No vacuum to VRO pump. Help?

[g-outdoors]

1989 Johnson 110 with no fuel flow. I bought an engine in a crate, had cylinders nachined and got it all put together. Compression is good on cylinders. But was not getting fuel from the VRO pump. Started checking at the beginning, pulse pressure from engine. I have 5-7 lb of positive pressure but no vacuum pressure. Any idea what would cause this? How much vacuum should there be?

 

[racerone]

???----The reed valves open and therefor you will only see a wee bit of negative pressure , if any at all.

 

[Bosunsmate]

Not sure on values but i always thought there was something measurable due to the vacuum rush of fuel air mix coming in but this is only a supposition

 

[racerone]

When piston goes up into the cylinder the pressure starts to drop.----Then through magic the reed valves open and vacuum does NOT build up.----Reed valves close and positive pressure builds up when piston comes down in the cylinder.-----Reed valves open AND close even at full throttle RPM !!!

 

[Bosunsmate]

When piston goes up into the cylinder the pressure starts to drop.----Then through magic the reed valves open and vacuum does NOT build up.----Reed valves close and positive pressure builds up when piston comes down in the cylinder.-----Reed valves open AND close even at full throttle RPM !!!

Not quite... vacuum does exist and can be measured due to it has created a built up value as there is a rush of air past that hole for the pump.
For example the similar vacuum pressure is what causes the fuel to be pulled through the jet holes in the carb and also in jet plane engines

 

[Bosunsmate]

Also it was my understanding reeds are constantly open at high rpm, thus one way to diagnose a faulty reed is that the backfiring from a faulty read will not occur at higher rpm. Due to the higher rpm force of air there is no backflow of carburettored air at higher rpm that the reeds need to reseal back against

 

[racerone]

Oh well.----Venturi in a carburetor develops a low pressure !!-----Sorta follows something called " Bernouli's principle "

 

[racerone]

Nonsense ---The reed valves have to close at full throttle RPM.----Please review the operation of a modern JOHNSON outboard !!

 

[Bosunsmate]

Oh well.----Venturi in a carburetor develops a low pressure !!-----Sorta follows something called " Bernouli's principle "

And that low pressure creates a vacuum in the jet that can be measured, same physics happens in the confined space of the crankcase which acts on the fuel pump hole!!!
Please review operation of all two stroke engines from time beginning!!!

 

[racerone]

The reed valves close at full throttle RPM----Review YOUR understanding of a 2 stroke engine !

 

[Bosunsmate]

The reed valves close at full throttle RPM----Review YOUR understanding of a 2 stroke engine !

I will double check this, high rpm statement of yours after work today.
The VRO pumps are vacuum pump operated, this is why it is not working for this bloke, the proof is in the pudding. You need to learn basic fundamental principles yourself!
G-outdoors, perhaps a lower seal is malfunctioning

 

[racerone]

The VRO and other outboard pumps work on a POSIVE pressure pulse !!

 

[g-outdoors]

The block has some repaired cracks in the water jackets. Any chance that could cause this if the repairs are leaking? I don’t think they are connected to the crankcase. But I’m not sure. If there is a crack I wouldn’t have pressure or vacuum correct?

 

[racerone]

Post pictures of where exactly these repairs were made.-----I have lots of those blocks and I can not imagine resorting to welding a V-4 block.-----These blocks are precision stuff and welding may cause all sorts of alignment issues !

 

[g-outdoors]

I will double check this, high rpm statement of yours after work today.
The VRO pumps are vacuum pump operated, this is why it is not working for this bloke, the proof is in the pudding. You need to learn basic fundamental principles yourself!
G-outdoors, perhaps a lower seal is malfunctioning

The lower seal you refer to is the metal ring around the crank?

 

[g-outdoors]

The VRO and other outboard pumps work on a POSIVE pressure pulse !!

Does that mean I would get positive pressure but no vacuum pressure when cranking the engine? If that’s the case, I haven’t opened the pump yet to know the answer to this question, is the pump spring and pressure activated? Or vacuum and pressure activated?

 

[Bosunsmate]

The lower seal you refer to is the metal ring around the crank?

Depends on what cylinder your pulse port is on, if its on the bottom cylinder then it could be the crankshaft seal, otherwise the metal rings around the crank. Were they replaced? I dont normally do this.
If you arent getting any decent vacuum at that port then theres no way sufficient fuel/air is getting pulled into the engine which is how normal operation works.
Its as fundamental as that to me.

 

[Bosunsmate]

The air motor converts the pressure and vacuum pulses from the crankcase to a linear motion. These pulses are routed through a pair of check valves above the engine crankcase pulse fitting. One directs pressure cycles to one side of the air motor's piston and an inverted check valve directs the vacuum cycles to the opposite side .

 

[flyingscott]

Is the pulse limiter on?

 

[Bosunsmate]

Does that mean I would get positive pressure but no vacuum pressure when cranking the engine? If that’s the case, I haven’t opened the pump yet to know the answer to this question, is the pump spring and pressure activated? Or vacuum and pressure activated?

Its both (pressure and vacuum)