Carb Rebuild or Not.. Help!

[BlackMax175]

Hi,<br /><br />Motor is a 1994 175hp Merc 2.5 liter carb model. Motor has around 400 hours. Has new fuel filter inline and external, and new plugs.<br /><br />Here is the situation. Cruising through the harbor around 5mph pretty smooth, but as soon as I increase the rpm to around 1800 or so to start to go on plane get a real shake and vibration. But as soon as I give it more gas and get it to over around 2,000 rpm smooths out and goes away. Same exact thing happens when I come back to the harbor after being on plane. I bring the boat back down to harbor speed and then once it hits that certain rpm spot shakes/vibrates until I bring it lower to a speed of around 5mph. I'd say it acts up at around 10mph or so. Could the carbs need rebuilding. If so, how dificult is somehting like this. I am very mechanically inclined. Is it easier to remove all three fromt he motor and bring them to a shop?<br /><br />Thanks for any input.<br /><br />Chris

 

[gss036]

Re: Carb Rebuild or Not.. Help!

I don't think that the carbs need to be rebuilt. I would think that you are hitting the crossover between the fixed high speed/low speed jets. Especially if it is very consistant in happening.<br />Could be in need of a link&synch check. Since I am not a mechanic, this is just my 2 cents. Maybe some with better knowledge will jump in and correct me.<br />When was the last time you decarbed the engine? That might help out.

 

[BlackMax175]

Re: Carb Rebuild or Not.. Help!

Hi Gary, thanks for the reply.<br /><br />To reply to your comment, it happens everytime I drive the boat at the exact same rpm. Also, I notice going through the harbor it shakes a bit more than I think it should and you can definitely feel it in the boat too. I have only owned the boat for a year, and I highly doubt that the previous owner decarbed it. How much work is involved in doing that. I just want this motor to run smoother. I have seen others in the marina even older than mine run still as a button when running and not even shaking.<br /><br />Thanks again

 

[andy6374]

Re: Carb Rebuild or Not.. Help!

Gary I believe the high speed jets don't kick in until the upper RPMs. As I not a mechanic either, but I think the RPM range in which he is having problems the carbs are still "using" the idle jets.<br /><br />A lync & sync sounds like a good idea.

 

[BlackMax175]

Re: Carb Rebuild or Not.. Help!

I think I will start with a Decarbing of it, since who knows when it's been last done.<br /><br />How big of a job is a lync and sync? I am mechanically inclined so will give that also a shot since i have the Seloc manual.<br /><br />Its got me baffled at that one rpm spot, why it gets all shaky and vibrates, which still makes me think somehting is up with the carbs.<br /><br />I just know that this motor should be running smoother than it currently is, since i have seen others in the marina run very smooth.<br /><br />Anyone else have any other sugestions. Thanks

 

[gss036]

Re: Carb Rebuild or Not.. Help!

If the decarbing does not help a lot, check the fuel pump, maybe rebuild it, you are only talking about $12-14.00 for the kit. Check your fuel connections and filters. Maybe a bad gasket on the back of a carb, or loose bolt for the carb mounting or reed block. Lot of work to check them though.<br />I know my 89 Merc 200 doesn't always run all that smooth, my wrench tells me to run premium gas, ouch, that about $3.40/3.50 gal presently.

 

[82RAYSONCRAFT]

Re: Carb Rebuild or Not.. Help!

Do a decarb with seafoam and then a link and sync. follow your manual instructions on the link & syc. <br /><br />My 225 drove me crazy with the same symptoms. the above helped dramatically. <br /><br />BTY carbed motors really don't like to idle that well even though I don't think think yours is a idle issue but more of a low end miss as mine was.<br /><br />Good luck!<br /><br />PS: What part of TN you in. I was born & raised in Crossville.

 

[82RAYSONCRAFT]

Re: Carb Rebuild or Not.. Help!

dissregard the PS message. Wrong topic member

 

[BlackMax175]

Re: Carb Rebuild or Not.. Help!

82RAYSONCRAFT,<br /><br />Thanks for the feedback. Definitely going to start with a decarbing and then do a lync and sync before pulling the carbs off.