1980's 70hp mercury power loss - troubleshoot

[boxboy]

Thanks in advance for your help.

I am having problems with power loss with the motor when put into gear.

Idles fine, but when put into gear under load it bogs down and loses power. But if you have ear mufflers or test tank it works fine in gear due to it having no stress or load trying to push the boat?

I had it at a shop they thought they fixed it but no same problem. After that they decided not to charge me their time, and not to try again.

Any thoughts on how I should trobleshoot this problem?

thanks
again
p.

 

[RaScLeS]

Re: 1980's 70hp mercury power loss - troubleshoot

i had the same problem today with mine, take the cap off the motor and run it, mine was peeing gas out from the rubber covering the fuel screen and i dont know where to get a new rubber piece. otherwise it could be the power pack

 

[DrWiffel]

Re: 1980's 70hp mercury power loss - troubleshoot

Sorry to revive an old thread, but this one seems to be the only one on here that I can find that someone else has the same problem that I'm having (Except mine is a 1979). Does anyone have any idea on what could be causing this? Any help would be greatly appreciated.

I did neglect (stupidly) to put fuel stabilizer in the tank before storage, and put 4 gal of fresh gas and oil before running the engine. I took the boat out last week for the first time this year and it ran great, but when I went to take it out on Sunday, I started having the same problem that Boxboy is having. Motor idles great, goes into gear just fine, and runs fine to about half throttle. When I push throttle down anything past half throttle, it will run fine for about 30 seconds then bog down (almost seems like its flooding). I then started to think that maybe the carb was a little gummed up so I put some Seafoam into the tank. I ran the boat for another hour or so with the same results. I pulled the plugs and #1 (top cylinder) was fouled up pretty good, and noticed that there was a small puddle of gas under the carb. I cleaned the plugs, and will be taking it out again soon to lake test it. If anyone could let me that I'm on the right track that would be great. I was going to try later this week to see if I could pull the carb and give it a good cleaning if it didn't work on the lake test. Should I even bother with the lake test, or should I just go ahead and pull the carb?

Any input would be a help seeing as I?m feeling pretty lost when it comes to these things.

Thank you in advance,
DrWiffel

 

[jeffreyr]

Re: 1980's 70hp mercury power loss - troubleshoot

Could be the fuel pump..Not totally sure though..If all plugs are firing then doesnt sound electrical soo it would sound like a fuel problem..Pump the fuel line bulb while at around half to 3/4 throttle and see if it picks up..If that happens then ur fuel pump may need to be rebuilt..If not then check fuel lines for any leaks or bad fuel line and of course if non of this does it, clean the carbs..Also make sure its not running to rich or lean..

 

[xxxrfb2xxx]

Re: 1980's 70hp mercury power loss - troubleshoot

[QUOTE=DrWiffel;3334535]Sorry to revive an old thread, but this one seems to be the only one on here that I can find that someone else has the same problem that I'm having (Except mine is a 1979). Does anyone have any idea on what could be causing this? Any help would be greatly appreciated.

I did neglect (stupidly) to put fuel stabilizer in the tank before storage, and put 4 gal of fresh gas and oil before running the engine. I took the boat out last week for the first time this year and it ran great, but when I went to take it out on Sunday, I started having the same problem that Boxboy is having. Motor idles great, goes into gear just fine, and runs fine to about half throttle. When I push throttle down anything past half throttle, it will run fine for about 30 seconds then bog down (almost seems like its flooding). I then started to think that maybe the carb was a little gummed up so I put some Seafoam into the tank. I ran the boat for another hour or so with the same results. I pulled the plugs and #1 (top cylinder) was fouled up pretty good, and noticed that there was a small puddle of gas under the carb. I cleaned the plugs, and will be taking it out again soon to lake test it. If anyone could let me that I'm on the right track that would be great. I was going to try later this week to see if I could pull the carb and give it a good cleaning if it didn't work on the lake test. Should I even bother with the lake test, or should I just go ahead and pull the carb?

Any input would be a help seeing as I?m feeling pretty lost when it comes to these things.

Thank you in advance,
DrWiffel[/QUOTE]Hi I had this problem with a Mercury 90 hp 1988 it was the Enrichner valve it was stuck open thus allowing fuel to be dumped into the intake and flooding out the motor.
This valve is used instead of a choke,I prefer the choke myself.
Hope this helps best regards .

 

[DrWiffel]

Re: 1980's 70hp mercury power loss - troubleshoot

Sorry I haven't been on. Just got a hunting and fishing buddy. I'll be sure to check that out. I worked on it a bit tonight to see if it might be the fuel diaphragm, and the hoses and connections, but didn't see any tears or cracks. So you you might be right.

Thanks
Wiffel

 

[DrWiffel]

Re: 1980's 70hp mercury power loss - troubleshoot

I replaced the fuel diaphragm, and now it appears to be wose so I'm thinking that I did something wrong.The motor now doesn?t seem to be getting hardly any fuel now. So I went through all the fuel lines again yesterday and replaced 2 tubes. One had some cracks and one a small hole. After replacing, the carbs are still not getting enough fuel. So I pulled the gas line that is leading to the fuel filter from the pump and gave it a few cranks to see how much fuel is being pumped. Not much fuel is going through and seems to be very weak. The only things I can think of now is that I installed the diaphragm wrong, the connections to the gas can or to the motor are bad, or the fuel pump its self is bad. Any advice would be much appreciated.

Thanks,
DrWiffel

 

[ajgraz]

Re: 1980's 70hp mercury power loss - troubleshoot

With the whole fuel system hooked up, can you hand-pump up the ball to reasonably firm without forcing fuel out of the little vents in the "floor" of the carburetor mouths? If so then the lines, fittings and ball are likely OK, and we know the fuel bowl needles and seats are working.

(If fuel does come out the vents, you definitely need to disassemble the carbs...though that may not be your only issue. You'll probably be disassembling the carbs before this is done, but let's focus on fuel supply first )

When you replaced the fuel pump diaphragm, did you also replace the two check valves in the fuel pump? They are critical to keeping the fuel flowing through the pump and are often overlooked.

EDIT: don't want to overlook the obvious, are you opening the vent on your fuel tank?

 

[MacDaddy21]

Re: 1980's 70hp mercury power loss - troubleshoot

Ajgraz is right about the check valves. However, when you rebuilt this fuel pump, I would have recommended that you take it completely apart, and soak all the parts in Chem-Dip. Sometimes the fittings on the fuel pump can get blocked by pieces of broken down fuel hose liner. IF fuel is not coming out of the hose that goes to the fuel filter, you need to completely rebuild the pump. Also, where the fuel line connects to the motor, disconnect that fitting, have someone hold down the valve with a screwdriver, and then you pump the primer bulb to ensure that adequate amounts of fuel are coming out of the fuel line and at least making it to the fuel pump.

 

[DrWiffel]

Re: 1980's 70hp mercury power loss - troubleshoot

Thank you guys for the suggestions.

When I replaced the Diaphragm I did not take apart the fuel pump its self, just replaced the gaskets and the diaphragm so you?re right, that might be the problem.

I will also take a look at the check valves. I haven?t done this before, I don?t really understand where they are located, but I?m sure after a few more searches I can figure it out. Thank you for the tip on checking the hose to the can. I think that will be my #1 to check as it would be the easiest.

I did make sure the vent was open on the tank, and even tried with the cap off to be sure that wasn?t the problem.

Thanks again for the help I'll let you guys know if I figure it out.
DrWiffel

 

[ajgraz]

Re: 1980's 70hp mercury power loss - troubleshoot

The valves are in the face of the pump, the plate you take off to get to the diapraghm and gaskets, held in by a screw and a little bracket. They are one-way valves, one in and one out. Their sealing surfaces can wear or get debris stuck in them, then the diapraghm does not have anything to push/pull against to get a good "siphon" going.

Most fuel pump kits for your motor only contain the diaphragm and gaskets, Quicksilver 76575A9 (or 21-13424A1) kit also contains the check valves.

 

[DrWiffel]

Re: 1980's 70hp mercury power loss - troubleshoot

Thanks ajgraz! That description will help me a ton. Thanks.

 

[DrWiffel]

Re: 1980's 70hp mercury power loss - troubleshoot

Thanks guys I got it figured out and you saved my weekend. I did have to redo the diaphragm, but it was still not running quite right and stopping after about 30 sec. At that point I decided that I just about had it and went to fleetfarm for a new tank and line connections. They didn't have the tank fittings needed for a new tank, so I ended up just buying the line with connections and a hand pump. Hooked it up and it ran normal a idle. So we took it out for the lake test and everything seems to be working great. And on the plus side no leaky spots on the water. Thanks again for your help