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

[FedUpWithBoatEngines]

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

Only use 1 gasket. The second gasket is for the other gen. carb.

And yes there is suction on those cyl. when openng the throttle.

On the balance tube. Should vacuum be present on the top cyl. as well as the bottom when running??

 

[FedUpWithBoatEngines]

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

Any other thoughts?

 

[sschefer]

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

Any other thoughts?

No not at the moment. The only other thing I can think of is the idle air screws that are sealed at the factory. There's red sealant on top of them and your not supposed to mess with them. You can remove them but make sure you turn them in and count the turns first then take them out. If they are plugged they carbs won't work right. I've never messed with them.

The only other suggestion I have is to buy a set of WME's on ebay and swap them out with yours. They usually go pretty cheap.. I think CharlieB still has a set that I gave him. He might be willing to part with them. You could PM him and ask.

 

[FedUpWithBoatEngines]

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

Yea I dont mess with those screws. I know they are not clogged though cause I can spray intake cleaner in the hole while the engine is running and it affects how it runs.

I dont think a new set of carbs will make a difference. I feel that there is something else wrong.

Does anyone know for sure, that while the engine is in neutral, out of the water and running will you be able to see fuel go to carbs 3 or 4 while revving the engine??

 

[CharlieB]

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

Yes, once throttle opening is cracked, suddenly, intake vacuum drops, airflow thru the lower carbs pulls fuel same as the top carbs.

Have you tried placing your hand over one of the carbs, cracking the throttle and 'feeling' the vacuum? Repeat on every carb. They should all feel quite the same.

Sometimes this works to pull a drop of water thru a carb and clear it, not that this is your current problem.

I think we are missing something very fundamental, and once we find it, it will be another of those D'oh moments.

I still have the set of carbs, but they are for a 90, not a 115. Still could be a worthwhile test.

Just for giggles, stick your timing light on 3 or 4 and watch spark while moving the throttle arm, looking for a failing trigger wire causing you to lose spark off idle position.

 

[sschefer]

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

I'm thinking it's time for a on the water test. The injectors transition you to the carbs and the carbs come on at around 2200 rpm.

With no backpressure to hold the fuel in the cylinders like it's supposed to then those cylinders may not ever fire. To tell you the truth, I never checked it that close at idle on the hose. I was so happy when my finally idled right I ran straight up to the lake and blew the lower unit When I got back home I bought a used l/u and then sold the motor. That took care of my frustration with that motor.

 

[CharlieB]

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

Mine starts pulling fuel as soon as the throttle plate are opened, the accelerator pump reduces the lean cough, hesitation, bog, to nil.

All 4 are in as low as 1400 RPM, acceleration pump continues to assist during throttle opening to WOT, even if just slowly 'bumping' throttle in small increments.

I am wondering if somehow he doesn't have an intake leak BETWEEN 3 & 4 which is canceling out the vacuum pulses of each other. Which is why I suggest the hand choke test, to feel for vacuum once the throttle plates are opened.

If there is air flow thru the carbs then there is still a problem within the carbs.

With the compression #'s he has then I doubt that a ring problem is limiting crankcase vacuum, unless there is a serious intake leak between the two cyls.

Stick the palm of your hand flat over each lower carb as if you are trying to block off ALL air. Crack the throttle, describe what you feel on each lower cyl.

Then crack the throttle and try the same to an upper, it should FLOOD and die.

On another note, a restricted fuel line between 2 & 3 COULD supply enough fuel to fill the lower 2 til the throttle is opened, then they could rapidly run out. However, they should still run for at leat 10 seconds or more til they ran low.

Even a broken trigger lead that contacts and has spark at an idle yet fails when advanced, the engine would STILL PUMP AIR and draw fuel.

I still think he is missing something in the fuel line and/or lower carbs.

 

[FedUpWithBoatEngines]

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

Thanks again guys.

I can cover the carb by hand and feel the suction it creates. In my opinion I think they are all equal as best I can tell.

I checked for intake leaks around the carb base, reed plate base and crank cover with intake cleaner. I could not get any change whilespraying the intake cleaner in every spot around those areas.

I just don't know what I could be missing in the carbs or fuel lines. I have taken compressed air and blown through the fuel lines I know they are clear. And even if those were the issue there is fuel in the bowl. It should still pull fuel. The engine will run for over 1 min at idle with fuel bowl full and fuel line disconnected from the fuel tank.

 

[CharlieB]

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

OK, if you can feel vacuum on both of the lower carbs then the motor is pumping air which tends to rule out in internal intake manifold leak between the two cyls.

Blowing air thru the fuel lines still does not rule out a 'flap' from an internal tear acting like a valve, limiting fuel flow. Replace the line between #'s 2 & 3.

When you 'choked' the lower carbs did it pull fuel and wet your hand or cause the cyl to fire when you first pulled your hand away?

Have you verified spark on 3 & 4 with a timing light or spark tester with the ignition ADVANCED, as when the throttle is moved?

Exhaust HEAT and resulting high pressure flow out the exhaust port contributes to 'overlap' flow, increasing crankcase vacuum, which increases intake flow.

Are the spark plugs wetted with fuel at all?

 

[FedUpWithBoatEngines]

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

Okay back again. I replaced the fuel lines and the problem is still there.

When I choke the carbs by hand fuel is not drawn up and the idle speed does not change, and there is very little vacuum present at idle. If you manualy choke #1 or #2 engine will die and wet your hand.

What seperates the cylinders internally from eachother in the crank case? Is it just the seals for the bearings? If one of these are blown do you think this could cause the issues I am having?

 

[sschefer]

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

Internally it's just the bearing seals. These seals are between the rollers on the bearings. You have double roller mains. I seriously doubt that's the problem.

Given that we've gone through every other possible cause, the only thing I can think of that would cause you to lose both cylinders is a rod strike on the front half or a cracked cylinder below the exhaust port.

You can put a pressure gauge on the bleeder circuit and see how much pressure you've got. Should be 3-6 lbs I beleive, check the manual.

I don't think a leakdown test would tell you much if you've got good compression.

If it was me. I'd be frustrated enough at this point to just tear it down and go through it. You can tear it down and have it back together in no time at all. These are real simple motors inside. The only special tool you need is a flywheel puller.

 

[FedUpWithBoatEngines]

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

I do think its time to rip this thing apart as well.

Pressure is present on the bottom side of the bleed line, and when we took it off there was a good amount of fuel/oil coming from it.

Vacuum is present on the top side. I do not have a guage that I can measure either of these with.

We also have done a leak down but the results were all good there.

When we had the reed plats off we inspected the inside of the cylinders as much as we could and everything looked like it was supposed to.

If the seal on the crank shaft is bad, would it swap the intake charge between cylinders??

Okay i think thats it for sure, it comes off tomorrow...

 

[FedUpWithBoatEngines]

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

Okay so tonight we pulled the reed plate off and played with the main bearing between 3 & 4. I can spray cleaner in the bearing and it will seep down to the number 4 cylinder. Not sure how much of a "seal" the seals actually create. But we could not duplicate this in 1-2 or 2-3, only 3-4.

We pulled the powerhead and got into the engine. Got the crank cover off and the crank shaft out. Everything looks peachy in here. No visible cracks and no sign of any rod strike anywhere. We did find that one of the check valves was sticking in the closed position but other than that everything looks good.

Can you think of anything special I should be looking for while inside here that I may be overlooking.

 

[sschefer]

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

There's not much there except that possible main bearing seal problem. Those are double roller bearings and the two seals sit in the middle of the bearing sets. You'll have to pull the crank to replace them and it's no fun putting those bearings back in. You'll be tempted to load them up with 2-4-C grease but try to keep it to a minimum.

 

[Dave1027]

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

I might be stating the obvious but I hope you realize no gas flows to the bottom cylinders until about 1800 rpm. This is because the idle circuit is capped off in the bottom two carbs. It only has a high speed circuit. Are you seeing spark to the bottom cyls?

 

[FedUpWithBoatEngines]

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

I might be stating the obvious but I hope you realize no gas flows to the bottom cylinders until about 1800 rpm. This is because the idle circuit is capped off in the bottom two carbs. It only has a high speed circuit. Are you seeing spark to the bottom cyls?

I understand that. It's not idle I have a problem with.

 

[FedUpWithBoatEngines]

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

There's not much there except that possible main bearing seal problem. Those are double roller bearings and the two seals sit in the middle of the bearing sets. You'll have to pull the crank to replace them and it's no fun putting those bearings back in. You'll be tempted to load them up with 2-4-C grease but try to keep it to a minimum.

The seals look ok but there was that slight seepage from 3 to 4 I mentioned in one of my previous posts.

 

[sschefer]

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

The seals look ok but there was that slight seepage from 3 to 4 I mentioned in one of my previous posts.

There's going to be some. Mine had a tendency to pool oil in #4 but it didn't have the problems you're having.

 

[FedUpWithBoatEngines]

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

I have no clue what the deal is with this engine. I think I am going to have a tech take a look at it. I am at wits end and have no clue where to go from here. Bad thing is that my mechanic is 2 weeks out right now. I guess that gives me more time to fiddle with it on my own.

 

[sschefer]

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

I have no clue what the deal is with this engine. I think I am going to have a tech take a look at it. I am at wits end and have no clue where to go from here. Bad thing is that my mechanic is 2 weeks out right now. I guess that gives me more time to fiddle with it on my own.

I have to admit, it's got me baffled too. None of it makes any sense. You've checked everything I can think of and several I didn't but nothing seems out of whack enough to make it do what it's doing. All the carbs pull the same amount of air throught the venturies regardless of the motor type. It's just the way the two stroke works. Yet yours isn't pulling air on 3 and 4. My 2+2 pulled good air on all four all the time.

Wierd...