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Jonathan Kidson/ TR4 won’t run on four

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I have a TR4 just being re commissioned. Engine rebuilt and firing but misfire on N0.1.Good compression on all cylinders. Using a glass plug it is apparent No 1 is sparking but not being fuelled until it hits 2500 rpm. Below this plug stays dry.

What would cause this ?

Have re skimmed head, new distributor, leads etc and plenty of sparks, timing fine just this problem. Could it be a broken ring not making enough 'suck' on the in stroke ?

Any ideas very welcome.

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Welcome to the forums Jonathan.

Have you removed the inlet manifold to check there is no obstruction in the air-way?  I seem to remember an instance of someone discovering a rag stopper in there, left by mistake after some head work.  Of course, another possibility is that the inlet valve isn't opening properly. 

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  • John Morrison changed the title to Jonathan Kidson/ TR4 won’t run on four

Jonathon, not being fuelled until about 2500 revs, a likely very bad air leak. The extra revs overcome the leak giving enough vacuum to lift the fuel. If you’ve just recommissioned the engine, check the inlet manifold with carbs fitted against the gaskets against the head. You’ll often find the manifold hangs up on 1 of the dowels ( there’s 2, ) one in between each inlet port of the head. The head may appear flat against the manifold but the dowels are a close fit and if you tighten one too much it tilts the manifold leaving an air gap next to the head. 
Use brake cleaner or Easy start and spray around the inlet manifold where it touches the head, masking the front of the carbs  with your hand so non is sucked in there. If the revs increase you have an air leak, refit the manifold and try again 


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Exactly what I found,

Rough Running, when I took the inlet manifold off the ears (clamps) that hold the inlet and outlet manifold to the head on the rear one although tight had twisted and was not clamping the inlet manifold .



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You may also find that if the head has been skimmed the bottom of the inlet manifold can overhang the head and hang up on the side of the block. 

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