Logo
FULL SITE MENU

Carb problems, still

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, 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...
 
To simply do a oil change to clean the oil system form gas or (water) which ever is the issue, use a very inexpensive oil, a non name brand 10-40 is fine and a couple of cheap oil filters.

Once the issue is resolved, run the engine until fully warmed up, say 30 minutes, do a cheap oil change, then repeat a second time. If you are sure all is good do one final oil change with reccomended oil and filter. Typically a higher viscosity (25-40 oem) or 20 -50 (any brand) or a synthetic, 15-50 (mobile one).
 
I'm not quite sure why some of us are recommending more than one oil change for flushing this gasoline from the oil system. You're not trying to purge water, nor debris contaminates from your oil. You're purging your system from a clean non-debris layden, highly volitile and easily vaporous liquid, that by all rights should have mostly dissapated during the one 30 minute run and warm-up on the cheap oil/filter.

Like I suggested.... drain the oil, leave the drain plug open for 15/20 minutes or so.
Remove the gasoline contaminated oil filter, and pre-fill the new inexpensive filter and install it.
Install your fresh inexpensive oil.
Run the engine up to temp for let's say 30 minutes ..... check the oil...... shut down and do your final oil/filter change.


However, if two or more flushing oil/filter changes gives you that "feel good" feeling, then I'd certainly do it. :D


.
 
Hi everyone , Tried to respond back last night but for some reason my post didn't go through.Wanted to thank everyone for bearing with me so long.You'r all really nice guy's to still be trying to see me through all this.the yellow tube was dry, but seemed stoped up at pump end.Lots of gunk in nipple when I got pump off and looked at nipple..Could be why no fuel entered line to warn of bad pump..I'm not really surprised that it's gone bad...Every thing else has...lol 20 years old and sat for at least three year's will do that. Back to the carb issue's. When fuel was dripping into intake, it appeared to me to be coming from the venturi area. Those two barrel shaped thinggie's appeared to be dripping fuel. But I could be wrong as my eye's aren't so good anymore without glasses on.But definetley coming from the venturi area.I feel the carb problem is fixed now as it sure ran well up til the oil/fuel mix started spraying out of pcv hole. Even re-started with no problem after sitting for a few minute's and still ran well.Will get a new pump as soon as I can and re- try. Would it be ok to use 15-w40 to flush engine out before putting the mercruiser 25-w40 in? Again, we're really greatful for all you'r help guy's.
 
Last edited:
Hi Everyone, Well still seem to be flooding cylinder's after replacing fuel pump.Started dribbling fuel into intake again.Think I went wrong way trying to set drop mesurment of carb to stop fuel alittle earlier.Was supposed to be set at 27mm's and I set it to 24mm's. Did that make my problem worse? Float level is still at 14mm's and level across bottom.Just knew I had it right this time too...Did another compression check. This time I had throttle at WOT when I checked each cylinder.#1 read 160..# 2 through 4 all read 175 psi. So #1 is 15 psi lower than the rest...Also noticed it was the driest of the four cylinder's. But the boat is sitting tilted down in the aft, so could that explain #1 being dry or is there a problem here.Should I buy a new carb (since I can't re-build worth a hoot)or look at other possible problems. All cylinder's are fireing, but I wounder if the spark is enough to set it off.Just doesn't seem to be a strong spark.Will almost fire up after spinning engine over a lot without plug's to clear fuel, and drying plug's..Just not quite before it seems to load up again..Did'nt really see anything wrong with the diaphragm's in the old pump. Could it be that the carb let that much fuel into crank case? Sorry, This has to be one of the longest thread's .I'm just lost...Thanks
 
Is the carb a 3 piece body? I had one that leaked from the casting plugs. I finally gave in and bought a Mercury reman. carb. The 3 piece carb body hasn't been made in years. You'll be glad you got rid of the old one. Besides the bushings are probably worn. It's time for a newer one.
 
Hi guyjg, No, it's a two piece mercarb. Really felt I had it right . This boats really been a money pit so far...lol New upper unit, bellow's, shift cable, seal's,shift shaft bushing's/seals.starter,fuel pump,dist.cap,rotor,plug's,Valve cover gasket,and two carb kit's so far...It's adding up fast to get it going again.Just hope it's not internal.See re maned mercarb's on e-bay for around $250.00.Wounder if I need to try one...Could the #1 cylinder being only 160psi and the other's pumping up to 175 indicate a bad problem with either ring's or valve's? And would that cause the loading up of fuel in cylinder's? Or, is it still a carb problem in you'r opinion? LOL,Grasping at straw's now..On the bright side,I'll need all these new part's on the long block if it comes to that..Thanks for replying back too.
 
douglasnc said:
Could it be that the carb let that much fuel into crank case?
Click to expand...
While running, I'd have to say no, in that if it runs OK the fuel is being burned.

However, if the carburetor is dumping excessive fuel after shut down, this fuel may perhaps make it's way into a cylinder or two, and eventually makes it's way past the piston rings, and into the crankcase.

However #2....... one shut down, and one dumping, it not likely to give much of a high reading on the oil dip stick.

I'd be more inclined to think that this would be an accumulation of many shut downs with a carburetor that is dumping fuel.

Here's a simple unorthodox test:

After the engine has been at rest for a while... let's say over-night or longer...., carefully remove the carburetor and dump it's contents into a clean container.
Measure this fuel volume.

Re-install and run the engine just long enough for the fuel pump to fill the bowl, and shut it down again.
Now immediately remove the carburetor, and again dump the contents into this container.
Measure the volume.

If there is a substantial difference in fuel volume, the differential will indicate how much fuel is being dumped upon each run/shut down cycle.

This may indicate that the carburetor is leaking or dumping fuel into the intake manifold.
X's the amount of run/shut down cycles, and there ya go!


If you are convinced that the fuel pump diaphram is NOT the culpret (rupture dumping fuel into the crankcase), then I'd think that this leaves only the carburetor.


.
 
Hi Rick ,New fuel pump($172.00) just installed. Still dribbling into intake.Re-checked float(new float) level and drop,and all was correct..14mm's on level from air horn gasket to toe; and 27mm's from air horn gasket to toe for drop mesurment.Now this float doesn't have the little dot's to go by like the old float..It has a raised seam across the center that I assume is the mesureing point...Is this correct? Am considering to change level adjustment from 14mm's to 17mm's to see if fuel shuts off alittle sooner and stops dripping into intake.After several attempt's to get it fired up, I rechecked oil level and it's up some from full mark. So fuel must be getting into crank case with all the cranking...Took all plug's out several times and ran a hose from fuel line to catch can while I spun engine over to blow excess fuel out of cylinder's. Then cleaned and replaced plug's..Would try to fire up but not quite. Then the cylinder's were flooded again. Whats you'r thought's on changing the float level from factory a few mm's to see if it helps the dribbling of fuel into intake? Hate to have to buy another carb, but if that's what it takes.Thanks
 
Last edited:
Take a look at the top gasket to see if there is a compression mark all around the gasket. If there is a small area near the venturi that is not compressed you could have a dip in the bowl wall or warped top plate allowing fuel to seep over the bowl wall from a maladjusted float or due to the boat sitting on an incline.

My 1972 Dodge Charger had a bowl wall dip from casting mold. Turned the bowl upside down on a sheet of glass and 80 grit sandpaper to level the top edge to cure the seepage. A far as getting an eBay carb make sure it comes from a Mercury marine dealer or you may just get someone's junk.

Do you still have the aluminum numbered tag on the carb? That will determine if you have the correct carb. You can check the carb for a cracked casting. The paint has to come off the body. Rub some sheet metal layout dye all over it and then wipe it off in one direction. The cracks will hold the dye.
 
Doug, if the float needle/seat, and/or incorrect fuel level are not the culprets, then the carburetor body itself has to be faulty somewhere.

In a rather crude comparison, this is much like a house toilet tank.
You have a water supply...... that's your fuel supply/pressure.
The supply is checked via the float and shut-off valve.... that's your carburetor float and needle/seat.
The porcelain tank is the float bowl.

If water is being spilled into the toilet, the water level is either raising to high and going into the over-fill tube, or it's being spilled via the stopper valve leaking.

A spill via the over-fill tube could represent the air horns if the fuel level is too high.
A spill via the stopper valve could represent an internal fuel leak within the carburetor body.

Crude.... but it does show a comparison.

.
 
Thanks for the tip's. I will try all you'r suggestion's, and thanks.. Haven't thought of that...That would mean a new carb but if that's what it takes....Will inspect the gasket's and chech for warpage , and fill bowl to top and watch for leaking .All good idea's! Thanks again
 
Filled float bowl up to 1/4" from top and venture started dripping until level droped maybe 5mm's from there.pulled venture off and checked gasket and screw with gasket.All looked ok.Could the little check ball with spring and t- shaped insert not be sealing off and causing this? Or could the new power valve be letting fuel in? In real life, bowl wouldn't be that full would it?
 
Problem solved! I went on line and found instruction's for adjusting a float like this new one. There was a difference...Re- adjusted float level according to these instruction's and fixed dripping.Used the ridge line on side of float to measure the drop adjustment But,used the lowest angled outside point (above) the raised center line(point of toe?) to measure the level. Maybe 4mm's difference from where I thought it needed to be.I feel kinda stupid for running you guy's through all this trying to help me, and I'm sorry for that.Want to thank all of you for all you'r insight. You'r a great bunch. Engine fired right up and runs pretty good. Will start easily with the touch of the switch.Do'es pop alittle if throttled up too fast, but I hope to tune that down better on the water.Really thank you all!
 
Do'es pop alittle if throttled up too fast...
Click to expand...
Check the timing. If it is correct then change the accellerator pump lever setting...move it to the next hole. Don't remember which outer hole is the most fuel shot...someone else will chime in. Does the idle mix screw adjustment change the idle?
 
Hi Douglasnc, i have the 2 barrel mercarb with exactly the same flooding problem. Fuel literally pours from the venture jets after trying to start the engine. From cold the engine normally starts fine. I've set the float level by the manual at 14mm. What do you think was the original root cause of your flooding, leaking float not able to shut of the needle valve? Thanks
 
The adjustment for accelerator pumps on marine engines is to make the shot as great as possible. (Unlike cars, marine engines don't get constant throttle changes--it's far more steady--so you aren't wasting fuel.)

The trick is to make the accelerator pump plunger move the furthest distance as the throttle is opened. That usually means making the arm going to the linkage shortest (using the nearest hole to the pivot).

Jeff
 
I think i may have solved the problem... I replaced the needle jet a few months back from a new kit of parts, not a genuine Mercruiser kit. After reading the posts here i came to the conclusion it must be adjustment of the float level so after checking again i noticed if i pushed down on the float it clicked and moved further than when allowing just gravity to do it's job. The problem seems to be the needle inner pin catching on the inside of the spring, with extra pressure it clicks past the last turn of the spring and would allow fuel to raise the level in the bowl. I've put the old needle valve back in and it seems fine again! Lucky i kept it. I've posted here in case there are other badly manufactured components in circulation, i'm sure like me most people tend to trust new components and then start looking elsewhere. This has cost me many weeks use of the boat. Not sure if these parts are available from Mercury Marine as the dealer said some bits were no longer available because the carbs are no longer manufactured.
 
Thanks for feedback. Often folks post, fix and disappear. Re: Mercury parts... Using your engine S/N, go to the "parts" section of this website. Both OEM and aftermarket parts as available are listed. FYI... Quicksilver = Mercury factory replacement. I would have thought "everyone" knew this until I spent 10 mins unsuccessfully trying to convince a customer at the big box marine store that I sometime work at, two weeks ago, that this was so. He actually said some unkind things about me trying to pawn off aftermarket as genuine factory.
 
Back
Top