low speed mixture screw... WHERE!!!

[Pontoonfoon]

Im having an issue with my motor idling like crap and dieing frequently when at idle or low speed (below 1200 rpm)

Over time ive narrowed it down to needing adjustment.

I have the manual for the engine
(2007 ELPTO 90hp)

and in section 2C under INITIAL STARTING ADJUSTMENTS
LOW SPEED MIXTURE ADJUSTMENTS

it says: With engine running at idle speed (in water) in
?Forward? gear (prop on), turn low speed mixture
screw, IN (clockwise) until engine starts to ?bog?
down and misfire. Back out 1/4 turn or more.


Problem is, on NONE of the diagrams it shows of the engine, do I see anything labled "low speed mixture screw"

now, on the 4 cylinder version.. I do see it, but mine is a 3.

what it DOES have labled is:

Throttle Arm
Idle Timing Screw

Full Throttle Stop Screw
Locknut
Cam Follower Adjustment Screw
Synchronizing Screws
Maximum Spark Advance Screw


at first I thought perhaps the idle timing screw and the low speed mixture screw may be the same thing, but after further reading, they definatly are NOT the same.

so where is the low speed mixture screw?

 

[saumon]

Re: low speed mixture screw... WHERE!!!

when you face the carbs, it's on the upper right side of them

as you seems to have the Merc service manual, check the page 3B-17, it can't be more clear (it's about the carbs adjustment...)

when you say that you narrow it down to adjustment, you've cleaned the carbs before, right? And you've got good compression and strong spark? I'm just saying cause,for example, a scuffed cylinder or a dead coil will also produce a ?running like crap at idle? condition...

 

[Pontoonfoon]

Re: low speed mixture screw... WHERE!!!

when you face the carbs, it's on the upper right side of them

as you seems to have the Merc service manual, check the page 3B-17, it can't be more clear (it's about the carbs adjustment...)

when you say that you narrow it down to adjustment, you've cleaned the carbs before, right? And you've got good compression and strong spark? I'm just saying cause,for example, a scuffed cylinder or a dead coil will also produce a ?running like crap at idle? condition...

well the motor is practically new.

we have replaced the plugs, drained the gas, run the merc cleaners through it.. seafoamed it.


so this is the next step, as it makes a bit more sense to go ahead and see if some simple adjustments will clear the problem up, before I start taking the motor apart LOL


Of course if your car quit running, you could pull the engine and checks the pistons, rods, head, have a valve job done, replace the connecting pins..

but first.. see if you our of gas..

 

[saumon]

Re: low speed mixture screw... WHERE!!!

Yeah, but compression and spark test are very simple and you don't need to split the crankcase for that

In fact, it's even more simple than carbs cleanup. In a case of a poorly running engine of unknown history, never assume anything (like ?low hours?, or the well known ?was running fine last fall?) and the more efficient approach was to check, IN THAT ORDER, for:

1- good, even compression on all cylinders (over 100 psi and within 10%)
2- strong (blue, crisp) spark at all cylinders (jump at least a 7/16 gap)
3- fuel system checkup (from the tank pickup up to the carbs with everything between, including the fuel lines, the primer bulb and the fuel pump)

The main reason for that particular order is that's worthless to spend time and money to clean and rebuild the carbs if, for example, a cylinder is worn. Got it?

 

[Pontoonfoon]

Re: low speed mixture screw... WHERE!!!

my problem is not very symptomatic of a damaged engine

from 1200 up to WOT the engine rungs perfect.. it just has a rough idle..

and before I buy a compression tester, take apart the ignition and rip out the fuel system and clean it, im going to turn a few small screws.

 

[backyard mechanic]

Re: low speed mixture screw... WHERE!!!

You MAY be right but before you stick a lot of money into the issue, I'd sure be getting a $20 compression tester added to my tool box.

BTW, you may not see those jets unless you take the front cover off the carbs. Seems there were some rubber plugs in the silencer to pull out to access the low speed jets.. ??

 

[cr2k]

Re: low speed mixture screw... WHERE!!!

saumon was speaking from normal marine tech procedures. Always the first things to check on any outboard are compression and spark. Why? Could be a low spark (bad/weak coil) condition that will run at WOT. A low cylinder will "pick up" at higher throttle. Or even a weak fuel pump that will pump enough at higher RPMs. Could even be a carb sync issue.

Could very well be an idle mixture issue, but if it is your carbs probably need to be overhauled because the dirt doesn't get in there from the outside of the needle.

When you ask for advice you will get what is the "norm" for the industry.

And 99% of ALL carburetor issues are electrical in nature.

 

[Pontoonfoon]

Re: low speed mixture screw... WHERE!!!

Well this isnt the inital reaction to this issue, ive been dealing with it for a while, and have tried a few different things

and I am working the advice of a mechanic.


his diagnosis.. which makes sense is..

running cleaners and seafoaming the carbs did NOTHING.. so its not an issue of dirty carbs.. if it were, doing all of that would at least have made SOME difference, might not have fixed the problem.. but it would have done something.. It made no difference at all... so its not likley that the carbs being dirty is causing this, especially on a relatively new, low hour motor. Its possably, but definatly not probable. and running all that stuff through it also amounted to good preventative maintenance anyway..

changing the spark plugs is brain dead easy and cheap so it was dontejust for the sake of doing it, again no difference what so ever, but hey now I know when they were last changed, I also changed the lower unit oil, again, just for the sake of knowing when it was last done.

so HIS opinion, is to next make sure everything is adjusted correctly, simply because ITS FREE..

it makes no sense in his mind (or mine) to go out and start buying testing gear, and pulling the motor and fuel system apart before checking some of the basic stuff first.. hence my comparison to pulling out your cars engine to see why it stopped running before checking if you were out of gas.

which is why arrive at where I am now.

If this doesn't work, ill move on to the next step, all the while learning and checking things as I go.


I am absolutely hell bent on learning everything I can and doing everything I can about this. I wanna know how it all works, and when something needs fixing, I want to fix it. Im not a fan of being ignorant of things I own, and thus being totally at the mercy of some mechanic if any little problem occurs.

 

[sschefer]

Re: low speed mixture screw... WHERE!!!

O.K the very first piece of advice I'm going to offer is to throw away that Seloc manual and get the Merc Service Manual. You can buy them on eBay dirt cheap and often bootleg copies of multiple manuals on CD. Just make sure it's really the Merc Service Manual. They run $100.00 from Merc. I've bought them for 10.00 on eBay.

Your stalling and rough idle are due to improper synchronizaition of the initial timing and carb opening. There is a clearance setting on the follower cam and roller that needs to be set to no more than .010 after the carb linkage has been properly adjusted.

Once that setting is correct, you adjust the intial timing screw to achieve a RPM of 750-800 while on the hose. You then final adjust the carbs by turning the idle screws on the carbs out 1/8 turn at a time followed by a 30 second pause. When the engine stumbles reverse that and turn them in 1/8 turn at a time, this time counting the number of turns. When the engine stumbles again (it may stall) then divide the number of turns by 2 and add 1/8. Lightly seat the screw's all the way in and then back them out the number of turns you calcualted. You can fine tune after that but never more than 1/8 turn.

If the engines RPM's have changed then re-adjust the intial timing screw only to achieve a steady 750-800 RPM. You should see a 50-75 RPM drop when then engine is in the water with normal exhaust back pressure and another 50-75 RPM drop when it's in gear. That will put you near or close to 650 RPM in gear idle.

Just so you know, the books initial timing setting is only a reference point to allow you to start the engine. It is not something you must adhear to when performing the final adjustments or re-check once the engine is running great.

 

[Pontoonfoon]

Re: low speed mixture screw... WHERE!!!

Ill give that a try.


I do have the Merc Manual though.

 

[will941s]

Re: low speed mixture screw... WHERE!!!

Just for added convo, I keep a compression tester in the bow storage in the boat. People call me crazy, until I do a compression test on a boat running like crap at a boat ramp. And every so often I pull the plugs, and run a test on my motor. It's interesting to see the change in the compression like for example, when I got the motor (98' merc 25) it had 110 pounds on both cylinders. Ran seafoam and it went to about 120. Since then with a water fuel separator and good gas and oil its now at 135 and holding. On hot days it gets up to around 137 or a little more. Cold days with cold water about 130psi. When my motor would'nt idle, the first thing I did, check the Compression right at the boat ramp. Traced it to the carb being knocked out of adjustment by rough water. I also keep a ratchet with a 10mm and a 13mm socket, and the same wrenches, a flat and phillip head screwdriver, adjustable wrench, about 2' of fuel line and hose clamps. Thats how you prepare for those little problems on the water that can make you scratch you head.

 

[sschefer]

Re: low speed mixture screw... WHERE!!!

Ill give that a try.


I do have the Merc Manual though.

Great.. Just follow the steps word for word. The intial timing setting is on the throttle arm. Its the smallest of the three adjustment screws. The carb idle adjustment screw is on top of the carb itself. That screw adjusts idle/air mixture and does not control idle speed. Idle speed is controled by the intial timing advance. This is what I mean when I say the book nrs for initial timing are just to give you a starting point.

 

[Pontoonfoon]

Re: low speed mixture screw... WHERE!!!

Ok just got back from the lake.

I took loose the 2 sync screws, the follower adjustment screw and lined everything up, I had to adjust the idle stop screw a TINY bit to get everything to line up perfectly.

fired up after the 3rd crank at the ramp (after sitting for 7 days) and never stumbled or died once, purred like a kitten and there was no hesitation when in transition from idle to full throttle..


the only thing now is in neutral it is idling high, at around 1100, though it idled high before as well.. just high and crappy, now its high and smooth.

I kinda got tripped up as I left the paperwork at home and subsequently forgot what to tweak the idle when in neutral


but all and all im pretty happy, just need to get that idle down now and I will be all set.