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Phil, there are ports just by the air bleed screws. These are capped with screw caps. You unscrew the caps and screw in an adaptor. The carbtune will come with a set of plastic adapters that screw into the ports. For 10.00 pound more you can buy brass fittings which are well worth it. You then fit the vacuum lines over the adapters and away you go. Once your done, you remove the adaptors and refit the screw caps. I forget the adaptor size but if you call carbtune direct and tell them carb you have they will send the correct size. Dellorto UK also has them. Sorry I don't have a photo to post.

IIRC there is a detailed step by step write by on tuning carbs listed on the YahooS1S2S3 group.

Edited by GavinS1

Cheers, Gavin

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If you are going to rebuild the carbs, remember that the Turbo uses pressure carbs which have different seals to the normal suction types! Also, when fitting the Carbtune connectors, the cast alloy tube from the turbo to the plenum gets in the way. I get round this by screwing in the relevant adaptor using the syringe that came with my mercury filled carbtune...the more modern ones have steel inserts instead of the mercury columns, I believe, so you could use a short length of plastic tube instead.


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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John

Seeing your comment about the plenum made me think to say that I had removed the cast tube from turbo to plenum on mine while tuning, which meant that that hose that comes from the top of the fuel regulator to the banjos on top of the carbs was not connected.

Could that affect anything?

I was not sure what that did, but I knew it was not carrying fuel so I thought it ok to try tuning the car like that.

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That hose links the fuel pressure regulator to the pressure in the tops of the carbs and the turbo output....which allows the fuel pressure to be maintained the correct amount above the carb input air pressure, and thus maintain the fuel system conditions as the boost varies. At idle, it isn't going to be doing much...but probably best to have it connected for final adjustments. Another thing I find useful when setting the carbs is to short out each plug in turn...I can slide the rubber caps on the HT leads back from the plugs to expose the metal connectors, so a touch with a screwdriver is all that's needed. If you can get the same RPM drop from shorting each plug, then each cylinder is contributing the same power...and this is a useful guide. If the engine slows down more and stumbles, then that cylinder is working harder than the others...if nothing much happens, it's being ineffective! You can do this by sound and feel...or squint through the rear window at the tacho...or have another instrument coupled in at the engine.   


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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I have now purchased a spare second hand pair of carbs and am going to rebuild them and put them on. This will take away the nagging doubt about the seized idle jet and give me the pleasure of learning how to rebuild them and the knowledge that they are checked and ok.

No doubt there will soon be questions about re-building carbs! 

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I had somebody come out to tune the car up yesterday. He had one of those sun tune units, which I remember from decades ago!

He confirmed I had the timing and balancing spot on, which please me, and then he started fiddling with the carbs. He could not get it to accelerate smoothly and without spitting and concluded that the diaphragm in one or both the accelerator pumps was probably perished, which seemed reasonable to me.

So today I got the carbs off and both the accelerator pump diaphragms looked to be in good order and when I pumped the throttle, nice long jets of fuel sprayed out, so that theory is out of the window and generally they looked to be in very good order inside. I realise there could have been a tiny bit of grit or something causing a problem, but they do look to be really clean and tidy inside. They are getting cleaned and rebuilt, but Its got me wondering if the issue was elsewhere.

Any thoughts?

Thanks

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What sort of condition are your fuel tanks as you may have corrosion contaminating your fuel, I had all sorts of trouble with my Turbo before until new tanks were fitted.

Maybe something else to eliminate if it still does not respond to a carb rebuild. Also make sure you have no other air leaks.

Dave :)


Do or do not, there is no try! 

 

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Float heights can make a significant difference and might need checking

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Hi and thank you for the replies.

The fuel tanks were re-furbished including the frosts tank lining treatment and they are nice and clean inside so they should be ok. The float heights is not something I thought of. The carbs are apart now but I will be sure to make sure the float heights are right when they go back together.

Thanks again.

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Quick thread resurrection for a related question.  My carbs are currently balanced and I'm getting a Colortune to check the fuel mixture.  If I find it's too rich or lean and adjust it, will the carbs need re-balancing again?

 

Apologies for this being a very simple question, but am still learning about carbs and such.

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No, you may have to increase the idle speed if the mixture was too week on any of the barrels but the balance will remain the same :-)

  • Like 1

Cheers,

John W

http://jonwatkins.co.uk

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