strange noise from the carbs

[Max]

Hi everybody,

i have a strange problem with my fulvia 1.3: i hadnt driven her for about 3 weeks cause i was on holiday, and now on my first ride after that time i realized a strange noise. when the engine is hot, there is a strange hissing sound coming from the carbs, but only if the throttle is closed or nearly closed. it occurs at all revs, and it is really loud. and idling is quite high and it takes quite long till the revs go down to idling speed.
i am really worried about that, cause i ve never heard such a noise on any car before..
do you have any ideas about the reason for that noise? how can it be fixed?

thanks a lot for your ideas

max

[Fulvia as is Claire]

it sounds like a split / cracked hose is sucking in air via the split or crack & not via its inteded path. could be old age or could be that some small animal nibbled on the tasty rubber. Last week I replaced a "whistling" hose. No more whistle & a better running motor.

[Phil]

Sometimes it's just silly stuff. Are you sure the choke is not activated slightly?

[Max]

hey,

thanks a lot for your answers!
no, the choke is not activated, and the noise is a completely different one as well, it s higher and sharper than the choke noise
i changed the only hose (apart from the fuel lines) i could find on / near the carbs, the hose going to the brake servo... now the brake performance is much better, cause someone had put the one way valve the wrong way round, (the strange thing about that is that my fulvia had even passed the german TÜV without them realizing that fault) and i m really happy about that improvement, but the whistling noise is still there..
any other ideas?
thank you very much

max

[Ed Levin]

A hissing together with a high idle suggests that additional air is getting into the carb downstream of th ethrottle plates. Have you checked the rubber mounts or the intake manifold for leaks? Usually such a leak will result in the carbs 'hunting' at idle rather than just staying at a higher rpm, but you never know.

[Huib Geurink]

I agree with Ed. Very likely the carb mount rubber is leaking.

Did you check the support for the air filter box? It should be firmly mounted. If not the carbs hang on the rubber only which is a sure recipe for ruining the rubber. Often the rubber grommet at the bottom of the support has gone.

If the support is bad, it is nearly a sure thing the rubber is leaking.

[Walter van Gruythuysen]

You can do a leaktest with WD 40. Spray it a bit when the engine is running idle on the carb mount rubber. If rpm goes up, you know the leak.

[Fu. a.i. Claire]

I don't have a problem with my Z "at this time", but I am going to check the mount anyway ! Thanks !!

[Randy Adams]

It's primitive and graceless, but you can also grab the airbox and push the entire assembly toward the engine and see if the hiss and running condition alters. I agree it almost certainly must be the carb base. The assembly of the two carburetors, drip tray and the airbox is fairly heavy. If there isn't a good solid support from the vertical strut (or worst of all, it's missing!) then the rubber mount will stretch and finally fail.

[Max]

thanks for your advise, but it cant possibly be the carb rubber mount, cause i ve changed it about 1500 km ago, and yes, it does have the support thing...
but i ve got some good news: the problem seems to have solved itself.. today i wanted to drive to my mechanic to show him the problem, but the hissing has totally disappeared. the mechanic couldnt find any fault on the carbs, so we decided to wait if it will reappear. but today, i ve driven about 80 km, and no more noises so far...