Do I need new spark plugs or rust in gas tank

[pecheux]

Good day.

This 1997 Force by Merc (I know it's Chrysler) has been running like a charm for many years until now. Runs great at WOT but after trolling for a few minutes it will just stop. At faster idle I can tell it's missing after a shorter while. Varies between 15 seconds to one minute then I turn the handle to WOT and it will just get there and stay there without any misfiring. This OB normaly starts on first pull but when it stops when trolling (idling) it need several more agressive pulls.

I took the plugs out and the center parts are nice light brown and electrode shows no sign of wear. but the outter part shows a bit of carbon. I dont remember if I changed then last year but it has not been used much.

Also I have switched to an OMC self venting metal tank that I owned since new and showned no sign or rust. (but who knows ..) the tube inside the tank has a mesh filter.

Any suggestions on what the source of the problem may be ? I will be replacing the plugs anyway. I am confused with the fact that is runs great at WOT.

Thank you.

 

[CaptainKickback]

Re: Do I need new spark plugs or rust in gas tank

I have a small outboard I used only once or twice a year. Ran great but wouldn't idle well. Once I started using it ever week, it ran great even at idle.

I think it cleaned out a carb jet.

 

[tater76]

Re: Do I need new spark plugs or rust in gas tank

First things first, what HP is your 97?

You need to start with the basics, Compression, Spark, and Fuel Delivery. These will lead you to the problem area. Then you can start turning screws or replacing parts.

 

[roscoe]

Re: Do I need new spark plugs or rust in gas tank

One of the simplest things that can cause it to run like this is ....... bad gas. water in the gas.

Dump the gas, start with fresh, see what happens.

If the carb sneezes back at you, it is running lean, either from not being set rich enough, or from a slightly dirty carb.

 

[pecheux]

Re: Do I need new spark plugs or rust in gas tank

One of the simplest things that can cause it to run like this is ....... bad gas. water in the gas.

Dump the gas, start with fresh, see what happens.

If the carb sneezes back at you, it is running lean, either from not being set rich enough, or from a slightly dirty carb.

Thank you, 15 hp Force 1997. Used it for the first time this season yesterday, had a fresh gas/oil fill. I guess I can dump it and use it in my lawn mower.

No it does not sneeze ... just stops when idling (then hard to start) + some noticeble missing as I accelerate to prevent it from stopping, then runs great once I get to WOT. Now that I think of it ... almost as if it was not firing from one piston ... which lead me to think PLUGS .

Will dump gas and start fresh and put new plugs and see what happens. How long should plugs last ? I dont think I used it for more than 3 gas tank full last season.

Regards.

 

[pnwboat]

Re: Do I need new spark plugs or rust in gas tank

When it stalls and you go to restart, try squeezing the primer bulb first if you haven't tried that. If that cures your hard start problem, it may be that the rubber fuel pump diaphragm may be old and stiff and not working well at idle speed.

 

[pecheux]

Re: Do I need new spark plugs or rust in gas tank

When it stalls and you go to restart, try squeezing the primer bulb first if you haven't tried that. If that cures your hard start problem, it may be that the rubber fuel pump diaphragm may be old and stiff and not working well at idle speed.

Thank you,
The primer pump and hose is bran new (used several times only) By hard to start I mean needing more than one pull as it normaly starts and seems to need more vigorous pulls. (maybe 4 or 5)

Have a great day. and tx

 

[CaptainKickback]

Re: Do I need new spark plugs or rust in gas tank

When mine would die at idle, it would be hard to start. I got pretty good at it though by choking it and pulling once. Then no choke and started on that second pull.

If your on a budget or don't like working on engines, go run it.

 

[pnwboat]

Re: Do I need new spark plugs or rust in gas tank

Maybe I wasn't clear on what I was getting at. I wasn't suggesting that the primer bulb itself was bad, I was suggesting that maybe the fuel pump diaphragm was in need of replacing. Squeezing the primer bulb just fills the carburetor bowl up with fuel. If the fuel pump was not working like it should, it may not be keeping the fuel level in the bowl up to where it needs to be.

 

[pecheux]

Re: Do I need new spark plugs or rust in gas tank

Maybe I wasn't clear on what I was getting at. I wasn't suggesting that the primer bulb itself was bad, I was suggesting that maybe the fuel pump diaphragm was in need of replacing. Squeezing the primer bulb just fills the carburetor bowl up with fuel. If the fuel pump was not working like it should, it may not be keeping the fuel level in the bowl up to where it needs to be.

Understood , thank you.

 

[pecheux]

Re: Do I need new spark plugs or rust in gas tank

When mine would die at idle, it would be hard to start. I got pretty good at it though by choking it and pulling once. Then no choke and started on that second pull.

If your on a budget or don't like working on engines, go run it.

got new gas/oil mix, cleaned plugs, and ran it in barrel for approx one hour, ended up idling great. Cant wait to decarb at WOT ... LOL
Thank you

 

[CaptainKickback]

Re: Do I need new spark plugs or rust in gas tank

got new gas/oil mix, cleaned plugs, and ran it in barrel for approx one hour, ended up idling great. Cant wait to decarb at WOT ... LOL
Thank you

Good news. Sounds like you're good to go. Have fun.

 

[bentle]

Re: Do I need new spark plugs or rust in gas tank

When and after the motor dies how does the primmer bulb feel when you prime it up?
If its kinda flat feeling then the tank may not be venting properly so the pump is unable to pump fuel properly.
As already stated you may need to replace the fuel pump diaphragm and any filters.
I have a 97 15 hp gamefisher and had to replace self venting tank because it wasn't getting the job
done.

 

[Frank Acampora]

Re: Do I need new spark plugs or rust in gas tank

If you own a Force by definition you must replace or clean plugs.

Low speed stalling, difficult starting, missing, yet excellent WOT running are all signs of fouled plugs.

Reason: The elecronic ignition on these engines is very much like a magneto in action. They generate the strongest spark when run at high speeds.

Thus: When you slow down for any extended period, with a weaker spark, the plugs will tend to foul and misfire. Yet, these same plugs will fire well at high speeds (if you can get there) where the higher voltage will bust through the fouling.

The remedy is to always carry a fresh set of plugs and a plug wrench. Slightest sign of difficulty--replace them. Clean the old plugs with a green Skotchbrite pad and work it into the surface gap. Reuse clean plugs indefinitely. They almost never wear out.

 

[pecheux]

Re: Do I need new spark plugs or rust in gas tank

When and after the motor dies how does the primmer bulb feel when you prime it up?
If its kinda flat feeling then the tank may not be venting properly so the pump is unable to pump fuel properly.
As already stated you may need to replace the fuel pump diaphragm and any filters.
I have a 97 15 hp gamefisher and had to replace self venting tank because it wasn't getting the job
done.

As I mentionned to someone else the OB ran great in a barrel after I cleaned the plugs, and you may have a point with the self venting gas tank as I tested the OB using my other gas tank (quicksilver) which has a vent screw in the cap. It never crossed my mind that a self venting tank would stop venting properly.
Tx

 

[pecheux]

Re: Do I need new spark plugs or rust in gas tank

If you own a Force by definition you must replace or clean plugs.

Low speed stalling, difficult starting, missing, yet excellent WOT running are all signs of fouled plugs.

Reason: The elecronic ignition on these engines is very much like a magneto in action. They generate the strongest spark when run at high speeds.

Thus: When you slow down for any extended period, with a weaker spark, the plugs will tend to foul and misfire. Yet, these same plugs will fire well at high speeds (if you can get there) where the higher voltage will bust through the fouling.

The remedy is to always carry a fresh set of plugs and a plug wrench. Slightest sign of difficulty--replace them. Clean the old plugs with a green Skotchbrite pad and work it into the surface gap. Reuse clean plugs indefinitely. They almost never wear out.

Thank you Frank, Your precisions is a clear as it can get.

I did brush the plugs with an old toot brush prior to reinstall. Admitedly they did not look dirty, where nice dark beige color and I could not see any carbon build up in the gap area but some around the edge of the plugs. Was using a 50:1 mix with a self venting tank (OMC) I also switched gas tank to the original Qwicksilver plastic one that came with the motor and made a new leaner gas/oil mix at 75:1 using xxxx brand oil which that motor is acustomed to. Whatever fixed it and solved the problem ... fixed it and solved the problem. LOL
Tx again for your instructive feedback.

 

[pecheux]

Re: Do I need new spark plugs or rust in gas tank

Question: can a self venting metal (OMC) gas tank stop venting properly ?? It's still like new but it's 30 years old.