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Running OK but puzzled (Air Filter)
RobBrown - 3/10/12 at 08:23 PM

After much faffinglearning,

I managed to get my car seamingly running OK with Bike carbs on. But I have a curious question about the over effectiveness of the air filter (PX600 pipercross sausage type).

Whilst trying to re-jet without the air filter fitted (I now know a mistake) I was heading towards a jet size of around 1.7-1.8mm (170-180), which seems OK you might think, but once the air filter was fitted to achieve the optimum airfuel ratio I had to reduce the jet right down to 1.1mm (110).

Now the engine runs pretty well at this size and seems to pull effectively on the short sprints up and down the road...

but would you expect the air filter to make that much of a difference and is there any consequences of squirting so much less fuel into the engine, in the same way that a too lean mixture is bad for the engine, is too little fuel bad for the engine?

I've seen many rolling road tune up sessions on YouTube with no filter fitted, and my experience now tells me that that can't be right for good AFR! Once the filter is refitted it all goes out of ratio and you'll be running too rich!

I know there has been much discussion on LB about differnt types of filters and I "shouldn't fit socks" for being too restrictive, but I thought the Pipercross route was a recommended one.

Other than lower BHP should I be worried?

Setup is standard dizzy, R1 carbs, 2.0 Pinto (205), 300 deg Burton Cam.

whitestu - 3/10/12 at 08:39 PM

I'd be amazed if a PX600 would make that much difference to jet size!

I must try mine with the AFR meter and the filter off.

Stu

RobBrown - 3/10/12 at 08:48 PM

It didn't make a huge difference at idle, but it was more noticable when I tried to get WOT right. AFR dipped right down to 9 with the larger jet size with the filter on.

It was WOT where I noticed the bogging down and black smoke out of the exhaust - which indicated the too rich mixture and validated with the AFR meter (Innovate LC-1).

I'd be interested if you did try yours, just to confirm what I'm seeing on mine as not unusual.

SPYDER - 3/10/12 at 08:49 PM

When we tried my mates Westie with and without foam filter on the RR there was hardly any difference in power or AFR.
Does the filter cover up any holes in the carb face that may lead to float chamber or pilot/idle circuit air supply?

RobBrown - 3/10/12 at 08:58 PM

quote:
Originally posted by SPYDER
When we tried my mates Westie with and without foam filter on the RR there was hardly any difference in power or AFR.
Does the filter cover up any holes in the carb face that may lead to float chamber or pilot/idle circuit air supply?


The backplate is screwed to the carb and covers the oval gaps in this picture

Description
Description

There are a couple of small holes in the backplate. Do you think these should be of a reasonable size to allow the filtered air through?

Davegtst - 3/10/12 at 08:58 PM

When mine was on the dyno it was tested with and without the pipercross filter. It only lost 2 bhp with it on.

SPYDER - 3/10/12 at 10:23 PM

Looking at your pic you may be partly blocking up necessary airways. You could try drilling the holes bigger in the backplate to reinstate the air passages.

[Edited on 3/10/12 by SPYDER]

mcerd1 - 3/10/12 at 10:24 PM

quote:
Originally posted by RobBrown
quote:
Originally posted by SPYDER
When we tried my mates Westie with and without foam filter on the RR there was hardly any difference in power or AFR.
Does the filter cover up any holes in the carb face that may lead to float chamber or pilot/idle circuit air supply?


The backplate is screwed to the carb and covers the oval gaps in this picture

Description
Description

There are a couple of small holes in the backplate. Do you think these should be of a reasonable size to allow the filtered air through?


I'm going to use the original rubbers off the bike airbox to make the connection to the filter back plate, that way it shouldn't block anything that shouldn't be blocked

I've also got an ITG filter partly as I've heard claims that ITG ones were better (but also beacuse some one on here had a s/h one going cheap )

Stott - 4/10/12 at 07:14 AM

quote:
Originally posted by SPYDER
Looking at your pic you may be partly blocking up necessary airways. You could try drilling the holes bigger in the backplate to reinstate the air passages.

[Edited on 3/10/12 by SPYDER]



I'd be inclined to agree.

Did it richen when you fitted the filter (clipped it on) or when you fitted the whole assembly including baseplate?

I'd test the afr with the carbs bare then fit just the baseplate and retest to confirm what is affecting the results.

RobBrown - 4/10/12 at 09:55 AM

quote:
Did it richen when you fitted the filter (clipped it on) or when you fitted the whole assembly including baseplate?


In hindsight when I fitted the whole assembly

Thanks all - I will try this over the weekend.

r1_pete - 4/10/12 at 10:10 AM

It certainly looks like yopu are covering the air bleed holes, which will richen your mixture, as already suggested test with just the baseplate.

MikeRJ - 4/10/12 at 11:12 AM

A friend has recently had the engine in his rally car rebuilt and was making ~275bhp on the dyno (from 2.0L normaly aspirated engine). It was tried without the Pipercross sausage filter and the power difference was a couple of bhp, probably less than the repeatability of the dyno. Unless you are making considerably more power than this, your PX600 won't be restrictive.

mcerd1 - 4/10/12 at 11:53 AM

a set of these rubbers off an R1 might help to make a neat job:



I got a set for mine when I thought I was getting R1 carbs (sold them on when I ended up with ZX9R ones instead)
here's a similar one:
Yamaha r1 4xv airbox | eBay

I also got a set of the little rubber trumpets to go with them - not sure how much difference they make, but the can't hurt at all....
LOOK YAMAHA R1 4XV YZF1000 YZF 1998 1999 98 99 AIRBOX INNER DUCTS *FREE UK POST* | eBay

[Edited on 4/10/2012 by mcerd1]