90 yamaha power loss

[killian]

New member saying Hi to all the forum members.I have a 2000 90 horse yamaha that recently started giving trouble.First noticed it when i went fishing after letting boat sit for two months.It idled rough from the start,i thought it was just cold and cranky, then when i powered up she wouldnt even plane the boat.I messed around a little looking for something obvious,couldnt see anything out of whack then when i started her up again that same trip she ran fine for about 20 minutes then bogged down again and would only make 7 knots. the next day i check the filters(all of them), and nothing.I checked out the oil alarm system and it was fine.The plugs were a little black, changed them.Linkage looks fine.What else can i do to fix the problem before taking her to the shop.I am handy with tools but dont have a shop manual.Any help will be greatly appreciated.

 

[fshng4]

Re: 90 yamaha power loss

I am dealing with an exact problem with a Yamaha 1994 - 115hp - 2 stroke (your symptoms are identical to mine). It is in the shop and they are just now troubleshooting it and they have found (to this point) a bad coil. I will repost my findings when I get my boat back and test run it on the lake.

 

[JB]

Re: 90 yamaha power loss

Hi, Killian.<br /><br />You may be dropping a cylinder.<br /><br />With the engine at idle (on the muffs) disable each spark plug in turn. If killing a cylinder doesn't cause a drop in rpm, that cylinder is not making power.<br /><br />If you have a dead cylinder, see if the plug wire will make an arc of at least 1/2" to the block.<br /><br />No spark? Start switching ignition parts between cylinders until trouble follows a part.<br /><br />Got good spark to a dead cylinder? Overhaul that carb.<br /><br />Good luck.

 

[ivar]

Re: 90 yamaha power loss

I have had the same problems on my 92 Yamaha pro-60. It ran fine when cold , but would suddenly drop down to 3600 or so after around 5 minutes<br /> I found it difficult to troubleshoot , as I got inconsistent results when I tried the swapping of parts that JB suggests. <br />It turned out to be the coil on the middle cyl. that crapped out when it got up to working temperature. <br /><br />How did the bog "feel"? - smoothly or somewhat abrupt?<br /><br />But your problem can as well be fuel related,<br />What happens when you squeeze the primer bulb? does it pick up some rpms? If so , it indicates problems with your fuel supply. That can be everything from faulty tank venting, gunk/water in the tank , defective fuel line connections , bad check valves in the primer bulb , fuel pump gone bad or gunk in your carbs.<br /><br />Some tips that will save you more grief: (<br />1: get a shop manual (e.g. from iboat,just click the "manual" link at the top of the page) , I just got mine and I cant realize how I did without for so many years.<br /><br />2: Replace spark plugs is a no-brainer , but also plug caps and spark plug leads. those detoriate (sp) with age and will give you symptoms that are inconsistent and difficult to troubleshoot.<br /><br />3: Replace your fuel line with preferably oem or another high-quality line. connections and primer bulbs also go bad with age. <br /><br />Hope this helps!<br />(and it would be nice if you post your results here when you find out what's wrong)

 

[killian]

Re: 90 yamaha power loss

Thanks for all the help so far.I just came back in from messing with the motor.All three cylinders have good spark (1/2 inch).All external wiring seems to be intact.When I remove plug wires at a fast idle all the cylinders drop but the middle one seems to drop a little less,but not by very much at all.Although the power loss started out as intermittent from the begining of the problem the motor has not idled right.It sounds a little like its choked out and it misses and pops . I removed the air box and it seems like the noise is coming out of the middle carb although when i hand choke each inlet the motor bogs and feul is sucked out of what looks like secondary jets located forward of the butterfly.The fuel system is in good shape all the way through and squeezing the bulb does'nt change anything.This is a motor that is run quite a bit over all in a variety of conditions, some of them rough and wet.I just cant ignore the fact that all this started after the boat sat for over 2 months with half a tank of gas.It points to a feul problem like shellac yet i can find no obvious signs of this.Any more suggestions will be appreciated and I am going to order a manual

 

[ivar]

Re: 90 yamaha power loss

Sounds like some issue with the middle carb. <br /><br />try a Search for "yamaha carbs" or something , I have read about similar problems in an earlier post.

 

[killian]

Re: 90 yamaha power loss

Still working on it.I might just rebuild the carbs or I may break down and take her to the shop.

 

[jray]

Re: 90 yamaha power loss

No one has said anything about overheating. If this is the case then you better get to fixing it before fiddling with too much else. Is the head too hot to touch. It shouldn't get too much hotter than 150 F., warm but won't burn you. <br /><br />OR<br /><br />It could be water in the gas. Try some dry-gas or just get rid of whats in the tank now and start fresh.

 

[FORCEfull]

Re: 90 yamaha power loss

If the float bowls are easy to get to on your carbs....take the one of the problem cylinder and check for any water in the bowl.

 

[Greg Lawrence]

Re: 90 yamaha power loss

choke it when it is bogged. that will tell you if its getting enough fuel or what.

 

[fishingbear5]

Re: 90 yamaha power loss

New member here. I just started having trouble with my 1987 90hp yamaha also. Was out yesterday pulling the grand kids behind the boat at about 3200 rpm when suddenly i lost power. The motor will only run up to 2000 rpm and then no more. When i take it out of gear, it will rev up as high as i want it too. No previous indications that anything was wrong. A friend of mine said it may be the power pack. So far i havent found out what this is or how to test it. If anyone has knowledge of this i would appreciate some feed back. I am also trying some of the things i have read previously on here. Thanks for any and all help. Tight lines

 

[fishingbear5]

Re: 90 yamaha power loss

To those interested in my problem, i found a bad spark plug wire. Replaced the wires and motor runs fine now. Tight lines.