Yamaha blues.....again.

[Spot77]

So some of you have read my other posts about a few issues I've had with my 93 Yamaha 85hp 2 stroke. All of those issues were pretty easily fixed thanks to all of your help and a little bit of luck.

Recently I've started having a new problem. The boat doesn't want to get on plane now with more than just me onboard. The boat used to leap up on plane even with 4 fat old guys onboard.:pp. Now with just my wife and me onboard I have to sit all the way up front and the poor thing struggles.

Last year the boat would run in the low 40's with 2 people onboard; this year best is about mid 30's.

The boat idles great and runs up to max rpm's at home on the hose just as smooth as can be, but when on the water.....well......different story. I trim down and throttle up as normal and the boat begins to jump, but then starts to bog down in the midrange of rpms and feels like it's starting to ventilate (it isn't, but that's sort of what it sounds and feels like.)

I marked my prop and hub and noticed that the prop was spinning on the hub a little so I replaced the prop AND hub hoping that would fix the problem but it didn't. Earlier in the year I had the boat serviced and a leakdown test was done with great results (Less than 2% if I recall correctly.) The fuel/water separator was changed as was the fuel filter. Spark plugs are new. Fuel is all fresh and treated.

I did some searching on here and other forums and found some things that could be the solution, but I thought I would describe my problem and see if anybody could help narrow down what the problem could be. I love my Yamaha and my little Cajun bass boat, so I'd really hate to have to start seriously thinking about repowering.:helpsmilie:


ANY help or suggestions are greatly appreciated. Thanks!

[Spot77]

Been a few days so I thought I'd give myself a free bump to the top.:cool:

[bottom scratcher]

Idling on the hose won't tell anything and running to max on the hose is dangerous. You have to check the idle in the water as the back pressure the water creates changes things. You can try it with a cut down barrel full of water for the idle. As for high speed, you may have dirty high speed jets. At the bottom of the carb bowl is a brass plug. Behind it is the high speed jet which you can remove to clean. I would suggest you get some Startron and put about 5 ounces in the separator. Take the boat down to the ramp and idle it for about 5 minutes and the run it hard to clean it out. I suggested this to one of the guys on this board and I was shocked. He regained the original top end of 31 knots and proceeded to get 36 knots at top end which he had never seen before ( He had bought the boat used.). Good luck.

[Bob H.]

If you don't want to repower keep rpm's below 2,000 when on a flusher or when not underway. You don't learn anything without a load anyway. Holeshots with "4 fat old guys onboard" isn't helping the longevity of an 85hp or your prop. Run a fuel system cleaner like Chemtrol for a bit to clean out the carbs. Now would be a good time to check the fuel filter too.

[Spot77]

The carbs were just cleaned and adjusted a month ago, and the filters were changed then too.

The "4 fat guys on board" reference was just a facetious way of saying that the boat can easily handle that kind of load; it's not as if I'm trying to win the on water version of NASCAR or anything.

I'll try both suggestions with regards to the Startron and Chemtrol. It's certainly the cheapest thing to try first. But having the work done recently (and then taken back to have the carbs re-adjusted) gives me the feeling that something worse could be at play.

[Bob H.]

Sorry, but you set yourself up based on your description of the problems and your actions. Did the problem start before or after the carbs had work done? Does the engine start to accelerate and then stumble (high speed mixture adjustment)? I don't let anybody touch my toys. Not sure what you think the shop did versus what you paid. Prop slippage could have been the sole cause of your problems and your description didn't establish a relationship for the corrective actions you've taken, prop and carb work. A timeline of events and actions would help (your initial post mentioned nothing about carb work).

[Spot77]

Sorry, but you set yourself up based on your description of the problems and your actions. Did the problem start before or after the carbs had work done? Does the engine start to accelerate and then stumble (high speed mixture adjustment)? I don't let anybody touch my toys. Not sure what you think the shop did versus what you paid. Prop slippage could have been the sole cause of your problems and your description didn't establish a relationship for the corrective actions you've taken, prop and carb work. A timeline of events and actions would help (your initial post mentioned nothing about carb work).


Ok.....I'll start from the very begining. Let's see. Dewinterized the boat in March. idled rough at home (figured it just needed some fresh gas perhaps. I did top off the tank before winterizing and added stabilizer to the fuel.) Took the boat out and it wouldn't run unless the choke was held open. Parked it for a few weeks then took the boat to Fairwinds and they cleaned and adjusted the carbs, changed the fuel filter and separator.

Got the boat back, launched and ran great wide open but then wouldn't idle when coming back into the 6mph zone (idled away from the ramp just fine.) Took the boat back to Fairwinds, they re-adjusted the carbs and all was well. In late May I took the boat for a week on the Pocomoke River and she ran great; no problems at all. About two weeks after that (into early June now) I had my two kids with me (7 and 11....certainly not big brutes)on the Magothy and the boat was having issues planing (You mentioned above "Does the engine start to accelerate and then stumble (high speed mixture adjustment)? " )and that pretty accurately describes what's happening. Not being a mechanic at all, "High Speed Mixture Adjustment" sounds like it could be the problem, but I won't pretend to know. The new prop came after I was already having issues with the motor. I wanted a spare prop anyway, so it seemed like the time was right to get one. Not sure how familiar you are with bass boats, but they can be a little picky about getting on plane if the trim isn't right; they tend to ventilate easily and the way the boat felt reminded me of when I first learned to handle the boat...thus the bright idea to check the prop since I knew I was trimming the boat correctly.)

The more weight onboard (I.E. another person) the more pronounced the problem is.

Hope this helps, and thanks for the advice.

[gw204]

Have you run a compression test yet?

[Spot77]

Have you run a compression test yet?

I'm going to do that today. My neighbor has a tester.

I was told that the leakdown test that was done on the boat was a better test to perform and I had that done earlier in the year with excellent results.......but I guess that was then and this is now...:rolleyes: So I'll do that today.