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Author Topic:   Engine vibration prior to plane

mustang7nh posted 05-25-2004 07:49 AM ET (US)
I posted a similar question about my family's other Whaler, but this one refers to my 1995 250 Yam carb on 1991 Outrage 22. Engine runs like a top, except that when you motor along at approximately 900 to 1400 rpms you get a bit of a vibration. Nothing that rattles your teeth but enough to vibrate the various objects on board and be annoying. It isn't evident at clutch speed or once on plane.
Not sure if this is a carb 2 stroke characteristic or if there is some kind of adjustment that is needed to smooth it out a bit. BTW, double nut on each mounting bolt so I don't think its loose on the mount at all. Thanks.
fyrdog posted 05-25-2004 10:37 AM ET (US)
Change your prop. I had the same problem at 1500 RPM. There was a small crack and curl on the tip of a blade. Have your prop reconditioned which is cheaper than a new one.
rtk posted 05-25-2004 10:53 AM ET (US)
I have a 1997 21 Outrage. Last year when I purchased the boat it had a 1997 225 Mercury carbed motor. I had a bad vibration at similar rpm. I had the prop reconditioned and it was better but did not eliminate the vibration. I just repowered this spring with a new 2003 250 Mercury EFI. I've tried two diiferent props, both new. With the four blade Vensura there was very little vibration if any. Now I am running a large diameter four blade PowerTech stainless prop. I noticed this past weekend that it is vibrating some at that rpm range. This prop is heavier then the previous. Once I am out of that rpm range she runs smooth with no vibration.
With two different motors and three different props the vibration seems to be there to some extent. I have heard that this is not uncommon when running the heavy stainless props.
Has your prop been reconditioned lately? Sometimes just a little ding will produce a vibration. If there is a fix for this I would be very interested also.
Rich
Bigshot posted 05-25-2004 02:55 PM ET (US)
Does that engine drop the lower 2 cyls at lower rpm? If so, you have your answer. If not most 2 strokes do not like certain rpm ranges and you have found yours. If prop looks good and vibration is not "excessive" then leave be or have a mechanic adjust your carbs and check timing, etc.
mustang7nh posted 05-25-2004 05:34 PM ET (US)
My prop is SS Stilletto 19". Never been reconned but it looks to be almost like new.
I'm not sure if this engine drops two cylinders or not, but I think the rpm band that it occurs is a bit wide for this to be the case. It does surge between 3400 and 3500 when cruising but no where else. Just stays a few seconds at each rpm and then moves to the other. I hate to mess with the engine as it runs perfect in all other regards. Does adjusting six carbs take a lot of a finesse for a mechanic to do and get correct?
fyrdog posted 05-27-2004 02:20 PM ET (US)
If you don't adjust the carbs correctly you may have one that doesn't get enough fuel, with a 2 stroke that means lack of lubrication and the risk of burning a cylinder out.
Salmon Tub posted 05-27-2004 10:54 PM ET (US)
It may be that the carbs are out of sync., but, before you go adjusting them, pull the spark plugs and take a look at them. Do this after a decent run and no longer than five minutes or so at slow or idle speeds. Look at the tip, the electrode and the rim. Compare them to each other, and if they look more or less the same, and the porcelain isn't completely white or black on any of them, then it may be best to leave well enough alone. This is even more so the case unless the vibration has only recently developed, or someone recently worked on the motor. If the plugs look decent then I would not worry about it too much, you will need computer controlled fuel injection in order to get rid of the vibration. All carbed 2 strokes get the shakes during the crossover from low speed to high speed jets. Some designs more than others. Best thing to do is avoid that range as often as possible. Just try not to pay too much attention to the DFI 2 strokes and EFI 4 strokes, they can drive a man with carbs crazy.
Clark Roberts posted 05-28-2004 05:56 AM ET (US)
You might want to check the motor mounts (power head and lower unit) as these are glued rubber pucks and adhesion can shear. On a big engine like your 250 a bad motor mount could cause some shaky business. Happy Whalin'... Spruce Creek Navy
raberwhaler posted 05-28-2004 06:23 AM ET (US)
I have the same problem with my 1976 Montauk. She has been repowered with a 90 hp Honda 4 stroke. The motor is smooth as silk at all speeds but at trolling speeds objects on the dash and grab rail rattle and is quite annoying. Has done it since the day it was repowered (when the prop was new). I'd love to have a solution. Raber

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Author	Topic: Engine vibration prior to plane
mustang7nh	posted 05-25-2004 07:49 AM ET (US) I posted a similar question about my family's other Whaler, but this one refers to my 1995 250 Yam carb on 1991 Outrage 22. Engine runs like a top, except that when you motor along at approximately 900 to 1400 rpms you get a bit of a vibration. Nothing that rattles your teeth but enough to vibrate the various objects on board and be annoying. It isn't evident at clutch speed or once on plane. Not sure if this is a carb 2 stroke characteristic or if there is some kind of adjustment that is needed to smooth it out a bit. BTW, double nut on each mounting bolt so I don't think its loose on the mount at all. Thanks.
fyrdog	posted 05-25-2004 10:37 AM ET (US) Change your prop. I had the same problem at 1500 RPM. There was a small crack and curl on the tip of a blade. Have your prop reconditioned which is cheaper than a new one.
rtk	posted 05-25-2004 10:53 AM ET (US) I have a 1997 21 Outrage. Last year when I purchased the boat it had a 1997 225 Mercury carbed motor. I had a bad vibration at similar rpm. I had the prop reconditioned and it was better but did not eliminate the vibration. I just repowered this spring with a new 2003 250 Mercury EFI. I've tried two diiferent props, both new. With the four blade Vensura there was very little vibration if any. Now I am running a large diameter four blade PowerTech stainless prop. I noticed this past weekend that it is vibrating some at that rpm range. This prop is heavier then the previous. Once I am out of that rpm range she runs smooth with no vibration. With two different motors and three different props the vibration seems to be there to some extent. I have heard that this is not uncommon when running the heavy stainless props. Has your prop been reconditioned lately? Sometimes just a little ding will produce a vibration. If there is a fix for this I would be very interested also. Rich
Bigshot	posted 05-25-2004 02:55 PM ET (US) Does that engine drop the lower 2 cyls at lower rpm? If so, you have your answer. If not most 2 strokes do not like certain rpm ranges and you have found yours. If prop looks good and vibration is not "excessive" then leave be or have a mechanic adjust your carbs and check timing, etc.
mustang7nh	posted 05-25-2004 05:34 PM ET (US) My prop is SS Stilletto 19". Never been reconned but it looks to be almost like new. I'm not sure if this engine drops two cylinders or not, but I think the rpm band that it occurs is a bit wide for this to be the case. It does surge between 3400 and 3500 when cruising but no where else. Just stays a few seconds at each rpm and then moves to the other. I hate to mess with the engine as it runs perfect in all other regards. Does adjusting six carbs take a lot of a finesse for a mechanic to do and get correct?
fyrdog	posted 05-27-2004 02:20 PM ET (US) If you don't adjust the carbs correctly you may have one that doesn't get enough fuel, with a 2 stroke that means lack of lubrication and the risk of burning a cylinder out.
Salmon Tub	posted 05-27-2004 10:54 PM ET (US) It may be that the carbs are out of sync., but, before you go adjusting them, pull the spark plugs and take a look at them. Do this after a decent run and no longer than five minutes or so at slow or idle speeds. Look at the tip, the electrode and the rim. Compare them to each other, and if they look more or less the same, and the porcelain isn't completely white or black on any of them, then it may be best to leave well enough alone. This is even more so the case unless the vibration has only recently developed, or someone recently worked on the motor. If the plugs look decent then I would not worry about it too much, you will need computer controlled fuel injection in order to get rid of the vibration. All carbed 2 strokes get the shakes during the crossover from low speed to high speed jets. Some designs more than others. Best thing to do is avoid that range as often as possible. Just try not to pay too much attention to the DFI 2 strokes and EFI 4 strokes, they can drive a man with carbs crazy.
Clark Roberts	posted 05-28-2004 05:56 AM ET (US) You might want to check the motor mounts (power head and lower unit) as these are glued rubber pucks and adhesion can shear. On a big engine like your 250 a bad motor mount could cause some shaky business. Happy Whalin'... Spruce Creek Navy
raberwhaler	posted 05-28-2004 06:23 AM ET (US) I have the same problem with my 1976 Montauk. She has been repowered with a 90 hp Honda 4 stroke. The motor is smooth as silk at all speeds but at trolling speeds objects on the dash and grab rail rattle and is quite annoying. Has done it since the day it was repowered (when the prop was new). I'd love to have a solution. Raber