PD carbs help required (old thread updated)

[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. 

[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.

[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.

[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]

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.

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

[mike the bike]

Interesting.   Sounds like a carbon expert may have identified your problem.

[Graeme77]

If the valve seats are worn cant you use the same dowel trick with some grinding paste to clean the seats up? The depth diesnt really matter.
I have an incomplete set of pd's I aquired and have no need for, ill see if I can check the valve seats on these if you want to try new bodies.

[royhall]

Thanks Graeme that could be a big help. Its No.2 (the one with the accelerator pump) that's leaking right now.

Am at the moment waiting for some Genuine Honda float valves to arrive. Took a chance on a bag of 6 genuine used ones from a breakers yard, the guy says they are all in really good nick. With the new Honda ones from DSS being £33 each, I thought £30 for a bag of 6 was worth a go.

Will let you know how I get on after they arrive.

Funny this old classic world, I've got 5 bikes and not a single one on the road that I can use. Weird.

[royhall]

Forgot to update this thread sorry.

Am now back on the road with a fairly simple fix.

When I stripped the bike I gave the tank a really good clean out with the detergent cleaner I use that shifts everything. Didn't really get much crap out and the insides looked squeaky clean. Sent the tank to the painters, and he said he also cleaned out the insides after sanding and before painting with paint thinners (said nothing came out). Just to be sure, I cleaned it out yet again before fitting with clean petrol. Checked inside with my workmates endoscope, and it was spotless. So the tank got fitted.

I filled the tank right to the top from a plastic Jerry can (that I have used for years without problem), and off we went. All was well for the first 160 miles and then I ran out of petrol and filled up from a service station. Then the petrol leak problem started again.

The fix.
Drained the float bowls into 4 new clear disposable cups (camping stuff). Had a look at the petrol that came out and in No.2 was a collection of little black bits. The other three carbs were clear (the PD carbs on the 750F2 fill via the No.2). Looks like filling up with the pressure nozzle at the petrol station had disturbed some very well hidden muck in the tank. So drained the tank back into the clean Jerry can via a filter paper and found some more muck.
Have now fitted a small inline petrol filter as the strainer in the tank (fixed to the petrol tap) had come off and would not stay on. Put the petrol back in and let it run through No.2 with the drain open to try to clear it. Put everything back together and it appears to be okay at the moment.

Summary
Such a small thing, and such a big lesson learned. From now on all my classics are being fitted with inline filters. A penny job that hopefully saves a pile of heartache. No matter how well you clean the tank nor how clean it looks, some gunge will hide away in the corners of the tank and bring the whole thing to a stop. No.2 does still overfill slightly if I leave the petrol tap on (very slowly can be hours), but the bike runs great now. Hopefully with use the No.2 float valve will fully reseat itself.