ausmini
https://www.ausmini.com/forums/

Twin fuel filters experiment
https://www.ausmini.com/forums/viewtopic.php?f=2&t=52083		 Page 1 of 1
Author:  74snail [ Mon Apr 13, 2009 12:14 am ]
Post subject:  Twin fuel filters experiment
I have been thinking about fitting twin fuel filters for a while now, obviously the best system would be - one before the fuel pump and one after, but I just wanted to try two after the fuel pump. Could I keep it neat and tidy ? Would the extra reservoir of fuel help with cold starting ? Would it have any effect on the SU ? Well the " Snail " has had a service and tune and is running very nicely now, and the twin fuel filters dont seem to effect the SU , fuel pressure should stay the same. Cold starting does feel more positive, I am keeping in mind that the choke cable has been adjusted so that it fully opens and closes. So this is a work in progress, and I,m sure there are people here with their own ideas and opinions , so any feedback is welcome.

[img][img]http://img4.imageshack.us/img4/5893/twinfilters1.jpg[/img]
[/img]Image
[img][img]http://img19.imageshack.us/img19/5023/twinfilters3.jpg[/img][/img]
Author:  mickmini [ Mon Apr 13, 2009 1:56 am ]
Post subject: 
i don't see how it can give you any extra fuel for cold starting if the filters are sitting below the inlet of the float bowl. It can't magically flow uphill without being forced by the pump. I am assuming that have a mechanical pump and are thinking that it does not pump much fuel until the engine actually kicks over right?

The idea of a filter before the fuel pump is that it stops the crap from entering the fuel pump and damaging the diaphragm or one way valves, or blocking said valves. This fiilter would generally not be as fine as the one after the pump because it only has the pressure due to gravity to force the fuel through it. The post pump filter can be finer because the pump gives more pressure, but the pressure is low anyway, otherwise those plastic filters would rupture as soon as the pump starts pushing.

I don't see any advantage in your arrangement. If they were in parallel then it might give you a slight flow advantage as there is twice the surface area, but really it would probably only increase the interval between filter changes, and for their price you would just change it more often.

cheers
michael
Author:  minifreak1 [ Mon Apr 13, 2009 7:13 am ]
Post subject: 
Ive always run two filters.
one just after the tank b4 the pump...and one in the enige bay b4 the webber.
never had any problems...one b4 the pump is like what you have used and the one in
the engine bay is a glass cylinder type mainly for looks.
was allways told to protect the pump from crap and to protect the webber as well.
Author:  sports850 [ Mon Apr 13, 2009 12:36 pm ]
Post subject: 
Just keep a close eye on the filters where they are touching in case they rub through each other and pour fuel onto your hot exhaust .
Author:  Harley [ Mon Apr 13, 2009 12:42 pm ]
Post subject: 
Two filters in a twin carby engine I could understand, but I don't see the affectiveness of two right before the single carby. Placebo?
:D
Author:  74snail [ Mon Apr 13, 2009 1:31 pm ]
Post subject:  I,ll have a look
sports850 wrote:
Just keep a close eye on the filters where they are touching in case they rub through each other and pour fuel onto your hot exhaust .


I tried to twist them around so they didnt touch but they seem to settle to the position their in.
If this was taken to the next level I would be measuring vacuum, fuel pressure etc.
At highway speed both the fuel filters are full, in theory I should now have in effect three float bowls, the fuel pressure should be the same, but it would be interesting to know how the vacuum effect of acceleration effects the pressure with the twin filters.
( And no I,m not doing this as a performance mod ! )
Author:  afh001 [ Mon Apr 13, 2009 2:38 pm ]
Post subject: 
I'd probably be removing the two filters and the hose in between, and replacing them with one straight filter (rather than the right angle ones you have).

Would look neater i'd think. Can't see any real reason for two filters in series in that position.

Andrew
Author:  Morris 1100 [ Mon Apr 13, 2009 7:06 pm ]
Post subject: 
Ok, to start with the basics. Why do you need a fuel filter? (I am being serious)
The reason to fit a fuel filter is to stop you from breaking down on the side of the road with a blockage in the carby.
The idea of a filter is to stop small particles from blocking up small passages inside the carby. This is why injected cars have very fine filters.
An SU carby does not need a filter. There are no small passages to block up.
The pickup in the tank has a gauze strainer and the Goss mechanical fuel pump fitted the the Delxue, K and Clubman is also fitted with a gauze strainer. Anything that gets past the gauze will pass cleanly through the carby without causing a blockage.

Now another point...
If you are going to fit a filter do you fit it so it works under suction or under pressure. The manufacturers say to run them under pressure. So the filter should be fitted after the fuel pump. This means the filter is under pressure.
When the filter is under suction it can collapse or block easier.

I don't run a fuel filter on any of my cars with SU carbs. They do not need them.
Author:  Wombat [ Mon Apr 13, 2009 7:23 pm ]
Post subject: 
Morris 1100 wrote:

I don't run a fuel filter on any of my cars with SU carbs. They do not need them.


Unless you have painted the inside of your fuel tank and poked out the striner gauze that got clogged up with paint. then you need something to stop the grit :roll:
Author:  1018cc [ Mon Apr 13, 2009 7:28 pm ]
Post subject: 
I had enough crud in my tank (about the size of 2 pea's stuck together) that it actually blocked the outlet from the tank (no gauze). It was a very frustrating problem to find :?
Author:  74snail [ Mon Apr 13, 2009 7:33 pm ]
Post subject: 
Morris 1100 wrote:
I don't run a fuel filter on any of my cars with SU carbs. They do not need them.


What about protecting the jet ?
Author:  mickmini [ Mon Apr 13, 2009 7:37 pm ]
Post subject:  Re: I,ll have a look
74snail wrote:
At highway speed both the fuel filters are full, in theory I should now have in effect three float bowls, the fuel pressure should be the same


You are missing the fact that there is a needle valve connected to a float in the carby float bowl which will shut off the inlet from your "two extra floatbowls".

There is simply no advantage whatsoever to this arrangement. But if it makes you happy, go for it.

cheers
michael
Author:  Morris 1100 [ Mon Apr 13, 2009 7:54 pm ]
Post subject: 
74snail wrote:
Morris 1100 wrote:
I don't run a fuel filter on any of my cars with SU carbs. They do not need them.


What about protecting the jet ?

Anything that can get past the gauze in the tank and the pump will go through the jet. The needle and seat will cause more problems than the jet.
It is not a Weber or Injection. An SU will not suddenly stop working due to a microscopic bit of grit that will stop most other fuel systems.

If it needed a filter BMC would have fitted them standard. :wink:
Author:  sgc [ Mon Apr 13, 2009 8:56 pm ]
Post subject: 
Morris 1100 wrote:
An SU will not suddenly stop working due to a microscopic bit of grit that will stop most other fuel systems.

If it needed a filter BMC would have fitted them standard. :wink:


Agree 100%, but it doesn't stop me fitting one anyway. Cheap insurance.

Same reason I change the oil & filter more regularly than BMC said I should..
Author:  Ziegech [ Tue Apr 14, 2009 11:14 am ]
Post subject: 
i found when i was running twin Su that sometimes grit would catch on the needle in the float bowl and wouldnt stop fuel filling it and eventually would over flow out the breathing hole but only happend once or twice and i didnt have a fuel filter so probably an idea.
Page 1 of 1 All times are UTC + 10 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/