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No fuel in top carb.

S

SJG

Contributing Member
I posted a problem I was having a while back that engine would only run 30 seconds and then quit. I have a 2000 40hp. Johnson. What I have determined is that the top carb. is not getting fuel. Primer bulb will fill the carb bowl, but fuel pump will not keep fuel in the top carb. Engine will run for 30 seconds then quit or run really rough. Take screw out of carb bowls and top carb has little to no fuel, bottom carb is full. I have swapped lines, no difference. Swapped carbs, no change, still top carb runs dry. I assume that the fuel pump is my problem. I have changed all fuel lines and vacuum lines. I have disconnected the oil to the VRO and I am mixing oil in the fuel. What are your thoughts on going to a (part #0438557)style pump. I have rebuilt the carbs also.
 
One thing I forgot to mention. When it does get running it runs great at WOT, just will not run at low speeds.
 
Look for blockage in lines going to the top carburetor.----Look for blockage at the float valve by removing the valve seat.-----Take VRO pump apart for inspection.----They are surprisingly easy to work on.
 
I have inspected the lines going to the top carb and even swapped lines going to bottom carb with same result. Took the VRO pump apart and did not see anything obvious that would be a problem. Do the VRO pumps ever get weak? I ask this question because I'm thinking it is not pumping strong enough to get fuel above the level of the VRO. The bottom carb is on same level as VRO. Could the pump be weak and gravity keeping fuel from getting to top carb?
 
Do a test as testing is the only path forward.--------Put a fuel tank 4 ' above the motor.----Run fuel hose straight to the hose that feeds both carburetors.----See if gravity feed will keep both carburetors full.
 
Racerone you nailed it, put auxins let tank above engine and it purrs like a kitten, both bowls staying full of fuel. What should I do next. One thing I noticed is that the bulb seems to stay a lot harder with the tank above the engine.
 
I don't have a socket that will fit to take the pulse limiter out to clean carbon as the manual says to do. Will it hurt anything to spray carb cleaner into it while it is still screwed into engine?
 
It has the VRO pump. Pulse limiter is behind the starter and screwed into the engine block. My manual shows this type or an inline one, guess I didn't get lucky enough to have an inline one. Need a thin walled socket to take it out.
 
Thanks for all the help, I will get the seafoam and let you know if this fixes my problem. May be next weekend before I get to the lake. Thanks again to everybody.
 
Took boat out today after cleaning pulse limiter with seafoam and decarbonized the motor like suggested. Seems like it ran a little better, but still doesn't want to idle for longer than 30 seconds. Runs great at WOT, bogs down a couple of times while planing out but great after that. This might sound crazy, but when I unplugged gas line to drain fuel out of engine it seemed to idle better with fuel line disconnected. Any ideas would be greatly appreciated.
 
Maybe the top cylinder is pulling fuel out of the carburetor at the proper rate.--The bottom cylinder is not and therefor you find it full when it stalls.--Look for issues with crankcase compression.-Check bottom seal and reed valves.
 
Thanks for the ideas, it will be a couple of weeks before I have time to look at the things mentioned. I will let you know what I find.
 
Just a random thought here, could there be an "air bleed", or "bowl vent" on the top carburetor that is blocked, or clogged. The only thing I can figure is that if it's not venting air, it's airbound, and it can't fill up with gas. This maybe only affecting the idle circuit.
 
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Had some time yesterday and today so I pulled the pulse limiter (took an old 7/8" socket to the bench grinder) and soaked it in seafoam, blew it out and replaced. Still no change. I did pull the pulse hose off of the fuel pump end and seem to be getting really good air flow to thee pump. Pulled the VRO apart and I noticed a spot on the diaphragm looked like it had been rubbed on something, not all the way through but therein rubber was rubbed off.
 
I am leaning toward just putting a regular fuel pump both for price and ease of future repair. Any thoughts on which way to go, the three hose pump and use the line from the pulse limiter or get a two hose pump and use the mount on the side of the block? I appreciate y'all's thoughts on this.
 
Did what you suggested kimcrwbr1 and it ran like new. Thanks for all of your help working through this. Thanks again.
 
Thanks for the info. I was a little concerned about the fuel flow when I installed it, but it seemed to run fine. Might have been a little sluggish out off the hole, but ran smooth through out the whole RPM range. I will keep an eyeing the plugs and I feel safe about the engine getting oil. Will also use the seafoam. Thanks again for all of your help.
 
Thanks for the info. I was concerned about the flow too, but it seemed to run fine through all RPM ranges. It might have been a tad bit slower out of the hole but other than that ran great. I checked the plugs today and they looked good, but I will keep an eye on them and also a good idea with the seafoam. Thanks again for all of your help.
 
It ran real good at WOT, hole shot not bad, just seemed a tad bit slower than it was with VRO pump when it was working correctly. I won't ever do any skiing with this boat so the hole shot is not a real issue. Just glad I can get back out and do some fishing.
 
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