Rough idle.

[bromfieldhall]

Hi, our Manta A 1,6S gradually became harder to start and idle and got to the point that the carb mixture made no difference on adjustment, we fitted a new weber carb same model that came off and we can now adjust the idle. The problem is the engine will just refuse to idle correctly?? I've checked timing, leads, plugs, it has electronic ignition so no points. Just when i feel we are getting somewhere and the engine seems to be on a decent idle the engine will increase its revs by its self?? Any thoughts or ideas would be welcome please.

[spiney_norman]

Sounds like an air leak somewhere. Have you tried spraying carb cleaner or WD40 around the inlet manifold, ie where the carb bolts on or where the manifold sits against the head? Have you checked the vacuum pipe to the servo?

[mantadoc]

If t was a GTE I would say lean on the plenum (manifold) to push it down, then pull it up but as I expect it to be bolted to exhaust the inlet / exhaust manifold gasket is less suspect 

[bromfieldhall]

Thanks for the suggestions. I've already tried the WD40 but there wasn't anything. I'll look at the vacuum pipe. I'm going to take off the manifold carb and replace all gaskets just in case. Long shot, but are the Manta manifolds prone to cracks or leaks?

[spiney_norman]

I've never come across a cracked inlet manifold but it's always possible. I've seen plenty of servo vacuum hoses break down and cause air leaks though, even when they look alright from the outside. For what it'll cost it's probably worth replacing just to rule it out, your local motor factors should be able to supply suitable hose.

[andyc]

As Rob has stated above. If you can't get any vacuum pipe from a factor then its still available from Vauxhall. The part number for it is 3434616 for the hose and if you are doing this then replace the valve as well which is 90304535. You will also need four hose clips and mind your fingers on the hose.

Hope this helps

Andy