Yamaha 9.9 2 stroke wont run

[maineiac5586]

I have a 2008 yamaha 9.9 2 stroke. Starts intermittently and when it does it starts off running fine and then it shuts off. Electrical is good. Compression 130 both cylinders. Carb has been cleaned and all adjustments set. I took it to a marine mechanic and he thinks it is leaking internally on the intake side of the powerhead. He said fuel is not getting pulled into the crankcase due to pressure loss in the powerhead. He said engine can be fine on the cylinder head side but lose compression inside. This engine is super clean and worth fixing. The mechanic changed the powerhead base gasket, the exhaust cover gasket and the head gasket.
before I pull this apart is it possible the seal that goes from the carb to the intake manifold is not sealing and creating an air leak? It uses a super thin o ring for a seal.

 

[maineiac5586]

I put my finger over the hole that supply's pressure for the fuel pump. I feel air pushing out of it when I pull the starter handle but I dont feel it sucking any air in.

 

[maineiac5586]

Sorry keep adding info. I pulled the fuel hose that goes from the pump to the gas filter cup housing after pulling it over about 20 times. There was a pressure release when I did that. I then pulled the motor over several times expecting to see fuel shooting out from the hose (attached to the fuel pump inlet) and got no fuel pushing out of that hose.

 

[maineiac5586]

I got it to start up it revs strong but after a little bit it starts sneezing until it stalls. I pulled the hose from the fuel pump inlet (pulled it off at the fuel filter cup and while it was running had zero fuel pulsing out of the hose. I looked at the fuel pump diaphragm and all seals and reeds inside pump look fine

 

[racerone]

The fuel pump runs on a positive pressure pulse.------The reed valves open so that is why there is only a wee bit of vacuum at that pulse hole !!-------I would be looking at fuel supply issues to the carburetor.------Does motor keep running when an assistant operates the manual pump ?----Perhaps borrow a fuel tank and hose that are known to be good.

 

[maineiac5586]

Shouldn't I be seeing fuel pulse from the hose coming out of the fuel pump when disconnected with engine running

 

[racerone]

Yes you should be seeing fuel pulsing out.-----So you have a defective pump or no fuel is coming to the pump.----That is why I suggested another tank and hose.----That is why I suggested operating the manual pump !----This should not be hard to figure out.

 

[maineiac5586]

When I squeeze the primer bulb the carb fills up fine. The primer ball gets firm. While running squeezing the bulb has no affect. When the hose is disconnected from the fuel filter cup there is no other connection to the carb. At this point I don't understand why fuel is not pulsing out of the hose from the fuel pump while engine is running. Do you think something in the fuel pump is causing this? The pulse hole in the intake manifold is supplying pressure outwards not sure if it is sucking in at all with engine running

 

[racerone]

When a 2 stroke is running It will provide a POSITIVE pressure pulse to the pump.------There is very little vacuum at this port because reed valves open to pull fuel / air into the crankcase.--------If it keeps running when you operate the manual pump then you need to look at your fuel pump.-----I would investigate / take your fuel apart.----Could be an easy fix !!

 

[maineiac5586]

Ok. I will check that tomorrow. Stay tuned

 

[Sea Rider]

Being a 12 year oldie. Have you inspected the pump's internal main diaphragm to check its condition, probably with hardened, ballooned diaphragm or just assuming that's working right ? There could be air being sucked in through any of the tank's fuel hose connectors and motor missing, dying specially at higher rpm aside from fast idle. If the carb's base o'ring is already hardened and flat, install a new one.

Happy Boating

 

[maineiac5586]

Does anyone know if there is a part number for the o ring on the intake manifold that the carb seals against? Boats.net only shows a whole intake manifold with reeds. And just to clarify these symptoms are present even with the carb not hooked up to the fuel line (after filling the system with fuel from the tank and hose) disconnect fuel line at filter cup and no fuel pulses from hose coming out of fuel pump

 

[Sea Rider]

When primming the hose's bulb must be done with the arrow pointing upwards till the bulb is firm, assume that have done so along opening fully the tank's air vent Have you checked the fuel pump's internal diaphragm condition ?

Happy Boating

 

[maineiac5586]

Yes primed system properly. Looked at fuel pump internals nothing looks abnormal

 

[maineiac5586]

Took carb off engine. When I apply air pressure to the hose attached to the fuel pump (on side of carb) I can blow into the hose and hear that squeaking red valve noise. I cannot suck any air in the other direction however. I also applied air to the hole in the carb that lines up with the hole in the intake for supplying pressure for fuel pump. When I try to apply air through there I get nothing. Air wont move in the pressure direction into that hole in the carb. I am running out of tests unless someone knows another way to test fuel pump.

 

[racerone]

One step at a time.---Install pump on the motor.------Remove outlet from the fuel pump ( hose to the carburetor ) .-------Then operate primer bulb on the hose.----Report what you see.-----I think your pump might be assembled wrong !!-----Or hoses are on wrong !

 

[Sea Rider]

One step at a time.---Install pump on the motor.------Remove outlet from the fuel pump ( hose to the carburetor ) .-------Then operate primer bulb on the hose.----Report what you see.-----I think your pump might be assembled wrong !!-----Or hoses are on wrong !

Might be, remember a time assembling the carb's internal diaphragm backwards, primed the bulb firm with no gasoline filling the carb's bowl, check.

Happy Boating

 

[maineiac5586]

Ok. Installed carb back on motor. Disconnected fuel line at fuel pump. Squeeze primer bulb. Plenty of fuel coming out of hose that goes to fuel pump. Attached hose to fuel pump squeezed primer bulb. Carb filled with gas until the inlet needle in carb closed (float came up to shut off fuel supply.)
removed hose from fuel pump. Pulled engine over several times. Observed no fuel pulsing out of fuel pump hose opening.
note. When fuel pump was assembled I blew into hose that goes on fuel pump nipple. I could hear normal squeak type sound that I have heard on other fuel pumps. I was unable to suck any air on the same hose. Only able to blow into it.
this damn outboard is so simple I dont get how it can be this difficult. Please help

 

[maineiac5586]

I dont understand how I can feel air pressure exiting the hole on the intake manifold (the hole that lines up with the carb hole) when pulling the starter rope can feel pressure coming out. Shouldn't that mean that pressure should allow fuel to squirt out of the fuel pump hose fitting when pulled over to start.
what if I remove the leaf check valves from the pump and then re assembled the pump and bolt the carb back on. Would that allow fuel to squirt out of fuel pump hose? Just running out of tests

 

[maineiac5586]

I took the metal leaf plates out of the fuel pump and re assembled pump. Now when I pull it over fuel pulses out of fuel pump nipple with hose removed. I was able to start engine and run for a while like this.
any suggestions?