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MG MGB Technical - Whats wrong with my carbs?

After fitting the new free flow filters and exhaust to my '72 GT and chatting to u chaps about tuning, I went for a drive. Unfortunaty after 5 mins, my engine died. It coughed and spluttered and then stopped. First i thought it was the battery so jogged home and brought a spare in my other car. This got me halfway home and then it happened again. Even with full throttle and/or choke the engine stalls.
Has anyone got a clue to why it stops - i can't start it (run it for more than 5 mins) so that rules out driving to a garage to get it fixed, so i need advice. I thought it might be running too lean but i dunno how to balance the twin carbs let alone adjust the fuel mix.

Help me...
Kev Williams

Kev,
Apart from fitting new filters to the car were any other adjustments made or changes performed and has this happened before?

Changing from one air filter to another should not make the car behave as it does unless something else was also done.

Cheers, Pete
Peter Thomas

No other changes, never happened before. I would of thought even if the carbs ran lean the engine would still run,i was thinking maybe an induction leak, i dunno. I was hoping someone else had made similar mods and had a similar experience
Kev Williams

Kev,
I was thinking the same thing which is why I mentioned the other changes.

Do you still have the old filters which were there before the change?

It may just be a co incidental fuel blockage occurring at the same time the other mods were performed.

The other item to suspect is a fuel lock (ie a vacuum being formed in the fuel tank caused by pumping fuel out and the passage of air to replace the fuel being blocked either by a collapsed breather line or by a faulty fuel cap breather)
Peter Thomas

What Pete is intimating quite strongly is, swap back to the original units ( not the exhaust) before you start using time to look for other causes.However, I will add :Before you do,double check every bolt, nut, pipe, wire you MAY have disturbed in the process of your changes. It is amazing how often we simply overlook doing up, connecting things we have undone in order to carry out a simple process. If both these suggestions fail to make an improvement, then it IS coincidental, and your problem is elsewhere.
Ken R
Ken Rich

Is your fuel system capable of delivering fuel with sufficient flow to keep the engine running? Take off the fuel line (after the filter), place the end in a Mason jar and turn on the ignition (to energize the fuel pump) DO NOT TURN OVER THE ENGINE. HAVE AN EXTINGUISHER HANDY. You should see a good amount of fuel being pumped into the jar. If not, check the pump or filter or a crushed/ pinched line. If the fuel flow is OK, check for sticking floats (lightly tap the body of the carbs with somthing) or somthing happening with the choke.

Mike
michael robert

Hiya

Check to see if the gaskets for the new filters or the new filter set-up is hard against the piston dashpots....this can cause the piston to stick in the dashpot and the engine runs badly, if at all. Also check the pistons are free in the dashpots.

Check the throttle linkage hasn't come adrift during your ministrations.Is the throttle opening?

The most common fuel starvation problem following carburettor re-fit is chunks of fuel line rubber breaking off and blocking the float bowls.

Peter
Peter Burgess

New free flow filters? Once had a buddy with an SU carburetted Volvo. He changed air filters, but let the gasket slip out of place as he tightened up the bolts. The gasket pivoted on the one bolt until it blocked the intake. Car ran miserably.
Matt Kulka

Could it be that the new filters are obstructing the drillings through to the dashpots? Take one off and you'll see four holes in the carb body - two are for the fixing bolts and the other two are air passages. Does the gasket and the filter housing have matching holes?
Miles Banister

This thread was discussed between 19/05/2002 and 22/05/2002

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