Fuel issues?

[caseymx]

I have a 1976 Johnson 115 "sea horse". I'm at my ends with it.. Smash the throttle and will scat, runs great for about 15 seconds or so and then dies down and runs rough at slightly above idle with throttle still wide open. I can back off and let it idle a few minutes and can do it again. Otherwise it will not run consistantly unless I keep it under 1/3 throttle. Everything from the tank to the motor is new. Line, bulb, connections, pickup tube, etc. I've been into both carbs and are clean as a whistle and floats seem to be adjusted good. The guy I bought it from days it has a new fuel pump. I disconected the discharge of the pump and let it idle and it is pumping but I'm not sure if it's good enough. It seems I'm draining the carbs when running above 1/2 throttle. What am I missing?

 

[ondarvr]

Re: Fuel issues?

Try pumping the squeeze bulb as it dies, if that works you may have a fuel pump issue, but it could be an air leak too.

 

[mrcj001]

Re: Fuel issues?

Did you use Sierra Kits on the carbs? If you did, order OEM from OMC.

Double check the float hight. My `75 135 is very simular.

Hold the carb right side up and make sure the float doesnt dangle more that 1" +/- 1/8 "

 

[caseymx]

Re: Fuel issues?

I didn't install any kits in the carbs but, I have been suspecting that the guy I bought it from did. The internals on the carbs were too new looking. My next guess was gonna be that he put the wrong kits in or something. The needle valve just looks too small and the float too big to be supporting two cylinders. this supports what you said mrcj. I was wondering if it was possible to get a kit that would fit but not work correctly. I think he did all of this to sell it but never ran it other than on the muffs.

 

[Daviet]

Re: Fuel issues?

When you had the carbs apart did you remove and clean the high speed jets?

 

[caseymx]

Re: Fuel issues?

Yes, I looked at the high speed jets. They are huge and clean as a whistle. The high speed jets are working fine, it runs wot for about 10 seconds or so.

 

[caseymx]

Re: Fuel issues?

Pulled one of the carbs off yesterday again. The float looks good but I keep looking at the needle and seat. This thing just looks way too small to be supplying enough fuel for two cylinders. I keep comparing to the size of the two power jets and thinking there is no way this thing is keeping up with these. These power jets are huge!
Is there any possible way someone could have put the wrong needle and seat in these carbs? Looking at the manual, I think there is two different carbs that could go on this motor. After comparing, I have the performance carbs. I'm wondering if the guy I bought it from replaced them with the needle and seat for the standard carbs. Is this physically possible?

 

[ondarvr]

Re: Fuel issues?

Try pumping the squeeze bulb as it dies, if that works you may have a fuel pump issue, but it could be an air leak too.

Did you try this?

Also hit the choke as it dies and see what happens.

 

[caseymx]

Re: Fuel issues?

I haven't actually pumped it while it's running but once it dies down and I pull it back to idle, the bulb is still tight. The pump is new but I still haven't ruled it out either. When it does die down, I can bump the choke and it does pick up a little but it only works once or twice then then there's no fuel left in the bowl, I'm assuming, to do anything else.

 

[wilde1j]

Re: Fuel issues?

Some things to try if you suspect a fuel delivery problem, which can have a number of causes, such as:
. air leak on pump suction side (bad clamp, cracked hose, cracked tank pickup tube, etc., etc.)
. malfunctioning anti-siphon valve
. plugged tank vent
. trash blocking tank pickup screen
. plugged fuel filter
. collapsed fuel line
. water or trash in internal and/or external filter
. try squeezing primer bulb or activating the choke/primer when RPM sag
. try an alternate fuel source (i.e. portable tank)

FUEL PUMP OUTPUT TEST

1) Pull the safety lanyard so the motor can't start
2) Disconnect the pump outlet hose
3) Crank engine ... should get long strong spurts, any less is reason to replace/rebuild

OR

Put a pressure gauge teed into pump outlet line ... should read ~ 3 to 6 psig on a good pump with engine running.

 

[ondarvr]

Re: Fuel issues?

I haven't actually pumped it while it's running but once it dies down and I pull it back to idle, the bulb is still tight. The pump is new but I still haven't ruled it out either. When it does die down, I can bump the choke and it does pick up a little but it only works once or twice then then there's no fuel left in the bowl, I'm assuming, to do anything else.

The bulb should be a little soft after the motor starts because at that point its under a slight vacuum with fuel just flowing through it. Bulbs go bad, some don't even work when new, so they are always suspect. If the float bowl is empty squeezing the bulb should fill it rapidly.

Have you adjusted the float level yet? With the carb upside down it should be level and parallel to the float bowl gasket surface.

 

[caseymx]

Re: Fuel issues?

I've checked the float and everything is new to the motor. Bulb, hose, etc. Haven't tried the spare tank thing yet but it has crossed my mind. I was wondering about the fuel pump pressure tho. I ran the motor and then shut it down. Then I disconnected the discharge line off of the pump and added a small line to reach outside the cowling to keep fuel out of it. Then cranked it and let it idle and it was pumping but just kinda rolling out the end if the hose and I could just about stop the flow by putting my thumb over it. It is a new pump but I didn't install it.

 

[ondarvr]

Re: Fuel issues?

Try pumping the squeeze bulb as it dies, if that works you may have a fuel pump issue, but it could be an air leak too.

Back to this.

 

[caseymx]

Re: Fuel issues?

Ok, managed to get a chance today to try things. This is what I found, when it starts starving, the bulb is hard but if I squeeze it hard the motor pick up and wants to run. Fuel pump?

 

[wilde1j]

Re: Fuel issues?

Most likely.

 

[kenmyfam]

Re: Fuel issues?

Yep !!!!! or a huge air intrusion somewhere.
My money is on the pump though.

 

[caseymx]

Re: Fuel issues?

Update..
Replaced the fuel pump last week and had a chance to run it this weekend. It is alot better but I still cannot maintain over 3/4 throttle. The starving effect is not quite as bad. I also replaced the crankcase line that operates the pump. I think my next step is to try a portable tank to eliminate everything back to the tank. The new fuel pump did confirm that it is definately a fuel delivery issue.

 

[caseymx]

Re: Fuel issues?

Ok, I managed to try a portable, small tank with about 5' of hose and primer. The hose and primer looked to be the same size as mine, but mine goes from the tank and connects to a bulkhead fitting and is 5/16" line from the bulkhead fitting to the motor. The primer hose almost looks to be 1/4". Well with the small tank and primer, the motor ran worse than it ever has. I couldn't even get to 1/4 throttle from the get go. I hooked my on board tank line back up and can manage to get about 1/2 to maybe 3/4 throttle.
Now I'm wondering if my primer setup is too small. I think that I may purchase a 5/16" primer setup or change everything to 3/8". I would think 1/4" would be large enough or even 5/16".?. Would there possibly be a problem with using 1/4" fuel line or primer hose? I just keep picturing those 2 huge power jets in each of the carbs! I'm almost to the point of bypassing the fuel pump and adding an in line electric pump.

 

[emdsapmgr]

Re: Fuel issues?

1/4" hose is no longer used for fuel-it is used for remote oil tanks only. I would not run any V4 on old 1/4" fuel hose-it won't supply enough fuel. Fuel hose today is either 5/16" or 3/8". Your 115 should run fine on 5/16" hose. V6 engines run on 3/8" line: it won't hurt if you install 3/8" line instead. While you are checking your fuel setup, make sure the brass hose barb coming out of the built-in fuel tank is at least 5/16" in size.

 

[caseymx]

Re: Fuel issues?

After some more troubleshooting, I have come to the conclusion that the restriction is somewhere after the fuel pump. Everything is clear and sealed to the pump and the pump is new. Plenty of fuel flow when I pump the primer. I pulled the drain plugs out of both carbs and drained all of the fuel. Then hooked the line back to the motor and started priming. It's really tough to get fuel into the bowls. I can hear it spraying into the bowls but it's flowing. Just seems slow. I am really leaning towards the floats, needles and seats. The guy did some work to the motor before I bought it and I'm pretty sure he didn't run it other than on the muffs. I can't find any reciepts and he can't remember if he replaced any of that. I'm thinking the wrong parts were put in the carbs. I'm not sure if this is possible but I think I'm gonna order oem floats, needles and seats.