Carburettor Madness Part III (bright orange exhaust)

• Further fine-tuning of the Weber DGV carburettor
• Adjusted timing at the same time
• Removed air-intake heating

• Exhaust manifold does not glow orange anymore
• No more vapour-lock

There are many sceptics on the performance of the Weber DGV (in fact, only hours after posting this I already got a nasty comment, see the comments section for this entry). It's often called inefficient, not performance-driven, needlessly complicated. Many 'other' MG owners swear by their SU's. I think I've even heard of someone liking their Zenith!

Well, they're all wrong. Completely wrong, in fact. The Weber DGV is a fantastic carburettor. It was not specifically designed for this car, so odds of it working right out of the box are often tiny (versus an SU that would probably work right away). However, online retailers are selling kits specifically tuned for your MG (Moss, Brittek, etc., see links on right) that make tuning much easier. You may even be able to take your MG for a spin the same day you install it!

For others, such as myself, who bought an MG with a Weber already fitted, you may find yourself in a bit of a bind, trying to figure out how to undo what others did. My Weber was set to over-rich, compensating for bad plugs and a clogged exhaust. My horrible rebuild attempt did nothing to improve the situation; throw in the new Peco exhaust and you've got a recipe for disaster I only overcame yesterday, about 4 months later (on and off, mind you).

That's where the internet comes in handy: through fora and blogs such as this one, we try to make owning an MG pleasant for other people so they don't have to deal with the same non-sense we had to. (Unlike Jaguar owners, I might add, who for whatever reason are part of some tightly knit club. How do I know this? Stay tuned...) So when in trouble, my recommendation is to search the internet.

Update 3/11/2010: OK, so I was being a bit harsh on the Jag people. Though I still think they are a very different breed to MG people, most are very willing to help newcomers. Being a Jag/MG person myself I am always ready to help a fellow Brit-car enthusiast.

My main point today is that it is crucial to set the timing right (about 14 BTDC for a Weber DGV) to make everything come together. Bad timing could be one cause of misfiring or backfiring (where the explosion happens too late, and ends up in the exhaust manifold). The mixture on my DGV was set properly, but the exhaust manifold glowed orange. Checking the timing, I noticed it was set to 5 BTDC. Resetting it to 14 fixed the exhaust problem.

Another problem I've been having lately is that after running for a while and stopping, the car would not start up again. All signs pointed to not enough fuel reaching the carb. The pump was working and the filter was full (one of those stupid clear Lucas filters actually came in handy for once), but the fuel kept evaporating when it hit the bowl. Without manifold vacuum that vapour was going nowhere. My solution was to get rid of the hoses used for intake heating (plugged them up with a bolt), which dramatically reduced the temperature in the bowl so fuel would stay liquid. The intake heater is a fuel-economy thing that I do not think really necessary. I may attach it again in the heart of winter.

So:

Bright red exhaust manifold?

• Mixture too rich
• Timing too retarded (advance to 10-14 BTDC)
  

Misfiring?

• Mixture too lean
• Timing too advanced (retard to 10-14 BTDC)

It's that simple. Please see my other posts (click 'carburettor' on the right) on fine-tuning the Weber DGV.

Also I passed my qualifier exam!

Wait, what's this??? :
More very soon...

Overheating - fixed

• Change temperature sending unit (thermocouple)
  

Once again, the hurricanes got the best of me and I wasn't able to do anything to Bonnie Delilah (as she's known now; screw Shelly). I had an interesting car-related Saturday (detailed on the main page: www.arunluykx.com), though.

But now, the moment of truth. The new temperature sending unit (can we please just call it a thermocouple?) arrived, and lo and behold the gauge works again! It even displays the correct idle temperature - just left of centre. Taking it out for a spin the temperature did indeed go up when I applied the gas-pedal more, and cooled off at idle. Folks, the engine is running well again. The issue was -I'm ashamed to say- a lose wire, from the thermocouple, that was grounded by touching the frame.

One should note when replacing the termocouple that it is submersed with coolant, meaning that when you pull out the old thermocouple your car will start leaking coolant. I didn't feel like flushing the system again, so I just quickly removed one and replaced it with the new one (Beck/Arnley). The new one had a different bolt size and did not seem to fit particularly snug. However the temperature was fine and -once sufficiently tightened- it didn't leak coolant.

I also replaced the left window-winder (up till now I was using a little nub and my hand to pull up the window), and fixed the headlight switch (so I don't have to keep winding two wires together with my hands, almost burning myself each time). I tried replacing the key ignition but have had no success with that yet, so that'll be for next time.

Anyway, Bonnie Delilah runs safely and confidently again!

Overheating (changing the thermostat)

• Replaced thermostat and gasket
• Flush coolant
  

Labour day. This generally means barbecues, getting quite drunk, and relaxing in the shade during a pleasant late-summer afternoon. For me, however, it meant hanging over a smoking engine inhaling various gasses while trying to figure out why the engine was overheating. And I loved it.

The manual suggests several causes for the overheating I leave to the enthusiast to check out. I had narrowed down my options to these possibilites:

• Failed thermostat
• Failed pump (either the propeller came loose or the bearing broke)
• Clogged radiator
• Too much anti-freeze in the coolant
  

As the engine oil levels were fine and clean I did not bother doing another oil-change. Another quick check would be the accessory belt tension (slipping causes bad water-flow), which was fine and the belt was new.

I started by testing out the bearings on the water pump. To do this I removed the accessory belt and turned the pump manually. I heard a squeaking sound when I turned it, but it did not shake and so I assumed the bearings were fine. There was also no leakage from the unit itself.

To look at the thermostat and do further testing on the water pump I needed to flush the coolant. Easy, in general, except for some reason my radiator doesn't have a drain plug! I couldn't find any help on the internet on the topic so I ended up removing the bottom hose and draining it like that. The coolant was filthy, and very green indicating a large amount of anti-freeze. This could be the problem. I flushed the engine with clean water for a few minutes before proceeding.

While it was without coolant I decided to take a look at the other parts at the same time. My reasoning was that the water-flow was somehow restricted, which was causing the overheating.Turning the water-pump sent water out the bottom hose, so it wasn't that (although the propeller has been known to come loose at high temperatures, and the engine was cold when I was testing it, but this is very rare). In the end I decided the thermostat needed to be replaced.

31 years can take a toll on some parts, so after removing the upper hose and the three bolts holding it in place (see right picture, circled in red) I needed to use large amounts of a solving fluid (like WD-40) and a small crow-bar to get the thermostat housing off (see left picture, thermostat indicated with arrow). It was difficult, but I got it off. The thermostat looked fine, but I replaced it anyway with a part I bought at Advance. I also bought a new gasket.

Removing the housing I scraped away whatever was left of the old gasket and put the old thermostat aside to test it out later. The new gasket was installed (though it looks symmetrical, orientation matters! By the way this goes on top of the thermostat) and the thermocouple replaced. I also filled up the coolant again with 75% water by pouring it directly into the engine while the thermostat was out. The remaining coolant/anti-freeze was entered after the radiator burped and the engine was running.

They say in old cars that when you fix one problem another ten arise. This car does not defer tradition. I don't know if the engine is overheating anymore because the gauge doesn't move!!! I stays below C all the time, even after driving it around for a while. All the other gauges work normally, and no amount of tapping gets this to even jump. The old thermocouple was submerged in boiling water later on to see if it was defective, which it wasn't (it opened up just before the water started boiling, around 195F/91C ). It is however possible that that the opening was not sufficiently large to let enough water through. I'll be testing the gauge and the sender unit out next.