What is wrong with my T8 - need some input

Enniberg

Enniberg

Well-Known Member
My Yamaha T8 has been very easy to start and always ran very smootly.
That is until last weekend - I had been using it for trolling for a couple of hours, but then after using the main to move from one spot to another, it suddenly was very hard to start, and when it finally ran, it appeared sluggish as if the carb was flooded, or choke sticking.
I also noticed that there is fuel in the water behind the boat.
What could be wrong?
I have been running the kicker from a portable tank and there is no filter other than the small one on the motor.
 
One of 2 things..hole in fuel pump diaphragm, or stuck open thermostat...either will cause the crankcase to overfill with unburned fuel. That is what you are seeing on the water as it pukes out. This isn't a guess...this is what you will find.
 
profisher - I really appreciate your feedback. I guess I will have a look at the thermostat first, and if it is working properly, then it is the fuel pump.

I should add though that the oil looks clean and to me it looked like the level had not increases noticeably.

Boat is in Ukee. I will have to get this fixed as soon as I get back over.
 
The t-stat is easy to check...it should be closed when engine is cold and will open up if thrown in boiling water. The diaphragm can appear ok but can still be allowing raw fuel to pass into the engine. Both are easy fixes that you can do yourself. I carry spares of both for my 9.9 as I can't afford to e down especially when working out of town in camp.
 
Second year I owned mine it wouldn't run right. Really pissed me off. Turned out the carb had something in it. Had it rebuilt. No issues last 2 years.
 
I have a yamaha T8 and it ran great the first year. Same thing second year nothing but problems cleaned the carb several times. Really pissed me off to the point I probably will never buy another yamaha. Bought new carb and now seems to run but i still don't have much confidence in it. just try and buy a new carb for these things now they are back ordered 2-3 months. Sounds like yamaha has a problem with these engines/carbs and try calling yamaha they don't give a chit.
 
Jimmy said:
I have a yamaha T8 and it ran great the first year. Same thing second year nothing but problems cleaned the carb several times. Really pissed me off to the point I probably will never buy another yamaha. Bought new carb and now seems to run but i still don't have much confidence in it. just try and buy a new carb for these things now they are back ordered 2-3 months. Sounds like yamaha has a problem with these engines/carbs and try calling yamaha they don't give a chit.
Click to expand...

I believe that generally the T8 is considered the gold standard in kicker motors. Mine is several years old and prior to this issue I am dealing with now, it has never given me grief.
 
Had a major problem with my Yami 9.9 last year making oil and fouling out plugs after a few hours with a little oil/gas sheen on the water. You could change the engine oil and plugs and it would run fine until it made oil (adding gas to the motor oil) and fouled out the plugs again. You can tell if it has made a lot of oil as when you pull the dipstick it will flow up out of it and may appear thin.

Pro is right in that the fuel pump (Pin hole leak in the diaphragm allowing fuel to get into the valve train and down into the oil reserve) or thermostat can be the problem but there are other causes, most notably the carb which turned out to be the problem for me.

In my case we replaced the plugs, thermostat, oil and the fuel pump with the new water cooled model which did not solve the problem.

One dealer replaced the enrichment circuit, oil and plugs, ran it in the test tank for an hour and said it was fixed, but had the same problem with the motor making oil and fouling out the plugs after a day fishing.

Took it to another shop who took the motor apart and cleaned everything especially the exhaust which was all gunked up as a result on being run so much while not operating correctly and did some other work. Motor ran great in the test tank for a few hours but once back on the boat and ran longer, it had the same problem – good size bill. Took it back to them and they swapped out the carb for free and the problem was solved.

Conclusion; it was always the carb that was the problem. Those carbs have some tiny passages which can get clogged. The motor runs like new now and not just for a few hours. The positive is that I now know a lot more about these motors. If it happens again I would check the fuel pump diaphragm by holding it up to the light for a pin hole leak and if OK put it back or buy a new one to be on the safe side, then clean and rebuild the carb. I would also check the thermostat with a thermometer in water on the stove to see at what temperature it opens or just replace it, they are not that pricy.
 
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Too bad they don't give you a choice of thermostat heat ranges.........

If it's making oil, it's running too cold........

I was also told that carburated engines are worse for making oil than fuel injected......
 
Over the last decade I went through 2 T8's and one T9.9 and with the exception of a buggered fuel diaphragm on one of the T8's, I NEVER had the carb or T-stat issues I'm hearing here.

But check this out---back in my Yammie days I spent a huge amount of time on Yamaha outboard forums (mainly because I wanted to keep my F150 in tip-top shape and wanted to learn how to do all the maintenance myself)

The one thing I learned from reading lots of posts about Yamaha and Honda kickers is this-- outboard manufacturers put that drain **** in the carb float bowl for a reason---they want you to drain the bowl when you're not using the outboard

I now have a Honda 9.9 and based on all that reading about kickers from the guys who work on them, I religiously drain the carb bowl if the boats going to be sitting unused for more then a week. The newer Hondas actually have the float bowls plumbed out so when you twist the fuel ****, the gas drains out of a hole just next to the impeller pee-hole. Easy-peasy (and a bit greener then the Yammies because you can catch the gas in a container instead of sopping it up with a rag or draining it down the leg into the....never mind...)

I'm not saying that keeping the float bowl drained will solve all your kicker woes but it will absolutely help take a gummed-up carb out of the mix when you're troubleshooting a cranky kicker (if you're filtering your fuel, that is...) ---both brands have very narrow jets---you can imagine it doesn't take much to clog them or impede the flow of fuel---

My Honda 9.9 has maintained sewing-machine status for two straight years now--- whether it helps or not, I also dope my gas with Yamaha ring-free---expensive habit but more constructive then cocaine
 
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Good point on draining the fuel Eric. I always used to do that on my previous Arima with a carbed main engine. I have never drained the carb on the T8 - it even sat for 6+ months last winter. However, I always have good dose of marine Sta-Bil in the tank.

I do need to finally get my kicker plumbed to the main tank, so the fuel goes through the 10 micron filter.

The philosophy behind the portable was to have the motors connected to separate fuel sources in case I get a dose of bad fuel at the fuel dock, but that does not seem to be working as planned.
 
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WOW you won't even find certified mechanics with such precise internet diagnostic. if the engines making oil your dipstick should indicate it, dirty carb fouled plugs ect.. there's a reason REAL mechanics have a checklist. check the oil look for a red ting or fuel smell. check your spark and spark plugs inferred temp guns are relatively cheap and great at checking the operating temp without pulling the thermostat. a tiny bit a of dirt or water in the carb and you also get the exact issues you stated.
 
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combover said:
WOW you won't even find certified mechanics with such precise internet diagnostic. if the engines making oil your dipstick should indicate it, dirty carb fouled plugs ect.. there's a reason REAL mechanics have a checklist. check the oil look for a red ting or fuel smell. check your spark and spark plugs inferred temp guns are relatively cheap and great at checking the operating temp without pulling the thermostat. a tiny bit a of dirt or water in the carb and you also get the exact issues you stated.
Click to expand...

Oil is bronze and clean. Level does not appear to have changed.
I have one of those infrared thermometers, never used it for anything other than measuring the heat on my barbecue ;)
 
I've had the unfortunate pleasure of having constant problems with my T8, the first issue was with a linkage on the carb. I took it in and they repaired it. Now I can't keep the darn thing running for more than 10 minutes and it dies. Mine is back in the shop for the professionals to deal with. Good luck, I hope it's an easy fix for you.
 
I would still check the t-stat by eye as it is only 2 screws and I have never damaged or needed to replace a gasket after checking it. Plus they are 2 bolts that should be removed and lubed up once in awhile so they don't seize in place and break off down the road.
 
A buddy of mine had a look at it today, he phoned me and said he found some water in there, but not a whole lot (his words approximately). Does that make sense for the symptoms I was seeing, or is it likely another unrelated issue?
 
Any water in the carb would cause the problem. Not sure why you would see raw fuel on the water behind the boat but it explains it running crappy.
 
Somewhat related to your issues...the fuel pump can run hot from engine heat being transfered to it. (I know the design should allow for that BUT not everything works as advertised )
I have a 9.9, cousin and uncle too, after fuel problems for a year, we all ran a small piece of ss tubing along the side of the fuel pump body - about 2" long ( ty wrap or JB weld works ). Then run the 'telltale' (cooling water discharge) tubing to the ss tubing before it goes to the cowl and then out. This keeps the fuel pump body much cooler and you have less chance of pump problems/ diaphram issues
 
And this engine is the "gold standard"?.........

Don't think I'll be buying one any time soon......
 
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