Merc 90hp 3 cyl. fine tuning

[Trampstamp]

Hi all,

So I've read a handful of the posts, and I think it might come down to carbureator TLC, but I'd appreciate some input from more experience wrenches, as this is mostly new territory for me.

Working on a 1995 2 stroke, 3 cyl, 90 hp ELPTO. In the process of buying the boat from a friend. He always maintained the boat and motor very well, but it had been sitting for about 7 years. I've pulled and cleaned the fuel tank, ran new fuel lines, new plugs, compression tests on all three cylinders right at 119 lb. put in a new impeller, new battery, and will be servicing the lower unit soon.

Hooked her up, fuel primed up great, (and once I realized I was cranking with the kill switch off), she started right up! She jumps to life with a 6 second choke and half throttle, and holds idle no problem. I know these motors are known to be not the smoothest idle in the world, but there seems to be a slight miss both at idle and continuous through the rev up to ~3000+ rpm. I have not had a chance to put her in the water (still waiting on some trailer hub parts), but I'm pretty confident she's just a step or two away from perfection.

I'm currently running 50:1 premix in the gas tank, and I assume the oil injection if working properly based upon its history of good maintenance and careful operation (drained old oil, put in new stuff). Basically, I'm treating it as a new "break-in" procedure since it had been sitting so long. It certainly doesn't seem smoky, she pees like a race horse, I just think her purr could be a little smoother.

I've pulled off the front of the air box, and peered thru the reeds, nothing jumps out as "dirty", but I figure attacking it with a little carb cleaner would be the next step. Should I pull the base of the air box to get to the carbs, or would shooting some cleaner through the throttle bodies be sufficient? Is the roughness an artifact of the extra oil that (I assume) is running through the system? Should I just let her idle for several minutes to see if it works itself out? Is there some other little idiosyncracy I don't know about???

Any further insights would be sincerely appreciated! Thanks much,

Dan

 

[Sea Rider]

Welome to Iboats,

Have the carbs been removed, disassembled and each one cleaned to immaculate perfection whether soaked in real carb cleaning solvent for some hours or with carb cleaner generic sprays ?

To perfectly synchronize inline carbs to idle spot on at neutral will need to count with a electronic vaccum tester, if done by ear sound will need to have a well trained ear to adjust manually each individual carb to perfection.

Remove the air silencer, order a can of CRC Engine Tune-Up and spray liberal bursts of product in each carb throat with motor running geared forward at fast idle, repeat the process several times, after last application let the motor run to clear the heavy smoke that product produced, install the air silencer and go for a wot run as if stealing the combo for some minutes to burn all product leftovers. Should idle much better....

A 2 stroke motor should not be tested too long out of the water at reduced rpm, could end fouling the plugs...

Happy Boating

 

[Texasmark]

If Sea Rider's comments don't work for you, a couple of suggestions from a previous owner of such....the engine in my Avatar to be exact...2002 model.

Fuel filter in the engine should be changed. Upon changing, cut open the old one and tell us what you see. Shooting spray through the venturis can clean up the passages and possibly some stuck rings which is a must do, but does nothing for any crud in the carbs, caked in varnish-old fuel deposits that didn't evaporate. Always a good idea to install new carb kits. Other thing is that the fuel pump diaphragm can loose it's flexibility so a fuel pump repair kit is a great investment in your time and money also. Your 119 compression numbers are Ok per the service manual.

You really don't know anything about your engine, other than what you told us about firing right up, until you get on the water and put it under a load. Money well spent is to get a service manual. They sell them here...top of the page under Shop. The manual tells you how to test your VRO oiler system so that you can quit the pre-mix. Pennzoil TC-W3 rated semi-synthetic is what I use, about 5 bucks a quart in WW sporting goods dept.

I kept Sea Foam in my fuel, reasons and directions on the can. You can pick it up at WW in the auto parts dept when you get your oil.