Engine help

[dfab]

Hello all,
I have a 93 Yamaha 175 2 stroke that is giving me trouble and I don't want to throw parts at it.
When I accelerate after getting out of the harbor I can only get the engine up to 2900 RPM sometimes it creeps to3300 but that's it
1. All cylinder's are firing used a spark tester.
2. If I put the engine in neutral I can get all the RPM I want
3. Did fuel sample after the primer bulb , no water or contaminants
4 No visible warning lights or alarms are sounding
5. Previous owner would replace the coolant sensors yearly, don't know why.
6. The air intakes are clear
7. Water out of the tell tail is cold , should that be cold or hot?
8. Thermos stats are a year old.
9. it seems to me that its going into de rate
10. with the engine cover off I can see the throttle has a full stroke.

 

[DennisG01]

It could be a number of things, but start with "free" things. Fuel starvation... clogged vent, collapsed vent/supply hose, internally failing fuel hose(s), clogged pickup, clogged AS valve. The easiest way to eliminate all of these things is to use a portable fuel tank plumbed right to the engine. If the problem goes away, then you start backtracking to figure out which one of those it is. If the problem still persists, then the issue is at the engine. FYI, throttling up in neutral doesn't mean anything.

 

[seasick]

As Dennis said, fuel starvation is the most likely cause. The tests are different for injected vs. carbed motors.
Also Dennis's recommendation to try a portable fuel tank is the simplest way to isolate a lot of potential problem areas. Start by connecting the line form the portable tank directly to the motor bypassing the filter and primer bulb. Take a run and see how thigs are. If the same problem occurs, the issue is in the motor usually.( some models with lift pumps may work OK on the portable tank but not on the main tank) If it doesn't , the problem is most likely in the fuel delivery system, tank, vent, filter, primer etc.

 

[dfab]

that was my next question abut at what point to connect the fuel line. I will connect after the strainer on the engine. I wont get a chance to do this till after the storm coming up the coast.
Out of Smith cove Gloucester Ma , sounds like it might get interesting on Sunday.
Thank you for the info every one.

 

[seasick]

Good luck with the storm. Hopefully it will stay on its eastern track

 

[dfab]

Well I finally got out to the boat with a portable fuel tank, went through 2.5 gallons of fuel. The boat was a totally different animal,
So new fuel lines and a filter to start and a more in-depth fuel sample.
Thank you all for your help

 

[blindmullet]

I had a 115 that would act like that and it ended up being the CDI box. You have to use a DVA attachment on your multimeter.

Does your motors warning beeper work? Just want to make sure it's not going into limp mode.

 

[seasick]

That's good news since it shows that the motor is OK.
Dennis mentioned the tank venting. It may be blocked. To check run with the gas cap off. If the motor runs well, your vent is clogged.
Additions tests:. Take off the external fuel filter and pour the contents into a glass jar. Let it sit for 15-20 minutes to see if layers develop. Also smell the gas. Bad old gas smells bad. Replace that filter and prime it using the primer bulb. It will take a lot of squeezes to fill. Eventually the primer bulb should get firm.
. If all works well, great. If not, connect the portable tank using a coupler to the fuel line that connects to the tank pickup. That will add the primer bulb but not the anti-siphon valve. If the motor runs poorly, either the fuel line is bad or the primer is bad. It motor runs good, you may have a bad anti-siphon valve. Generally for outboards, you don't need to have an anti-siphon valve, a regular brass fitting will do.