Yamaha tuning troubles..

[willyfish1]

89 175. Motor has been flawless but recently started lugging at idle and has no power above 4k. Started diagnosis and found outside 4 cylinders (1,2,5,6) all very rich at idle per piston top reading and wet plugs. Strange thing is that middle 2 (3,4 are close to normal at idle and scary lean anywhere above 1500 rpm. (I mean ready to stick one lean). I have gone through carbs (6g502) and all is good with them. I just tried a 225 excel carb on 3 &4, Still lean on 3 &4... Any suggestions would be appreciated!!! This thing is workin me good, so i figured i would make this my first post here and see if i can get some expert help from yall!!

thanks, Will

 

[cousinabe]

Re: Yamaha tuning troubles..

have you checked the fuel pumps?
have you considered T'ing in a vacuum gauge between the engine filter and fuel pumps to see if you are getting any king of restriction?

 

[willyfish1]

Re: Yamaha tuning troubles..

Rebuilt both pumps first then replaced, neither set made any difference. I have not check fuel flow with a vacuum gage yet, only visual with lines off and squeezin ball. It had adequate flow checking it that way..

After all i have done i can only think that somehow the fuel from the middle cylinders is getting sucked into the outside 4 cylinders, but i cant in no way figure out how or even theorize how that would be possible, unless something strange is going on in the exhaust side of this thing????????

thanks, will

 

[cousinabe]

Re: Yamaha tuning troubles..

are you sure fuel is getting to that middle carb?
have you tried disconnecting all fuel lines to carbs, pump ball to see if fuel is flowing?

 

[willyfish1]

Re: Yamaha tuning troubles..

thanks for the replies.. Yes i am 100% it is getting fuel into the carb without any type of restriction through the line.. I can put my finger behind the main nozzle while running on the hose and fuel is being pulled out. I want to add that if you pull a wire and disable a middle cylinder while running it will almost kill the motor. Pull a wire on any of the outside 4 holes and you only get a small change in idle quality!!! keep the replies coming, fresh ideas always help with nightmare jobs!!!