A7 ss 1960 500cc single carb

[greeneunos]

Hi
 Im sure its been asked before , but i thought i had an oil leak starting as saw oil on the floor under the bike , i've got it on the lift and cleaned the casings and underneath and No Leak !!!!
 I have however noticed petrol dripping from the air screw on the carb and started to think was it fuel ?
I thought it was a good time to drain the sump as it wet sumps when not used and  i have the  srm conversion plate with 19mm sump plug but when i opened it i got about a quarter of a pint of petrol out of the sump !!
 Never happened before , any ideas , both fuel taps were in the off position . thanks mike

[limeyrob]

What type of tap? 

[Worty]

Hi
 Im sure its been asked before , but i thought i had an oil leak starting as saw oil on the floor under the bike , i've got it on the lift and cleaned the casings and underneath and No Leak !!!!
 I have however noticed petrol dripping from the air screw on the carb and started to think was it fuel ?
I thought it was a good time to drain the sump as it wet sumps when not used and  i have the  srm conversion plate with 19mm sump plug but when i opened it i got about a quarter of a pint of petrol out of the sump !!
 Never happened before , any ideas , both fuel taps were in the off position . thanks mike

Fuel from the sump - never heard of that before.  Only thing I can think of is the float in the carb is stuck AND you have a tap seal problem allowing fuel to bypass the tap in the 'OFF' position and fill the carb until it leaks past the valves, into the cylinder, past the rings and into the sump.

Of course, this may be total *cock* and someone with more knowhow will put me right.

[berger]

modern fuel is a nightmare for going off and also absorbing moisture. it also rots things like tap seals and if left for a longish time will coat jets and other bits like float needles with a horrible varnish type goo. maybe your taps have been passing fuel and this has resulted in a slow coating of your float valve needle allowing fuel to bleed into the cylinder head and down the cylinders into the sump.

[limeyrob]

It is horrible stuff and quite chemically aggressive.  It will have worked its way pas the taps, past the float out the jet and ran down the inlet past the piston into the sump.
Use the bike more to keep the bores oiled and the valves seated.
Without knowing what the seal in the tap is - rubber, metal to metal or cork its hard to know what to do.  My understanding is cork is best but happy to be corrected.  I'm in the process of swapping metal to metal 1/4 turn to pull cork.
The diesel is no better, it hardened all the seals on my Land Rover fuel pump and it leaked like a sieve.

[muskrat]

G'day Mike.
I agree with Bergs and Rob.
I see the ill affects of E10 fuel every day with gummed up carbs/fuel filters.
What type of taps do you have?
Cheers

[Worty]

There you go Mike, I wasn't making it up after all - no other way for fuel to get into the sump.

I think at least one of my 'modern' taps is toast - started to leak a bit in the left hand tap.  I only use E5 in the Beeza, but not sure if that's the cause.

To try to alleviate varnish build up, I always run the carb dry before putting it away.  However, thinking about it, is this the best way?.  If there's a residue of petrol left in the carb, will it turn into varnish quicker? The issue doesn't seem to affect the Kawasaki as much, but the only way to drain the carbs on that is to remove the vacuum pipe and then run it out.

One other thing, and I don't know if this is right either, is that I put a bit of Valvemaster Plus in the BSA, which is supposed to stop the fuel stagnating - does this also reduce the likelihood of the fuel turning to varnish?

[jhg1958]

I have pondered the benefits of running the carb empty each time, or draining it. I reckon that it takes a couple of days for the fuel to evaporate in the bowl depending on the weather. So if you are using the bike daily then it has limited benefit.

On the other hand the small amount of deposits only matter over a repeated evaporation in the bowl so if you only use it once a month draining the bowl will only be of minor benefit.

So yes, I try and empty the bowl when I am finished but I do not worry too much about it.

Am I being a bit too relaxed about this?


John

[Worty]

I have pondered the benefits of running the carb empty each time, or draining it. I reckon that it takes a couple of days for the fuel to evaporate in the bowl depending on the weather. So if you are using the bike daily then it has limited benefit.

On the other hand the small amount of deposits only matter over a repeated evaporation in the bowl so if you only use it once a month draining the bowl will only be of minor benefit.

So yes, I try and empty the bowl when I am finished but I do not worry too much about it.

Am I being a bit too relaxed about this?



John

I'm just musing really John.  I have left my bikes for a few months and they still seem fine.  One day, when the carbs need to come off, I'll check them out.

[greeneunos]

Hi guys thanks very much for all the replies.
I  fully agree with the reasons , I have the 1/4 turn taps so I will see if one or both are leaking and rectify , on the plus side the oil leak (  green in colour which was confusing me , which was obviously petrol and oil ) isn’t an oil leak .
Thanks again cheers Mike

[limeyrob]

You could leave the carb bottom nut (or drain in Concentric) loose so its drips out.  Far from ideal but better then in the engine.

[Black Sheep]

The float needle must be the culprit. If it is seating properly, fuel can't get into the carb. Your petrol taps must be leaking too. SS Nortons with their steep downdraught are notorious for this. An engine full of petrol is not unheard of.

[greeneunos]

Thanks yes carb strip and clean today , regards Mike

[CheeserBeezer]

Yes, definitely tap(s) and float needle. I have come across this before. Whilst the original taps with corks look nice, unless the corks are quite stiff they will fail and are guaranteed to fail in time. The best option for reliability is to fit taps with nitrile seals and a float needle with a viton tip. Fuel level in the monobloc carb should be level with the dot on the chamber cover. This can be checked by adapting a main jet nut to take a clear pipe which can be turned up wards to check the level. A Mistake some people make is to put a fibre washer under the carb banjo. This lifts the float needle seat too high so that, in the worst case, the float bowl hits the inside of the carb body before the needle shuts the fuel off.

[greeneunos]

Hi  thanks mine are the 1/4 turn taps not the pull type like on my previous A7 and I did have to replace the corks on one of them , I will be investigating the taps aswell today , hopefully I can repair the culprit , cheers Mike