93 Rude 175 making a rattling noise over 4100rpms

[jdcarter]

Guys - question for you - my 175 rude is making a rattling noise when it gets over about 4100 rpms and for some reason it seems to have lost a little power on the top as well. Seems like I can trim it down some and it'll go away but if i trim it back up to where it needs to be it starts back. Now granted the boat was loaded with two guys - me driving at 230 lbs and my partner probably around 260 or a lil more - all of our fishing gear and a cooler. All i could get was 4400 rpms... Seems like I was able to get around 5400 rpms earlier this year. It has a 24 pitch raker on it if that helps...

Any idea what I may be looking at here? I know this is vague but hopefully this will start a conversation...

thanks!!

Also - she fires up with a bump of the key every time and idles perfect... Planes off with no problems and cruising without any issues - just when I hammer down on her and try to stretch her out.

 

[jonesg]

Re: 93 Rude 175 making a rattling noise over 4100rpms

Get a compression guage and remove all the plugs and make note of plug conditions in your service manual, if you don't have one git one.
www.outboardbooks.com

then take compression readings and write em down.
Should be around 90-120 as close as possible to each other.
Within 15 psi of each other is the limit spread.

 

[jdcarter]

Re: 93 Rude 175 making a rattling noise over 4100rpms

compression's good - lower than what you commented on but I was told the bigger motors have lower compression but mine are within the correct range of each other...

What I did find was one of my plugs was messed up - the center electrode is missing the tip - stops below the ceramic - not sure what happened to it - these plugs were put in at the end of last year and i've probably run the boat 15-20 times since (Champion QL77JC4)... I didn't put them in but a shop that cleaned my carbs did... Anyone ever seen this happen before... I'll post some pics... they're not the best but gives you an idea... Also I think I found my rattling - I'll know definite saturday morning but looks like the vent in the hood came unglued and is vibrating when the air flows thru it...

Click below to see image of the plug:

http://s695.photobucket.com/albums/...tion=view&current=IMG00056-20100623-0932.jpg&

http://s695.photobucket.com/albums/...tion=view&current=IMG00053-20100623-0931.jpg&

 

[cougar1985]

Re: 93 Rude 175 making a rattling noise over 4100rpms

hard to tell but that could be a factory defective plug.if it was the motor you,d think the plug would of been crushed maybe but not like that.good reason why you couldnt reach wot rpm,s for sure.

 

[d.boat]

Re: 93 Rude 175 making a rattling noise over 4100rpms

compression's good - lower than what you commented on but I was told the bigger motors have lower compression but mine are within the correct range of each other...

What I did find was one of my plugs was messed up -

I've had two V-6's, one early 80s, one early 90s - so my guess is yours is similar in compression. Mine have always been ~90 psi give or take a couple of pounds. Not even 100. This is normal for the big V6's as far as I've been told by good mechanics. So if yours is in that range (low 90s), it is probably normal.

As far as the plug.... I'm no mechanic, but one thing I know and have actually trouble shooted (trouble shot?) before is the drop in RPMs by approximately 1/6 often indicates that a single cylinder is not working and that points to a bad plug -either filthy fouled or defective, or a bad coil if there is one coil/cylinder. Your RPM has dropped by almost exactly 1/6 (normal ~5400?, now ~4400).