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Small hole in inlet manifold?
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Author:  beerbunny [ June 10th, 2011, 1:08 pm ]
Post subject:  Small hole in inlet manifold?
I'm in the process of cleaning the inlet/exhaust manifold prior to refitting it and I noticed a small hole at the bottom of the inlet side, directly below the carb flange. Is it meant to be there? I don't want to fit the manifold until I know for certain one way or t'other.

Can anybody shed some light on this, please?

Thanks in advance,

John
Author:  Tom Duckpower [ June 10th, 2011, 1:09 pm ]
Post subject:  Re: Small hole in inlet manifold?
yes, it's meant to be there..
it's there to let fuel leak away in case the engine is flooded
Author:  beerbunny [ June 10th, 2011, 1:30 pm ]
Post subject:  Re: Small hole in inlet manifold?
I wondered if that might be the case; it doesn't look accidental. Why it bothered me was that in several decades of messing about with bike engines, I don't think I've ever seen a deliberately introduced leak in the inlet. In fact, as far as I know, this is universally reckoned to be a BAD THING. :shock:

Anyway, thanks for clearing that up. I can get on with putting the beast back together now.

Hartelijk bedankt,

John

PS The first motorised vehicle I ever rode was a Solex. It belonged to my aunt who lived in Ommen (near Zwolle). Happy days. :)
Author:  ken [ June 10th, 2011, 2:48 pm ]
Post subject:  Re: Small hole in inlet manifold?
Not if it's a calibrated drilling, which affects all (or both?) cylinders equally and the carburettor settings take account of the tiny air bleed. ;)

As Tom said, it would be much worse to have neat fuel entering a cylinder, if the needle jet in the carburettor got stuck, for example.

ken.
beerbunny wrote:
I wondered if that might be the case; it doesn't look accidental. Why it bothered me was that in several decades of messing about with bike engines, I don't think I've ever seen a deliberately introduced leak in the inlet. In fact, as far as I know, this is universally reckoned to be a BAD THING. :shock:

Anyway, thanks for clearing that up. I can get on with putting the beast back together now.

Hartelijk bedankt,

John

PS The first motorised vehicle I ever rode was a Solex. It belonged to my aunt who lived in Ommen (near Zwolle). Happy days. :)
Author:  beerbunny [ June 10th, 2011, 4:11 pm ]
Post subject:  Re: Small hole in inlet manifold?
Quote:
Not if it's a calibrated drilling, which affects all (or both?) cylinders equally and the carburettor settings take account of the tiny air bleed.

Obvious, really. I really should try thinking these things through before commenting on them. :oops:

Thanks.
Author:  ken [ June 10th, 2011, 6:21 pm ]
Post subject:  Re: Small hole in inlet manifold?
No bother, it helps to keep the cogs ticking over... ;)

ken


beerbunny wrote:
Obvious, really. I really should try thinking these things through before commenting on them. :oops:

Thanks.
Author:  beerbunny [ June 10th, 2011, 6:36 pm ]
Post subject:  Re: Small hole in inlet manifold?
Quote:
No bother, it helps to keep the cogs ticking over... ;)

It's good to know that I perform a useful function, even if it is just to help others to keep their brains in good nick by demonstrating the shortcomings of my own! :)

Cheers,

John
Author:  Devils Advocate [ June 10th, 2011, 9:16 pm ]
Post subject:  Re: Small hole in inlet manifold?
It must be a very precisely sized hole?

Any tiny leak at the carb/manifold join will make your car behave very poorly indeed - idling will be near impossible.

As I found to my cost.
Author:  ken [ June 10th, 2011, 9:51 pm ]
Post subject:  Re: Small hole in inlet manifold?
More to do with the fact that it's barely 0.5mm in diameter, so flow through it is insignificant compared to the amount of air drawn into the engine through the carburettor, even at tickover when only the idle system is active. ;)

ken


Devils Advocate wrote:
It must be a very precisely sized hole?

Any tiny leak at the carb/manifold join will make your car behave very poorly indeed - idling will be near impossible.

As I found to my cost.
Author:  Sean [ June 11th, 2011, 8:00 am ]
Post subject:  Re: Small hole in inlet manifold?
Devils Advocate wrote:
It must be a very precisely sized hole?

Any tiny leak at the carb/manifold join will make your car behave very poorly indeed - idling will be near impossible.

As I found to my cost.


the fact that the hole is central and therefore affects both sides may be the key, a leaky manifold will affect one side more than the other, a cracked carb insulator is the cat in the pigeons as it has a equal effect and there is very little air to leak if all the bits are there.
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