616 replies to this topic

[timmy850]

I wonder how they would all go if you ran them one at a time and saw how much they flow in a certain amount of time. You could also try raising the bowl to close the valve and see how building the pressure in the line changes the flow once you open the valve again

There should be a couple psi backed up in the fuel line if the bowls are working correctly and I’d think you’d get better flow?

[johnR]

In the interests of science I set up the first top so that the input was into the top of the 'T' and left the outlet with the little tag unblocked, then ran the pump again.

This time both tops ran at equal speed and nothing came out of the unblocked outlet, confirming that this is a vent/overflow feature.

The top I've ordered has a vent but no overflow pipe - as far as I know it's not needed - the electric pump stops pumping when there's no demand?

[KTS]

..have you done a test run with that setup ?  ..appreciate you're changing the top anyway, but might allow you to confirm that was the issue

 

my old GTM had a facet fuel pump, which would kick in as soon as the ignition circuit was armed and then stop 'til the engine was started, which suggests it stops when a certain back pressure is reached.  i assume the vent/overflow would opens at a certain (hopefully, higher) pressure to protect the float valve & chamber from being exposed to very high pressures

 

there's probably some documentation on what the maximum fuel pressures the float valve can/should be exposed to, likewise your fuel pump should have some figures on what it'll push out.

[timmy850]

Sorry I didn’t pick up on that before. You need to have both bowls vented otherwise they won’t fill. The bowl is essentially a sealed jar, so you can’t add in fuel without letting the air escape.

They all have a vent, some are small holes and some can have hoses attached- if the needle valve gets stuck open (on a piece of dirt or grit) it’ll send fuel out the overflow hole - if you can connect the pipe you can make sure the fuel doesn’t end up on the exhaust

A couple of photos of different types here;
https://sites.google...tbowl-lids-info

Edited by timmy850, 18 July 2019 - 09:30 PM.

[johnR]

..have you done a test run with that setup ?  ..appreciate you're changing the top anyway, but might allow you to confirm that was the issue

 

my old GTM had a facet fuel pump, which would kick in as soon as the ignition circuit was armed and then stop 'til the engine was started, which suggests it stops when a certain back pressure is reached.  i assume the vent/overflow would opens at a certain (hopefully, higher) pressure to protect the float valve & chamber from being exposed to very high pressures

 

there's probably some documentation on what the maximum fuel pressures the float valve can/should be exposed to, likewise your fuel pump should have some figures on what it'll push out.

No I can't easily set it up to run because of the pipe orientation required for this top to operate correctly - I am 99% sure that this is the root of my problem and I've got a AUE272 top arriving any day so will wait 'til then.

My pump also stops once pressure is reached, it's an old (discontinued?) Moprod pump that I had lying around from a previous project many years ago so I can't find any figures for it. I'm not worried about not having an overflow on this low pressure system - if I was racing it might be a different matter. Whilst it doesn't sound ideal to have any overflow fuel in the engine bay, as you will know Mini's aren't exactly hermetically sealed so you'd soon smell it and stop whereas if it was venting down a pipe you'd only know when you parked up and saw a puddle (or ran out of petrol!) 

Edited by johnR, 19 July 2019 - 09:02 AM.

[johnR]

The correct top arrived yesterday so I fitted it and  went for a test run. 40mph, 50, all good, 55..same problem!!! Back to the workshop, tested the new top on the jamjars, runs evenly so next step was to quantify flow rate. One minute of pumping produced a total in both jars of 75ml of fuel which by my calculations totals 4.5 litres per hour - nowhere near enough! Then today I connected the test rig direct to the pump with a couple of feet of pipe and ran the test. Result: over 12 litres per hour. so 7.5 litres p.h. are being lost in the pipe! As a reference I connected up the old fuel pipe that I'd kept when I re-built the car and that flowed at about 8 lph, suggesting that a) the pump isn't up to the job and b) there is some constriction in the pipe on the car.  I think I'll get a fast road Facet cube and see what the extra psi produces.

[johnR]

Changed my mind and ordered a Posiflow 60106 as they are said to be quieter.

[johnR]

PosiFlo pump has arrived - free postage, ordered Sunday on Ebay (other suppliers take note!)Bracket made, undercoated and now drying overnight

Edited by johnR, 24 July 2019 - 08:09 PM.

[johnR]

I connected up the Facet and the flow from the pipe in the engine bay is vastly improved - surely delivering more than can be required at any level of acceleration. However, on the test run, although I gained an extra ten mph it still cut out at about 65. Very disappointed as I really don't know what else I can do, and even more so because the clutch has now started rumbling in neutral. F..k!
Hopefully it's just the release bearing - which I think was the only bearing in the whole engine and gearbox that I didn't replace!

Edited by johnR, 25 July 2019 - 03:12 PM.

[johnR]

So far, since April I've had an air leak which caused the exhaust to burn all the new plating off the LCB, the heater valve failed, the heater matrix failed, I'm assuming the clutch release bearing needs replacing, the tacho has stopped working, the choke cable needed replacing and I've still got the fuelling issue which has so far led to me getting a new floatbowl top and a new fuel pump. In that time nothing has failed on my Focus - it's a good job we love these little cars! 

[johnR]

Some slightly better news - today I connected up the heater matrix to the tap with the other outlet blocked off and the only leak seemed to be from the pipe stubs so I might get away with two new 'O' rings.

[theclassicminishop]

Hi John

 

I have read all your post on the carb issue you are having.  Just for interest sake check the vent on your fuel tank and ensure that it is not blocked.

 

Have a friend that raced minis back in the '70 and '80 ran split 48 Weber carbs on a full race 1275 engine and he kept having fuelling issues, eventually when he fitted a bigger vent to the fuel tank, it solved his problems.

 

Cheers

[johnR]

Yes I know fuel tank venting can be an issue - but I have twin tanks, both with vent pipes and presumably vented caps. The system worked perfectly with the standard 998 I had in it up to last year. When I test ran the new pump there was loads of flow at the carbs fuel supply 'rail' - I cannot believe now that it is lack of supply that is the issue.

[johnR]

Engine out again to investigate rumbling from Wok, have exhaust manifold re-plated after the air leak caused rich running and excessive heat which burnt off the original, investigate slight oil leak from back of engine.
I've replaced the clutch release bearing but worryingly the old one seemed fine. Manifold has been sent off and returns tomorrow.

[CharlieNZ]

I'm going to sound like a noob here, but maybe you can solve a problem for me. I have an ongoing problem with rich running as well. When I put the engine in, I noted that there was potentially an issue with an air-leak on the manifold, as the mating surface looked marginal. However, I had assumed that an air leak would cause lean running, so this couldn't be my problem. You seem to have a really good handle on things, and you're suggesting otherwise - are you able to explain?

 

The car looks fantastic by the way; I've been a long-term follower of progress and I love your mini! The endless niggly problems are all just part of the joy of ownership...