Subject: Re: [Mgs] Down on power -- where to look first?

From: Barney Gaylord via Mgs <[email-masked]>
Date: Mon, 20 Apr 2015 23:36:20 -0700

Simon,

You need a helper for this (or get creative).  Have a helper press 
the accellerator pedal to the floor while you watch the throttle arm 
on the carburetor.  It may be the linkage is wrong so the throttle 
does notvopen all the way.

At 09:26 PM 4/20/2015 -0700, Simon Matthews via Mgs wrote:
>I took a drive in my daughter's '71 MGB-GT yesterday.
>
>It felt like it did not have power at wide open throttle. It starts
>fine, ran fine with small throttle openings, but when I floor it,
>nothing happens. Flooring it results in a slight hesitation, then no
>more power than light accelerator depression. This isn't a high rev
>problem -- it happens at 2000-3000 rpm.
>
>There is no noticeable miss -- nothing that would point to an obvious
>ignition issue. The problem is steady-state -- hold down the throttle
>for a while and still nothing happens.
>
>So, where do I start looking? I plan to replace the plugs, check the
>distributor cap, points, etc.. I did pull the vacuum tube off the
>distributor when replacing the valve cover gasket, but I made sure
>that the tube is in place a both ends.
>....

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From: PaulHunt73 via Mgs <[email-masked]>
Date: Tue, 21 Apr 2015 11:33:00 +0100

The first thing to do is look at the  tach.  If that's jumping about then 
you have an ignition LT issue i.e. ignition supply, tach pickup, coil, 
points and distributor earth wire.  If it's steady and looks like it is 
showing the correct engine speed then it's HT or fuel, or possibly the 
condenser if you have points.

HT problems would normally cause misfiring, and explosions in the exhaust. 
Condensers usually work or they don't, but as a quick check temporarily add 
one from the coil -ve terminal (where the points wire goes) and earth.

It does sound more like fuel though.  Assuming SU or Zenith carb check the 
oil level in the dampers.  Unscrew the caps, lift them up, press them back 
down, and you should feel the resistance of the damper in the oil before the 
cap reaches the neck.  If the cap goes straight down they need more oil, up 
to the top of the tube down inside the neck.

Another quick check is the fuel delivery.  Remove a delivery pipe from a 
carb - be aware that if the ignition has recently been on you will probably 
get a spurt of fuel - and direct it into a container.  Turn on the ignition 
and you should get a continuous series of regular pulses with minimal 
bubbling, delivering at the very least one Imperial pint per minute and in 
practice double that.

Checking the throttle operation is not unreasonable, the cable could have 
slipped through the clamp at the carbs or the nipple at the pedal, although 
normally that would result in a very sloppy pedal with little travel.  But 
if you can still feel resistance at the throttle pedal in the latter half of 
its travel and that isn't resulting in any increase in engine noise, revs or 
speed it is unlikely.

Air filters could be choked, or anything to do with the setting up of the 
valve clearances, ignition system i.e. plugs, points, dwell, timing etc. or 
carb set up.  Set them up in that order i.e. carbs last.

PaulH.

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