Throttle Adjustment

I took my next door neighbour for a spin round the block the other evening and as we trundled back up the hill, I thought to myself, I recall there was a lot more pedal travel on the throttle… That’ll need some investigation.

The accelerator pedal is connected to the carburettor by a series of linkages. It’s all mechanical, no cables.

The throttle travel is regulated by a very simple nut and bolt in the floor of the footwell. I was reaching this bolt quite quickly, which made going up hills quite sluggish…. there had to be more on tap.

With the camera phone ingeniously balanced on a block of wood, I call it the iBlock™ I set the timer and depressed the throttle to see how far the bell crank was opening the carburettor. You can’t press the pedal and see whats’s happening in the engine bay at the same time.

As the pedal is pressed down, the Linkage is pushed up and rotates the bell crank so that Point 1 touches Point 2. This equates to full throttle (or there-a-bouts). It looks like I’m only using about 50% of whats available.

On further investigation, it became clear that the pedal had actually rotated on its shaft. The linkage was correctly adjusted but as the pedal was not “high” enough at tick over, it hit the throttle stop (which was way to low) long before full throttle was reached. A quick adjustment was made to the pedal on the shaft and the clamp tightened up.

But I needed a longer throttle stop bolt. If I left the shorter one in place, I would only end up with the same issue. Full throttle would be met but the pedal could still rotate on the shaft until it reached the head of the bolt.

Remove the outer nut and pull the bolt out from inside the footwell


Conveniently I found a 70mm M6 bolt in the metric fixings box (I don’t go in there very often) and some penny washers.

With the pedal position correctly set on the shaft and the throttle stop installed, it was time to see I could reach maximum opening…

With the pedal set at the right height on the shaft, the throttle opens almost fully.
New throttle stop bolt adjusted to stop the pedal just before max throttle is reached. Only thing left to do is refit the floor mat and pack the iBlock™ away 😉

Popping in the Exhaust

As I mentioned in the last post (which seems an age ago) there was some popping from the exhaust whilst on overrun. Not sure if this was as a result of having a lean mixture or something else. I posted the problem on the Series 2 Forum to see what others thought. There were 2 clear answers…

  1. There is an air leak in one or more of the connections in the exhaust system, including the manifold.

  2. Mixture is too lean.

I didn’t want to fiddle with the mixture too much so, I thought I’d eliminate the air in the exhaust system. I would have expected things to have slackened off since the vehicle has been running, so it made sense that air was being pulled into the system… by the way, I have no idea why air being drawn into the exhaust system would cause the popping sounds either… but here we go.

Exhaust manifold fixings are highlighted in red. Obviously, these are mirrored on the other side of the cab. Most needed a good 3/4 to a full turn to tighten fully.


With the manifold sorted, it was onto the exhaust system. Down pipe first. Theses were tight.


Mid section… tight


Rear box… tight. I like the colours in stainless steel once its gotten hot.

I took LGL for a spin to get the engine up-to temperature, it was great to have more power on hand but the pedal had a tendency to still slip on the shaft. I think I will have to remove the pedal and rub back the paint on the shaft… and the popping is still there.

So, it’s on with option 2… the mixture is too lean… and by this I mean there is too much air and not enough fuel entering the cylinder. A lean air–fuel mixture will burn so slowly that combustion is still take place during the exhaust stroke and ignite on the red hot exhaust manifold… thus creating the popping sound or to give it its correct technical term “after-fire”.

I’ve adjusted the mixture screw on the carburettor “out” by 1/8th of a turn, so we’ll see what happens next time I take the car out.