We're not paranoid but...............SORTED?

[bristolmod]

...............TV175 S3 totally standard apart from:-

1) 42 mm Clubman
2) 12v electronic.
3) Rebore and new piston 2k miles ago

Has always been a good starter whether Cold, Warm or Hot, but over the last couple of months has been a pig when warm/hot.

However, the moment I take off the carb bellows, it starts first kick, so I think its mixture related

Very good spark so no problems there.

Choke working OK

Have changed everything carb wise and have even put on a duplicate carb with replacement jets etc etc No difference- still a pig when warm/hot but fires up well with no carb bellows.

Changed plug- no difference

I had an idea that it might be a blown flywheel seal letting more air into the system, but that wouldn't explain the fact that it fires when the bellows are removed (thus letting more air in and diluting any vapour in the carb throat/ inlet manifold....)

Tried drilling a small hole on the bottom of the bellows- no difference

Any ideas before it ends up in a skip?

Chris

[ArmandTanzarian]

Probably not the same but my scoot gave all the signs of running too rich when the LT Coil on the stator plate was on the verge of giving up.

[Rich_T]

I assume you've checked the obvious, like over trousers under the seat blocking the air scoop? Or even running without the air filter?

[bristolmod]

yep! There's an air filter in there- do you reckon its worth removing the "swan neck" inside the airbox?

[Muppet]

yep! There's an air filter in there- do you reckon its worth removing the "swan neck" inside the airbox?

try anuther filter cus some of the ones yer can get are crap,
muppet,

[chris37]

If you do decide to put it in a skip,let me know where.....

[bristolmod]

I'll try another filter and see what happens.

As Mr Innocenti initially produced bellows with a one way drainage system (lets fuel escape but seals shut on the induction stroke), this was obviously a "problem" in the past ( I think all bellows, including early versions of the 22mm type had the drainage system plumbed in until it was dropped for cost cutting reasons)

Consequently, as the "problem" has been highlighted by Innocenti, there must be some cause as to why this has suddenly raised its ugly head- for some reason the bellows/ carb throat area is becoming saturated with fuel/ air at a ratio that will not allow it to "fire" on start-up. Once the bellows are removed, the fuel/ air ratio in that area return to normal and the engine starts (thats mny theory anyway)

So what's caused the fuel to accumulate there?

Can't be the carb as I've changed it/ duplicated it

Spit-back? worth considering . Why?

Air Filter blocked? Possibility.............

Air-box damaged/ blocked?

Strip down tomorrow and report back methinks...........(I'll phone the skip hire company anyway.............................)

[vRSG60]

I see you've checked the choke, but when mine suffered exactly the same symptoms it was the choke that was stuck on. The choke piston didn't return down the barrel.

[bristolmod]

I see you've checked the choke, but when mine suffered exactly the same symptoms it was the choke that was stuck on. The choke piston didn't return down the barrel.

Good point- I'll replace the choke mechanism tomorrow- thinking about it even though I've changed/ duplicated the carb, the choke unit has remained constant.

Could be that little bugger that's out to get me............................. :baddevil:

[sideout]

Ethanol in cheap unleaded fuel? I've had this a couple of times over the past and now use Super Unleaded, (BP if I can). I've also seen the float bind on the pin with Jetex carbs owing to Ethanol causing the plastic to swell.

Hope this helps Chris.

Nigel