1975 Mercury 9.8 Dies Under Load (Video)

Hi guys ive posted about this motor (1975 9.8hp 110) before and since then I have fixed my hard start issue (starts on 2-3 pull when cold) , have a new lower unit with good seals , and a new kill swith.

The motor will idle perferct forever I had it running for about 20mins in a barrel , but when I put it in gear and gave it some gas it stalled out, What could be causing this? the carb and fuel pump was rebuilt, and the float and needle valve are in great shape.
Also when I rev the motor up it makes like a scratching/pop noise is this normal? Ill post a video of it running and you can hear what im talking about when I give it some gas.

One more thing , should I have to re-prime the bulb everytime I go to restart it? Ive never had to do this with any other outboard. But after the motor has been running and you shut it down you have to re prime the bulb to get it start again , is this normal for these motor?

Sorry for the bad quality i took it on my phone
Thank You

(Click On Picture to Play Video)

Re: 1975 Mercury 9.8 Dies Under Load (Video)

Being that it is in a barrel/trash can when you are testing it , it could be that the exhaust from the motor is being sucked into the carb and will cause some troubles as it changes the oxagon level being burnt . Otherwise it sounds fine as the noise from the motor in the vidio covers up most everthing else. As for having to reprime the motor when restarting it. It could be that there is still a air leak somewhere in the fuel supply. Could be the primer bulb, hose connections , motor connection, or the tank connection. JMO
Oldman570

Re: 1975 Mercury 9.8 Dies Under Load (Video)

If you have to re-prime the fuel bulb after each run you may have a clogged fuel line in the motor itself which would starve it of gas and cause it to die under load. Have you removed and inspected the fuel lines for blockage as well as the fuel filter on the motor?

Re: 1975 Mercury 9.8 Dies Under Load (Video)

The fuel lines and tank are brand new , along with the inline filter I put on it. I rigged up a new fuel quick connect because I was not going to pay $60 for the old merc butterfly one. I'll try to get it out on the water this weekend and see if that's helps it out. Also I'll try to get a better video of the sound im talking about with the cowl off. Thank you for the replies.

Re: 1975 Mercury 9.8 Dies Under Load (Video)

Blake0912 said:

The fuel lines and tank are brand new , along with the inline filter I put on it. I rigged up a new fuel quick connect because I was not going to pay $60 for the old merc butterfly one. I'll try to get it out on the water this weekend and see if that's helps it out. Also I'll try to get a better video of the sound im talking about with the cowl off. Thank you for the replies.

Click to expand...

I saw the new fuel line and inline filter on the outside of the engine in the video. Do you have a fuel line on the inside of the engine that runs from your outside line to a filter attached to the block back to the carb? That was the one I thought might be clogged. I also heard (I think) the popping sound you were describing from the video. It sounds like just back firing as it only seems to happen when you let of the gas fast. When you let off the throttle slowly I didn't hear it. I could be wrong but it sounds like you have a fuel blockage at the engine (engine dying under load) and or a venting problem at the tank as the bulb shouldn't have to be pumped beyond the initial filling of the motor with gas.

Re: 1975 Mercury 9.8 Dies Under Load (Video)

There's a line that goes from the fuel pump (it's the style that is attached to the carb) so from the inline filter you see on the outside it goes directly to the fuel pump. There's a filter in the fuel pump diaphragm itself it's just like a black screen , but the new carb kit I got did not have a new "black screen filter" it was just a normal gasket , so I just put both on. Do you know of the filter/gasket im talking about? Maybe this could be causing the problem. It's not leaking at the carb/fuel pump so I assume it's not letting any air in there.

The fuel line/primer bulb/quick connects are all new , but I noticed a little fuel leaking out around the primer bulb maybe this is letting air in the system.

Re: 1975 Mercury 9.8 Dies Under Load (Video)

You should not have any leaks anywhere in your gas line. Possible it is sucking air in when engine is looking for it causing it to be starved for gas when the demand is high. Did you use marine or Merc quick connects on the hose you made?

The black screen filter needs to be there it prevents any small particles from getting into the carb and gooking it up. You can re-use the old screen if you still have it, just clean it and re-instal it. If you threw it out I'd recommend getting another one or risk clogging your carb and having to have it disassembled and cleaned again.

Re: 1975 Mercury 9.8 Dies Under Load (Video)

Some aftermarket bulbs will not seal as they should and will suck air that could be causing you trouble. As for the old filter and new gasket in the fuel pump, as long as you have thge filter inline as shown then the old filter gasket should be removed. This also could be the trouble. JMO
Oldman570

Re: 1975 Mercury 9.8 Dies Under Load (Video)

The quick connect and line is actually a Johnson/rude because I had it for my 9.9 Johnson but it is still brand new. I'll inspect the bulb closely this weekend.

So since I have the inline filter I should take out the small black screen filter ?

Re: 1975 Mercury 9.8 Dies Under Load (Video)

Blake0912 said:

The quick connect and line is actually a Johnson/rude because I had it for my 9.9 Johnson but it is still brand new. I'll inspect the bulb closely this weekend.

So since I have the inline filter I should take out the small black screen filter ?

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Don't know for sure how restrictive the inline filter is as I can't see the filter inside the case but is looks big enough to allow sufficient fuel flow. The square black screen filter should go back in place regardless. You can try taking out the inline filter if the problem persists but the engine was designed to have the other filter in place. I'm not a big fan of trying to re-design what a whole bunch of factory engineers thought was best to begin with. Particles may get around the inline filter but they won't get past the black one. I had twin 260 hp Mercs (I realize we're talking apples and oranges) with a paper based water separating filter coming directly off of the gas tank that acted like the inline filter you installed AND a screen filter at the carburetor. The screen filter would routinely catch particles that the paper based filter would miss. Adding the extra inline filter can only help (to better filter the gas) not hurt assuming it is not so restrictive as to drastically reduce the fuel flow. If the bulb itself is leaking, new or not, you need to replace it.

Re: 1975 Mercury 9.8 Dies Under Load (Video)

Thank you for the replie , the inline filter is the same one I use on my 40 merc so I don't think it's causing any type of restriction, plus the black screen filter is still installed. As I said earlier today I'll go try it out on the flat bottom instead of the barrel and see if it helps. Also I'm going to go to the auto parts store and buy a new bulb / line set up because I've had always had problems with these attwood pre made fuel lines from academy and see if that helps the motor out.

I will also make a better video of it out on the water if it's still acting up.

Re: 1975 Mercury 9.8 Dies Under Load (Video)

Blake0912 said:

Thank you for the replie , the inline filter is the same one I use on my 40 merc so I don't think it's causing any type of restriction, plus the black screen filter is still installed. As I said earlier today I'll go try it out on the flat bottom instead of the barrel and see if it helps. Also I'm going to go to the auto parts store and buy a new bulb / line set up because I've had always had problems with these attwood pre made fuel lines from academy and see if that helps the motor out.

I will also make a better video of it out on the water if it's still acting up.

Click to expand...

Good luck! Let us know how it goes.

Re: 1975 Mercury 9.8 Dies Under Load (Video)

I realize you have a 9.8 and a different set up but pictures are for referene to fuel line set up. Check the plastic cover that covers the screen they get old, and brittle, and crack on the inside, and isn,t noticeable on the outside, Air could be sucked in throught the screw hole as a result. Here is my setup with the screen removed and the inline filter between the pump and the carbs. Nothing should be between the primer bulb to the fuel pump except the quick disconnect as an inline filter can hold air and affect the suction of the fuel pump when pulling fuel from the tank. It can push through air put it will not pull correctly through air. Also as stated check the tank vent fix the leaking primer bulb, and you should see a difference. I recommend that you bypass the screen temporrarilly to see if the condition improves, View attachment 179848 I had a better picture but it,s been deleted should give you an idea though. This is a 70 HP this wiring has all been re done scince then View attachment 179849 If the problem seems to be resolved you can if you choose to replace the outer screen cover. The screen is in fact the OEM filter Cleanable. But still the filter and can be adapted to a regular inline filter alone. JMO

Re: 1975 Mercury 9.8 Dies Under Load (Video)

I didn't hear it "die" when it shifted into gear. I have had problems with the exhaust getting recirculated in the carb and killing the engine. It also seems the engine is able to rev too high in the "start" range, that should be adjusted so it can not over rev. I believe the book max speed in the start range is 2,000 to 2,500 rpm. The popping is normal on decel.

Re: 1975 Mercury 9.8 Dies Under Load (Video)

thank you for your replies. 79Glastron the motor does not die in the video I forgot to record it doing that , it was dieing when I gave it gas in forward it will idle in forward with no issues. Good point about the high reves while in the start range ill look into adjusting that.

Maxz I understand what you are talking about , thats how much larger outboard inline fuel filters are rigged. But on this motor the fuel pump is part of the carb so that set up is impossible to do.

I will try it without the inline filter after the primer bulb to see if that helps.

This is the best pic I have at the moment showing the fuel pump/carb the blue part is where the fuel line connects , but from there it is just part of the carb. There is not fuel line going from the pump to the carb so I cant have the inline filter hooked up that way. I will check out the plastic cover you are talking about but when I had it off I seem to remember the plastic being in great shape and I replaced the quark gasket behind it.

Re: 1975 Mercury 9.8 Dies Under Load (Video)

Blake, under the blue cover is the black screen I was talking about. That's the one I think you should leave on. Good luck with your test.