Merc 140 Running problem

[bds85466]

Hi Fellas,

I got a call from a buddy who was stranded on the opposite side of the lake. He has a Merc 140. Said he had been running fine for about 3 hours, idling and WOT etc. Then in idle, it began to sputter and die. He couldn't keep it started unless the rpm's were high, and then when he'd lower them to switch into gear, it would kill.

He couldn't get it into F, so he paddled to an empty slip and parked. I went over last night to look and it was the same deal. Couldn't stay lit unless the rpms were high. Choke/spring appeared to be working correctly as it heated it opened, as it cooled it closed -- so I'm thinking more carb/jet related?? Something worse?

Any carb experts out there to shed some light? Possible adjustment or need for rebuild?

grainy pictures are more to show which carb it is as I didn't pull the model.

 

[zbnutcase]

Re: Merc 140 Running problem

I would check points first to make sure the rubbing block isnt worn out, then I would check for water in the gas next.

 

[bds85466]

Re: Merc 140 Running problem

Thanks for the quick response. Don't know the 140 (or points/gaps) very well. Where would I locate that capsule?

He filled up with a full tank right before his outing with a new fuel water seperator filter -- I can pull that and see if there's water in it I suppose. Either that or would you take some from the tank and let it seperate in a mason jar or something?

 

[antsmands]

Re: Merc 140 Running problem

Hello bds85466;

The points gap is .022in (0.5mm) and dwell is 28-34d for the Merc 140. If the boat is starting ok but dying out after a recent fill up it sounds like bad fuel or a fuel delivery problem to me. From the pics the carb look to be dirty and may be in need of a rebuild. My 140 was very ruff running until I rebuilt the carb. Runs great now. Not that hard to do with a kit. I also did away with the points and got a Pertronic electronic ignition conversion kit. Works like a charm and no point or dwell angle to adjust. Hope this helps.

Tony d.

 

[bds85466]

Re: Merc 140 Running problem

yeah it helps, not being near the boat, it's tough trying to figure out where the points and everything are located...

 

[jagilbert]

Re: Merc 140 Running problem

There is a sticky thread that describes how a points ignition system works.

To check the points:
use a flat head screwdriver to remove the distributor cap. Under the cap you will see the rotor, which spins to point at each plug wire terminal of the cap. The rotor is attached to the distributor shaft. The points are a small switch which opens and closes as a cam on the distributor shaft pushes on the spring-loaded cam follower as it rotates. Points open widest when the highest point of the cam is under the cam follower and that is where you measure the point gap. With the distributor cap still off, bump the starter until the points are at their widest gap. If you have a feeler gauge, measure this gap to ensure that is somewhere in the neighborhood of 0.22". If you don't have a feeler gauge, 0.22" is about the thickness of beer-box cardboard. To adjust, there is a small screw that holds the points down on the distributor plate. Loosen this screw and scoot it closer or further from the cam as necessary. Some points have an additional adjustment screw that does this, most don't but provide a slot for you to insert and twist a screwdriver to directly fidget the little sucker around.

If the point gap appears pretty close to correct, I wouldn't suggest messing with it. Poor point gap usually manifests itself as poor running at high rpm, not low.

You asked about the carb. You might check the idle mixture screws. You may have one (meaning you have a mercury carb) or two (meaning you have a rochester). Count how many turns it takes to tighten it(them) in case you want to put it back where it was before. Then loosen it(them) 1.25 turns.

Good Luck

 

[bds85466]

Re: Merc 140 Running problem

jagilbert,

Thank you for the clear and concise information. I appreciate the insight.

Am I getting you right that checking the points for this condition is more of a sanity check than anything? If his gaps are for example @ .021-.023" its not wise to try and fuss with them I'm guessing. Feeler gauge is sensitive to the operator and the variation in measurement is far wider. However, something wildly off would cause problems.

Before I open up the distributor, would it be wise to disconnect the battery?

The carb has a gold merc tag on it. Or might it have 2, be a rochester, and actually still have a tag on it. My guess from the tag is that this means one jet.

I'll look closer tomorrow. Thanks again; seriously this is more objective information that someone's doled out to me in the forum. Thanks.

 

[antsmands]

Re: Merc 140 Running problem

From the pics you appear to have a Mercarb just like mine. Single screw.

 

[bds85466]

Re: Merc 140 Running problem

From the pics you appear to have a Mercarb just like mine. Single screw.

Cool, where's the screw?

 

[fat fanny]

Re: Merc 140 Running problem

Your air idle mixture screw is @ the base of the carb on the right side looking straight @ the motor. easily turn the screw in until it stops do not turn it hard gently or you will damage the seat for the screw @ that point rotate it out to start 1 and 1/4 turns to start and fine tune it from there (on the water). But before all that I would try to get it to idle as close to spec as possible and then adjust from there. Good luck

 

[cr2k]

Re: Merc 140 Running problem

No you wont damage the seat it's cast iron, BUT the screw is soft brass so treat it accordingly. The Mercarb kit comes with a new screw too.

Wondering, since you are not real savvy as to knowing where the points or idle screw is, if you should be messing about too much.

 

[jagilbert]

Re: Merc 140 Running problem

Am I getting you right that checking the points for this condition is more of a sanity check than anything?

Yes, thats my opinion. Setting the gap is actually just a rough way to set the dwell. It should actually be set by a dwell gauge. Since it was probably set by a dwell gauge before you got it, I was suggesting that you check to see that it has .022ish gap as a sanity check.
Tangent: What is dwell? the points open and close as the distributor shaft turns through 360 degrees. The Dwell is expressed as the number of degrees that the points stay open. A dwell meter thus displays this information in degrees. Your motor should have a dwell of between 28 and 34 degrees. You can envision that a smaller point gap would result in the points spending less time open and vice versa. I bought this Actron CP7677 Automotive TroubleShooter - Digital Multimeter and Engine Analyzer on Amazon that includes a dwell meter and tach for $40. You can get the exact same one at either autozone or Advance for $60

Before I open up the distributor, would it be wise to disconnect the battery?

Wouldn't hurt I guess. I don't worry about it. Maybe I'm livin' on the edge.

re: "Should you be messing around too much" Thats how you learn. Keep asking questions, be methodical and before you mess with something, make sure you keep in mind how you are going to put it back together.

Good Luck,
Jeff

 

[bds85466]

Re: Merc 140 Running problem

Thanks all for the info.

Wondering, since you are not real savvy as to knowing where the points or idle screw is, if you should be messing about too much.

Respectfully, it's not my boat and I have only seen it once -- for 20 minutes. I'm relatively new into boating <4 years so I haven't seen a lot of engine set ups -- though I don't like to fiddle without knowing first. I mean, I can tell you where these items are in my boat, what they look like, and what they do, but I was hoping to get some good general prep on these items before I went back because I won't have much time to peek around. However, I appreciate the words of caution from your experience. I like cautiously digging in, as that's how I learn.

 

[bds85466]

Re: Merc 140 Running problem

Your air idle mixture screw is @ the base of the carb on the right side looking straight @ the motor. easily turn the screw in until it stops do not turn it hard gently or you will damage the seat for the screw @ that point rotate it out to start 1 and 1/4 turns to start and fine tune it from there (on the water). But before all that I would try to get it to idle as close to spec as possible and then adjust from there. Good luck

This adjustment should be done after the choke has opened all the way, correct?

 

[fat fanny]

Re: Merc 140 Running problem

Like I said it is a starting point. But with the engine cold if it does indeed start let it warm up and then move it to the point where it performs the best but if a rebuild on the carb is in the line of buisness things might change some on the adjustment side making sure your tach is accurate to get the proper rpm's and setting the idle is the correct starting proceedure. But if your point gap and dwell is incorrect that would be my 1st to do list the setting the carb. Hopefully there are no other underlying issues such as timming and or compression loss. I would suggest you download the service manual from the adults stickies section and read it very insightfull and is almost word for word what you reading from us here. good luck and post back

 

[bds85466]

Re: Merc 140 Running problem

Thanks for the response.

So last night I helped my buddy tow from the random slip he parked in after he couldn't start it back to his own. So now at least we have some breathing room.

Before we tried to start it, I checked the needle adjustment. Here's the chain of events:

It was only at maybe 1/3 turn. Not sure if this is neccessarily wrong/right -- but given that it won't run in "idle" throttle, something's wrong. So on your recomendation I opened it up to the starting point of 1-1/4 turns. Set the choke, fired her up, started very easily -- a bit of white smoke for the first maybe 15 seconds.

It was running quite high in the rpm, even at the lowest throttle setting before shifting it back to N. After I watched the choke begin to open a bit, it came down a touch, but even after fully open, the rpms were in the 1500-1600 range, which is high (obviously the tach could be inquestion too). It sounded good, better than the night earlier.

I let it warm for a bit, watched the choke open completely, and then went ahead and tried to close the needle more towards where it was originally. Here's the strange thing, I didn't notice any rpm difference at all between 1-1/4 turns and fully closed!

I'm not sure what this means (screw shot?) but it really made me wonder. As it ran, I went from closed to 1-1/4, and back down to closed. No diff in the rpm. Furthermore, every time I tried to move the throttle lever back to the N position, no matter how swiftly, it would kill. I'm wondering if there couldn't be a throttle/shift adjustment needed as well.

 

[tschmidty]

Re: Merc 140 Running problem

The idle mixture screw does not entirely shut things off and I have found setting it doesn't make a huge difference but would like to hear more informed opinions.

The stalling going to neutral is probably the shift interrupt switch or lower shift cable need adjustment/replacement.

 

[antsmands]

Re: Merc 140 Running problem

Thanks for the response.

So last night I helped my buddy tow from the random slip he parked in after he couldn't start it back to his own. So now at least we have some breathing room.

Before we tried to start it, I checked the needle adjustment. Here's the chain of events:

It was only at maybe 1/3 turn. Not sure if this is neccessarily wrong/right -- but given that it won't run in "idle" throttle, something's wrong. So on your recomendation I opened it up to the starting point of 1-1/4 turns. Set the choke, fired her up, started very easily -- a bit of white smoke for the first maybe 15 seconds.

It was running quite high in the rpm, even at the lowest throttle setting before shifting it back to N. After I watched the choke begin to open a bit, it came down a touch, but even after fully open, the rpms were in the 1500-1600 range, which is high (obviously the tach could be inquestion too). It sounded good, better than the night earlier.

I let it warm for a bit, watched the choke open completely, and then went ahead and tried to close the needle more towards where it was originally. Here's the strange thing, I didn't notice any rpm difference at all between 1-1/4 turns and fully closed!

I'm not sure what this means (screw shot?) but it really made me wonder. As it ran, I went from closed to 1-1/4, and back down to closed. No diff in the rpm. Furthermore, every time I tried to move the throttle lever back to the N position, no matter how swiftly, it would kill. I'm wondering if there couldn't be a throttle/shift adjustment needed as well.

Sounds like you need to adjust the idle screw which is located on the rear of the carb. Try this: Start the boat - Turn the fuel/air mixture screw (single screw) 1 and 1/4 thru and let it warm up - check the rpm - if still 1500 rpm check the idle linkage to assure that it is free but pushing down of the idle screw to assure that it is resting on the screw stop -if it is free and on the stop then adjust the idle screw by turning it counter clockwise until the idle is down to 700-750 rpm. This should stablize the boat on the muff or be just about right if boat is in the water.

Tony d.

 

[bds85466]

Re: Merc 140 Running problem

Sounds like you need to adjust the idle screw which is located on the rear of the carb. Try this: Start the boat - Turn the fuel/air mixture screw (single screw) 1 and 1/4 thru and let it warm up - check the rpm - if still 1500 rpm check the idle linkage to assure that it is free but pushing down of the idle screw to assure that it is resting on the screw stop -if it is free and on the stop then adjust the idle screw by turning it counter clockwise until the idle is down to 700-750 rpm. This should stablize the boat on the muff or be just about right if boat is in the water.

Tony d.

I'll try that. Thanks for the advice

 

[fat fanny]

Re: Merc 140 Running problem

If what ants said doesn't work disconnect the throttle linkage completely from the carb and start from scratch set the choke while cold manualy start it and let it warm up until choke opens up and set the idle that way. Also if your saying the air idle mixture screw is making no difference I would highly suggest a carb rebuild. It's a pretty simple job especiallyif you have ever built a model car do a search on mercarb rebuild and you'll see keep organized and clean work area real simple. I think your close to a solution just keep plugging away post back! Good luck