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Stromberg 150 jet thread size?


Paudman

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I've stripped - literally! - a pair of Stromberg 150s from a GT6 Mk1 and found that one of the jet assemblies has cross threaded the alloy body. The rest of the thread is good and the body looks like it can be saved; only the first two or three turns require cleaning. Does anyone know the size of tap / die required to rethread both the body and the jet assembly thread?

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hi there I suspect the size of thread that it was possibly done by machine lathe, you might have to find a local engineering firm to help
or a friend who has a old school tap and die set,it maybe worth giving a carb reconditioning company a call and enquire on repair, tricky one.
chaz

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Appears to be 24 TPI so not a usual tap size for that diameter.

Would be best and probably cheapest, to see if someone has a spare, second-hand, replacement.

You may be able to clean the threads with a thread file, but these are tricky to use on female threads.
I would definitely replace.

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Not far off the mark, Junkuser.
I went to the father-in-law of A J M Engineering fame, he didn't have a tap to suit the threads. The jet cleaned up more or less (!) with a thread file but I fear he did more damage than good trying to sort out the alloy body threads. In the end he ground off the damaged threads leaving about 75% new clean threads and I'm not sure if that's sufficient to hold once the full jet assembly is replaced. I think I'll say nothing to him and quietly source a good S/H or recon one.
I wouldn't have believed that the alloy body threads could destroy two brass jets without suffering severe damage themselves.

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Did think of suggesting removing the the damaged threads but did not think the suggestion would be well received on this forum.
Was thinking scraping the damaged threads out rather than grinding the base off, but only if just 1 or 2 threads damaged.

What has been done may work however.  Try it and see. may give you time to look for a replacement at the right price.

The lower jet holder in your picture does not look like a genuine Stromberg part, unless the design was changed in later versions than I have worked on.  ? home made, in which case the threads may not be smooth and could be the cause of the damage to the threads in the bowl.
What material is it made from?

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Lower one came from a Stromberg bought NOS for £10 on eBay, looks like a later model than the others, possibly Hillman Hunter. It's steel rather than brass. It was dug out of storage to replace the damaged brass one and ended up the same way. Carbs are now reassembled and with the full jet assembly made up there appears to be enough thread holding everything firmly in place. I'll not be able to try starting the engine until the weekend.

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Dead carb... possibly! Fitted it and fuelled up only to get gallons of petrol running out of the bottom; I found to my amazement that none of the float chamber screws were even close to tight. Can I really have refitted the carb without tightening even one of the six? In any case even after tightening them all and cleaning off the fuel there appears to be a drip out of the jet assembly. I can't take the chance! Now... anyone know where I can get a good CD 150 carb, the one with the choke assembly cams etc? New, good S/H or whatever?

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