Air Bleed Valve on Universal 25XP

The Universal engine manual says in order to bleed the fuel line after a filter change, to unscrew the knurled knob at the base of the injectors, run the fuel pump and wait for the bubbles to stop and a flow of clean fuel is observed. I did that and observed nothing from the knurled knob, no bubbles, no fuel, nada. The engine would not start so in desperation I loosened the nut holding the knurled knob to the engine, got bubbles and finally fuel flow, engine started OK. How to fix this so that all I have to do is loosen the knurled knob?

HerbertFriedman said:

The Universal engine manual says in order to bleed the fuel line after a filter change, to unscrew the knurled knob at the base of the injectors, run the fuel pump and wait for the bubbles to stop and a flow of clean fuel is observed. I did that and observed nothing from the knurled knob, no bubbles, no fuel, nada. The engine would not start so in desperation I loosened the nut holding the knurled knob to the engine, got bubbles and finally fuel flow, engine started OK. How to fix this so that all I have to do is loosen the knurled knob?

Click to expand...

Herb, our knurled knob seemed to take forever to bleed as well. Could be some debris in the small hole needs removed. I like the bleed on top of the secondary filter. Hard to get to, but bleeds quite well.

Rick, When I could not get the knurled knob to bleed, I loosened the nut holding the knurled knob and bubbles came out with the electric fuel pump running. I was wondering if there is some debris in the hole behind the knob, would removing the entire bleed valve and cleaning it work out. If so, do you see any problem with removing this bleed valve? I guess I would remove it when I am changing the filter since I would have to bleed the system anyway. And did opening the bleed valve on the secondary filter bleed the system OK, there is still some areas between that valve and the injectors which could trap some air.

also, most of the discussions about bleeding diesels involve loosening the nuts holding the injectors into the block, but for Universal diesels, they never mention that step. Does anyone know if you have to bleed the injectors separately?

HerbertFriedman said:

Rick, When I could not get the knurled knob to bleed, I loosened the nut holding the knurled knob and bubbles came out with the electric fuel pump running. I was wondering if there is some debris in the hole behind the knob, would removing the entire bleed valve and cleaning it work out. If so, do you see any problem with removing this bleed valve? I guess I would remove it when I am changing the filter since I would have to bleed the system anyway. And did opening the bleed valve on the secondary filter bleed the system OK, there is still some areas between that valve and the injectors which could trap some air.

also, most of the discussions about bleeding diesels involve loosening the nuts holding the injectors into the block, but for Universal diesels, they never mention that step. Does anyone know if you have to bleed the injectors separately?

Click to expand...

Bleeding at their injectors definitely works.

Here is a long thread on this topic that cites many of the discussion points.

http://www.sailnet.com/forums/gear-...versal-m21-long-story-fuel-line-question.html

I think two issues don't get quite enough chat:

1. Racor 200-series spin-on filter assemblies don't last forever. The threads get burred. The casting can crack (invisible). The priming pump can leak. The irritating little hand pump, which takes 100-200 miserably unsatisfying strokes to prime an M25, is a natural pathway for air when it gets old.

2. If you fill the replacement filter with fuel before spinning it on, the electric lift pump often will prime the system in moments. Just turn on the lift pump, unscrew the fuel line under the injectors and be ready with a baby diaper. When fuel spurts out in a strong stream, priming is complete. If using the hand pump to fill empty filters, prepare to pump for a long time.

Christian, Just want to make sure I understand your bleeding procedure. The air bleed valve, with the famous knurled knob, appears to be just where the fuel line from the secondary filter enters the injector block. So by turning the knurled knob, in theory, that should have the same effect as loosening the fuel line in your procedure. But now I am back to my original question, turning the knurled knob has no effect on my engine so I loosened the nut holding the knurled knob, am I doing the same thing as you suggest? And does this one bleeding procedure work if you change both the primary and secondary filters, or do you have to first loosed the air bleed plug (hard to get to) on the secondary filter first? I understand the part about refilling both the primary and secondary filters with fresh diesel first, makes sense. Still wondering how to get the knurled knob on the air bleed valve to work? Turning the knurled knob seems like a better way than loosening the nut.

Also, I do not see the lever supposedly on a a mechanical lift pump mounted to the engine, maybe I dont know what to look for. I do have the electric fuel pump mounted close to the primary filter. I have the photo with call outs from the Universal engine manual but dont see any call out for this lever, can you describe where I should look?

Presently I wired a simple on/off switch to a long cable with alligator clips at the end and "short out" the starter key switch at the engine panel in the cockpit from my position at the engine, saves having the admiral do that with the key switch, that turns on the electric fuel pump. If the lever does the same thing saves me some work connecting my jumper switch to the key switch. I understand from your comments that that lever is poor but if you refill both filters with fresh diesel, that might work ok, if I can locate that lever.

Rick, the metal tubes that feed the injectors have nuts on both ends of each tube. Does it matter at which end you loosen the nut, i.e. the input or output end. The tubes have complicated shapes to get where they have to go and I could see air getting trapped in some of those bends. Also, I imagine that the seal on those ends are made by O rings not tapered threads a la normal plumbing fixtures, any problem with repeatedly loosening and tightening those nuts?

Herbert,

1. Sure, you can just disconnect the fuel line. Same thing.

2. The hand pump is located on the top of the Racor 200-series filter assembly. Unscrew it, it pops up. The pump action is vertical (and inefficient).

3. When priming with no helper, I turn on the lift pump from the cockpit ignition. Then I use the on/both/off switch on the cabin panel (within reach of the engine) to turn the lift pump off when the fuel spurts.

I rewrote my previous comment above to be a little more specific.

Actually, the best description of this whole deal is in this write-up, which I keep on the boat and shjould've posted first:

http://realitycheck.me/replacing-fuel-filters-on-the-universal-m25.htm

Christian, many thanks for the website, would have saved many questions.