Merc. 115 L4 - No Fuel To Cyl. 3 & 4

[FedUpWithBoatEngines]

I need some help here guys. I have beat my head against every wall trying to figure this out.

This is a 1990 Merc. 115 inline 4. I am getting no fuel into cyl. 3 & 4. There is fuel in the bowl, but no fuel comes up the emultion tubes into the throat of the carbs. The carbs are clean and all passages are clear.

With carbs off the engine they seem to function just as designed. I can hook a shop vac to the carb and pull water up through the emultion tubes with butterfly open.

I am not sure what direction to take please help me before I light this thing on fire.

 

[pigeon laker]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

You will get very little fuel at idle.There is only enough fuel to #3 and #4 carbs for lubrication.They kick in around 1800rpms.If there is still no fuel at these rpms check out the accelerator pump or filter for it.

 

[FedUpWithBoatEngines]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

The accelerator pump is new as the old one had a bad diaphram and was leaking, also there is no fuel filter to worry with at this time.

I should have mentiond before that I was not concerned with idle as the engine runs fine up to 1/4 - 1/2 throttle. I am aware that this engine operates on the top 2 while at or just above idle. It is not until after this where the problem comes into play. Past this throttle position the engine will bog and eventually shut down if you continue at WOT.

While in gear and running I can gas it and clearly see fuel going into cyl. 1 & 2. This is not the case with 3 & 4. There is no fuel going into the cyl. I can however spray intake cleaner into cyl. 3 & 4 and get the engine to rev up to speed.

I simply have no fuel in those cyl. Again keep in mind there is fuel in the bowls of those carbs and all passages are clean and clear.

It just doesn't make sense.

 

[pigeon laker]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

There are 2 fuel filters.A big one near the fuel pump and a small one behind the oil tank.If both are missing maybe there is debris caught somewhere .

 

[ENSIGN]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Check the reed valves and make sure there all in place.

 

[CharlieB]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Tho there is fuel in the bowls, the question is 'How Much?'

Is your fuel PUMP is weak it will not provide enough fuel for much more than an idle,

OR

air leaking INTO the fuel lines, a restriction anywhere from the tank dip tube to the carbs.

Three tests.
Running
Squeeze the primer bulb firm and keep doing it while opening the throttle.

Install a clear hose between the pump and carbs, watch the fuel looking for any air bubbles indicating air sucking into the lines before the pump.

Cranking
Pull the fuel line to the carbs and watch the stream, it should be a strong pulsed flow, @ least 15 GPH or more, any less the engine will starve for fuel, bog and die.

 

[CharlieB]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Oh

and what is the compression?

You need to make sure that there is not any mechanical problem with those cyl's.

 

[FedUpWithBoatEngines]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Thank you all for your help with this.

Compression is cyl 1 125, cyl 2 127, cyl 3 123, cyl 4 125

I did not physicaly measure how much fuel was in the bowl but there should be plenty as the floats are set to specs. There is definately enough in there.

The fuel pump s another item that was redone. I rebuit the pump with new diaphrams, check valves, springs and gaskets. The pump flows fuel well.

I will recheck the lines from the tank to the engine but I suspect these are up to par as well since I am running from a test tank with primer bulb in known wiring order.

I will also check the lines with clear tubing for air bubbles.

The reed valves are new brand new as well. I recheckd them last night to make sure they were instalwed properly. All gaskets are new as well on the reed block.

I know there is supposed to be fuel filters in place but there are none at this time. All lnes are clear of debris.

Thanks again for your replys. Maybe we can figure this thing out as I am totally at a loss as to what to do.

 

[CharlieB]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Carb synch, throttle pick-up roller, and accelerator pump setting are all critical to making mine come in correctly.

 

[FedUpWithBoatEngines]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Carb synch, throttle pick-up roller, and accelerator pump setting are all critical to making mine come in correctly.

Yes these are critical and have been done again and checked and re checked. I'm lost.

 

[sschefer]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Are the piston tops on 3 and 4 clean and shinny?

 

[FedUpWithBoatEngines]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Are the piston tops on 3 and 4 clean and shinny?

Yes piston tops are clean and shiney. No build up on them at all.

 

[sschefer]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Yes piston tops are clean and shiney. No build up on them at all.

Hate to tell you this but that sounds like water intrusion. Could be comming from the exhaust baffle plate on the port side of the engine. It would be best to show what you've found to your mechanic and only mention the exhaust bafflle plate if he seems stumped.

You could try retorquing the plate to specs. 18ft lbs but you need the torque sequence. I can't make the page small enough to attach it.

 

[FedUpWithBoatEngines]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Hate to tell you this but that sounds like water intrusion. Could be comming from the exhaust baffle plate on the port side of the engine. It would be best to show what you've found to your mechanic and only mention the exhaust bafflle plate if he seems stumped.

You could try retorquing the plate to specs. 18ft lbs but you need the torque sequence. I can't make the page small enough to attach it.

The pistons do not look like brand new perfect but they are clean.

I have a Merc. Service Manuel, the torque sequence is in there. I really do not think there is a water intrusion problem. I recently had the exhaust baffle and cover off of the engine and replaced the gaskets. This problem was there before I took the baffle and plate off.

Please continue to pick me over with questions and theories. I will answer or reply to each of them. I have spent much time and coin on this engine it has to run sooner or later right?...

 

[sschefer]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

The pistons do not look like brand new perfect but they are clean.

I have a Merc. Service Manuel, the torque sequence is in there. I really do not think there is a water intrusion problem. I recently had the exhaust baffle and cover off of the engine and replaced the gaskets. This problem was there before I took the baffle and plate off.

On some of these #4 will run pretty clean but #3 usually looks like 1 and 2. The intake cover plates behind the carbs on these are prone to loosening up because if you over torque them they will flex and suck air in behind the carbs. You might want to check them.

The baffle plates are also prone to warping so if you missed that check when you replaced the gaskets you might still have that problem. I hate to say that because you just replaced them and now you'll be questioning them until you can't stand it anymore.

If it was bad reeds you'd likely be seeing some fog comming out of the carbs when it was running. You didn't mention that and it would have caught your eye so I think you can eliminate it.

I'm also assuming that the floats are all set correctly in the carbs and that there is fuel going to the bowls. You can pull the jet cover off and see if you haven't already done that.

If by chance, the needle seats were changed and a piece of old gasket was left behind, the seat will sit high and the needle will close prematurely even though the float hangs correctly.

Just some swags for you to contemplate.. I really can't think of any other reason for your problem.

 

[FedUpWithBoatEngines]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

I hear you there. There is just no plausable reason that I or any other can seem to think of that I have not either already done or checked.

The #3 does have a bit of brown of the top of the piston but very little. #4 is cleaner than 3 but again its not brand new looking.

I still have the 3 & 4 carbs off the engine as well as the reed plate. I will take extra care when re installing them. I have new gaskets for them as well. And yes the reeds are new as well.

For the baffle plates, they fit so darn well. They came right off and gasket clean up was minimal. They looked really good and there was nothing obvious that said hey look at me. I mean they just fit like a glove really. But I guess you never really know until you physicaly check it..

The floats are set to just over 11mm which is within range of the 11.1mm it calls for. There is plenty of fuel in the bowl.

The needle seats were changed and I did remove all old gasket material. Im a real stickler for getting rid of all left overs.

Ponder this.. This engine is on an old POS SeaRay bow rider. I got this for really cheap with the engine and only plan on getting the engine running to go on my flats boat. Anyway.. This boat is scary, rotted floor with a new (old) plywood floor on top of that. It has sat out in the rain and had maybe 400 gallons of water in it when i got it. Is it possible that this boat is so waterlogged, that its so heavy that the engine can not get over the hump and get to speed, therefore no fuel to #3 or #4?? Just a random thought..

 

[sschefer]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Well that's a possibility. Have you had the electrical plate off and taken the injectors out of 3 and 4 and serviced them? They're just mechanical backwards check valves... acutally they're more like spring loaded needle seats. There's also that little 1/8" filter behind the oil tank that no body knows about. Those injectors are where the fuel from the accelerator pump goes so if they're plugged or the filters plugged or the lines are pinched they won't work. Given that you're pushing a barge that might be just enough to cause the problem.

It's just another swag but might be worth looking into.

Steve

 

[FedUpWithBoatEngines]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Hey now were talking. I have not even thought about that. Tomorrow when there is light I will remove those injectors, inspect and clean as necessary. you know I only replaced the accelerator pump because it was leaking like the diaphram was broken. I never even thought about checking the lines from it to the engine..

Thanks so much for everything! Ill post up tomorrow on how it goes.

 

[FedUpWithBoatEngines]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

Ok I got those njectors cleaned out. They were clean with no blckages. The needle was in good shape and the springs also looked good.

Got it all back together and still same deal. Revving the engine can see fuel spray to #1 & #2 but nothing to #3 & #4. Once again I'm lost.

What would make there NOT be enough vacuum to these cyl. to not be able to pull fuel??

 

[sschefer]

Re: Merc. 115 L4 - No Fuel To Cyl. 3 & 4

There's no traditional crankshaft sealing rings in that motor. The sealing rings are between the double roller bearings.

Refresh my memory, can you feel air being pulled in by the carbs?

When you rebuilt the carbs did you double or single gasket the idle circuit covers? They give you two gaskets but I've only used one.