Slight shutter

[fishhawk16]

My 96 90Hp evinrude has a very slight shutter. This only happens every once and a while. Sometimes after a full day of being out on the lake it doesn't happen.<br /><br />It seems to be load related, I noticed it more when I was pulling a skier. From dead slow in forward, I would push the throttle forward in a smooth and gradual motion, just before the boat starts to plain I feel a little vibration and shutter for a second or two then smooth running, for the rest of the run. <br /><br />Any ideas on what this could be, or if I should worry about it.<br /><br />BTW I think I'm still a little over pitched I get 5100RPM at WOT. Could this be the cause?

 

[Hooty]

Re: Slight shutter

I would say you are definitley over-propped and the "shutter" you feel just might be the engine lugging. Get the engine speed up or prepare for major ($$) problems.<br /><br />c/6<br />Hooty

 

[walleyehed]

Re: Slight shutter

If skiiing is your thing, drop 4" in pitch from what you have now if we know the tach is correct.<br />5800-6000 would be best.<br />That shudder you feel could be a transition of the fuel system from Idle circut thru high speed circut.<br />I believe I would install a new set of Champion QL82Cs as well.

 

[fishhawk16]

Re: Slight shutter

Thanks Hooty<br />Im looking into a 17"pitch<br /><br />One mechanic I spoke to said that the operating range for this engine was 4750-5500 Rpm he said I should be fine and that he would be happy with the 5100 I was getting?

 

[walleyehed]

Re: Slight shutter

Fishhawk, take my advice, please...5100 is loading up the piston ring lands, and WILL cause problems-of course the dealer will say it's ok, he wants to replace your engine.<br />5500 would be minumum acceptable if it were mine.

 

[fishhawk16]

Re: Slight shutter

Will do Walleyehed, I haven't been out to much lately. Weather hasn't been co-operating. <br /><br />Now you have me concerned. I just purchased this boat this year. The boat came with the 19 pitch prop. The prevous owner was not into skiing, mostly fishing. Should I be worried?<br /><br />I did a compression test 120 on 3 and 110 on the lower port side.<br /><br />What are your thoughts?

 

[walleyehed]

Re: Slight shutter

That sounds reasonable on the comp. test. I would do a decarb, possibly 2, then re-check compression....do it at the same engine temp as you did the first.<br />The problem with low RPM is high combustion temps, and the formation of deposites under ring-lands, heads, exhaust chambers, etc.<br />The book does say 4500-5500, but it has been proven that 5500-up is best.<br />If you don't know the particulars on decarbs, do a search on this forum for "decarb", you should get plenty of info...<br />What sparkplugs are installed now???

 

[fishhawk16]

Re: Slight shutter

Based on what I read here I did 2 decarbs shortly after I got the engine. Only did compression test after the decarb so I don't have anything to compare it to.<br /><br />The only issues I have had with the motor are the very intermittent aforementioned shuttering and a little bit of rough idling. Not having owned a V4 in the past, my previous motor was a 3-cylinder 70Hp merc I really don’t know if the idle is normal. <br /><br />The plugs look good brown to black coffee colour slightly on the damp side. This is good right?

 

[walleyehed]

Re: Slight shutter

Color sounds about right, just make sure plugs are always fresh....change out every year-some will argue this, but they don't understand a sparkplug builds resistance over time during use and puts more and more strain on the ignition system-to the point it may not fire even though the plug "looks" good.<br />What plugs are you using????

 

[fishhawk16]

Re: Slight shutter

OK didn't know about the resistance building up on the plugs. Its interesting that you would say that. On my 70Hp merc I used to change the plug every other year regardless of condition. Then for some unexplained reson I stopped and just kept using the same plugs for about 5 years or so. Last year I started to have starting troubles then it wouldn't keep running at idle, eventually it would not start at all. Of coures this was happening just aroudd the time I was selling it. Well the stator and the switch box went, fortunatly for me the guy I took it to had used parts and put them in with a 30 day warrentee. Still cost me 400 bucks but it ran real good and started first turn.<br /><br />On current rig I'm using the champs QL82C's<br /><br />Thanks for your help Walleyhed! Do you think there could be any damage on the motor? One thing I didn't mention was that when I got the boat it had a 21" pitch prop would push 4800RPM! First thing I did was take it off and put on the 19? Now again he just fished and the boat weighs less that 1000lbs wet minus the motor of course.

 

[seahorse5]

Re: Slight shutter

Just to be sure you have the correct plugs for a '96 90hp, if the motor mounted trim switch is on the starboard side, you have the crossflow motor and it uses the QL82C plugs. If the trim switch is on the port side, you have a looper V4 and that uses a QL78YC sparkplug.

 

[fishhawk16]

Re: Slight shutter

OK<br />Looks like I have a looper, I thought that I read here that either plug would work, no?<br /><br />I know the difference is basically temperature right?<br /><br />Will using the QL82C be a problem?

 

[seahorse5]

Re: Slight shutter

If you are sure of having a looper V4, use the QL78YC as they have an extended nose for better foul resistance and smoother low speed operation, compared to the standard plug design.

 

[fishhawk16]

Re: Slight shutter

Yep port side engine mounted trim switch.<br /><br />thanks Seahorse I'll get a set of teh QL78YC's.<br /><br />This is a great board, learn more here than calling my dealer!

 

[walleyehed]

Re: Slight shutter

Thanks for covering my Bu77 again, seahorse...too much crossflow time and not enough looper...

 

[fishhawk16]

Re: Slight shutter

thanks for checking up on me and thanks for your help Walleyehed!<br /><br />I hope it warms up a little I want to get back on the water