1997 120hp wont idle properly

[Llunker]

I don't know what is going on with my motor.

I can't seem to keep the boat at the correct idle? My Mechanic and I both worked on the unit yesterday to just give it a tune up as it was cutting-out in the water from two days ago.

So yesterday we cleaned the carbs -checked compression on all cyclinders all but the top cylinder were ok and within 5 of each other. the top was about 10 off.

Anyways we put the muffs to it and i had new plugs in it from last year and it doesnt have alot of time on the new plugs. on the Muffs the engine was idling ok and the carbs were adjusted to make it run at 1100 rpm at idle. which was perfect for muffs i guess but not the actual water run. She sounded pretty and ready to go. Mind you we didnt leave them on the muffs long as the neighbors might start coming over and yelling at me.

I think there is a different compression factor as the muffs force the water in and the lake water has to be sucked in--so the real adjustment had to be made on the water as i came to later find out.

Anyways--sorry bout such a long post but i get to the water and almost immediately the engine will not idle properly and keeps dying. I had to keep pumping the fuel bulb to keep it going. Called my mechanic from the boat(several times) and he said to run around the lake while my buddy pumped on the fuel bulb.

We did so and it ran fine for while and then he let go and it ran fine too for awhile.

So I am thinking well its not the fuel pump. or is it??? It did ok until we got back to trolling speed or neutral and it died again. Would not start unless we pumped the bulb up again--ran the battery down a couple times and had to keep switching over to trolling motor battery to start it and then switch it back to top off the other battery--what a pain that was in the middle of the lake. The motor would start and then idle down to 800 and then die.

So i am thinking this is just an idle issue --took the cowling off while on the water and did a simple adjustment on the water of idle and carbs to get me 1100 in idle and about 900-950rpm's in forward trolling gear.

This did fine for a hour or so --so i called my mechanic and said hey i fixed it --i think we are all good here....not so--just ten minutes later while in the middle of a 4mph troll at 900rpms it just suddenly without notice Dies again.

I run through the whole procedure all over again --had the main battery die on my again and switched over to a trolling motor battery and had forgotten about pumping the bulb--but did so and it started again. Had my buddy keep pumping that bulb while we ran it out full throttle again around the lake --thinking now i have bad gas or something???

I dunno--i had him let up on the bulb and it does fine for about 15min and dies again--repeatedly

Is this a Fuel Pump or Fuel filter problem--or is it bad gas--or maybe one of the plugs is fowled??

You got me on this one

My mechanic is ordering a fuel pump and fuel filter to replace but really don't know what the problem could be and neither does he?

What do you guys think?

ps--oops forgot to mention my mechanic was not a fan of me putting any type of stabil in the fuel. But said (by the way it ran in the driveway) it was a little lean(or was it rich)i can't remember but said to dump in 2-bottles of rubbing alcohol and added 3gal of gas without the oil to a 3/4 full fuel tank. don't know if that information is helpful or not

 

[DavidW2009]

Re: 1997 120hp wont idle properly

I've got a '97 120. also. Bought it last Sept. and have had it out three times.

The first time out it stalled once while idling thru the marine.

I followed the instructions on decarbing a two-cycle O/B. Not had the problem return, and it starts and runs better, too, both in and out of the water.

It sounds like you may have fuel pump or fuel supply problem, but decarbing it every year may help.

 

[pnwboat]

Re: 1997 120hp wont idle properly

If the problem goes away when you squeeze the primer bulb, then I would suspect a fuel delivery problem. Bad fuel pump diaphragm would be my first choice.

I assume it runs fine at higher rpm's?

 

[Llunker]

Re: 1997 120hp wont idle properly

yes it runs just fine at WOT. In fact she purrs like a kitten at 52mph. GPS

But my mechanic was saying a fuel pump would not just go in and out like that--but agreed to go ahead and order the part. He said the fuel pump is like your heart --its beating and working or its not. not just working here and there???

 

[pnwboat]

Re: 1997 120hp wont idle properly

Also might check out the primer bulb itself. There's a check valve in there that may not be working correctly affecting fuel delivery. Both the diaphragm and primer bulb are relatively cheap items.

 

[Llunker]

Re: 1997 120hp wont idle properly

thank you--So what does the check valve do exactly?? I will change out the fuel pump, fuel filter and the primer bulb--see if that works.

What about the Plugs ?? should i try another set of plugs? but if it wasn't really missing I guess not?

once i get it back on the water--and the next time my mechanic goes with me so he can see what i am talking about--we should know more.


thanks for the help pnwboat

 

[pnwboat]

Re: 1997 120hp wont idle properly

It's a one-way check valve. Only allows fuel to flow one way. Usually consists of a spring and a ball or flat plastic disc. If the ball or disc doesn't move freely, then you may have problems. Very simple set up.

 

[Llunker]

Re: 1997 120hp wont idle properly

yes i might try this first before the fuel pump to try and diagnose more of what the problem is...

Or just go ahead and do all 3 and hopefully be done with it all and throw some new plugs in it.

Thanks for all your help pnwboat

 

[Llunker]

Re: 1997 120hp wont idle properly

I just don't get it--i went outside to make some adjustments to maybe a carb or something and she fired up and worked like a charm for 15min straight--not a burp nothing--purred like a kitten....but i guess under stress from a lake and not the muffs is where the problems begin. ??????????

Just don't understand--am still going to change it all out but My mind is telling me --did i sit on bad gas all winter and am just getting through the bad stuff now and getting to the fresh?

I dunno--it's a puzzle to me.

 

[pnwboat]

Re: 1997 120hp wont idle properly

The lake is always the true test. If there is any question regarding the gas, you can either get rid of all the old gas and start fresh, or just top it off with some fresh gas. Either way, I'd still go ahead and replace the fuel pump diaphragm.

 

[Llunker]

Re: 1997 120hp wont idle properly

had already placed 30gal of premium on top of the old gas.

just replaced the primer bulb with new hose, fittings and clamps. No changes --purrs like a kitten-- for this time about 20min...hmmm.....Although the new bulb seems to be a bit firmer and stays somewhat firm while running. But again goes to a somewhat normal feel when running(i know this is normal). So that is one thing done. Re-adjusted carbs to exact specs from book -1 1/4 turns out from lightly seated(clymer) and re-did the Idle to spec.

Like i said --she seems to run perfect out of the water. I will get the Fuel pump and filter in this next week and add them as well.

I will let you know how it goes. Thanks pnwboat

 

[pnwboat]

Re: 1997 120hp wont idle properly

I know what you're going through. They always seem to run better, start easier on muffs. I suspect it has to do with the amount of back pressure on the exhaust, especially at idle. That's why the real test is out on the water. Unless you have a test tank, it's hard to duplicate true running conditions in your driveway or backyard.

I built a test tank out of a sheet of 4 X 8 plywood. It's 2 feet deep but even at that, I can't get the lower end as deep as I'd like to. It is a lot quieter than running on muffs though. The exhaust snout is about 6 inches deep so it does a better job of approximating the back pressure on the exhaust than muffs.

 

[Llunker]

Re: 1997 120hp wont idle properly

So it is the True Back pressure of the exhaust is what you really have to go by to set the Carbs and idle properly correct?

You really can simulate the proper back pressure in your dirveway. Therefore something that looks and sounds good in the driveway will not necessarily be that way on the water.

I am going to the lake today to see if that primer bulb did the trick or not. I will know if it stalls again that it is probably and still in need of replacement --the fuel pump and filter.

Wish me luck

 

[pnwboat]

Re: 1997 120hp wont idle properly

Sometimes it has a minor affect. Not on the actual mixture settings themselves, but the way the motor acts. I think it depends on the individual motor. I know on mine, if I set it for say 1000 RPM's on muffs, when I get it in the water, it idles around 800 RPM's. Mixture settings are the same, just that it doesn't idle exactly the same.

Good Luck!

 

[Llunker]

Re: 1997 120hp wont idle properly

pnwboat,

You won't believe it if i told you now. Went to the lake today(over 5 hours there total) and had just replaced the primer bulb with new hose and fittings.

The dang Motor didn't even Burp ---she ran like a Brand New Motor !!!!

WT$$%#@$@#$ ---

I don't believe my eyes or my ears--she ran like she has never run before !! It didnt even try to quit...1100rpm idle and 950 -1000 in gear...purrrttttyyyy.

Do you think it was the gas from last year?? and i just got through it now and am on the good stuff? or maybe a combination of that and the primer bulb. My mechanic said not to even worry about the fuel pump as the old adage states--"don't fix it if it ain't broken". Sounds to me like its fixed for now.

dunno--strange things do happen i guess--what a perfect day of fishing today.

 

[pnwboat]

Re: 1997 120hp wont idle properly

Well I'm happy to hear that all turned out well. As far as the gas being the culprit, I would expect it to run poorly at all RPM's not just at idle. It's been my experience (not that I'm an expert or anything) that my motor (1988 125HP) seems to be very tolerant of different quality gas. Regardless, you seem to have gotten a good bang for your buck with minimal cost and good results.

As far as replacing the fuel pump diaphragm.....well that's your call. There are a few items that I change on a regular basis every few years to prevent being stranded out on the water. They are the water pump impeller and the fuel pump diaphragm. Both items are relatively cheap and easy to do. Pay attention to your mechanic's advice. That's the voice of experience speaking.