yamahaaaa 130 issue again

[z-drives]

ok i posted about this back in the fall before putting her away, but the problem is still here.<br /><br />1991 130, precision blend.<br /><br />my family yamaha tech went through the engine a few weeks ago changed waterpump, poppet valve, t-stats and generally gave the engine a checkup; compression, spark ect. everything was fine, and said the engine ran wonderful, as far as he could tell with the flush kit. it idles smooth as a 2 stroke can and does not miss a beat. it has great smooth power all the way until WOT (not that i run there..lol), but after about 5 seconds of getting to WOT the rpms drop down. sometimes they will drop down to 4700, sometimes 4300. first time i give it the throttle it goes up, if i try it again it usually goes up but for even shorter. a few tries later i usually cannot get those extra rpms at all. the engine still runs strong at those rpm's once it drops down and shows no sign of stalling or anything. its just annoying to know it has more balls i just cant use. wouldnt hurt to have it limited with these gas prices, but want those extra revolutions for outrunning a surprise thunderstorm.<br /><br />the o-ring on the fuel filter was missing; we initially thought this could be the problem-- sucking in air at that high fuel demand. i have replaced the oring and repaced all filters, still no luck. the plugs are fresh, and mechanic (ours since late 80's) says the engine is healthy. i havent been able to get him on the boat to run it himself due to his busy schedule this time of year and my own schedule. i'm handy with a wrench and would like to take a crack at solving this. any more ideas? oh, fuel pump is new.<br /><br />fuel is on the whole new and any old fuel had stabilizer.

 

[rodbolt]

Re: yamahaaaa 130 issue again

go through the fuel system, most likly some trash in the carbs or a weak fuel pump. however a fuel system vacum check will quicly check for any leaks or restrictions between the enine mounted filter and the liquid level in the tank, anything over 4"Hg and its restricted anything less than about 1/2" Hg and you most likly have a leak or a weak pump.

 

[z-drives]

Re: yamahaaaa 130 issue again

thanks for the quick reply. so you say put the vacuum gauge inline the fuel system before the engine?<br /><br />this should just be at the trouble rpm, right?<br /><br />figured it is a fuel issue somewhere. any specific areas that you see as problematic to look if it is a leak, not restriction? as far as restriction, do you think carbs? if not any other problematic places to look?<br /><br />i know you cant say for sure without being with the engine, just looking for 'typical' problem areas you may be familliar with.

 

[rodbolt]

Re: yamahaaaa 130 issue again

T the vacum guage in between the pump and the engine filter, if it passes the tests you just eliminated all but the carbs and pump. if it does not pass stat moving the T fitting back and rerunning the test.

 

[z-drives]

Re: yamahaaaa 130 issue again

got the mechanic down to the boat tonight, sooner than i expected so i never got to the vacuum test. we ran the engine at high revs-- sustained power while pumping the primer bulb. engine was also tested with a seperate standalone tank as to eliminate the boats fuel and fuel system.<br /><br />the carb gaskets were put on incorrectly so we are thinking the float adjustments are most likely incorrect, if the gaskets are on wrong something else may be. the floats seem to be the most likely cause. he will be removing them tomorrow and inspecting/cleaning the carbs then reasembling poperly.<br /><br />i will update this thread as to have a referance for the future if someone else may have a simmiliar problem.<br /><br />p.s. those engines SCREAM with the carb baffle-thing removed. nice sound.

 

[z-drives]

Re: yamahaaaa 130 issue again

alrighty... still need some help here rodbolt et al.<br /><br /><br />i feel bad because this guy's always fixed everything of ours on the first shot, so all of the sudden he looks bad. good thing it doesnt cost much as a close family friend. we pay most service fees in days taking him fishing.<br /><br />we tested it and all as in my previous post, and isolated the issue to the engine. basically the carbs were incorrectly installed from his opinion (gaskets on backwards causing restriction) so it was our thought to take them off, dissasemble clean and rebuild--if someone messed putting the gaskets on imagine how they assembled the carb. orings on something inside the carb were junk, as was the float adjustment (not even close to level), whitnessed by myself, the orings disintigrated in my hands. needless to say, i would think it safe the carbs needed service anyways.<br /><br />however, after this service the problem has not gone away, but it seems to possibly gotten worse. now it holds the rpms even less, and loses power to an even lower power...so instead of the usual 47 where it would level out it will drop all the way down to 38 at "WOT."<br /><br /><br />he should be looking at the engine and running it again tomorrow night (no lack of water tests at problem speed/rpm's) to hopefully figure it out. he admits he is stumped for the most part, although i continue to suspect the fuel pump. the pump was replaced in the fall before winterizing the engine. since the mpup is new, he does not think it is the problem. basically i'm just looking for an opinion whether defective pumps exist or not. like any other part i am sure they do exist, but is it feasible within normal odds to actually end up with one?<br /><br />if not the pump to suspect anymore, any other thoughts?<br /><br />fresh fuel, filters, clean/adjusted/gasketed carbs, tight fuel lines, problem isolated to engine with external fuel supply.<br /><br />thanks for any help.. we appreciate it.

 

[seahorse5]

Re: yamahaaaa 130 issue again

A common Yamaha carb problem on engines like yours is debris, usually rust from the original fuel pump check valve screws, gets lodged between the carb's fuel inlet fitting and the float's needle and seats. <br /><br />The debris floats around while the motor is running and can restrict the flow of gas to one or both needles and seats. When you stop or slow down, the debris falls away and the motor works fine for a while. <br /><br />You can see this by running with the air box removed and watching the fuel spray out of the high speed nozzles. Some motors will not run well with the air box removed as that leans out the mixture.<br /><br />The Yamaha Marine Technical guide and an older service bulletin show how to machine the carb bodies and tap them for an access port to clean out the trapped debris. In about 1993, Yamaha included a clean out screw in the carb bodies.<br /><br />Your Yamaha mech may not be familiar with this problem, or he may never have gotten the technical guides which are given out to the techs that attend the annual one-day service training seminars.

 

[z-drives]

Re: yamahaaaa 130 issue again

thanks. do you think this problem could foreseably get worse with the carb rebuilt/cleaned?<br /><br />i know he goes to florida or something every year for a few days. maybe he did not go that far back, or just does not remember.<br /><br />we test ran the motor with the carb baffle whatnot thing off watching the spray patterns and timing. those things are really nice sounding without those. whatever he saw was the motivation to rebuild the carbs.<br /><br /><br />is there any way you could send me the instructions on that procedure if for some reason we cannot look it up? he works on the side outside of his shop for us, so the shop resources are not exactly easily available... both physically and politically, if you know what i mean.