Motor uses way too much fuel

[iggyw1]

Hi guys,

I have a 75 H.P Evinrude, 1965 model # 75553 Speedi-four motor. I just picked this motor up with a boat and trailer. I had problems with it overheating when I first bought it. I have had that repaired and it is ok now. The motor starts and runs fine, however, it seems like it uses a hell of a lot of gas. Yesterday I went out fishing, and I went out about two miles, not WOT either. I pulled back on the throttle once I planed and just cruised and about 2/3 throttle. I moved around a bit while out there, but only short runs and not far at all. I came back in and used 3 and 1/2 gallons of gas for the approx. 5-6 miles I drove around. This seems like a lot of gas to me. Is it?? I have a 16 ft fiberglass boat. Its a 1965 Geneva.

I read on another section of this forum that one guy replaced his diaphragm in his fuel pump because he was using a large amount of gas. After he replaced this diaphragm, his motor used much less gas compared to what it was using. Is this possible for a bad diaphragm in a fuel pump to cause excess gas usage??? The parts are still available for the fuel pump repair kit for $30. It is really a cheap fix if it helps. Any thoughts on this?? Thanks!

 

[racerone]

If diaphragm is ruptured the fuel will go straight into the motor and bypass the carburetor.----Worth checking out.

 

[iggyw1]

If diaphragm is ruptured the fuel will go straight into the motor and bypass the carburetor.----Worth checking out.

Doesn't look like too much of a job to rebuild it in the shop manual. I have a step by step manual and good pictures of the few pieces that are in the fuel pump. Not much in there. If the diaphragm is not ruptured or torn when I tear it apart, does that mean it is good? I think I might just get the kit and renew whatever comes in the kit for the price of $30. Probably would be good to do.

 

[F_R]

Well, yes a ruptured fuel pump diaphragm will cause excessive gas usage. But lemme tell ya something. That motor WILL use a lot of gas. About 9-10 gallons per hour at full throttle. That's 4-1/2 to 5 gallons per half hour. Of course less at part throttle. But you are in the ballpark. Better get used to it..

BTW, I used to have one. Couldn't carry enough gas to go where I wanted to go................

 

[kbait]

You should be able to remove fuel pump and install nuts on the mounting bolts to hold it together like it's mounted, and squeeze the primer bulb to see if any fuel comes out the pulse hole in the back of the pump. If no gas comes out, I would assume that the pump diaphram is intact.

Good luck!

 

[racerone]

Just remove the pulse hose on that pump to see if there is a leaking diaphragm.

 

[iggyw1]

Well, yes a ruptured fuel pump diaphragm will cause excessive gas usage. But lemme tell ya something. That motor WILL use a lot of gas. About 9-10 gallons per hour at full throttle. That's 4-1/2 to 5 gallons per half hour. Of course less at part throttle. But you are in the ballpark. Better get used to it..

BTW, I used to have one. Couldn't carry enough gas to go where I wanted to go................

I.m starting to think that its normal usage too. I have the same problem about not having enough gas to get to my fishing hole! I will have to pick up another 6 gallon can and caryy three of them out there filled each fishing trip!!

 

[iggyw1]

You should be able to remove fuel pump and install nuts on the mounting bolts to hold it together like it's mounted, and squeeze the primer bulb to see if any fuel comes out the pulse hole in the back of the pump. If no gas comes out, I would assume that the pump diaphram is intact.

Good luck!

Thanks for the great tip. I will try it.

 

[iggyw1]

Just remove the pulse hose on that pump to see if there is a leaking diaphragm.

In my manual, there are two hoses. One is labeled "INLET" the other is labeled "CRANKCASE PRESSURE". I am only assuming that the crankcase pressure and the "PULSE" hose are the same, correct?? If so, when I remove this hose, what am I looking for? If I get gas coming out when I squeeze the primer ball I have a bad diaphragm? ( I am talking about squeezing it on a dead motor). Thanks for the info you posted , please reply this post of you would so I can go to it. Thanks.

 

[racerone]

Remove the pulse hose .-Squeeze the bulb and observe what happens.

 

[F_R]

Gas should NOT come out the pump's pulse hose fitting when you squeeze the bulb. If it does, the diaphragm is holed.

 

[iggyw1]

Remove the pulse hose .-Squeeze the bulb and observe what happens.

OK thanks again, however, I still have the same question that maybe you can answer: Is the PULSE HOSE and the CRANKCASE PRESSURE HOSE one and the same? I have two hoses connected to the pump. Again, one is labeled inlet while the other is labeled crankcase pressure. I don't see another hose labeled pulse hose in the manual and looking at the pump it looks like only two hoses on it. Is the pulse hose inside the pump maybe??

Thanks.

 

[racerone]

There are 3 hoses-------- Fuel into the pump.-----Fuel out of the pump.------And the pulse hose.---Maybe removing the pump will make clear and simpler to understand !-----Havent worked on one of these in about 20 years but that how I remember them.

 

[Will Bark]

Crankcase pressure and pulse hose are one and the same.

 

[F_R]

Inlet and outlet hoses both come out the bottom and point straight down. Pulse/Pressure/Crankcase hose (whatever you want to call it) comes off the left side and elbows downward.

 

[iggyw1]

Inlet and outlet hoses both come out the bottom and point straight down. Pulse/Pressure/Crankcase hose (whatever you want to call it) comes off the left side and elbows downward.

OK I can see which is the pulse hose now. It is the only hose which is on the outside of the diaphragm, and comes out of the cover with the elbow pointing downward. So if I just remove that hose and pump the primer ball, if I see gas come out of this elbow, I have a hole or rip in the diaphragm. If I see no gas come out of this elbow, this is telling me that the diaphragm is ok, correct in this??? Thanks for a reply on this!

 

[racerone]

I believe we have been saying this a few posts back ??

 

[iggyw1]

I believe we have been saying this a few posts back ??

You are absolutely right racer. I've been reading and posting sooo much, I guess I forgot what I read. I went back and re-read the posts and yes, it is definitely there a few posts back like you said. Thanks for your great advice. I will go to it now that I know how.