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Q & A: Cough Upon Acceleration

Wednesday March 27th, 2002
Q & A, MGA, MGB, MGC, MG T-Type, Midget
I have a 1976 MGB that I'm in the process of restoring. I must say the restoring process has been a learning one for me. I do have a problem with an intermittent cough or putt upon acceleration. The car starts and idles fine. Gas mileage is in the high teens. I have done the following
power train items over the last two years since I've been restoring:
1. SU HS4 Conversion (AUD 135)
Throttle shafts rebushed on both carburetors
New jet bearing kit on both carburetors
New jets on each carburetor
New needle valve and seats for both carburetors
New floats on each carburetor
New metering needles for each carburetor

2. New exhaust system (Headers through tailpipe)

3. Valve Job

4. Head machined (trued for flatness)

5. Electronic Ignition (Crane XR-700)

6. Changed spark plugs and wires

7. Changed the thermostat.


This item may be of note.. I tried to check the metering needles to see if the same needle was in each carburetor. The front carburetor metering needle was removed easily. It had a 6 on the portion of needle that goes in the piston. I was not successful extracting the metering needle from
the rear carburetor. I'm sure I could get it out of the piston but, I didn't want to damage the needle. I remember the needle was quite tight when I changed them with the carburetor rebuild. The cough or putt seems to happen within the first 1/2 hour of running usually at speeds 50 mph or greater. After 30 minutes or so the car seems
to run well. Engine temperature is is the normal range after several minutes. Could I have the wrong metering needles installed? Any ideas on what to do next? I would be glad to purchase metering needles or any needed items
from University Motors. Unfortunately I'm located close to Chattanooga Tennessee or I would bring the car in. Any help will be gratefully accepted.
Thanks, Dan Lamb

DAN!
I suspect you have a problem with timing -- not carburetion,
as you are using the rich needles for that application -- but there are several other considerations, too. Those carbs (needles, really) are designed to be us... read more