Intermediate and WOT issues with 850 4 cylinder....flooding?

[centerline]

I need some Ideas from mechanics who have lots of "top end" experience with these older motors.

I have an 85hp merc that starts and SEEMS to run fine on the muffs, but will not accelerate when its on the lake... it does run rich at times and floods easily during start up, but the carbs have been went thru without any change in performance..

I have had it into the merc repair shop and he double checked the carbs then did a compression test. all 4 cylinders read about 140psi (all within 3lbs of one another). the spark plugs looked fine and all even, but it seemed like the motor was still running a bit rich, so the tech changed the plugs and re-checked the tune of the carbs and the timing, and claims it should run great now.... but it doesnt.

after three trips into the shop, the mechanic thought it might just be me expecting too much from the motor, so he went with me to the lake to see what I was complaining about... and he finally agreed that there is something seriously wrong, but he has absolutely no idea what to look for next, other than tear it down and do a rebuild of the motor.
while we were on the water, he pulled the plugs to look for water, and the plugs showed no side of water in any of the cylinders.

he said the motor has some top end noise, but again, has no idea what it could be, as the compression is good (we rechecked it to make sure the first readings were correct, and he also looked into the cylinders with a bore scope, and it checks out good....

on the muffs it accelerates quickly and seems to run normal, although sometimes it seems to want to flood when starting, but most times it starts and idles immediately....
on the water, it will increase rpms VERY slowly only if you move the accelerator slow... if you move the lever too fast, the engine will start to load up and you have to back out of it to keep it running... any quick "hole shot" acceleration will flood the engine and kill it.


even though its a 1975 motor, it looks nearly new. it's very clean and the original paint is still shiny, and without any corrosion whatsoever.
the only history I have about it is that the motor sat for several years without running, and then when it was sold, the new owner (who I got it from) could never get it to run right... after tinkering with it himself he got tired of it and just replaced it with a new 4stroke motor.

I am not familier with the reed valves in an outboard, but I am wondering if they could be stuck or broken causing this, and if so, why couldnt the merc tech suspect this....

any suggestions as to what else could cause this issue or where I should look....

I have some advanced mechanical skills, and even though I have had a few merc engines before, I an not an outboard mechanic.... the mercs I have owned in the past always started quickly and had no problems. so i dont really know what to look for here.
Thanks for any help or suggestions

 

[racerone]

Some simple thing to do.----Start the motor in the water.--Remove one plug wire at a time.----What happens ?------And no reed valves do not stick.------Very common for low speed needles to be set for a really smooth idle.-----But that leads to stalling on acceleration.----You could try opening them 1/8 turn at a time to see how it responds.

 

[GA_Boater]

Do you know if the mechs adjusted the idle adjustment needles in the water?

 

[merc850]

I bought a 75 850 and it needed a new ignition trigger, fuel pump, removal of the carb filters and a total re-timing the P.O. had taken the flywheel apart and put it together wrong, check for socket circles around the inner bolts that's a giveaway.
It's possible that the carb filter screens are plugged if you have the carbs in the image remove the tops and discard the screens.
When you pump the primer bulb does any leakage happen at the carbs, are there gaskets between the carb bodies and the block - there should be. It's possible that the P.O. did something to the fixed jets, you can check this by undoing the brass plugs at the front of the carbs.
Do you have a tach? the idle should be (in Fwd. in water) 550-650 the max rpm is 5500 - timing max 23*. Check that both carbs are opening full at the same time - the plugs are L76V. A timing light can be used to check the wires for spark, also check that there is no sparking between wires and block when the distributor turns to max. position.
Are the distributor cap and rotor contacts clean?

 

[centerline]

the mechanic as well as myself have tried adjusting the needles at various times on the muff AND in the water, and while the motor was trying to accelerate but couldnt... it acted like it was loading up. if it dies before returning to idle, it will be flooded with fuel when trying to restart it..
so adjusting the needles does NOT make it accelerate any better at any setting, but does make it run worse....

the mechanic did remove the plug wires one at a time (although he said that doing so could damage some ignition components) to see if there was any change in how it ran... all cylinders are firing, and dropped out as expected when the wires were removed....

before I had the mechanic work on the carbs, when I pumped the primer bulb tight and then pumped some more, fuel would come out of the carbs somewhere near the top.... I dont know if it still does it after he worked on them...

I did put a full valve kit in the fuel pump before I ever took it to the mechanic.

the carbs ARE opening fully, and at the same time... we have checked and rechecked this.

distributor is clean and the rotor is clean... everything inside the motor cover is like new condition. it was a little used and well maintained motor...

it does seem to be a fuel issue, and my thoughts about the reed valves were if they were broken the gas may not be vaporizing as it passes thru them as it should and possibly demanding a higher flow because of it... which in turn, may cause a rich running condition??? this is speculation only because i dont know what the reed valves do or are there for...


and it is possible that the previous owner could have had the flywheel off, and I told the mechanic as much, and so he "said" he checked the timing and it was good.... but if the timing was off, in addition to running bad and possibly a rich condition, could that account for the extra bit of top end noise also?

im not sure if the gaskets are between the block and carbs or not, but as the mechanic "said" he went thru them, I would assume they are assembled and installed on the block correctly, but I dont know this for sure....

make no mistake that when I say it doesnt run right, its not just a little bit out of tune, but it is nearly unusable when trying to push the boat... AND, it wont even shift into gear without dieing. i had to over ride the neutral lockout switch so i could start it in gear... its the only way to get it started and moving forward.. or reverse.

 

[merc850]

If a reed is broken gas will be blown out of the front of the carb, the reeds prevent this. You should set the low speed needles at 1 1/4 turns out from seated as a starting point then adjust them at 600rpm while running in forward on lake. A tach is a way to tell where you are or are not.

 

[DavidMoore]

If everything else is normal and it won't shift into gear without dying then either the engines not warmed up, the idle speed is too low, or the low speed needles are set incorrectly. - See above post.

When were the fuel lines last changed?
Have you checked the entire fuel system for leaks and blockages, even the pick-up inside the tank. Also check the fuel tank is venting properly.

 

[Chris1956]

If she idles, the reed valves are good. Have you verified the year of the motor via serial number?

Idle pickup timing for a distributor motor should be 4-6* BTDC. Max spark advance should be 21* BTDC. Idle speed should be about 900RPM.


The carb idle mixture must be set very rich in order to allow the motor to accelerate. If it is set for best idle, the motor will stall when trying to accelerate.

Loading up at idle would be a symptom of a bad fuel pump diaghram, bad carb floats (or adjustment) or bad inlet needles. These should have been replaced when the carbs were rebuilt.

Check the spark plug wires for arcing to ground. This will cause a miss, and could cause acceleration issues. The dist. rotor is non-removeable. Both the dist cap and rotor are expensive, but should never need replacement.

 

[centerline]

well, its possible the mechanic took my money and didnt do squat to it, as he only ran it on the muffs at his shop, UNTIL we took it to the water and ran it, and he still didnt have any ideas left to try....
and as for everyone here pointing to the needles, adjusting them will make it die, it will make it run rough at an idle, or they can be adjusted to make it smooth out at an idle, but ant NO STAGE OF THEIR ADJUSTABLE RANGE will opening them up a little, make the motor accelerate any better.....

as the engine tries to accelerate, its like someone is slowly closing the chokes....it sounds as if its being choked and it starts running extremely rich... and it will die if its not returned to an idle before it does... but the choke is fully open.

 

[GA_Boater]

I didn't see that the fuel pump has been rebuilt with a new diaphragm. Or did the check valve include a new one?

 

[Chris1956]

When you say the engine runs rich as you open the throttle, is the opposite of what I have seen on that motor. What I have consistently seen is that the motor runs too lean as you open the throttle and starts to stall. Returning the throttle to idle allows the motor to run fine.

If she is truly running rich, I would suspect the fuel pump diaphragm is leaking.

Also, the 4 cylinder Merc 850 converted to ADI ignition in the 1975-76 time frame. ADI ignition is a different animal from the battery powered distributor ignition. That is why I suggested you verify the exact year of the motor via serial number. The Maxrules web site identifies the exact year by serial number.

 

[DavidMoore]

+1

Normally stalling / bogging down on shifting is a lean condition, the quick fix is to wind out the screws a bit. In your case adjusting the screws make no difference, so I'm thinking it's fuel starvation.

So considering the work already done, and assuming it was done correctly, I'd be looking for leaks / blockages in the fuel system. If you get black marks on your hand when rubbing them on the fuel lines, change the fuel lines. Old and deteriorating fuel lines can (do) cause of so many problems and can contaminate a freshly cleaned carb in the blink of an eye.

Once you verify there are no leaks / blockages in the fuel system (including inside the tank) and that the tank is venting properly, then is it time to revisit the fuel pump and carbs.

Starting with the fuel pump including checking that any pulse holes / lines are in good condition and not blocked.

 

[Faztbullet]

1) Will it idle in gear in the water...forget muffs.
2) Does the distributer rotate when advancing throttle?
3) When cleaning carbs did the vent jet and high speed get swapped around?? Vent jet in high speed would push it rich....
4) What series plugs and what does electrode show???? rich or lean??

 

[tallcanadian]

Were the carbs just cleaned or rebuilt. I took mine off and rebuilt them. New needles, gaskets, etc. Floats were good. Taking them apart will let you at least see whats going on inside.

 

[centerline]

Thanks for all the Replies... I cant seem to do multiple quotes here, so my responses to everyone is included below

When you say the engine runs rich as you open the throttle, is the opposite of what I have seen on that motor. What I have consistently seen is that the motor runs too lean as you open the throttle and starts to stall. Returning the throttle to idle allows the motor to run fine.

Also, the 4 cylinder Merc 850 converted to ADI ignition in the 1975-76 time frame. ADI ignition is a different animal from the battery powered distributor ignition. That is why I suggested you verify the exact year of the motor via serial number. The Maxrules web site identifies the exact year by serial number.

I cant seem to find the serial number/year cross reference on the maxrules site... my serial number is 4314221, as near as I can tell its a '75... the high speed running problem has been there since I got the motor, and one of the first things we did was to put a kit in the fuel pump, with new valves... no change at all.

this is still the older style ignition with the distributor and 4"x4"x1" electronic box mounted directly in front of the top carb, and the coil mounted aft of the starter on the right side of the motor..

the fuel lines appear to be in great condition and without deterioration, BUT i did NOT take them off and check them inside, nor the pulse lines/ports/holes... the tanks and line from it are new.. and I have ran a rich mixture of seafoam thru it, and let it set for a week, and still no discoloration of the fuel...

it idles fine in the water, and will rev up, but NOT under a load... but it has to be started in gear as it will die if placed into gear from an idle. when on the muffs, it will idle fine and rev up AND can be shifted into gear without it dying...

the distributor does rotate with the throttle as it should.
im not sure if the jets got swapped by the previous owner during his attempt at making it run... and im not sure if they were checked by the merc mechanic.

the plugs are the correct plugs for this motor, as designated by mercury. they show it to be running a bit rich. not abnormally so, but definitely NOT lean..

the mechanic "said" he disassembled and cleaned them... so I dont know, but he definitley didnt want me hanging around to see what he was doing to it...

it sounds as if the carbs need to come off and the entire fuel system gone thru by me so that i know they are correct....

 

[Chris1956]

OK, that serial number looks to be a 4 cylinder Merc 850, from 1975. Spark Plugs should be NGK BUHW. Remove, clean and rebuild the carbs with new gaskets, floats, inlet needles and seats, or at least inspect them to make sure the mechanic did it.

Invert the carb bowl cover and see if the float levers are parallel with the cover. That is the proper adjustment. Make sure the float is hard plastic and has the little spring on top. Clean or replace the banjo filter in the cover over the carb bowl cover.

Initial idle mixture adjustment is 1-1/2 turns open. Final mixture must be set on the water, at idle, warm engine, fresh fuel mixture.

It probably makes sense to get a service manual, so you can check the timing as well.

 

[racerone]

What did the mechanic say about the ----" top end noise " ---Did he have any idea ?----Did he do any inspection looking for this noise on a new looking motor ?

 

[achris]

Restrictors..... They melt and get sucked through the enigne. When they're gone, you get the problems you have....

 

[racerone]

In the past I installed 8-32 stainless setscrews to replace the plastic ones.

 

[achris]

In the past I installed 8-32 stainless setscrews to replace the plastic ones.

Always thought the next engine I have to replace the restrictors, that's exactly what I'd do. Drill a 0.3mm hole in them and be done with it.

Chris.