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PD carbs help required (old thread updated)

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royhall:
Cheers for that Mark. No there wasn't any cracks. See your point though. The guy that said to clean the float valve seats with a soft wood dowel in a drill has just taught me a new trick. Did it this afternoon, very carefully, and its worked a treat. I am so relieved you wouldn't believe. The bike is now officially finished. Will post some pictures tomorrow. Thanks to you all out there that helped me get to the end. :)

MarkCR750:
Great news Roy, look forward to seeing the pics.

JamesH:
Well done Roy, nice tip re. Dowel method. Glad you finally got there...pics now..

royhall:

--- Quote from: royhall on April 17, 2015, 03:16:31 PM ---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. :'(

--- End quote ---


Well, am 160 miles in now and everything has been going great. Went for a 40 mile run today when it spluttered and started to die. Went onto reserve and all was well again. Filled up to the top at the nearest station, and 2 miles later it was running rough again. Pulled over and looked, petrol was pouring out of one of the overflow tubes. Was fortunately only 5 miles from home so got there by turning the petrol tap on and off. The tank had been initially filled to the top without problems.

These carbs are becoming impossible. Not sure how to go about fixing this as just keeping on re-cleaning them and throwing new parts at it is not working. Am unsure why this would suddenly start again after being spot on for the first 160 miles, clearly associated with slightly raised pressure from a full tank. Think I may need to replace the carbs as the seats for the float valves are not replaceable in the PD's. Tried everything else, a worn float valve seat is now a possibility.

Any idea's guys.

royhall:
Just found this online. I don't have enough experience to know if this is correct, but appears to be exactly my problem.  http://www.motorcycleproject.com/text/float_valves.html

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