6 replies to this topic

[charlieheal123]

Hi Guys,

 

I went to install my new cone filter on the back of my HS4 carb today, on my 1991 1275cc cooper, Maniflow Exhaust, and it runs like a sack of excrement. 

 

I put the filter on and took it up the road, and it was just terrible. I do have a couple of richer needles to try with different profiles that I got from Mini Spares, but it seemed so bad that I can't put it down to just air/fuel ratio and fuelling. Lumpy/didn't idle and had flat spots pretty much everywhere...

 

So my question is, what do the 2 vacuum lines that are on the stock intake do, and do you need to block off the little inlet (that one of those vacuum lines went into) on the intake manifold when you fit an aftermarket filter???

 

I know the needle needs to be changed (I'll do that tomorrow) but the difference between what it was like before, to what it is like now, seems to drastic to be put down to just some wrong fuelling? Can it? So do you need to do something to these vacuum lines and the inlet of the intake manifold?

 

Many thanks and any help is appreciated!

 

 

[charlieheal123]

Sorry, I have a HIF44 by the way, not HS4

[Spider]

There's a couple of vent holes on the SU Carbs on the Intake Face, there's 2 from memory on the HIF44, about 6 mm in dia at a higher centre line than the Intake itself.

 

If when you put the filter backing plate on you put it on upside down or it doesn't have these vent holes, the car will start, but have next to no power.

 

I'll see if I have a photo.

[Ethel]

Vac lines shouldn't be affect by a filter swap.

 

As Spider says there are communication ports to the air filter via the gasket face. All Su's have ones that feed  atmoshpheric air pressure to under the piston so it rises when the pressure above the piston is lower - those holes in the bottom of the piston downstream of the needle allow the manifold depression / venturi effect to suck it up.

 

Some Hifs also have a port to the float chamber.

[Icey]

I agree with Moke - this isn't just the change of filter, you've got something wrong. Quickest way to double check is to put it back to how it was before and see if the problem persists. Just changing a filter doesn't always need a needle change.

 

I'd also suggest (bit late now, however) that if all you're doing is 'bolt on' mods then just stick with a replacement filter element rather than the cones. They give better all-year-around running.

 

Anyway!

 

Vacuum lines - are you talking about a little 1/4" that goes off to the dizzy or the 1/2" tubes that go to the engine breathers (crank/gearbox)? Either way, they should really be connected to the intake. The former, if disconnected will cause the car to run terribly, the latter can do the same if the connection to the carb is left open (if blocked it has other effects but not as dramatic).

 

 

Edit:

And what Ethel said (forgot about those). Check you're not blocking the two air lines into the dashpot with the new filter.

Edited by Icey, 23 April 2017 - 09:54 PM.

[charlieheal123]

Thanks for the replies guys.

 

It turns out I have a HIF38 instead of a 44.

 

I've gone from the standard intake with a K&N filter element in it, to a K&N cone filter.

 

There are two vacuum lines. One that goes from what seems like a MAF/MAP sensor (but not because there is no electrical connection, only this vacuum line) into the main body of the intake, into a device inside the intake housing with the logo 'AC' on it. There is then another vacuum line coming out of this device into a port of the intake manifold about an inch from the block.

 

I'm guessing this is what has messed everything up... I've tried blocking it off and it still runs like rubbish. When it is left open the running is unpredictable and all over the place, and when it is blocked, it seems just as bad, but more consistently bad. Feels like it has no power, at all, and coughs and splutters.

 

My car is at my garage not at my house, so I'll be able to get some photos when I get some time this week.

 

Would it just be advisable then to keep the stock intake with the K&N element, as it was dyno tuned with this setup and ran perfect.... I feel I'm just opening up more work than I need, and can afford, right now ahah! 

 

Just wanted this new filter to get the big plastic intake out of the engine bay and give it a cleaner look... Guess it's more complicated than I originally thought!

[Icey]

One that goes from what seems like a MAF/MAP sensor (but not because there is no electrical connection, only this vacuum line)

You won't have one of those with a carb unless you're using a Megajolt. It sounds like it could be an anti-run-on device but I'm guessing, you'll need to get some pictures up.

 

It shouldn't be any more complicated switching to a cone filter but if you're using the car as your daily driver it's form over function - you're not really going to gain anything while generally making the car a little less pleasant to drive. If you really want to get rid of the filter housing I'd probably opt for a dome filter (e.g. ITG) and a stub-stack (e.g. from MED) but with an eye on switching back in winter to get the warm air feed from the manifold back.