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MG Midget and Sprite Technical - Weber 45 help?

OK, I know I've posted this before but I still have the problem.
Firstly engine spec:
1430 stage 2 (Minispriint engine)
Lumetition optronic ignition
Head: 35x29 Msr158 025 2100
Oselli pistons
MGOC exhaust system & manifold: (C024)
I have a note by the prev owner in the manual, that says Kent cam 286.
I know he de cammed it. Ive just spoken to him, he's not sure if that
is the cam thats in or the original. It was too lumpy in traffic so he
de cammed it.
He thinks it may be a 256 now
Frontline 5 speed box
----------------------------
The only time I get this problem is on the motorway.
I can cruise smoothly up to 4,000 rpm but if I exceed this for more than a few seconds I get a terrible missfire that will not go away.
I can throttle through it, but as soon as I back off to light throttle it is back and will not clear.
The only way to limp home is alternate hard throttle/back off.
If I try light throttle the missfire is back.
The car behaves in town and under 4,000rpm.
I can accelerate for short bursts around town past 4,000 rpm (my engine will, according to the rolling road report, rev to 7,200)
By the way, I've had this problem in varying degrees for around 6 years!
I'm thinking some kind of flooding problem, as the car is fine the next day.
please, anyone out there..... can you help!





Mallorcaben

Hiya

Sounds daft but check the tightness of the chokes and venturis, also the main jets.

Peter
peter burgess

What type of washers have you between the carb & inlet?
Brad (Sprite IV 1380)

You do have ram pipes fitted inside that shallow filter case don't you?
Daniel Thirteen-Twelve

Your right Daniel, that is a narrow K&N.
Just reread the thread,
-The only way to limp home is alternate hard throttle/back off.

I actually drive like that anyway :-)

What cam was in for the original rolling road test? a 256 seems rather tame for a 1430. What are your jet sizes?


Brad (Sprite IV 1380)

Is the fuel pump providing enough fuel? Or are the float chamber inlet valves large enough?

AndyB
Andy Borris

i had this happen with a faulty coil......
Stefan

Can you cruise normally for prolonged periods under 4k?

If it's ok under strong throttle, sounds like the pump jets are curing the problem i.e. giving enough fuel.

Matt
Tarquin

has it ever been on a roling road for a proper tune?

and a 286 in a 1430 should deliver enough grunt to pull city driving without a problem

all sounds a bit stange

but studying the pic i think Brad gave you the right hint

there should be a set of rubber o rings between the carb and the manifold to dampen out the vibration
crucial with a weber!
Onno Könemann

I'm with Andy - not enough fuel for sustained high power. That means the pump can't provide it, or the needle valve in the float chamber won't flow it.

Other thing might be fuel line passing near exhaust manifold is causing the pipe/petrol to heat up and vapourise.

At 4K rpm, the Weber is only just getting going.

Sounds like yo'd be better off with a single 1 3/4 SU...

A
Anthony Cutler

You are using a decent pump & fuel regulator aren't you?
Brad (Sprite IV 1380)

Just got internet back to checked the thread...
Fuel pump is a facet, high pressure. All good.
It goes to a fuelking pressure regulator. Not sure if its set right.
Got the weber spring washers to prevent frothing.
Have ram pipes inside the K&N.
Cruises fine up to 4k.
Newish coil (lumenition & ballast resistor)
No rolling roads here in Mallorca.

Car is absolutely fine under 4k, or for short bursts of over 4k.
Also, it's fine when hard on the throttle, its just when you back off and try light trottle.
One this missfire is evoked, it does not go away till the next day.



Mallorcaben

Check your regulator, i had the valve fall off on one of mine. Easy enough to set the pressure you just need a Tee & a guage.
Brad (Sprite IV 1380)

Funny you mention the regulator. A few years ago somebody messed with the screw on the top. I have no way of testing the flow, except to pull the pipe & look.
Anyone know how much fuel it should put out without having a gauge? ie, to give so much ml per minute?




Mallorcaben

Doing it that way will measure the flow not the pressure, you really need a tee & a gauge.
Brad (Sprite IV 1380)

Ben you may have a mismatch of components, which Facet pump do you have, they make many types and models, can you identify it from this doc?
http://www.fuelsystem.co.uk/web-facet.pdf

You say 'high pressure' but if it's 7 psi or less how about just bypassing the regulator and seeing what happens? (If the pump is matched to the engine's needs then a regulator is not needed, I regard them as something else to mess around with and/or go wrong).
David (davidDOTsmithAT stonesDOTcom)

Webers require about 3.5-4 psi fuel, I agree with David, remove the regulator and see if that makes a difference. If that didn't work try setting your regulator to about 4 psi.

I have simular issues with my Weber DCOE45, and it turned to be too much heat being transferred to the fuel line. The heat from the headers was causing my problem once the car warmed up, especially around town.... vaporizing the fuel.

I have a stainless steel heatshield, soft-mount carb gaskets, and a fuel regulator set at 4psi to prevent any fuel problems on my DCOE 45.


Ron Koenig

Ron,
any chance you could dimension that heat shield?
Brad (Sprite IV 1380)

Brad, measure the mounting bolts om the underside of the weber and you should be able to scale it roughly from that... also there's a chap in Oz who sells them on ebay and does international post...
David (davidDOTsmithAT stonesDOTcom)

Also available on uk ebay.......
d brenchley

This thread was discussed between 26/07/2009 and 31/07/2009

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