High Racor Vacuum

[bobk]

Looking for ideas. About 120 hours ago I switched out a pair of 30 micron Racors for 2 micron hoping I'd polish the fuel a bit. The 30's had been in several years, perhaps 6000 gallons of fuel and still read nice an low vacuum, about 2", at my 1000 rpm cruise and perhaps 5" at WOT.

So, I ran the auxiliary tank feeding the port engine out of fuel by accident and the vacuum gage showed a significant increase when I switched to the main. After a week of running at 1000 rpm with the 'dirty' 2 micron filter at WOT the vacuum reading was approaching the red line, so I replaced the 2 with a fresh 30 micron filter. Cranked it up in neutral and at 1500 rpm, found higher vacuum than I expected. The old filter seemed clean, and the bowl had very little sediment. I still have 300 miles to go on this treck, 2/3 in the Chesapeake Bay where things can get stirred up.

Any thoughts on where else to look for a restriction before I start opening fittings? We will be underway again in the morning.

Bobk
1981 48MY
692TAs

P.S. the filter gages are mechanical and mount on the Racor cap.

 

[Boatsb]

Maybe a piece of something in the valve and or lines. Id blow back to a bucket from the filter inlet to the line before the pickup and see what comes out.

 

[racclarkson@gmail.com]

Like you said, you ran the tank dry. Compressed air treatment for the lines.

 

[bobk]

I do not have compressd air on boad. Do you think lung pressure might work?

Bobk

 

[Boatsb]

The systems only tested at 4 psi. I'd be careful putting high pressure through. It's more volume than anything else. Also remember there is a binh of fuel in the lines.

A pump for an inflatible may be a good option if your lungs are not up to it. Then again hopefully it's easy to dislodge and clear.

 

[bobk]

The systems only tested at 4 psi. I'd be careful putting high pressure through. It's more volume than anything else. Also remember there is a binh of fuel in the lines.

A pump for an inflatible may be a good option if your lungs are not up to it. Then again hopefully it's easy to dislodge and clear.

Scott, good thought, I have both an inflatable pump and tire pump.

Bobk

 

[Boatsb]

I also use a primer bulb and hose. You could back flush it with clean fuel too.

 

[Walter P]

Bob, Did you change the secondary filters as well. Since you have been using a 30 micron filter, most of the small stuff passed by and possibly got caught by the secondarys. I personally prefer the 2 micron in the Racor filter. If it gets clogged (and it probably will after all the use you give it), it only requires a new primary (Racor). Just a thought based on my own experience.


Walt

 

[doc g]

Clogged secondary would not cause high vacuum at the primary . Actually could be the opposite as the pump would not be able to move enough volume.....Pat

 

[finatic]

Could a clogged vent line cause the high pressure?

 

[rob71]

My experience with clogged Racors has always been crud around the check ball inside the turbine.
With it removed you could back blow the line. A shop vac works well for this.

 

[bobk]

Bob, Did you change the secondary filters as well. Since you have been using a 30 micron filter, most of the small stuff passed by and possibly got caught by the secondarys. I personally prefer the 2 micron in the Racor filter. If it gets clogged (and it probably will after all the use you give it), it only requires a new primary (Racor). Just a thought based on my own experience.


Walt

Walt, It was a 2 micron that showed the high vacuum. When I replaced it with a 30, it still showed higher than normal vac. I did not replace the engine mounted one since the 2 mic would not have allowed anything through that the final filter would have caught.

Bobk

 

[bobk]

I also use a primer bulb and hose. You could back flush it with clean fuel too.

That sounds easiest. Ran 80 miles today and pulled into Coinjock and had a look at what I'll need to do to get to the back of the fuel selector valves. It will be a PITA so I'm going to wait till I get to BYC.

Bobk

 

[bobk]

My experience with clogged Racors has always been crud around the check ball inside the turbine.
With it removed you could back blow the line. A shop vac works well for this.

Thanks. I thought about that too. I have a spare kit too, so if easy doesn't work, I'll take down the Racor again.

Bobk

 

[saltshaker]

That sounds easiest. Ran 80 miles today and pulled into Coinjock and had a look at what I'll need to do to get to the back of the fuel selector valves. It will be a PITA so I'm going to wait till I get to BYC.

Bobk

Have a steak for me! The scallops are pretty good too. Tell Louis Jack from Saltshaker said hi.

 

[Avenger]

Could a clogged vent line cause the high pressure?

It could cause vacuum. Easy enough to check out. Open the fuel fill while the vacuum is high.

 

[bobk]

It could cause vacuum. Easy enough to check out. Open the fuel fill while the vacuum is high.

Yea, but I changed tanks so that is not in play here.

Bobk

 

[Glory]

My experience with clogged Racors has always been crud around the check ball inside the turbine.
With it removed you could back blow the line. A shop vac works well for this.

And easy to check. Pull off the supply line and fitting and look in.