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PD carbs help required (old thread updated)

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royhall:
Hi all. Cant get over the finish line with my 750F2.

Am struggling to get the carbs to stop leaking petrol.

Short history: they were totally stripped and the gummed up bits soaked overnight in carb cleaner, they were then cleaned using guitar strings and compressed air, they were then ultrasonic cleaned and the outers vapour blasted, they were rebuilt with new float valves and gaskets/o-rings. They were bench tested for leaks and a crack with the mallet settled everything (no leaks), fitted them to the bike and gave the engine a run (no leaks), fitted the tank and went for a short ride around the block (no leaks), fixed a couple of non carb related small issues then helmet on for a longer run. Turned on the petrol and a leak from No.2, went for a short run in the hope it would settle (it didn't).

Stripped the carbs yet again and found all the float heights were perfect. So replaced the float valves again with Keyster items from DSS. When tested they leaked from 2 &4 and would not settle. Stripped again and set floats a bit higher to try to shut the valves a bit sooner. Now leaking on 1 2 & 4.

Am I missing something here as I'm starting to get desperate with this. Everything is spotlessly clean, the floats move freely, the float heights are right, the valves are on the third new set. I now have no idea where to go with this as I just don't know what's wrong with them and therefore how to fix it.

Could anybody who has knowledge of these things and lives anywhere near Thornton-Cleveleys Lancs call round and give me some pointers please. Or failing that, does anybody know a carb expert that I could send them to.

HELP!!! Yours sincerely, Desperate of Lancashire. :'(

tom400f:
Very sorry to hear about that (though the (no leaks) humour made me laugh)

Are you sure there is no source of crud somewhere along the way, possibly in the tank as it seems to affect all or most of the carbs?

royhall:
Cheers Tom. Definitely not crud. Am using a bottle tank to test on the bench and that is see through plastic. Not a trace of debris and fresh petrol. Good job I haven't got any rope, I'd be swinging from a tree by now. O wait a minute, I haven't got a tree either.  ;D

royhall:
Just been told to take the Sherlock Holmes route. "After you eliminate everything else, whatever is left must be the problem".

Then he said the difference between the F2 carbs and the K series is pressed in jets (including the float valve seat). Apparently ultrasonic cleaning can make these seats worse depending on what fluid is in the ultrasonic tank. Doesn't matter on K's as the seat gets changed. I'm advised to use a soft wood dowel sharpened to about the correct angle in a battery drill. Just using carb cleaner on the wood to spin it in the seat with gentle pressure. Then clean out with compressed air, says it works every time.

Has anybody else any experience of this technique before I blunder in and totally f**k it all up.

Cheers. Not hanging from a tree yet. ;D

MarkCR750:
I don't think this is your issue Roy but it's worth a mention in case anyone else has it happen to them, I had a carb leaking and tried all of the above, eventually I found a hairline crack in the brass snorkel tube in the float bowl, so fuel was exiting through the crack and down the overflow, a quick check is to take the bowl off, fill it with fuel and see if it leaks, the crack was so fine that it was almost impossible to see with the naked eye.

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