Well after leaving this a while, fitted the new pump and still the same issue. So I hooked up an old SU electric pump from my Mini Cooper to ensure the carbs are primed and it started on the button. While it was running I swapped the hoses back onto the mechanical pump and it carried on running fine. So it is just fuel starvation at startup. While the engine was running on the electric pump I checked the mechanical pump output, 3psi and inlet 5 inches Hg. Will fitting an NRV solve this ?. If so should it be before or after the pump?.
Mechanical Fuel Pump Testing
- Thread starter E3_UK
- Start date
It shouldn't really matter where in the line it goes, as you shouldn't have any leaks. Normally, some fuel will evaporate from the carb bowls and without the non return valve, gravity will pull the fuel back through the lines and pump towards the tank. Putting the valve anywhere in the fuel line should stop the flow back to the tank but if you put it before the pump, it should guarantee keeping fuel in the pump and lines to the carb. In a perfect world, the valves in the pump would do the same, but they weren't designed with that in mind. So if you want a stock looking engine compartment, you could put it under the car, close to the tank, otherwise I'd just put it between the fuel filter and the fuel pump as it's possible that debris in the line could block the valve action and keep it from closing securely.
I installed valves on in my E3 and my E9..between filter and pump. They are very cheap and do the job. I have a 67 mustang that I need to do this to. If it sits for a month, I have to pour fuel down the carb to get it to start up.
The pump on my MGB will shut off when the carb is full and the needle and seat closes. Maybe your Mini pump does the same? If so, run the pump until it shuts off, then start the car. If it still runs badly for 8 minutes it isn't a fuel flow problem.
Good question about what has changed that now requires a NRV. I've had some older carbed cars with mechanical pumps that can sit for a month and fire right off and some that do just as your BMW does. I'd like to know too.
That's exactly what I did. The SU pump ensures the carbs are full before cranking and it fires on the button. It's reassuring listening to the pump tick until the chambers are full. On the other hand I also carry a length of 2x2 in my mini to reach under and clout the pump to spur it into life when it sticks
This is so familiar. Similar SU fuel pump in my Healey 3000. But I can pound on the right side, rear floorboard with the knock off wheel hammer, and "stimulate" the fuel pump, if ever those inner contact points begin failing.That's exactly what I did. The SU pump ensures the carbs are full before cranking and it fires on the button. It's reassuring listening to the pump tick until the chambers are full. On the other hand I also carry a length of 2x2 in my mini to reach under and clout the pump to spur it into life when it sticks
My dad had a car with the SU pump under the hood. He had a wrench dangling on string tied to the hood so that when the pump stuck he could swerve the car side to side to knock the pump with the wrench to bring the pump back to life. Not a laptop in sight
Brilliant!My dad had a car with the SU pump under the hood. He had a wrench dangling on string tied to the hood so that when the pump stuck he could swerve the car side to side to knock the pump with the wrench to bring the pump back to life. Not a laptop in sight
That is exactly it! I think the regular use also kept the battery strong and startup was no problem.
In my opinion it is down to wear on the camshaft and pushrod reducing suction. When operating the pump by hand I can draw fuel up to the pump with a couple of pump strokes. Cranking the engine it takes ages for any fuel to appear. Now with the nrv fitted it fires instantly as the pump is effectively already primed therefore can deliver immediately. It's not the battery as this is on a battery conditioner all the time. If I could be bothered I'd try reducing the thickness of the insulator block to compensate for the loss in pump stroke, however as the nrv effectively cures the problem I probably won't bother. It's not like the problem occured after weeks, it was only a couple of days. When new this would never be an issue, not everyone drove their car every day, infact my car in particular was a high day and holiday car for the original owner and he never had starting problems.
OK, but if I recall correctly, this engine has but 60K miles. Not a lot. Explaining this situation by way of wear and high mileage, well, I would expect many more miles needed to produce enough wear on the pushrods. Am I missing something here?
That is correct, 60k, that does kind of go against my theory. When I first got the car I never had starting issues after days or weeks lay up and I've only put another 4k on it since then. I'm glad it's resolved anyway, whatever the reason.
The final solution, the nrv still seemed to be allowing the carbs to empty over several days so I replaced it with a manual primer and it works a treat. Half a dozen pumps and the system is full and the fuel pump is able to keep up with demand thereafter. I know it's not a cure as such but if it works I'm perfectly happy with it.
20200423_193806 by Robin Derrick, on Flickr
20200423_193806 by Robin Derrick, on Flickr
Fredomatic
Well-Known Member
the hand pump is brilliant! A great talking point for sure.
It has solved a starting problem I've been suffering from for years. Now starts on the button every time once primed.
Fredomatic
Well-Known Member
I'm about to replace the original mechanical fuel pump on my e3. I thought I was running on two cylinders but upon inspection I found a significant amount of fuel leaking from the pump onto the engine. That could have ended bad!