[Nadar]

I have a -71 Bedford TK with the 330 diesel (MP044) naturally aspirated with the hydraulically governed CAV injector pump. I've had it some years, and even though the engine is definitly "worn" (some smoke, turns easily), it's always been very easy to start - even in -20 C.

This winter however, it suddenly wouldn't start one day. After a lot of glowing and grinding I finally managed to get it to "start" on one cylinder. That's not uncommon in the cold (was about -10 C then), so I tried to keep it alive on this one cylinder until the others would heat up enough to start firing. But it never happened, and in the end I gave up. I figured it could wait until the weather got warmer to save the battery and starter. Since that I've had a couple of tries where I haven't been able to start it at all, just some random ignites a very few times.Now it's spring and my plan was to get it ready for MOT.

Some years back my feed pump died, and I made an "emergency repair" by replacing the valves with some I found from an old Massey Ferguson feed pump that were, as far as I could tell, identical. However, I didn't really trust that the valves would stay in place since you have to "stake" the housing to secure the valves, which doesn't work as well the second time. In addition to that the threads for the incoming connection had seen their best days. So, I ordered a NOS pump from the UK - which I've never come around to actually install.

Everything points to lack of fuel, both that it would fire on one cylinder only and the fact that it will temporary start when spraying starting spray into the air filter. I therefore figured that the feed pump must have died, so I replaced it with the brand new one I had. I also changed the fuel filter since I can't really remember when I did that last, and it was definitly due.

My problem now is that I can't seem to get the bleeding/venting "right" for some unknown reason. Btw, I'd like to congratulate whoever figured that it was a bright idea to install the feed pump and the injector pump on opposite sides of the engine - it really makes bleeding easy for one person..! Anyway, I've bled this engine, and many others for that sake, many times before and this Bedford has always been very easy to bleed. This time around though, I keep getting small air bubbles no matter how long I bleed. I also experience a strage phenomena where the feed pump handle is really slow to return even though the bleeding plug is open. It feels just like it does when you have a pressurised system when I pump. It does come diesel and air of the bleeding plug hole though, but I think it flow is a bit small.

Normally when I see small air bubbles like this, I assume it's a leak on the vacuum side of the pump, so I've unscrewed the input connection again, cleaned and reinstalled it with thread tape to make extra sure there's no leak there. Still the result is the same. I've looked over the fuel line from the tank to the feed pump, and it's completely dry as far as I can see, except close to the pump where I've made a mess each time I've disconnected it.

So, in short, I've really got no idea what could be causing this at the moment. The most logical explanation would be that the "input fuel line" would be partially blocked somewhere so that the vacuum manages to pull some air in at joints that would otherwise be "sealed". That would also possibly explain the slow return of the feed pump handle, but I'm not sure simply if a vacuum is strong enough to cause this. A blockage after the feed pump would better explain the slow return, but that wouldn't explain the small bubbles at all. I'm stuck.

I haven't yet pulled the fuel intake out of the tank since I'm a bit scared about how many of the bolts that will break when I try to disconnect it, but I've tried to look inside with a optical scope camera, but they aren't as easy to control as one would imagine. I can't really see that much except that it seems to be a plastic cylinder in there probably containing the fuel indicator float. Does anybody here have any experience with those, often there is a small filter in the bottom which could possibly be blocked. I've also considered it a leak could have arisen inside the fuel tank above the fuel level sucking in air. Is this likely at all, or am I focusing on the wrong part of the fuel system here?

Any ideas/experience appreciated.