1971 Mercury 50Hp 500 Trolling and pumping Bulb

idahobrett · #1 July 31st, 2009, 03:22 PM

I have a 1971 Mercury 500 50hp I have been working on for 2 months.
I cant get this to keep trolling speed. It runs great atanything above trolling speed. But at trolling speed I cant go more than 60 yards without pumping bulb up.
I have put kits in both carbs with floats.
I have put new fuel pump kit in twice valves and diaphram.
I have reveresed valves and inlet hoses/carb lines
New pumper. and lines and tank.
Replaced vacume lines on engine.
I even went as far as putting a different power head on with all my parts.
It has 135 psi all cylinders.
What in the heck could make it keep running out of gas at trolling speed.
This is driving me crazy.
I am running premium and 50-1 oil.
One thing ive been wondering if i pump bulb to hard gas will come out of carbs , is that right?
Any help would be much appreciated.
Brett in Idaho

milehighboater · #2 July 31st, 2009, 07:55 PM

I have almost the same problem with my 99 3 cyl mecr 75hp. It idles great but when I idle in gear for trolling and "no wake" the motor cuts out after a few seconds after running below 2000 rpm. It often helps out if I tap my choke, sometimes this will pull it back from dieing. Do you ever have any problems throttling up after trolling?

milehighboater · #3 July 31st, 2009, 07:56 PM

Oh thus far I have not replaced anything yet.

idahobrett · #4 July 31st, 2009, 09:28 PM

I have tried hitting the choke momentarily, it doesnt do much good on mine,
when at trolling speed when its out its out.

I been trying for a month asking everyone I know about putting on a electric fuel pump and try it but havent been able to figure out the PSI to use or anyone else that has tried it.
I did order one on ebay today 12 volt 1.5 - 4.0 PSI
Hey what have I got to lose, well besides money and at this point I would give my left N*t to have it fixed.
I'll let you know it will be a week or more with shipping.
Brett

corm · #5 August 1st, 2009, 12:17 AM

Hi Brett,

You may have the wrong pump kit in the motor. Merc made several different valves for their pumps. The difference being the spring strength on the check valves. if you have to original one check to see if the new ones are the same.
If you have a vacuum gauge you should have 1 lb of vacuum on the tank side of the pump.
Your 4 lb ele pump will work fine for your engine.

idahobrett · #6 August 1st, 2009, 04:41 PM

Corm
Thankyou very much for your imput, sounds like you know more than the average person.
I dont have original valves . But you say electric pump will work, thats great I will try it when it comes, if for some reason it dont ..... will try making sure I have or get the right valves.
Again Thanks Brett