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MG Midget and Sprite Technical - Mixture issues - mystery solved

I previously requested help with mixture issues on my stock '67 1275, and get reams of good advice. While I have yet to work out the 5,000 ft. altitude + corn-fed fuel calculus, one large piece of the puzzle (lean mixture at altitude instead of rich) fell into place this weekend.

With the rear end out (swapping wires for disc wheels, so needed a new axle), I decided to pull the tank, as the fuel pump seemed to be 'de-priming' sporadically. With the external feed tube snug, fitting polished and installed with teflon tape, and sufficient gas to cover most of the sock (so, plenty of petrol left), I was drawing air bubbles out of the tank using a hand siphon.

The last owner had installed a Moss Motor's tank (471-230 - sticker still intact). It has a nylon mesh 'sock' around the end of the inner feed tube. The sock appeared to be torn, so I removed it to examine the end of the inner feed tube for muck. I was surprised to see that the end of the feed tube is a plastic extension with a knurled plastic flange at the upper end. With the fuel level below the top of this extension (leaving ~1" of petrol in the gank), you could plainly see fluid--and thus air--passing back and forth through the I.D. of the extension and the metal pipe as I squeezed the siphon's bulb.

So, I'm guessing I'll have to either: (1) somehow remove the extension and bend the pipe down into the slight depression to get at the last sip of fuel; (2) grind out the brazed fitting and accomplish #1 or install a new inner pipe; or (3) buy a new tank. However, if I opt for the latter, perhaps I'll end up with the same problem.

So: has anyone experience this before? Has anyone bought a better-quality tank elsewhere, preferably without a cheesy plastic extension at the end of the inner feed tube? I have an in-line filter before the Facet pump, and a filter-regulator up under the bonnet, so I'm not worried about the lack of a sock in the tank.

Thanks - Joel.
JM Young

Might consider a plastic fuel cell.

Look Ma, No rust. maybe add a clean out drain to clean out the muck every couple years

just an example from summit racing... they got several 10s of hundreds of these in differant specs. and manufactures

agian just an idea...for equel moneys

Prop

http://www.summitracing.com/parts/BOB-10993/
Prop

My boat had a similar problem, a screen in the tube at the bottom of the tank. After asking around I found that most folks remove the screen and rely on their accesable fuel filters to do the job.
I see no problem doing that in a car.

If the tank is in good nick, fix/modify the intake tube and use it.

Phil 'just my 2 cents worth'
Phil Burke

A while back I removed my fuel tank to clean it, just for peace of mind. I guess it had been cleaned in the past, because it was spotless... and the pickup screen was gone. The little cylindrical screen holder was there, but no screen. I figure that somebody had cleaned the tank before, and whatever cleaning process they used had dissolved the screen. I'd already taken Phil's approach by then, and had fitted two filters - one at the pump (mechanical pump; this is a 1500), and another at the carb. I've been driving my midget for 15 years with no problems at the tank.

Cheers,

-:G:-
Gryf Ketcherside

Prop - helpful as always. Thank you. I'll consider this route if I can't rig the feed tube.

Phil & Gryf - I would *love* to leave the black plastic extension in place (the white screen basket came out when I yanked on the torn fragments). I've installed filters before the pump and under the bonnet as well. So long as there is sufficient fuel to cover its top end--where the little knurled flange is--it would probably be fine. Problem is, it's passing air through the extension's I.D. when the level gets below the top.

When the pump starts sucking air, it deprimes intermittently and the engine starts hiccuping at speed, stalling at lights, etc. With a teensy tank, big state, and plenty of 100+ -mile stretches between towns, I'd like to use as much of the tank's capacity as I can.

So, I'll probably try to yank the extension off with long pliers, bend the metal pipe down into the stamped depression or 'sump,' and see what's what.

Thanks again,

Joel
JM Young

If you put a filter before an SU pump, be very careful that it never plugs and starves the pump for fuel.

I just saw a great write up on SU pumps by fellow list member, David DuBois
http://homepages.donobi.net/sufuelpumps/Fuel_Pumps/SU_Fuel_Pumps_Facts_and_Myths.pdf
that clearly makes the case for expensive damage to the pump if it's starved for fuel. It will fry the big resistor and windings inside.

This warning doesn't apply to mechanical pumps or the noisy Facet pumps, just the expensive SUs.

If you go with Phil's sockless routine, don't put a filter upstream of the SU pump.

Lee
Lee Fox

This thread was discussed between 18/07/2010 and 24/07/2010

MG Midget and Sprite Technical index

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