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4T Carburettor


trapezeartist
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Is the taper on the end of drain screw rusty or not smooth, as this will prevent a proper seal when snugged in. One other thing to check, I am not familiar with the bsr33, but on some other carbs the float bowl overflow tube also tee's internally into the same exit spout as the drain (obviously, on threaded out side of drain screw taper)....

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46 minutes ago, pauls320 said:

Is the taper on the end of drain screw rusty or not smooth, as this will prevent a proper seal when snugged in. One other thing to check, I am not familiar with the bsr33, but on some other carbs the float bowl overflow tube also tee's internally into the same exit spout as the drain (obviously, on threaded out side of drain screw taper)....

The taper is in pretty good condition, but I just think that trying to prevent petrol leaking past a metal-to-metal joint is taking optimism to an absurd degree. I've spoken to Beta UK and BVM and no-one seems to know if there should be an O ring. I'm just going to dollop some thread sealant on it and be done with it. I can't see that I'll ever need to undo it in the future, though it should still be possible with (perhaps) a bit of difficulty.

The carb has breather tubes all over the place but none going into the area of the drain. That's another interesting little conundrum with this carb installation: keeping all the plastic tubes away from the exhaust.

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Right. I put the screw in with thread sealant. It stopped the leak. :) It also stopped the engine idling properly. :(

It seems to be ridiculously lean on idle. Basically it won't idle, and pops like crazy in the exhaust as the revs fall back from a blip of throttle to stalled. I took it all apart again, and at first I thought the idle jet was blocked (I couldn't see light through it). I blew threw and it cleared so unfortunately it was probably just a little petrol hanging around in there. I've turned the idle screw up about a turn and a half and it still won't run. I'll try some more tomorrow in case I can finally sort something. It's a pain as I should be doing a trial on Sunday.

But the good news is that I am getting pretty good at removing and refitting the carb.

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I assume you checked your hot start?

   Mine got pulled out by a stick the other day, it was popping, snapping and running quite lean. Fortunely Billy mentioned if it was lean to check- and I saw it had gotten pulled.  (I ride in lots of sticks and brush).

 

mark

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Panic over! Somehow the idle screw had got turned out a huge amount while the carb was on the bench. (Now who should I blame for that? :wacko:) Today I just wound the screw in a lot (lost count of the turns) and I had an idle, albeit too fast now. A few minutes to adjust it down to a nice level and it's all good to go. Feeling happy again. :)

On the subject of the hot start thingie, mine won't stay out on it's own anyway. As I wear the cut-out lanyard on my left wrist, it's quite difficult to pull out the hot start, get my right hand back to the throttle and kick it over before it's popped back in. But it's rarely needed and then only momentarily, so it's not a significant problem.

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