Saturday, 7 May 2016

May, 2016. Carburettors

Since I fitted the alloy carb mounts last year I have never been happy with the idling speed.  It never wanted to go much below about 1000 or even 1100 rpm and because there has been stuff going on I have not bothered about it.  The engine runs perfectly, apart from the idle, with good power and reasonable economy so I decided it was time to investigate properly.

All the linkages etc were free and lubricated with no signs of sticking. There was no signs of any air leaks and all the breather hoses are connected and in good condition. Next thing was to put a flow meter on the carbs, and sure enough the front carb was drawing much more air than the rear one. The next thing was to loosen all the links between the carbs and set the idle on each one but even with the throttle stop completely undone the front carb was still drawing way too much air.

Synchrometer, air flow meter I use.
Something was obviously going on with the front carb so I decided the only thing to do was take them both off and have a proper look. First thing I noticed was that the fuel level in the jet of the front carb seemed much higher than the rear one, not an answer to the main problem but something else to sort out as well.  With the carbs off I found that the throttle butterfly on the front one was not closing fully. Holding it up to the light I could see the butterfly was clearly not centered properly in the spindle because light was still visible with it "closed". I was able to slacken off the two screws holding it and get it adjusted so no daylight showed. The butterfly must have been like since the engine went in the car and I think the old suspect rubber mounts had masked the problem.

Next thing to look at was the float levels. The newer types of SU carbs have a one piece plastic float which is non adjustable. Some folks put washers under the needle valve to alter it but I decided I might as well fit the best new ones from Burlen Fuel Systems. These are called StayUp Floats and come complete with a new needle valve and gaskets as well so should be an answer to the fuel level problem. They also have a metal lever so are adjustable as well if needed.

Burlen SU StayUp float kit
Well the new float kits came and are fitted in the car. It was a really easy job to fit them and adjust the floats to the correct setting.

The engine now runs much smoother and I can actually adjust the tickover to a nice 750/800rpm. It also drives nicer and pulls strongly from low revs. I popped into my local garage and checked it on their emissions tester.  CO2 levels were a little high so I set them down to a comfortable 4.5% .

We are out on a little Sunday tour with our GLAVON TR Register group tomorrow so it will be interesting to see how it goes in normal driving.

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