yammy fouling plugs

[wartiger57]

I have got a 90hp Yamaha carbed with in engine mix. I bought it used and have had it for 2 years and it has ran great. It actually converted me from Merc. Now the problems start. I took it out about 2 weeks ago and it ran perfectly for about 5 miles then I lost nearly all power. Came back in and made all the usual checks. Ah ha! 3 fouled plugs so I change them. I take it out yesterday afternoon for a motor check and it runs great for about 20 miles down river and then it starts again hardly any power. I turn around and head back in. It will normaly push me alone with no gear about 45mph. On the way back in it will not get over 30 and the motor is surging. At the landing I check the plugs again. Top cylinder fouled, middle cylinder on the verg of fouling, bottom cyinder not too bad. I know enough about 2 strokes to know fouled plugs usually means too much oil and if it was a self mix I would say it was mixed too rich. But with this direct injection I am lost. Is the gas and oil mixed in the cylinder or before it gets there? Is there anyway to control the mix on a direct injection? Has anyone else had this problem or know the solution? Is it gonna cost my first born son to fix? Thx for any help!

 

[spete]

Re: yammy fouling plugs

Have you checked the ground wires on your coils and made sure that they're tight and corrosion free? Do you have good spark to all three cylinders (do a search on this site for the aligator clip method of testing for spark or you can get a spark tester)<br /><br />(info below from a 96-98 model book - would suggest getting a manual if you don't have one) <br /><br />There is a linkage on the oil pump that can be adjusted - my book indicates .039" for a 90hp on the wide open stop clearance. <br /><br />You have to remove linkage from oil pump lever, place carb in full throttle position, rotate pump lever until it contacts wide open stop, back lever away .039" from wide open stop, adjust linkage with jam nut if equiped to keep the specified gap at full trottle. Operate throttle several times from idle to wide open and recheck your gap with throttle wide open.<br /><br />I know these Yammy oil systems are pretty solid and would doubt if you're having a problem at that end.<br /><br />When was the last time you performed a compression test? May be losing compression on the top two cylinders.

 

[boating brad]

Re: yammy fouling plugs

i agree with spete. im wondering about the compression, but also could be carbs. im pretty sure the ratio wouldnt neccesarily foul plugs. if the carbs are clean and in tune, with good compression you could run 20:1 without fouling. i learned this breaking in my evinrude, after 10hrs 25:1 the plugs looked like new. i would perform a compression check and come back with the results.

 

[jim dozier]

Re: yammy fouling plugs

Pull the airbox off of the carbs and check for leaking gas. Pump the fuel bulb and see if any is spilling out of the carb. You may have 1 or more stuck open float valves on your carb dumping too much fuel into the engine and fouling the plugs.