of Autolight 3923 today and try to get them in before it gets too late tonight.  I am headed for the bahamas early tomorrow so after today it has to wait til late next week.

I will say that bore-sighting the track fin seemed a bit out of plumb.  I am curious as to the effects this would have on the slipstream to the prop.  I sure hope I didn't bend it.  If anyone has any experience with a bent fin please chime in.

[blindside]

When you are turning the engine is working harder thus I still say plugs. If the vibration was only in your steering wheel then I would look at rudder. The longer your boat sits the worse the plugs can get. This year mine started out terrible and cleared up with fresh gas and a bottle of sea foam. It took about 30 minutes of run time. If the problem never goes away, change the plugs. I've had to do this twice in 8 years.

[breakawaydaze]

The Bahamas are pretty far away,  if I was you I would get it fixed before I left!   How much gas will you need?  I know the Epic is pretty efficient, but depending on the current I would bring extra.  ( just kidding, have a good time!)

[swordfishman]

Love it!  Thanks I needed that.

I didn't get to change the plugs today.  The wife had other priorities.
I took it out tonight with no problems in a 5 mile cruise.  Maybe I shook loose some varnish from sitting for 4 years.  I had pumped the tank dry but there is always residue.

I will post back after I get back from vacation.

cheers and thanks for the help.

[swordfishman]

Well I am back from the Bahamas and have put about 10 hours on the boat without any vibration.  maybe I did foul out a plug with some varnish and it cleared up.  I never felt or heard a miss when the vibration occurred but blindside seems convinced it could explain my symptoms.
As an engineer I hate self healing phenomena but as a boat owner I'll take it!

Cheers and thanks for the help.

[cyclone]

Ditto on the self healing, but bad gas and fouled plugs sometimes work their way through system. My boat is finally back to 100% after 3 years of little use. Best thing to do, run it!!

[tryme]

because of this I replace my plugs every spring now.  use the autolite.  $10 every spring is worth it.

[breakawaydaze]

Ditto That!