No vacuum to VRO pump. Help?

[Bosunsmate]

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

????????.......Racerone This is wrong......Review your basic understanding of two stroke engines!!

 

[racerone]

No I am not wrong !----Tell me why there is a spring in a simple non VRO pump !

 

[Bosunsmate]

No I am not wrong !

??So you disagree with the fact that 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 .

 

[racerone]

Please review your understanding of the working / cycling of the airmotor piston.

 

[Bosunsmate]

Please review your understanding of the working / cycling of the airmotor piston.

I sure did, i reviewed it by reading a passage from the Association of Marine Technicians on VRO operation which says this-

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 .

So are you saying that AM Tech is wrong????? lol

 

[racerone]

Over and out.

 

[g-outdoors]

Is the pulse limiter on?

Yes it is

 

[Bosunsmate]

The positive pressure does most of the WORK.

AHHHHH so you are correcting yourself now by admitting there is vacuum pressure built up in the pulse port.
Im happy to teach.
Ive no idea if pressure or vacuum does most but his pressure side seems within spec!! That would contradict your "most of work theory too"
I predict the lack of vacuum to be the cause of his no fuel

 

[g-outdoors]

The positive pressure does most of the WORK.

All I have to measure vacuum is a hand vacuum pump with a gauge. When I connect it to the hose from the pulse limiter that gauge drops by what looks to be 5 lbs or so but only returns to 0. I was expecting it to show an equal amount of vacuum to the pressure. Someone commented that there should be measurable vacuum. Are you talking a pound or 2? I asked this question before tearing into the pump. But sound like I should should look there

 

[Bosunsmate]

Over and out.

???? Dont run away, school isnt out yet LOL

G outdoors, i suggest for invoice of rebuild to check what was done regarding the seals

 

[racerone]

Bosun ---Let me know when you understand the operation of the reed valves at full throttle !!!_--And the vacuum pulse is no where near as strong as the positive pressure pulse

 

[Bosunsmate]

All I have to measure vacuum is a hand vacuum pump with a gauge. When I connect it to the hose from the pulse limiter that gauge drops by what looks to be 5 lbs or so but only returns to 0. I was expecting it to show an equal amount of vacuum to the pressure. Someone commented that there should be measurable vacuum. Are you talking a pound or 2? I asked this question before tearing into the pump. But sound like I should should look there

Ive got to go to work now, but you said you didnt have an vacuum pressure in your first post, so i dont know what you mean here. If you mean in simple terms -5psi then that i assume is ok but i dont know exact specs

 

[Bosunsmate]

Bosun ---Let me know when you understand the operation of the reed valves at full throttle !!!_--And the vacuum pulse is no where near as strong as the positive pressure pulse

Yes they close at full rpm, thanks for that.
And that pulse port has vacuum which is used for air motor operation, which im pleased to of taught you a major about two stroke crankcase pressure fundamentals.
This is a win win!
i must go to work now as sun is up cheers

 

[cfauvel]

I'm not sure putting a vacuum gauge at the pulse limiter is the best place to test...I would think that the POS and NEG pressure there would be near equal at idle.

Indeed ANY air motor requires the POS and NEG pressure to work.. The VRO uses a main spring to shoot oil through the passage way into the mixing area, but the drawing of fuel into the mixing area is way slower and smoother action...that drawing of fuel is the same stroke that pushes the fuel to the carbs.

Now if you tee a vacuum gauge on the fuel line going into the pump, you should get around 3 - 4 INHG of vacuum at idle.

if NO vacuum is present, then either there is something wrong with the engine (reed valves or other air leaks etc), or the check valves in the VRO's intermediate housing are bad, there are air leaks in the VRO on the air motor side or the air motor's diaphragms are split.

I got a VRO2 for testing purposes and found that the check valves faulty so that a vacuum placed to it was pulling vacuum from both in front of the air motor diaphragm as well as behind the diaphragm...thus couldn't squeeze the main spring and draw fuel....

still dissecting the unit to see if it is one check valve or two...and WHY the check valve failed. really should be a serviceable piece...Just like the check valves in a lawnmower style pump is.

I hope the OP doesn't have a motor problem, and it is just a fuel pump problem.

 

[Tim Frank]

AHHHHH so you are correcting yourself now by admitting there is vacuum pressure built up in the pulse port.
Im happy to teach.
I

Not sure why you are picking scraps with others in here or why the smugness. You no doubt mean well, but it sure does not help the OP; and your accuracy is ummm....not as good as you think.
Anyone who would use the term "vacuum pressure" clearly does not understand either vacuum or pressure....and by extension should not be teaching anyone. :facepalm:
The fact that you cut and paste an excerpt from a technical document from the AMT does not mean you understand that, either.
And it is Bernoulli's Principle that allows carburetors to function, just as Racerone indicated....not vacuum.. In fact, Bernoulli does not even mention the term vacuum.

Any way, to the topic....

If the OP only has a gauge from a vacuum pump it is unlikely to be effective in the very low range generated by a pulse operated fuel pump. A gauge for auto fuel systems has a suitable range for this.

The term vacuum probably complicates this unnecessarily.As my OMC manual states, clearly and simply, "Alternate suction and pressure in the crankcase is transmitted to the pump diaphragm through a flexible hose".

Measure those values accurately and you will know whether it is an input problem, or an issue with the "black box".

 

[Bosunsmate]

Well Mr Frank you obviously dont read most of the posts otherwise you would of seen i was just having fun doing some mimicry. Perhaps you should go back to the beginning of this post then maybe you will see the irony in your comment LOL!
And the point is, as you say, that there is a vacuum in the crankcase which the pump needs to operate and thanks to the document from AMT i understand it well which is why i shared it with the likes of you and others like Racerone to learn from.
My pleasure:rockon:

 

[racerone]

Post # 1 says that a positive pressure was found !----Reason being that reed valves are closed.-----When piston goes up in the cylinder the reed valves open and you are merely pulling air into the crankcase and not a vacuum.----If reeds were removed and intake blocked you would start pulling a vacuum.-------Post #1 and 2 explain it clearly.

 

[Bosunsmate]

Vacuum/suction whatever- if you put a piece of paper over that pulse port you will see it blows and sucks so the OP needs to check its sucking when he gets back from where ever he has headed off too

 

[racerone]

When the piston comes down the reeds are CLOSED.----Therefor a pressure develops in the crankcase !-----When the piston goes up,in the cylinder the reeds open and you can not pull a high VACUUM on an open container.------I

 

[Bosunsmate]

When the piston comes down the reeds are CLOSED.----Therefor a pressure develops in the crankcase !-----When the piston goes up,in the cylinder the reeds open and you can not pull a high VACUUM on an open container.------I

Suction/vacuum whatever, it is needed to get the VRO pump to work so clearly it isnt inconsequential hence the inverted check valves for it in the vro