Carburation Hell

[Checkld]

Hello all, just brought myself a 1973 GT6 Mk3 and joined the Club Triumph to gain all the wisdom and knowledge you good folk have to offer. So the Car was mid way through a restoration project but the guy couldn't carry on with it. He had the engine rebuilt, new gearbox, new rear suspension doughnut thingy's and had both carbs refurbished professionally. I picked up the car yesterday and to say that she was lumpy and missing power mid range was an understatement. I knew she wasn't running great when I test drove her but the journey back home (all of 25 miles) were a bit rough and ready. When I got her home I noticed that petrol was dripping out of the front Air filter and after viewing some you channels I came to the conclusion it might be the float valve sticking. Took the carbs apart this morning and sure enough it was a tad sticky, so with a bit of WD40 soon loosened things up a bit. Put everything back together and she is now revving at c4000rpm instantly and petrol still comes out of the front air filter (K&N's).

Does anyone have any sound words of wisdom or guidance please and also help me understand what the heck I've done to make her rev so wildly.

Many thanks all

Dean

[RobPearce]

Hi Dean, Welcome to the club and the forum.

I have to say, mention of a PO's engine rebuild with "professionally refurbished carbs" and K&N air filters... rings alarm bells straight off.

Sticking float valves is a very common cause of fuel overflow but it's far from the only one. Strombergs can very easily be set wrong so that the floats don't operate the valve at the right time, or even at all (if the floats are fitted upside down). Also, if it's had the fuel pump replaced, a lot of the currently available ones put out way too much pressure and the float valve can't cope. Or the rubber hoses might have got nicked when re-fitting, resulting in tiny slivers of rubber that jam the valves open.

As to revving at 4000 RPM idle, that's often an air leak - depending what you disturbed - but could equally be a stuck throttle. I've had, in my time, badly fitted gaskets, hoses gnawed through by mice, rubber caps fallen off unused servo unions, slipped coupling between the carbs, and even a radiator overflow pipe wedged in under the fast idle cam, all causing really high idle. The Vitesse with the throttle pedal jammed full open by a rusty hinge shouldn't happen on a GT6, though. So check the throttles are closing properly first.

[thescrapman]

Is it still running Stromberg  CD150?

[Checkld]

Hi both and thanks for your replies. To confirm yes its running the CD150's. I spoke to the guy who did the carb refurbishment yesterday and he has said that he is more than happy to have a look at them, so have packed them up this morning ready to ship back to him. He'll do another refurb of them FOC, so that can't be bad. 

I think in terms of the high revving I agree it was down to too much air getting in. Stupidly I used the wrong gaskets and hey presto, didn't work. To say I'm an amatuer at this, is an understatement but I guess we all have to learn on the job :-)

[PeteStupps]

Realise it's academic if you've sent the carbs off, but my guess is your 4000rpm tickover was caused by the throttle cable outer not being correctly located, or something similar. 

On flooding CD150 carbs, I had no end of trouble with a new float which didn't fit correctly. I think there were different castings of the CD150, and I had the earlier type (1967 car) but could only get a later-type float which kept sticking open. Eventually I had the carb off the car (drained of petrol) and tested it by turning it upside down and blowing down the fuel inlet pipe. That proved that the float wasn't closing the needle valve, and it wasn't over-pressure from the pump in my case.