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CR Series TR6 Inlet Manifold - Setting Butterflies

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Good evening,

I have just spent a rather frustrating few hours this afternoon trying to set the butterflies on my 1973 CR series TR6. First a little background information; the car is fitted with the 'prestige' throttle linkage kit together with refurbished inlet manifolds (3,000 miles ago) and prior to me 'meddling' was running OK with the exception of a little hesitency at low revs. I took previous advice on the forum that the hesitancy could be as a result of the butterflies not being set correctly. To help me with the task I purchased a Dellorto carburretor balancing tool although in reality I think this may have confused me further. What sort of readings should I be looking to achieve from the balancing tool and at what point should I be looking too take readings? I have been working at idle although I suspect that providing the readings are roughly equal across each manifold this will make little difference. Happy to be corrected if I'm wrong here of course.


Firstly I have set each pair of butterflies to just 'grab' a cigarette paper with the throttle closed following previous advice on the forum. When I started the car (with the air-box removed) I was surprised that it fired happily with no choke and had a very high ticker even with the air-bleed valve fully closed. I assume this was because there was air flowing into the inlet manifolds with the throttle closed as I had set them partially open albeit only 2 thou (thickness of paper). Closing the air-bleed valve did not stall the engine so clearly this was not the correct set-up. I tried setting the butterflies firmly closed with no throttle but the car drove terribly and I had to have the air-bleed valve virtually fully open to achieve a reasonable tick over.


I would appreciate some simple step by step instructions to set and balance the butterflies as clearly this makes a significant difference as to how the car drives especially at low revs (so i'm told). In hindsight I wish I had left things alone as I have now rendered the car un-driveable which is a shame. Having said that it would be really great to be able to set the car up properly and get it running properly once again.


Thanks for reading my post and as always all suggestions and/or ideas are greatly appreciated.


Best Regards, Peter

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heres what I did....


set the throttle cable to give an idle speed of around 1500rpm. then use the airflow meter tao give the same reading across all three sets of butterflies by adjusting the throttle linkages. this is fiddly and took me about half an hour. hot work and lots of cross checking as adjusting one effects the others. once i had the same airflow at 1500rpm I reset the throttle cable to allow the butterflies to fully close and adjusted the idle speed to 8oorpm with the air bled screw


made a huge difference and totally eliminated the rough running i was experiencing a low speed and light throttle openings.



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Hi Peter


I don't know how the CR linkage compares to the CP that I have. But I changed the pivot shaft bushes (some sort of plastic) for flange oilite bushes from local bearing supplier. These located the shaft much better and a lot smoother, and easier to balance.Also changed the throttle links as available from Moss.


Regards JohnR

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Gary's method sounds simple enough, I would suggest you make sure car is at operating temp before you start



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Would proceed as Gary says.

Just a little trick: I stop the engine after each measurement

and do the adjustment of the levers.

Than I pull the cable and let it snap back to let the levers settle.

Best to de done with a second person.

Avoids the horrible heat from the exhaust that makes fiddeling

with the lever adjusters a pain .

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Worth also considering that the linkages change due to the ambient temperature.. So making sure everything is warmed up is important. Although does lead to the risk of burning fingers while doing the tuning..


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The CR series throttle linkage is a design fault. The throttle cable operates one set of butterfies which in turn operates the next set. More like a set of dominoes than synchronised even when set to perfection.


I would advocate chucking it in the bin and buying an after market one from Revington or Prestige as it will save you from hours of frustration!

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