BRDM Driver Posted June 20, 2014 Share Posted June 20, 2014 Would I be right in assuming that a mechanical fuel pump should be able to pull air, such that it can create a vacuum? In other words if you stick your finger over the inlet and operate the lever, it should suck your finger tip? My pump only seems able to pull fuel through if the outlet is not open to the atmosphere... I guess the valves are leaking air. Quote Link to comment Share on other sites More sharing options...
R Cubed Posted June 20, 2014 Share Posted June 20, 2014 Does not sound good, either you have got something jamming a valve open or the rubber diaphragm has a split in it this could allow fuel into the engine sump depending how the pump is fitted to the engine. You need to investigate soon and not use it the fuel will effect the performance of the oil. Quote Link to comment Share on other sites More sharing options...
BRDM Driver Posted June 20, 2014 Author Share Posted June 20, 2014 The diaphragm is fine, the valve is not airtight, so it's not drawing fuel up the pipe. I did read somewhere that a dry pump my not be airtight. I need to check the valve seats. The pump is out of the vehicle at the moment. Quote Link to comment Share on other sites More sharing options...
David Herbert Posted June 20, 2014 Share Posted June 20, 2014 (edited) If the pump is off the vehicle you could try trying to blow through it the wrong way. The valves should stop you so if there is any air getting through with lung pressure you need to change both valves. I assume they are like most 'western' ones and can not be dismantled to get at the actual sealing faces. This will only show up if both valves are dodgy but is so simple to do that you might as well. Similarly you could remove the valves and try blowing through them individually. Just remember which way up they fit! Reading your post again I suspect that the outlet valve is not doing its job and when you put your finger over the outlet it is your finger that is acting as the valve. The valve may just have a bit of muck in it stopping it seating, it is amazing how small a bit of rubbish will cause a problem. Try removing the valve and blasting air through it, you might even be able to see the seat to some extent. Good luck David Edited June 20, 2014 by David Herbert Quote Link to comment Share on other sites More sharing options...
BRDM Driver Posted June 20, 2014 Author Share Posted June 20, 2014 Bleeding pump! I really must stick an electric one in! I have just stripped it down and the valve disks where so hard they actually snapped in my fingers! The little mushroom shaped metal caps that hold the spring and valve disk are press fitted into the casting, so I wasted a bit of time making a tool to unscrew them! I cut new valve disks from nitrile and cleaned up the seats. There was some signs of pitting on the seats so really I should re-cut them with an end mill or similar. Anyway I opted to just give them a polish and it seems ok now. It will hold a vacuum with a finger over the inlet/outlet for ages. You can hear the diaphragm jumping back when you take your finger off, so I'll stick it back in tomorrow and hopefully we'll get the beastie (BRDM) started. It's been sitting for best part of six months having the brakes sorted so I really didn't need the pump to start messing me about. I suspect this might also explain why I need to prime it after it's been sitting more than a few days. (I usually manually prime it to save caning the batteries). Fingers crossed for tomorrow as next week it's booked into Tank Fest! Quote Link to comment Share on other sites More sharing options...
David Herbert Posted June 21, 2014 Share Posted June 21, 2014 Sounds like you fixed it! Don't forget that electric pumps have all the same problems a mechanical ones plus dirty contacts and coils that decide not to conduct electricity. Also usually not so repairable. Well done David Quote Link to comment Share on other sites More sharing options...
stinkypete618 Posted June 21, 2014 Share Posted June 21, 2014 Must be Russian, mine failed after having the engine rebuilt. New valve rubbers and diaghram as the fuel makes them swell alot on the Russian/ eastblock kits ive had laterly. I can get a new rebuilt pump to suck on to my thumb. Quote Link to comment Share on other sites More sharing options...
paulob1 Posted June 23, 2014 Share Posted June 23, 2014 mechanical pumps better than an electric one when working...i dont like electric ones but we use a lot of them. Quote Link to comment Share on other sites More sharing options...
Grasshopper Posted June 23, 2014 Share Posted June 23, 2014 At least you can tell what some electric pumps are doing by the rate that they tick. This aids the diagnostic process before you even break into a fuel system. With old vehicles, it is not uncommon for dry mechanical pumps to not create a vacuum with your finger over the end. With one of our trucks that sits for long periods, it won't lift fuel initially. I suck a bit of fuel up from the carb end of the hose, then it will run fine all day long and continue to do so until such time that it dries out again. This particular pump has been stripped a few times and the valves are in good condition having been replaced in recent times. Lack of use seems to be the cause. Vince Quote Link to comment Share on other sites More sharing options...
BRDM Driver Posted June 23, 2014 Author Share Posted June 23, 2014 All sorted now, just prepping for the weekend! Quote Link to comment Share on other sites More sharing options...
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