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Triumph Repair/Mark ll Spitfire


Hello again Howard, and thank you for prior help with valve timing/ chain installation. I am pleased to report that engine is running very nicely as long as I do not attempt to reduce idle speed below
1500 RPM. Upon cracking throttle both carbs will  sometimes backfire. My feeling is that camshaft timing gear/ chain is still a bit retarded. Believe it or not, I am beginning to enjoy toying with  this little British stinker. If you are once again able to share your knowledge with me, it would be greatly appreciated/


Hi William,

If you set the cam timing as per their marks that is all there is to that.

Carbs not idling and back fire can be out of adjustment. Cam must be correct first and it it is as the marks say then forget that and go to ignition timing and set that as per specs and that is done. Carbs always are last to set and can not be set right if the other two are not correct.

With the engine off and the throttle stop screws backed off so that both throttles are closed all the way. Look closely with a bright light to see that the throttle opens both throttles at the exact same time. If mot loosen the pinch bolts and adjust the small links on the shaft so it opens both at the same time. When you have that done turn each stop screw in with a piece of cellophane under the screw to act as a feeler gauge. When both are set to just lightly hold the cellophane then turn each in 1 1/2 turns exactly. Start the engine and warm it up and see if it idles at all. If not turn BOTH stop screws exactly the same amount until it will idle what ever that speed is. The screws are hex head so you can count the number of flats to be exact on both.
Now lift the small spring loaded pin under the lip of the top pot on the front carb and note the reaction. If the engine dies the OTHER carb is too lean so turn the adjusting nut on the jet down by two or three flats and test it again. If the engine speeds up when you lift the pin the other carb is too rich and you must turn the jet adjusting nut UP several flats.

Do both carbs the same way and the idle will change so reset the idle on BOTH carbs the same number of flats to get an idle again.

Continue this process until you are able to get a 750 to 900 RPM idle.
And when you lift the piston with the pin you get an RPM drop to running like an old John Deer tractor. The mixture is then correct. Rev the engine between each adjustment to clear the engine a little.

Let me know how you do. Don't stray from or try to skip any of the sequence.


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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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