What causes..........

[bristolmod]

fuel to accumulate in the carb air-hose?

Standard 1962 TV175 S3 apart from electronic ignition and a 42mm Clubman (main jet is now 108 instead of 106).

Recently, starting when warm has been problematical and I have carried out the following:-

1) changed standard 20mm Delly to an identical spare (same jets; slides; atomiser etc) no difference.
2) new plug- no difference; good spark on both
3) checked fuel flow thru tap- good

I have noticed that the air hose does accumulate fuel from somewhere, and removing said hose does allow the bike to start first kick when warm.

The hose is the "old type" with the drainaway system on the end and the metal perforated plate at the bottom.

Any ideas as to why fuel is collecting gents?

Was rebored 2000 miles ago; piston is standard oversize with no skirt removed on inlet side.

When bike runs it runs very well indeed- just a pig to start when warm, which I firmly believe is down to the excess fuel.

Any suggestions welcomed

Chris

[soullad]

starter for ten ...

Maybe the rings have worn some after your rebore causing more blow back than normal, which collects as excesisve fuel in the air hose?

[coaster]

Could it be the warm weather? Ass Soulad said, it could be down to premature wear on the rings or maybe a sticking ring, what's the compression feal like?

You know the normal dodge for warm starting with spitback I take it? i.e. fuel off before you stop and leave it off when re-starting until it fires, throttlle closed wjhilst kicking. Works a treat until the time when you forget or it stalls in traffic

[dapper]

Agree with Coaster about the turning off fuel just before switching off ignition, etc. But you say its collecting even though you have the old style drain in the bottom of the bellows. Surely any fuel should drain out of here (that's what it was designed for) so either the valve is blocked or the drain hose.

[bristolmod]

had a closer look this morning- whilst the drain itself is clear, the perforated metal plate that slots across the bottom of the hose, isn't particularly "free flowing".

Have removed said item just leaving the vent to the atmosphere, and all appears good now (touch wood!!). Starts first/ second kick either hot, warm or cold.

Thanks to all for their input

Chris

[dapper]

On the later style bellows without the drain, there have been recommendations to drill a 1mm hole in the bottom of the bellows to allow accumulated fuel to drain and eradicate your issue. Can still make a bit of mess on the runner boards.

[sideout]

I've had this on a couple of engines. The give away is removing the bellows when it refuses to start when hot, if it bursts into life it's excess accumulated fuel. Obviously, the excess accumulates owing to the mixture being too rich somewhere in the carb jetting circuits. IMHO with simple carbs, on piston port engines, the main jet does effect the mid range and to a certain extent the low range, it's been my experience that this causes the problem. Significantly so when running in with a delibrately large main.
Personally, I am very uneasy about drilling holes in the air hose having seen what happens to engines that have suffered split hoses in the past!
Maybe we need a drain valve for 22mm carb bellows?