Logo
FULL SITE MENU

Carb problems, still

D

douglasnc

Contributing Member
Hi everyone, Well this carb is getting the better of me so I thought i'd see what everyone here thinks i'm doing wrong.. It's a mercarb 2 barrow. It is still fowling my new plugs in this 1993 3.0LX... Put a carb kit in it, Adjusted the float level at 14mm and the drop at 27mm's...Rechecked it several times before mounting it ,but carb is still dripping fuel into intake and flooding cylinders.Not as bad as it was, but still bad enough to flood after sitting over night..Seems to be running rich also. When I tried to adjust the air mix screw, no setting I turned it to seemed to help reduce the gas fume's or help engine go from idle to half throttle with out back fireing. Checked for fire and plugs all fire when cleaned and connected to their wire's. Timming is ok as far as rotor is facing #1 wire on cap when on TDC and on compression stroke.It fires up with a bump of the switch once the cylinder's are cleared of excess fuel.Considering re-adjusting float to shut needle off sooner, and also woundered if moving the accelerator pump rod from middle hole to lower hole to maybe reduce amount of fuel coming in and see if engine takes it better. Just removed carb again and noticed that fuel would pour from venture cluster if tilted just the least bit.Any thought's on what I need to change would be appreciated...:confused:
 
Last edited:
The float level can cause what you are seeing if adjusted too high (with carb right side up), Basically the 14 mm is a precise measurement, the float should have some kind of reference you are adjusting to, WHat is it? what ever it is when the carb is upside down the float should be (rule of thumb) perfectly level. If it is not then you have adjusted it wrong. WHat/where are you "bending" to adjsut it?

here are a few things to do,

remove carb AGAIN.....lol

take top off as if you were to adjust the float again,

drain all gas (safely) into a glass for later use.

turn carb upside down and gently blow into the gas inlet fitting. Continue to blow and it should take a bit of pressure to force the needle off its seat. Of course if you could set up an air supply set to 8 psi that would be an exact test.

If air is getting by the needle /seat....that is your problem. Could be dirty, not seating properly or just a bad needle or the seat area is damaged.
The picture looks like the needle is spring loaded, is this so?

If that is all OK

If the float is brass then remove the float, fill a glass with water and put the float in it and sunmerge it and see if there are any bubbles

I would even do this if it is not brass to see if it floats, I would also replace the water with gas so you have the correct specific gravity as you should.

The "plastic" type will just float and NOT sink if it sinks it is no good.

Is the float clean? it should e free of residue as possible.


The accelerator pump has no effect on excess gas flowing into the engine if the throttle linkage is NOT activated.
there may be a check ball at the bottom of the accelerator well inside the carb, if so its function is to allow gas to flow when pressure is applied by the umbrella and to close when no pressure is applied. I may be wrong on this as it may be from the rochesters not the merccarb.

If you suspect the accelerator pump, leave it out and retest. You will have a very bad lag if you throttle up quickly maybe even a lean back fire but it will rule it out if need be, I dont think it is that though.



There can be only three issues at play, wrong float hieght, bad float, nonseating needle.

The emulsion tubes that are attached to the discharge nozzles wick (cappilary action) feul up so if the level is too high it will seep out the nozzles.

The discharge nozzels is also where the accelorator shots come from so it can be confusing......the accelrator feul just comes from a different circut.

Hope this helps and of course it is winter and i personally have not looked at a mercarb for a couple years so my memory may be a little off.....
 
Did you use the thick carb base gasket from Merc or the thin one w/the kit? It requires the thick one. I have one left PN 27-807982 you can have since I don't need it. Shoot me a PM w/your mailing address if you need it. All that Kghost said is great advice. Make sure the float adjustment tang that rests against the needle valve is pushing the valve closed when you check the float settings. Is there fuel leaking out of the casting hole plugs? They look like BBs and are epoxied in place. I soaked an old carb once and they started leaking.
 
Thanks for getting back with me so fast KGHOST. Right off I can say I missed that check valve in the accereator pump well.The needle is the three peace spring loaded that calls for 14mm instead of 3/8"mesurment between air horn(with gasket in place) and float lip.My float is plastic and floated.Has two dot's on it for reference point's,and though the instruction's didn't say, a post either here or some where else I searched ;said to use the same dot for both level and drop adjustments.Will double check my note's on this as I forget off hand which dot I needed to use.I think it was the lowest dot when float is in droped position.Will take it apart tomorrow and see to that check valve in the pump well and recheck my adjustment;s on the float.Wounder if I could rig up my coolant system tester to pump 8psi into fuel line....The only check ball I found was under the venture and it along with the spring was held there with a t-shaped insert.Just don't remember one in the pump well.I will check though.Will let you know what I find, and thanks again for all you'r time.
 
Hi guyjg,I used the kit gasket...Didn't know there was a difference in them. Maybe the one I took off was a thinner kit gasket also that lead to a bad adjustment and leaking condition before I bought this boat.Thanks for the offer but I'll use you'r part number and pick one up around here.You may need your's some day.Are the casting hole plug's on the outside of carb? If so ,I don't have any dampness on outside of carb...just dripping from venture cluster inside.Tilting carb the least bit will make lots of fuel run out from same area.Thanks for you'r insite also guyjg...need all the help I can get...lol
 
Some carb.s just can't be rebuilt.

Copied and pasted here.

Get yourself down to a auto parts store, get a can of berrymans carb soak comes with a screen in the can, like a deep fryer.

Also get a can of compressed carb cleaner.And a carb rebuild kit.

With a clean area on a table or bench i place a old cookie sheet with sides.

Break down the carb and remove all the rubber.

Remove the jets they should just screw out.

Everything goes into the berrymans, let soak for a few hours.

Remove the parts from the berrymans, start with the lower carb housing and blow it dry with compressed air, it clean?

Piece by piece build it, make sure every passage is clean blow it dry and use compressed can carb clear blow it dry again.

Jets clean, Float, floating no gas in it ?

Push the float under water and if you see bubbles it's time to replace it.

Ok when you install the pin in the forks that hold the float are they pressing on the float tounge and not allowing the float to move freely ?

So if you did your job correctly the carb should operate freely, and when you install the adjustment screws be gentle.

Do not bend the tips. All the way in with them gently and out 2 turns to start.

Final adjustment on the water.

Have someone else drive about 2000 rpm maybe a little more and you do the final adjustment.

If you take your time and there are no distractions, you should be ok.

Good luck !
 
douglasnc said:
Thanks for getting back with me so fast KGHOST. Right off I can say I missed that check valve in the accereator pump well.The needle is the three peace spring loaded that calls for 14mm instead of 3/8"mesurment between air horn(with gasket in place) and float lip.My float is plastic and floated.Has two dot's on it for reference point's,and though the instruction's didn't say, a post either here or some where else I searched ;said to use the same dot for both level and drop adjustments.Will double check my note's on this as I forget off hand which dot I needed to use.I think it was the lowest dot when float is in droped position.Will take it apart tomorrow and see to that check valve in the pump well and recheck my adjustment;s on the float.Wounder if I could rig up my coolant system tester to pump 8psi into fuel line....The only check ball I found was under the venture and it along with the spring was held there with a t-shaped insert.Just don't remember one in the pump well.I will check though.Will let you know what I find, and thanks again for all you'r time.
Click to expand...

When I mentioned the check ball in the accelorator pump well I could be mistaken.......been a while.

The one under the discharge nozzle (venturi) I believe does what I suggested, when the pump umbrella pushes fuel the ball raises up and allows the accelorator squirt. when there is no pump pressure the ball seats (under spring pressure by the spring under the T) and stops fuel.
Removing that T and spring and ball can be tricky, the carb body around T is peaned over so removing the T needs special care and when installing it you have to repean the carb body back over it. A good thin slotted screw driver works well to re pean the carb body. Not a lot just enough. you just dont want the T to come out/up.


Yes the dots are the mark to set the float hieght. For reference the float hieght is the critical setting. The float drop is important and should be set but is not as critical, As long as it drops enough to let fuel out when the level has dropped down in the carb. BUT I hope you are adjusting the two at two different locations?????? "typically" a TANG on the end of the float is used for drop, and the area of the float metal that connects to the plastic float is where it is bent to adjust float level.
When you say plastic you are describing a solid foam type like plastic, correct? Not a hollow plastic float? They are typically brown and solid not hollow in the mercarbs.
The old rochesters used a brass two piece hollow float that was soldered and could leak and gas would fill it up and the float would sink and the carb would flood over.

Again when adjusting the float with or without the gasket in place it should be level by eye when the needle it fully seated and as described you may be required to put light finger pressure on it to over come the spring pressure and this should also be done when setting the float hieght.

Did you adjust it this way? If not then maybe this could be the issue?????
 
Has crossed my mind, but can't test pressure until I get a pressure gauge.This pump look like it has a filter on bottom held on with a nut and band. Haven't looked at it much as I was getting fuel.Kghost mentioned some thing's that I didn't do, so I just went back in and re-did what I missed.That may help.I'll get carb back on as soon as I can and let all you guy's know how it went.I soaked carb body in lacker thinner over night after taking it apart,then washed it out with soapy water and compressed air. Then sprayed all passage ways again with two large can's of gum out carb cleanner before putting it back togeather. Called myself doing a compression test on engine, but may not have did that right...Took all plug's out and did one cylinder at at time by spinning engine over maybe six rev's...Each cylinder pumped up to 150 psi, then slowly leaked down.Don't know if that was good or not. Don't have a leak down gauge, but I know I need to do that too...Plugs were all sutted up(black sut) and dripping fuel when I removed them. They were brand new and ran for maybe ten minutes.Hopping the carb is my problem,but the engine is 20 years old now. It's a 3.0LX, 1993...Thanks for offering you'r help too.
 
Didn't pean that check valve tee! Just opened it up again and did this. Also re-checked float and found level was at 17mm's instead of 14mm.Must have disturbed it while putting it back togeather.Re-set that too.Did adjustment's just as you mentioned on float.Maybe this will work now...Thank you Kghost!
 
Your compression check is fine, no need to do any more... the leak down is related to the guage not the motor.........150 psi is great!!

No additional leak down test is needed..........(which is a different test all together.


Looks like you may have found some issues so lets see what the results are.

Also Guy mentioned there was an issue with the base gasket being to thin and a thicker one was available.

Message him and see what he can do for you.. Using a very thin base gasket can not seal very well unles both surfaces are extremely flat and clean of defects....
 
http://www.marineengine.com/parts/m...856559-thru-0f603999/fuel-pump-and-carburetor

#1 is the carb there is a yellow hose ( actually clear but yellowed from time ) that runs from the fuel pump to the carb if it has fuel in it means the rubber went and is pumping fuel into the carb.

What that all means crank the engine with the yellow hose disconnected and inserted into a clear container see if fuel shoots out the hose.
if yes you need a new pump.

Please check the psi of the pump.

Please make sure the choke is opening when warm.
 
The Mercarb w/a single fuel/air mixture screw requires the thick base gasket in order to get the right fuel atomization. W/out it the mixture will not adjust to get the right idle no matter how the screw is adjusted...I found out the hard way years ago.
 
Hi all, I'm thinking float now as problem still comes back after trying for a few minutes to re-start engine.Fuel level in bowl was high enough to spill over into the accelerator pump well where that open slot is on side of well.Not sure if that is normal.Engine will flood quickly if it doesn't fire up fast upon clearing cylinder's of fuel and cleaning all plugs.Will get a new float and the thicker base gasket, and try it again.Keep woundering about that fuel pump, but am told that if no fuel is presant in clear line it's ok.How about a weak coil? Could it be too weak to fire the plugs before they get too wet and flood?Can remove all plugs and clean them,spin engine over several times to blow out excess fuel; then re-try starting.Engine will almost fire up but then flood again.Dripping doesn't start right away.Only after several atemp's of cranking will I notice the fuel dripping.But any dripping means something wrong in carb.There's no ball and screen in accelerator pump well. Just the ball, spring and t shaped retainer under venturi.With some fuel in bowl,I noticed none would flow into well so I put some in there and stuck accellarator pump in and pushed it down. fuel would come out at the ball and spring when I did so. Is that correct or does the spring supposed to hold the fuel back? Anyway, it's off to find a new float and base gasket and re-try again.Thanks again to everyone...
 
Last edited:
Your test of the accellorator pump/well is correct, that is how it is supposed to work.

the slot in the well is how fuel gets into the well if I am not mistaken. so that is good also.


Remember if there is to much fuel in the bowl it can only be two things.

1. bad or incorrectly adjusted float.

2. needle is not stopping fuel from enterning the bowl.

did you try to put light finger pressure on the float to close the needle to make sure it closed?

The float drop is what affects the amount of feul in the bowl.

If you adjust the drop so it is more than the spec the amount of feul should be less. The float will close the needle sooner.

does this make sense?

The only other thing I can think of is the check ball and spring under the venturi/discharge nozzles is not seating... If this does not seat propperly then excess feul can drip out.

one quick test would be to place a small pice of something like plastic papper or just paper over the T/spring/ball under the venturi and see if this stops the feul...Of course you would want to start the motor get it running and then shut it down and remove the vebturi from the carb.
maybe this might reveal something. if gas is leaking out of the spring/T/ball port this might be your problem......
 
Morning Kghost,Bought another carb kit and some Barrymans carb soak;and a new float.Watching one of Mikes carberator's video's on u-tube, he showed how to seat a check valve that wasn't seating good.So I tried that method.It involved inserting a soft brass(I used a flattened aluminum pop rivet)dowl into the hole, and lightly tapping on the steel ball to get it to seat better.Woundered if I had it clean enough, I took it apart and it's soaking again..This new float has a ridge (raised line)around it's mid section instead of the dot's.Will need to research where to measure from when adjusting it.Seems that it's covered in manual though..Bought a cheaper vacume/ fuel pressure tester just to make sure that pump isn't pumping too much.Hope to get to all this in a few hour's.Thanks for being here for me...Really want to learn how to deal with these carb's.
 
As far as the feul pump over pressurizing the carb.........I doubt that is the issue,

the line on the float is the reference mark.

Again with the carb top upside down, rule of thumb is the line or refrence mark be perferctly level no matter what as a starting point. If you set the float there and then measure it will be clear to you. DOnt get caught up with wierd set points, back in the day some auto carb kits had stupid measurements like 39/64ths...........really!!

Most merc manuals spec out like 3/8ths or 9/16ths ect ect.

You still have not confirmed whether or not the needle is seating properly???

Have you confirmed this?
 
Last edited:
DO you have the merc service manual for this engine/carb?

If not send me a personal message with a good email address that will accept large files and I will attempt to send you a merc manual in pdf form. it is very thoruough!!
 
I'm coming in very late on this one....... forgive any redundancy.


New kit installed, new needle/seat, float height adjusted, high speed metering allows fuel to dump at the air horns.
Does that describe your issue????

Obviously the fuel level is raising too high... no doubt about it, so the cause needs to be found.

Could it be that the needle/seat cartridge itself is faulty?
IOW, the two seating surfaces may be doing their job, but brass portion may be faulty.

Testing the buoyancy of the float is a great idea, however, and IMOO, when testing a float, we should use the same liquid media.... gasoline, not water.

I highly doubt that the base gasket or carburetor base surface is influencing this since you're apparently not experiencing a lean scenario...... you're experiencing a flooding or rich scenario.... correct?

The fuel bowl should be at ambient pressure since these are vented to atmospheric pressure.
If the accelerator piston check ball was missing, the accelerator pump would not function.
The fuel level or bowl pressure would need to be excessive in order to force fuel through the accelerator nozzle circuit.
If it was to force fuel through this porting, the fuel would be spilled at the accelerator nozzles, not through the air horns.

The air horn metering is restricted to the main fuel metering circuits, and may perhaps be influenced by a high fuel bowl level.


Agree..... testing fuel pump pressure should be part of this. By design, the float and needle/seat are engineered to "check" against 4 to 7 psi.
If the fuel pump was to over-pressurize by several psi or so, this may be your answer right there.
However, I'm with Kghost on this one.............. I too doubt if the pump is over-pressurizing.

If this is a mechanical fuel pump, the fuel pressure is predicated by the diaphragm spring pressure.
Regardless of pump arm action or RPM, this spring controls the amount of maximum fuel pressure that the pump can generate.
The two check valves simply ensure that the pressure is captive, and that the fuel flows in the correct direction.

When/if a mechanical pump was to fail, I'd think that it would fail and default to a low pressure (or the absence of pressure) scenario, not necessarily greater pressure.... unless there's some mechanical fuel pump failure phenomena that I'm not aware of.


For the time being, I'd focus on the float buoyancy, the correct float adjustment, and the needle/seat cartridge.



.
 
Last edited:
Hi Rick,I just re-built carb for second time.. This time I replaced the float.Fired right up and I started to try to adjust the air mix to get the shake out.Was getting there too, when oil started spraying out of the pcv hole big time...Shut engine off to try to figure out what was going on.After a few moments I dicided to re-start it to see if it was going to do it again. Engine was running good but saw fluid ozzing out of dip stick tube.Shut off again and checked oil.. Was three inches over full and smelled of gas .No fuel was coming out of clear tube from pump to carb though..How did the fuel get into the crank case? This isn't water in there.It's thinned that dirty oil to the point it looks almost new..Guess if pump can't be rebuilt from a kit i'll buy a new one, then change the oil a couple of times to get the fuel out of the crank case before it scalds my bearing's..Kghost kept mentioning getting a new float,but I really thought the old one seemed fine...I was wrong there too...Thanks for the insite from everyone..Will keep every one posted on my head way.
 
douglasnc said:
Hi Rick,I just re-built carb for second time.. This time I replaced the float. Fired right up and I started to try to adjust the air mix to get the shake out.Was getting there too, when oil started spraying out of the pcv hole big time... Shut engine off to try to figure out what was going on. After a few moments I dicided to re-start it to see if it was going to do it again.
Engine was running good but saw fluid ozzing out of dip stick tube.


Shut off again and checked oil.. Was three inches over full and smelled of gas . No fuel was coming out of clear tube from pump to carb though..
How did the fuel get into the crank case? This isn't water in there. It's thinned that dirty oil to the point it looks almost new.. Guess if pump can't be rebuilt from a kit i'll buy a new one, then change the oil a couple of times to get the fuel out of the crank case before it scalds my bearing's..
Click to expand...
Doug, your mechanical fuel pump diaphram has ruptured.
Once ruptured, fuel is dumped directly into the area that would normally be surrounded with oil.. or IOW, a direct path to the crankcase area.

Change out the fuel pump with a Marine fuel pump... not automotive!
Drain the oil and let it drain for a while.
Then install some inexpensive oil and an inexpensive filter.
Run the engine and purge the oiling system.
Then drain again, reinstall the good stuff and a good quality oil filter.
One time should do it.
Any residual fuel should quickly evaporate.

Since you ran this with no load, I doubt that any damage occured.

.
 
Just for the record. I never said replace the float. I said make sure
It still floated..

I am using my smaht phone and will check back later. If gas is getting
Into motor from pump lever side of pump i have to say this is the first
Time ever heard of this...

But if it is so there is a first for everything.
 
Will do Rick, But gasket area where pump arm sticks out looked dry when I took the pump off. You'd think it would be dripping wet.I don't know...Could anything else cause this much fuel to mix in oil so fast as it did here?Can I get a re-build kit for these pumps?LOL...running out of money to throw at this project.Hoping to get it going for spring crappie.Wife loves to fish as much as me, but she's into her second round with cemo treatments and cant climb on and off v-bow's so I found this old 25' pontoon. So far it's a money pit,but i'm too far into it to quit now.LOL Thanks again to you and everyone.Never could have gotten this far along with out you all...
 
Doug, the only other possibility would be fuel getting down past the piston rings, but this would require a tremendous over-fueling at the carburetor while the engine is not running.


As for a fuel pump over-haul kit.... good luck on that one.
Try NAPA or look on line.... you may get lucky.


kghost said:
If gas is getting into motor from pump lever side of pump i have to say this is the first
Time ever heard of this...
But if it is so there is a first for everything.
Click to expand...
Actually, this is quite common with a rupture.
The lever arm actuates the diaphram at the pump side, and rides on it's cam within the crankshaft case area.
This becomes a direct path into the crankcase.



.
 
Something is a miss here..

Where is the fuel comming from?
Is it from the yellow tube? (Which typically means a ruptured diaphram).

Is it from the carb? Due to carb issue not excess fuel from the pump (as in ruptured diaphram)

I think that needs to be clarified.

If you need to change the fuel pump to test. Borrow or purchase a cheap automotive for testing purposes only.

Get your oil and filter changed and try to find out what is going on...
 
.......................................

kghost said:
Something is a miss here..

Where is the fuel comming from?
Likely from a ruptured diaphram.

Is it from the yellow tube? (Which typically means a ruptured diaphram).
Yes..... perhaps a small leak from a small rupture. But consider a large rupture, and how much fuel that would spill.

Is it from the carb? Due to carb issue not excess fuel from the pump (as in ruptured diaphram)
The yellow tube typically dumps fuel into a higher elevation at the carburetor, and typically at an area where a back flow would be unlikely.
Also.... he stated originally that the excessive fuel was noticed coming from the air horns.

I think that needs to be clarified.
Agreed.

If you need to change the fuel pump to test. Borrow or purchase a cheap automotive for testing purposes only.
His engine is a 1993 3.0LX...... that's a 20 year old fuel pump....... Changing out a 20 year old fuel pump is not a bad idea.

IMO, the excess amount of fuel in the engine oil is a dead-give-a-way for a ruptured diaphram.


Get your oil and filter changed and try to find out what is going on...
Click to expand...

In this image you can see the opening for the mechanical fuel pump mounting.
The fuel pump lever arm rides underneath the fuel pump cam of the main valve train camshaft.
This opening is a direct path into the crankcase area.

3.0_marine_short_block1.JPG
 
Last edited:
"Is it from the yellow tube? (Which typically means a ruptured diaphram).Yes..... perhaps a small leak from a small rupture. But consider a large rupture, and how much fuel that would spill."I had a fuel pump that ruptured but did not leak out of the yellow tube. I found the nipple on the pump plugged solid w/hardened varnish.
 
Before installing the new float I was noticing fuel dripping from the venture area. Would remove all wet plugs and clean, then spin engine over to expel excess fuel from cylinder's.Engine would generally fire up and run roughly, and i'd try to adjust it.But it would stall and not re-start with out cleaning plug's again.Engine was alittle low on oil due to a leaking valve cover.Have a oil change that I planned to do as soon as I got the bug's out of carb.Have checked oil every time before trying something, and it was still just alittle low as I caught it and fixed leaking gasket.When I say leaking from venture area, I say it was dripping from venture area, it seemed to be drippind from those hollow tube shaped thingie's on the venture.Didn't see a rise in oil level during all these attempt's to get carb right.I'm with Kghost on the yellow tube showing sign's of bad fuel pump, but the fitting on the pump appears to be blocked or stoped up.Maybe that's why it didn't give the pump problem away by filling with fuel.Good side of thing's is if it's the pump...that's fixable...lol Engine was running the best it has when this happened. seemed pretty smooth from jump just before the mix started spraying out of valve cover.Even then, the engine re-fired fine and idled good.If the carb was still the problem you'd think it be flooded after that.Oh. would it be ok to use some 15-w 40 to flush engine before using my mercruiser oil and filter.?It's got a Napa brand oil filter on it now but I bought the one recommended at boat shop when I got the mercruiser oil.Really thank you all. Feel like I need to mow you'r yard's or wash you'r boat's or something for all you'r help. I really appreciate you all...
 
Back
Top