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!

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More very soon...