Air filter types

Post by **winger300** » Thu Dec 18, 2003 12:43 am

I recently swapped my mushroom type filter housing for a saucepan which had been chromed. I thought it would make it look nice, but its causing me problems.

When the engine is cold it idles really low, and cuts out, but when its warmed up the idle speed is fine.

The fuel mix is perfect (set with a colourtune) and if i increase the idle speed then its too fast when the end is hot, and causes run-on when i turn it off.

So im guessing i've not done something right. Is the mushroom type filter better since the intake is closer to the exhaust manifold? or do i just need to change the carberetter needle for one that suits the saucepan type?

Post by **Kevin** » Thu Dec 18, 2003 6:44 am

Do you mean the so called sports type about 6" in diameter with a foam sandwich type of filter, did the old one have the breather pipe going to the air filter and if so where is the breather pipe now.

Post by **winger300** » Thu Dec 18, 2003 12:43 pm

No, the saucepan filter is the standard one. But someone has had it chromed.

one of those types. It uses the same filter that my mushroom one used.

It does have a breather pipe but the old pipe used to connect the the outside of the filter housing, which meant that the anything coming through that pipe was filtered. Whereas the new saucepan one has the breather pipe connecting to the carb, under the saucepan.

What seems to be happening is that when i accelerate quickly, and then close the throttle a vacuum builds up somewhere, and the engine almost stalls. But then it makes a kind of smacking sound somewhere in the carb/air filter housing.

Post by **Benjy** » Thu Dec 18, 2003 4:04 pm

My engine has the same problem with stalling when dropping from high revs, though it idles fine. I wondered if the oil in the dashpot might be too thick, causing the piston to fall too slowyly, but would be interested to hear other comments. It has the same (saucepan) type air filter.

Ben

Post by **57traveller** » Thu Dec 18, 2003 4:47 pm

This is only a guess - but I wonder if the temperature of the incoming air has anything to do with this?
My Traveller is fitted with the conical shaped filter housing and the air intake is close to the exhaust manifold. In no time I am able to push the choke right in and the idle is fine.
My saloon has the 2nd type where the air intake is pointing to the front of the car and as a consequence the air temp will probably not be much higher than ambient. It takes much longer before the engine will idle with the choke fully home.
Both are set up almost the same, timing, mixture, fast idle etc. Same oil, same fuel, both 1098cc, both unleaded.
It still doesn't solve your problem though! If there is one.

Post by **winger300** » Thu Dec 18, 2003 5:29 pm

yeah, that sounds about right.

My problem is that with the choke out for too long the mixture is too rich for the engine to run properly, but putting the choke in means it idles too slowly.

I think i should just switch back to the connical filter i had before and sell the chrome one on ebay

. Someone is bound to pay a stupid amount of money for it!

Post by **rayofleamington** » Thu Dec 18, 2003 6:52 pm

This is only a guess - but I wonder if the temperature of the incoming air has anything to do with this?

If you swap back you may find a similar effect - it's got cold recently..... ;-)
but yes - the conical one allows you to suck in warm air by putting the inlet on top of the exhaust manifold. (and then move it away in summer! - great design

)

Post by **Willie** » Thu Dec 18, 2003 8:10 pm

If an engine tends to stall on deceleration and you get the
'spitting' sound then it indicates a weak mixture usually. The
pic of the filter housing which you posted is facing the radiator
and, in this colder weather is not efficient enough. The later
type can be swung to pick up heated air and stops carb icing
up. ALL carb systems create a vacuum on deceleration, that is
normal

Post by **Peetee** » Thu Dec 18, 2003 9:01 pm

This is only a guess - but I wonder if the temperature of the incoming air has anything to do with this?

It can certainly have the sort of effects described. At this time of year the incoming air can be so cold that moisture condenses out within the intake system and stalling can occur at low revs. I have mucho experience of this on certain other marques with auto choke Pierburg carbs [spit]

.
I'm not sure what you mean by the 'mushroom' filter box, but on the 1098 car the airbox intake is pointed toward the exhaust manifold so sufficient warm air is picked up for there not to be a problem under normal running.

Post by **winger300** » Thu Dec 18, 2003 11:21 pm

yeah, i had problems with my Golf in cold weather too. Carb icing up on motorway runs became a real problem.

Post by **Cam** » Fri Dec 19, 2003 9:12 am

Yep, my mate has the same on startup on his '89 Jetta 1.6. It's OK after it has warmed up a bit though.

Post by **Benjy** » Fri Dec 19, 2003 10:35 am

I know it helps the engine warm up, but doesn't warmer air entering the filter reduce power as it's a lower density? What we really want is a thermostatically controlled intake system

Also, where should the mushroom type be pointing in the summer. The one on my pickup seems to only point at the exhaust, anywhere else and either the intake tube or breather pipe foul the carb / float chamber or something!

Peetee - Must agree about Pierburg autochokes, evil things. Thankfully never owned a car with one, and my mate has sold his Astra now

Ben

Post by **Kevin** » Fri Dec 19, 2003 1:09 pm

but doesn't warmer air entering the filter reduce power as it's a lower density?

Yes it does but we are not looking at a modified car where every ounce of performance is reqd, also the longer taken to warm up will waste more fuel anyway.

Post by **Peetee** » Fri Dec 19, 2003 1:42 pm

yeah, i had problems with my Golf in cold weather too. Carb icing up on motorway runs became a real problem.

Exactly

Would you like to know how to solve it?

Post by **Peetee** » Fri Dec 19, 2003 1:50 pm

What we really want is a thermostatically controlled intake system

This is what the VW's had. The problem was that if the car stopped after a short run (at traffic lights for example) the system temperature increased because there was a reduction of cold air flowing through the engine bay. This was enough for the system to believe the car had warmed up sufficiently to shut down the autochoke.

Post by **winger300** » Fri Dec 19, 2003 2:51 pm

i fixed my Golf in the end by disconnecting the cold air intake and putting it nearer the back of the engine to draw in warmer air.

Post by **salty_monk** » Mon Dec 29, 2003 11:18 am

Pieburg Auto's are OK. Just remember, foot to the floor to open it before starting & then if it's reluctant to release give the throttle a very quick "tap" to the the floor.

You'll also find that a good clean up with Wynns carb cleaner & keeping it well lubricated with a penetrating spray will help.

As for the Moggies, I too have the "mushrom filter" & it's currently in "winter mode". Still a bit reluctant to run smoothly for the first 5 minutes from cold though, just a result of the weather..! You could try winding in the idle screw a little to give you an increased tickover speed, might solve your stalling problems with the choke in. Not too far though!

Mine also threatens to stall at idle after a blip of the throttle, (even when warm). I thought that maybe the carb was gunked up, isn't there a float filter in there somewhere?? My idea was that if this is partially blocked the float chamber could be running low...

Post by **Willie** » Mon Dec 29, 2003 10:38 pm

If your car tends to stall when the throttle is blipped it indicates
either a slightly weak mixture or too slow a tickover usually.

Post by **winger300** » Tue Dec 30, 2003 9:25 pm

I've solved it now. Thanks for the advice given.

It was a combination of not enough oil in the dashpot, ignition timing too far retarded and a poor seal on the rocker cover.

Its running sweetly now, plus i filled up using leaded 4 star which it seems to appreciate!