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Triumph Repair/Early Stromberg CD's


Early Stromberg CD's ex TR4, fixed needle. So no 'O' ring,yet every time I look down the air valve tube,the oil level is down at the bottom? it needs oil to bring up to the 1/4" from the top.
Any ideas?
Thanks, Nick.

Do you have the adjustable jet in the bottom of the carbs?
If you are flat black sooting up your plugs then you must see black smoke out the tail pipe and your carbs are either flooding or the choke is on all the time or no one ever put the correct needles in to match the engine. The only way you can use a carburetor from another engine is to either have adjustable needles, adjustable jets or get the correct shaped needles for your engine. Plus you still may have other problems with the carbs like a flooding float chamber, a stuck on choke or even a float chamber vent problem.

The dry black soot on the spark plugs is proof positive that there is too much fuel per air going into the engine.

When an engine has it's compression raised it does two things it raises compression ratio and it increases manifold vacuum.

Another thing to look at is the Stromberg pistons, they must slide up and fall by them selves and the piston diaphragms must be good with no holes. The oil in the top is a dampener like a shock absorber that restricts quick movements of the piston. When you open the throttle quickly the increase air that enters the carbs causes a vacuum to form above the piston and the piston it slammed upward which allows more air to enter the combustion chamber and even though it also lifts the tapered needle out of the main jet it is not sufficient fuel for acceleration so the oil holds the piston down. This increases the air velocity over the jet which supplies an increase in fuel for just the time it takes for the oil shock to slowly allow the piston to raise. It takes the place of an acceleration pump in a conventional carburetor. The oil dampener also restricts the pulse of low idle that normally tries to make the piston jump up and down due to low RPM vacuum pulses.

To check the top pot of oil all you need to do is to unscrew the cap and lift it up a little and push it back down and if you feel hydraulic resistance it is ok. It uses up the oil supply because the oil is also used to lube the shaft that the piston slides on and the vacuum of the engine will draw that small amount of oil off of the shaft.

At this time you need to check float level in both carbs and check the vent tubes from the float chambers. Check which kind of choke your Strombergs have and see that they are not on all the time. Then if you have adjustable jets you need to go through the procedure of adjusting them correctly. If you don't have adjustable jets you will need to acquire several different needles sets to try to get the mixture correct. There are a vast number of different profiles of needles and if this is what is necessary you need to seek out the help of someone who builds racing engines to help you with the process which is very extensive. Not an easy job. Not just the size of the needle but the profile (taper) of the needle is very important.


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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.

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