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65 merc 650 fuel pump issue

S

sledheadkevin

Member
Hi all, pretty new here got a nice old merc 650 that I've rebuilt from the ground up. wanted a project and it's been fun. The problem I'm having is that I can start the motor if I prime it good but only runs for a few seconds. I think that my fuel pumps aren't working, I've rebuilt them all new gaskets not much to them. Any suggestion on how to test them out or what I can do? Please help thanks
 
Is the pulse hoses in good condition and fit tight on the ends? Did you replace the check valves in the pumps? What is the serial number of the motor?
 
Serial number 1621922
All hoses seem tight I replaced them so their all new, I didn't replace check valves but I tested to make sure they were working I guess they still could be bad.
 
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No just the check valves you can get the kits for about the same price. Lightly surface the flats on a glass table with 220 grit paper just put center pressure and pull in one direction it takes very little to knock down the high spots.
 
With full carburetors the motor will run for more than a few seconds !--------So likely it is not a fuel pump issue.------------Try opening the low speed jets 1/4 turn at a time and test again.
 
racerone said:
With full carburetors the motor will run for more than a few seconds !--------So likely it is not a fuel pump issue.------------Try opening the low speed jets 1/4 turn at a time and test again.
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No it only runs while the carbs have fuel they run out of fuel and motor stops running, I've pulled one of the lines off and can see fuel come through when pumping the primer bulb but when cranking the motor over nothing.
 
racerone said:
Fuel pump is assembled wrong or there is no crankcase compression to drive the pump !
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You know of any diagrams so I can see if I've assembled it correctly? Also how I can test for crank case compression, I wouldn't think it would fire up if it didn't have a good seal/compression.
 
Pretty simple the two gaskets with large holes sandwich the diaphram inbetween the two housings. If it is not leaking when you pump the primer bulb then you possibly have a leak in the base gasket or the check valve/s not working properly. All it takes is a cat hair in one of the check valves to keep the pump from working properly. You are correct it would not run with no crankcase precharge but you have two pumps and not being able to keep it running you cannot do a cylinder drop test to see if all four cylinders are firing. Disconnect one carb at a time and see if you have fuel running through both pumps. You can test the check valves with you mouth just blow and suck it should only go in one direction and stop completely. Did you surface the pump parts while it was apart?
 
kimcrwbr1 said:
Pretty simple the two gaskets with large holes sandwich the diaphram inbetween the two housings. If it is not leaking when you pump the primer bulb then you possibly have a leak in the base gasket or the check valve/s not working properly. All it takes is a cat hair in one of the check valves to keep the pump from working properly. You are correct it would not run with no crankcase precharge but you have two pumps and not being able to keep it running you cannot do a cylinder drop test to see if all four cylinders are firing. Disconnect one carb at a time and see if you have fuel running through both pumps. You can test the check valves with you mouth just blow and suck it should only go in one direction and stop completely. Did you surface the pump parts while it was apart?
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I did not do any surfacing while they were apart, how do I go about doing that? All I did was clean them, I ordered new check valves so when they get here I'll throw those in.
 
Had problems with check valves myself. If you can rig a pressure gage at the carbs you'd see what's happening. It should make around 5 psi at idle.

Jeff
 
Like I said above on a glass table with 220 grit paper just press in the center of the housing and just pull in one direction until it all shines the same. I use a fine flat file to clean the block up just be careful you dont gouge the surface.
 
kimcrwbr1 said:
Like I said above on a glass table with 220 grit paper just press in the center of the housing and just pull in one direction until it all shines the same. I use a fine flat file to clean the block up just be careful you dont gouge the surface.
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Ok so I did the sanding got my new check valves just wondering which direction to put them in, I know one goes upside down and the other goes right side up. Which is which just want to double check before I put it all back together thanks.
 
Isnt one hole larger than the other for the check valves? You will know its right when you blow on the in side and i goes out the other one.
 
Ok so fuel pumps back in and engine starts but won't idle, I can shift into gear and run at full throttle anything below 3/4 throttle and it doesn't run. (Tis id's with engine hooked up to a garden hose.) Any suggestions on where to start? Thinking maybe checking the carbs I cleaned them and replaced a few parts inside but who knows.
 
Oh yea with mercs especially you need to make the carb adjustments with a load on the prop put the gearbox in a barrel with the water level at least five inches above the antiventilation plate and in forward gear you need both the load on the prop and the backpressure in the exhaust.
http://www.maxrules.com/
 
I dont have a book for the larger motors and only worked on one 1964 50hp. You shouldnt need to mess with max timing advance unless you did something to it. Preadjust the idle air jets out 1 1/2 turns and make sure both carbs open exactly the same time. Engine idle is on timing advance the important adjustment is the throttle pickup. Have you check compression and spark gap? Use a open air spark gap tester pull all the plugs and all the plug wires must jump a gap of at least 3/8 inch open air gap with a crisp blue snap. Get back with the numbers compression and spark gap and I will try and decipher the throttle pickup adjustment.
 
Mercs are a three tier pickup adjustment basically you can use a caliper and multimeter. Put the caliper in the #1 spark plug hole and find true TDC just hold the caliper with the bar extended and rotate the flywheel until the caliper stops moving up then add .015 inches to it and lock it down then rotate the flywheel clockwise allways almost one complete turn until the piston touches the caliper thats .015" BTDC mark the flywheel to a certain point of the motor it must not move. then you connect the multimeter reading diode to the distributor and ground and turn the distributor all the way to the slow speed stop. Slowly rotate the spark advance until the points just barely open. At that point the throttle pickup lever on the carbs should be barely touching the throttle cam on the distributor. Check it a few times the carbs should just begin to open as the points open at .015" before top dead center.
 
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