starting

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myoldjalopy
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Re: starting

Postby myoldjalopy » Sat Nov 23, 2019 5:27 pm

Although (assuming the float lid is the kind that has the float itself attached to it) removing the float lid will also remove the float which displaces a volume of fuel, so I would expect the level to then be (20mm?) lower in the float chamber......

MikeNash
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Re: starting

Postby MikeNash » Sat Nov 23, 2019 7:42 pm

Kevin,
If you're still concerned about your pump pressure a cheap way of testing it is to measure the height to which your pump can raise fuel when it stops ticking. A length of clear plastic hose from a pet store (mine came from "Pests at Home" in Andover for a few pence per metre) heated at one end in hot water to get it over the pump outlet and then the rest tossed up over the rafters in the garage will do the trick. You'll need at least 70 inches above the pump - mine raised it 60 inches - not necessarily in a straight or vertical line of course but you'll be measuring the height fuel is raised above the pump.
Petrol density varies between .72 and .755 so a lift of 60 inches of fuel equates to a lift of 43.2 to 46.5 inches of water and using the on-line conversion facilities this equates to 1.55 to 1.68 psi which is close to John's figure of 1.7 psi for a AUA66 pump.
MikeN.
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kevin s
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Re: starting

Postby kevin s » Sun Nov 24, 2019 10:59 pm

Thanks , it is the type with an integral float so difficult to see what the actual fuel level was.

As suggested I'll measure the fuel pressure, i'm away for a few days so I have left the fuel line off and I'll see how it starts when I return.

When I pulled the line off there was quite a spurt of fuel but when you key it on after a few days the pump clatters away for a few seconds, that fuel must be going somewhere....

oliver90owner
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Re: starting

Postby oliver90owner » Mon Nov 25, 2019 12:03 am

kevin s wrote:
Sun Nov 24, 2019 10:59 pm

When I pulled the line off there was quite a spurt of fuel but when you key it on after a few days the pump clatters away for a few seconds, that fuel must be going somewhere....
Not necessarily. The volume may stay (almost) the same but the pressure might be atmospheric. That would mean that any fuel lines would not be under pressure, so no flow when there is an open end. Fuel contains volatiles (even dissolved hydrocarbons which are normally gaseous, so they may well evaporate and disperse. The pump then has to raise the pressure, at switch on, butbdoes not necessarily move any fluid.

However too high a level in the carb might cause flooding at cranking speeds. Sooty plugs could well indicate too much fuel, even without any starting aid.

kevin s
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Re: starting

Postby kevin s » Mon Nov 25, 2019 11:44 am

The plugs were a fairly reasonable brown colour so when it runs it seems to be running fine, the other thing I have noticed is the plastic in-line fuel filter 3/4 full when I park it up but only 1/4 full when it's been standing for a few days.

If it starts fine when I am back plan is to check the float level and the float in hot water, if that's OK measure the fuel pressure.

philthehill
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Re: starting

Postby philthehill » Mon Nov 25, 2019 11:51 am

What you are describing is normal.

Ditch the in line fuel filter and have a plain fuel line between SU fuel pump and carb float chamber.

Check the float level as per illustration below.
img239.jpg
img239.jpg (137.75 KiB) Viewed 416 times
You may not have the same float chamber arm as the diagram but the measurement will be basically the same.

Whilst the float needle seat can be removed with a bit of a fiddle - it is much easier if you use the right tool.

http://sucarb.co.uk/tools-flow-meters/t ... anner.html


kevin s
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Re: starting

Postby kevin s » Thu Nov 28, 2019 9:38 pm

So after 5 days parked up with the fuel line removed, pulled the choke, turned the key and after a couple of compressions it fired straight up. So it's definitely fuel.

Checked the float and float level both were fine.

So it looks like the fuel pressure, I'll see if i can find some clear tube and measure the pressure over the weekend.

Assuming it is fuel pressure I think I have 3 options:

1. re build a su pump. Only issue aside from cost is I'm not keen on points.

2. Fit a fuel regulator, about the same cost as re-building a pump for a decent one, should work well.

3. Fit a return line as used on the likes of SD1's
cheapest and would make sure there are no fuel vaporisation issues in the summer also means there will be no pressure at all in the lines when parked.


Might try the the last one first as an experiment.

kevin s
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Re: starting

Postby kevin s » Sat Nov 30, 2019 7:36 pm

Borrowed a gauge but the scale goes up to 2 bar so not particularly accurate, seemed to be around 2-3 psi.

Now I know it's not massively high I will check it with some plastic tube as described a above. I have also bought a filter king regulator, and will use the plastic tube method to set this to around 1 psi.

kennatt
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Re: starting

Postby kennatt » Sun Dec 01, 2019 7:11 am

if its a fuel pressure problem,then it has to overcome the needle valve to flood the carb.If so you would hear the pump going all the time,and when parked and switched off no pressure to carb at all so no flooding . When switching back on to start surely no time to flood before turning engine over and starting then once engine running any flooding would be seen via overflow vent on carb. Not quite with the idea of a pressure supply problem.

myoldjalopy
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Re: starting

Postby myoldjalopy » Sun Dec 01, 2019 10:58 am

Nor me......I can't see how an engine would flood with ignition off. You would expect wet plugs if the engine has been turned over without firing.
Sometimes this car starts, sometimes it doesn't. I'm beginning to suspect the electronic ignition gizmo....it is quite normal for the pump to clatter a bit when switching the ignition on after the car has been parked up for a while.

kevin s
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Re: starting

Postby kevin s » Sun Dec 01, 2019 4:45 pm

Its been exactly the same with points and now a different electronic distributor coil and leads so I am pretty confident it's not electrical. It does hold the fuel pressure in the fuel line with the ignition off, ( does a su pump do this?) when you pull the pipe off even some time after it has been parked there is a noticible squirt of fuel. Also if I release the pressure when I park it up it starts fine.

I think what is happening is that it is slowly leaking past the needle which is not enough to affect the running (ie at a slower rate than fuel us used) but over a few days is enough to flood the engine.

kennatt
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Re: starting

Postby kennatt » Mon Dec 02, 2019 9:55 am

ok, but how does it get into the cylinders from the carb to flood the engine,if its getting past the valve it would run out of the overflow on top of the carb, because that's how the su carb is designed ,unless the vent is clogged,then it would run out past the jet and into the air inlet,it cant get into the engine until it spins over.You could test that by taking the inlet off the carb body and looking in at the top of the jet/needle before trying to start the engine. But if so would start without choke since mixture would already be enriched. Don't know which carb you have but if standard su it should have the lift pin on the side to check basic mixture try that if not done already .so again still not sure you are on the right track.....Yet good luck.

geoberni
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Re: starting

Postby geoberni » Mon Dec 02, 2019 10:11 am

I have trouble understanding how a pressurised fuel line of only some 18" could possibly push enough fuel past the carb and into the inlet manifold to cause all this trouble. We'd be talking perhaps a teaspoons worth? Its then trickling along the bottom of the manifold and a few drips getting into a cylinder or two. Remembering that there's no air being pulled in by the engine running, so it's not vaporised to ignite, but equally isn't getting to the plugs to short them like a flooded engine would.....

I know it's where the signs are pointing, but are the signs being misunderstood?

It might be the problem, but I just can't understand how. :-?
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kevin s
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Re: starting

Postby kevin s » Tue Dec 03, 2019 10:19 pm

It does have quite a large plastic filter in the line which loses a good half the fuel in it over time as suggested above I may try just removing this.

The route I would have thought the fuel takes is as the level rises it leaks past the jet into the carb and then the manifold, is this feasible?

kennatt
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Re: starting

Postby kennatt » Wed Dec 04, 2019 6:24 pm

only If the vent in the carb bowl is blocked,if not it will run out onto outside of carb,thats if you have a standard su fitted.allthough I suppose it could if there was enough overfill,but have a look in side the carb after taking off the filter before trying to start engine,should be obvious if so.Should e able to smell petrol if its overfilling carb.Can you?

don58van
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Re: starting

Postby don58van » Wed Dec 04, 2019 9:32 pm

Kevin

Is the fuel filter before or after the pump? Does it normally have air inside it (as well as fuel) when the engine is running ?

I think it is a good idea to remove it.

Don

kevin s
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Re: starting

Postby kevin s » Wed Dec 04, 2019 9:44 pm

It's between the pump snd the carb, it is usually about 1/3 full of air.

I did try it the other side of the pump but it would not suck fuel up.

kennatt
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Re: starting

Postby kennatt » Thu Dec 05, 2019 8:37 am

the only way fuel can get into the inlet manifold is by getting past the jet,after getting into the bowl past the needle valve,the system is designed so that when running with the pump working,as soon as there is sufficient fuel in the bowl the valve shuts stopping the flow and the back pressure stops the pump. If you do have pressure AFTER the pump stops it can't be higher than when the pump is supplying fuel.and therefore less pressure on the needle valve.
So if the system is not flooding when running,and fuel is not being pushed out of the vent,then the needle valve is ok and working as it should with the higher pressure.
Therefore with the lower pressure with no pumping no flooding takes place. The only other possibility,and I can't see it, is that for some reason the float slowly sinks when stationary and allows the slight residual pressure to feed a small amount of fuel into the bowl lifting the level higher than the jet (But you state that you have checked the float ).
Again, to check, take the filter off after standing and have a look inside the carb at top of jet to see if the level is just below the housing,or alternatively take the bell /jet needle assembly off and look down at the jet . Check carb when running to confirm needle valve working and no flooding at higher pressure. Check carb adjustment (screw nut right up and twelve flats out )using lifting pin.

oliver90owner
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Re: starting

Postby oliver90owner » Thu Dec 05, 2019 9:01 am

Back on November 25 PTH wrote to ‘ditch the filter’. Clearly the OP is ignoring good advice. With non-standard fittings he expects standard operation? Often not the case. These cars were designed by engineers and work perfectly adequately as designed. There is a filter in the tank. The pump also collects foreign particles, I believe.

If the float valve is leaking by (ever so slightly) that fuel could be filling the carb float bowl above normal. Then along comes someone who immediately fully chokes the engine. Not a surprising outcome?

Personally, I would also be doing the simple check of the ignition system to check for stray energy leakage. An obvious initial check if there is a starting problem which has likely been over-looked by this poster.

kevin s
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Re: starting

Postby kevin s » Thu Dec 05, 2019 7:34 pm

I haven't had a great deal of time to look at it i've spent the last 4 weeks welding up my range rover, before I can remove the filter I need to order a longer piece of fuel line, the stuff available locally cracked inside a year when I used it on the range rover, it's on the way now.

I am confident the ignition is OK, there was a fat spark at the plug but it wouldn't start, took them out, dried them, put them back and it fired straight up.


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