fuel pump not creating vacuum

[janco126]

Hello, I have a 1996 25hp Mercury, Serial Number--0G343179. The problem I am having is the fuel pump is not creating a vacuum, the motor will only run if you keep pumping the bulb. Things I have done so far include:
new lines, rebuilt fuel pump, carb apart and cleaned, new primer bulb and line, new fuel tank, fuel filter replaced.
I have read many threads on here about the topic and still cannot figure it out. I do have a service manual for this motor. I ran a compression test and came out with 145 and 148, which I believe is good. I have also done the fuel pump/vacuum gauge test under load and it showed I have no vacuum from fuel pump. I have done the air leak test as well which was fine. So where do you think I should go next with it? I was thinking maybe a passageway between the carb and reed block is blocked or the gasket on the reed block needs to be replaced. I dunno . Also, i did open the fuel vent. So what do you guys think?

 

[carholme]

Re: fuel pump not creating vacuum

Your s/n comes up as;

MERCURY - ( 25 H.P. (1996 ))
Serial No: 0G343179 Model No: 1025201SD



It still suggests that you have a problem on the fuel pump side. When you pump the bulb and the engine continues to run, you have become the fuel pump. Did you replace the check valves when you did the pump?

Gerry

 

[janco126]

Re: fuel pump not creating vacuum

No I did not replace the check valves however i did test them and they were working, flowing only one way.

 

[racerone]

Re: fuel pump not creating vacuum

If you are not getting pulses ( positive and slight negative ) from the port for the fuel pump you may have reed valve problems.--Could also be a lower crankshaft seal.

 

[janco126]

Re: fuel pump not creating vacuum

I have never actually looked at the reed valves. What do you look for to determine if the reed valves are damaged?

 

[carholme]

Re: fuel pump not creating vacuum

When you say that you re-built the fuel pump but you did not change the valves, did you only inspect the diaphragm as well? It only takes a pinhole on the diaphragm to ruin the pump. If the engine will run by squeezing the bulb, it still suggests that the fuel pump was not built correctly or new parts were not installed. However if you are going to leap straight away to the reed valves, that is quite a leap at this stage. As for lower crank seals, have you seen any indication of water intrusion? There is an old adage, KISS. Eliminate the obvious problem areas and ensure they are working first.

Gerry

 

[racerone]

Re: fuel pump not creating vacuum

Lets start at the beginning.------Did you just buy this motor ?-----Did it quit / start acting up while running.----Won't run properly after long term storage.----These details can often pinpoint where the problems are.

 

[janco126]

Re: fuel pump not creating vacuum

Gerry, I purchased a rebuild kit for the fuel pump and a carb gasket kit which came with it. I assembled per the instructions in my service manual, I am certain it is together correctly. When you say the check valves I am thinking the check valves for the bleed system. Is this what you are referring to?

Racerone- the outboard was a friend of mines. I have been helping him fix it for about a month. He was running this engine 3x a week on the water and just pumped the bulb and never fixed it for about a year now. He replaced the entire boat side fuel delivery system, which I have replaced and tested again. Also he sold the motor to me about 2 weeks ago. The motor will start on first pull if you do not squeeze the primer bulb every minute it will cut out at any rpm including idle.

 

[janco126]

Re: fuel pump not creating vacuum

Also Gerry, there is no evidence of water intrusion.

 

[racerone]

Re: fuel pump not creating vacuum

Sounds like you need to revisit the fuel pump.----Check for pulses at the port that drive the fuel pump.

 

[janco126]

Re: fuel pump not creating vacuum

Ok I will revisit fuel pump. When you say pulses at the port how do you determine which port drives the fuel pump. Sry if this is an odd question. I understand the fuel pump just not which ports do what.

 

[janco126]

Re: fuel pump not creating vacuum

ok so after looking at the fuel pump again it was fine. However, I have fixed the problem. The new gasket for the carburetor did not have the vacuum line cut into the gasket.The old one my friend put in was not right either. So the hole in the gasket for the carburetor was non existent thus the vacuum from the engine side was sucking on the gasket. I fixed the problem by cutting a circle in the gasket were the vacuum line was located. Worked like a charm and runs perfectly fine. Also I did not buy the incorrect gasket kit I checked already and i purchased the correct kit. Thanks guys for your help I appreciate it.

Also Gerry, KISS is a great concept and applied very well here.