Hesitant only at throttle up and throttle down 115 98 Mariner

bfan781

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Jun 18, 2010
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93
Hi,
I have 115 Mariner outboard (98). Need some assistence. I have been having other issues and have worked through a few and made the boat run better.

Currently, I notice an issue only when throttling up and throttling down. When at the speed it runs perfect. No more drops (rpms) at WOT. Only when throttling.

When throttling up here is a hesitation. It takes a second or two to react. (a delay) When you get to the speed it it perfect and runs smooth and flawless. When throttling all the way down, there seems to be like a gurgling or chugging sound. (only when going from speed to no wake) Other than that it runs great. What could that be?

It seems one of the plug wires doesnt seem to snap onto the plug like th others do. What that cause it? a bad connection?

If not what else should I check?

I already cleaned/rebuilt carbs. ( i did not remove the jet in the fuel bowl, but soaked for a while and then ran a wire through them) to clear any buildup.

Changed all filters, running on portable tank with new gas, bulb and lines.

Issue is only when throttling from idle up (hesitation) and throttling down ( gurgling) Other than that it runs great.

I need some help big time!!!

Could that just be the engine?
 

hawkster

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Jul 13, 2010
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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

If your 115 has an accelerator pump that will effect performance durring an increase in speed. I was working on a 93 115hp and the accelerator pump was gummed up and one of the injector check valves was stuck open and it ran terrible durring acceleration. Clean the pump and injectors. Reinstall pump and set with .020 gap between the pump plunger and the throttle linkage.
 

bfan781

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

ok, I believe it does have an accelerator pump. I will check the manual. Does that get cleaned the same way as carbs? Clean the parts in carb cleaner? Can I just get away with cleaning and re-using everything? Stores are closed to today so I may not be able to get gaskets and so forth.
 

bfan781

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

The injectors in the accelerator pump? Manual doesn't say to much on that. Any thing I should look out for?
 

hawkster

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

I know what you mean about the manual not having much on these items. The pump is quite simple to clean just be sure not to tear a gasket while taking it apart. It has a check valve, diaphragm and a spring if I remember right. It's easier than a carb to clean, just check for anyting that might foul the check valve or a hole in the diaphragm. You can test it after you assemble it to make sure its pumping. The output hose goes to a tee on the other side of the block which branches off to cylinders 3 & 4. The injectors look like brass fittings and the hose connects to them. Inside them is a needle valve and spring. Debri can keep the needle valves from seating properly. I found them hard to get to so I took the hoses off at the tee then loosened the injector from the block. I then turned the hose to spin them out. I also got them started back in that way so this may help you too. Good Luck
 

bfan781

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

Thanks, I no longer thing that is the issue though after yesterday.

For the accelerator pump, do you just test it by making sure that button on top goes in and out freely?

BAsically what I did yesterday was remove the acelerator pump completing took it apart gave it a quick dip in carb cleaner (not the plastic or rubber part) Rinsed it and then blew it off with compressed air. There was some dirt or something in there too. But I did not know how to actually test it. When connected and the throttle accelerates that lever pushed down on that button and everything seemed to move freely.

I did adjust the setting to what the book specified, it seemed to be a little off when I took it off. When at full throttled, the manual states .30 in and it was greater before I removed it.

For the test run, nothing changed though so either I did not actually test it (just cleaned it) or that is not the issue.

Yesterday, it seemed to idle a little rough when first started.

It also yesterday, seemed more like a fuel bog than say a miss. When at idle or moving slowly and throttling up it bogs, hesitates, and then reacts and gradually moves to where it should be. Like it isnt getting the fuel through. once it gets going 3k, 4k, you can throttle up more or down and there is no problems at all, runs smooth, but it is already running smoothly. It reacts as it should. Its just that "catch up" hestitation from a standstill If you drop it all the way down, and then throttle up it has the issue again. . Not sure if this helps trouble shoot but it almost sounds that the engine is sounding lower and then the sound increases until it reaches where it should be at, but the throttle is already there.

You can run at 5200 RPMS and it runs perfect noe (after the carb rebuild) no drops at all.

Yesterday once, then throttling up from a crawl, the rpms went up to about 6000 but the enigine was in that hesitation period like it wasn't getting the fuel.

Any other possiblities ot things to try? I have to figure this out. Thanks again for your time.
 

hawkster

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

When idleing (below 1000rpm) cylinders 3 & 4 are shut down.That's why there is no idle adjustment on them. The ouput of the accelerator pump gives cylinder 3& 4 a shot of gas to bring them online durring accelration to get through that lag period. After you reach the upper rpm's the carbs take over. If this shot of gas does not reach 3&4 via the injectors, acceleration is slow and rough at best. To test the accel. pump take off the output line and pump up the fuel bulb. Take a screwdriver , push on the plunger and see if fuel flows out. If so I would really take the time to check the injectors. It saved me alot of headaches. Also some systems have a fuel filter betwen the accelrator pump and injectors. Just another thing to consider and your symptoms are very much the same as what I had going on. Good Luck
 

bfan781

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

hawkster,

Ok bare with here, I'm new to this.

so the accelerator pump, has those two brass fittings where the fuel hoses conect to. Those are the injectors? I removed those hoses when I cleaned it. I also removed the pump from the engine completely.

So to test it, leave it all hooked up and remove only the output hose only (the one that tees to carbs 3 and 4). When I pump the bulb, I should see no fuel come out that output injector. The plunger is that white button on the top of the pump. If I push that down with screwdriver (what the throttle lever does) I should see fuel come out of that output injector? Or should I not see fuel come out?

When you mentioned you loosened the injectors from the block, do you mean the whole pump from engine, or did you take those brass injectors off the actual accelerator pump?

I believe I changed that fule filter already. Is it a little one behind the oil tank?

Little confused by that. So you had similar symptoms? And that fixed it. I want to try this tonight or tomorrow.
 

bfan781

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

Hawkster,

OK, makes sense to me now, I just re-read your posts a few times. Sorry new to this. Trying to put it all together.

So the injectors are not on the accel. pump they are on the other side branching off the tee and connect to the cylinders. I already removed the pump and cleaned. Now I should do that test you mentioned to make sure that once the plunger is depressed to see what happens. Should fuel come out or not come out?. If it is correct, I should take a look at those injectors on the block.

So if a needle in the injectors is stuck open is that what causes the issues? Fuel is constantly flowing? how does that cause the hesitation?

Is it something I will be able to tell when I see it?

Now it makes sense when you were explaining taking the injectors off by spinning the hoses.

How did you clean the injectors? or did you need new ones.

Did this fix your issue.

Sorry for all the questions, this is starting to make sense to me.

Thanks so much for all your help.
 

bfan781

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

I am going to try the test and look at injectors possibly tonight, not sure how much you check this site and if the post will get lost, but I will post back what I find.
 

hawkster

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

The hesitation comes from not getting fuel either at the right time or in the right amount. I know this can be frustrating but all of these pieces of the puzzle have to work properly or the engine does not perform to it's ability. You can clean the check valves in the injectors and reuse them. Once you get them apart you will see how they work. The motor I worked on the owner had beed using alcohol fuel plus there was no filter between the pump and injectors which allowed gunk to get in the system and foul them.
 

bfan781

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

Hawkster,

ok here is what happened, I had to take off the accel. pump to be able to cut the zip ties, when I removed the output hose from the accelerator pump and primed the bulb, fuel poured out the output nipple without even touching the white plunger piece on top. If i pressed in the plunger it squired out, but if I left it alone it poured out.
Is that not supposed to happen?

Looking staight on at the pump. the two hoses, the one on the right is what goes to the cyl 3 and 4 and the one on the left looks like it comes from the second carb.

I didnt not go any farther with the injectors because I was not sure if the accel. pump was supoosed to act that way.
After you cleaned your injectors did that correct the hesitation?
 

hawkster

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

When you pump the bulb, gas will flow out of the accel pump this is normal. When you push down on the plunger it should develope pressure or squirt the gas out of the pump with some force. Yes cleanning the injectors sloved my hesitation problem and hopefully it could yours.
 

bfan781

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

Hey Hawster thanks alot for all your time and help. I am probably going to pull off the injectors and inspect and clean this weekend (saturday)

Ok, so I guess the pump is actually working properly then , fuel does pour out and when the plunger is pressed in, it does shoot out. So seems good. So Does that mean that fuel is constantly going into the 3 +4 cyliners? Can't grasp how it actually works.

Any other tips or tricks to getting the injectors out and cleaned? I will leave the hose attached like you did and spin them. How did you clean them? Carb cleaner? When going back in how tight do they need to be.

I wil post back with the results.
Thanks Again!!! You've been a big help.
 

MercGuy

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

I'm a little late chiming in on this, but a quick and dirty way to test the accellerator pump is to use a thin blade to push the plunger down while the engine is idling. If the pump is working you will hear the engine jump as 3 & 4 light up from the squirt of fuel.

Very simple and nothing has to be taken apart.

Of course that test doesn't let you know if one of the injectors is clogged, as the engine could jump from one cylinder lighting up. And it doesn't tell you if the injectors are dirty and not injecting enough gas.

But it will eliminate the accel pump itself from the equation.
 

bfan781

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

Hey Mercguy,
Thanks for your input. I will try that test as well. Most likely tonight. Seems like the accel pump is working but that should def. confirm.

If working I am going to look at the injectors like hawkster recommended. So are there any other any tips or tricks to getting the injectors out and cleaned? I will leave the hose attached like you did and spin them. Whats the best way to clean them? Carb cleaner? Did you do anything else? Soak them or anything. When going back in how tight do they need to be.

Still confused as to how the whole setup works. Boggles my mind. Seems like gas is always going to those cylinders since it flows out always. But if the injectors are dirty and after I clean them it fixes it I'll be happy.


I will post how I make out, so keep a look out for this thread!!!
Thanks
 

bfan781

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

Hmm, will it definitely rule out the accel pump mercguy. What do you think of this? I have a good feeling that the issue will come from this accel/injector piece of the motor.

I started it up tonight on muffs in the driveway. I noticed I was idling at about 1700 rpms. That is really high isn't it? Does that need to be adjusted. Will it drop down like a car when warm? I had it running for a few too.

So get this, when I used a screwdriver to push on the plunger, sometimes the engine would rev higher (3+4 coming on) but many times it did not? More often than not it wouldn't. Theres the hesitation I bet, right? The engine stayed and souned the same.

When I tested it the other day like Hawkster recommended, I depressed the plunger I got a shot everytime. ( maybe I'll take it off and test again that way) to double check.

So is it possible that the pump is working, yet the injectors are clogged/dirty/stuck? Or is the accel. pump having issues and working intermittantly?

Think I am getting close to resolving.
 

MercGuy

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

A couple of things bother me about your test.

Personally, I've never had an outboard run well on muffs. I think you would have better results with the lower unit in the water so that the engine could run with the normal backpressure.

Also, 1700 RPM is an awfully high idle speed. That is just about where the lower 2 carbs will start to kick in, so it is possible that the accellerator pump didn't have much effect because 3 & 4 were already running.

I'm only guessing on all of this. I'm not an expert and others on this board will know more than I.

Good luck !!
 

bfan781

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

Mercguy,

i agree totally. All I had time for when i got home from work last night was to throw it on the muffs.

Also like I mentioned, sometimes when I pushed it in it definitely revved higher, many other times it didnt. That makes me feel like it wasn't running on all four. So. now the shot gas occurs even went it is slightly deprressed right? Because the engine isn't at full throttle when 3+4 kicks in. Its at 1700-1800 which would only be throttled up slightly or so. The times it did rev higher, I had the plunger fully depressed. So it must be the injectors or something with the accel. pump.

I thought that seemed like a high idle. What should it be? Should it/can it be dropped down? I do feel confident that my issue is related to all of this just need to put it all together. That is def. where the hesitation on throttling is coming from, when throttling up, the shot of gas isn't getting to the 3+4 at all or maybe not until fully throttled.

Hopefully hawkster will chime in and have some advice on the idling and cleaning of the injectors. He seems to know the motor and has worked through the same issue.

Can't thank you all enough
 

hawkster

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Re: Hesitant only at throttle up and throttle down 115 98 Mariner

The injectors have check valves in them. If they are stuck open there will be fuel going to cylinders 3&4 . It could be possible that your idle could increase because of this. The fuel pump output pressure is approx. 4psi. Then after flowing through the accel pump it drops to around 3.5 psi. The check valves in the injectors unseat at 11 to 14 psi. That is the job of the accel pump to boost the pressure to open the injector check valves only durring acceleration. I agree with MercGuy about idle with the muffs. It's much better to have it in the water. Sounds like your getting close just have to eliminate one thing at a time and the benefit is that you get to know your motor insde and out. I would not adjust anyting concerning the idle until you solved this issue.
 
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