CO screw on AFM... anyone played with it?

[pupp]

Have been playing with this over that last couple of weeks.... has more of an effect than you might imagine doesn't it (if nothing else, it certainly has adirect effect on the volume of pops and bangs)?

[chassis 33]

Yup!!! there's info on the RPi site if you want to set it to some figures, as opposed to a finger in the air.

Had my popping like a good 'un over the weekend...
Regards
Iain

[pupp]

chassis 33 said:

Yup!!! there's info on the RPi site if you want to set it to some figures, as opposed to a finger in the air.

Had my popping like a good 'un over the weekend...
Regards
Iain

Thanks Iain, I did start off with the recommended values as a starting point but mine is a half-way house in that it's decatted but still running with lambda sensors on the cat tune resistor (Tornado chip). After a period of fettling and fiddling, I've settled on a value somewhere between the two that my seat-of-the-pants dyno and aural appreciation tells me is 'best'. Was a bit surprised at the apparent influence of this adjustment over running characteristics as it seems more pronounced than just idle/off idle as I expected... maybe my expectations were just wrong

[chassis 33]

That sound like a very similar configuration to mine, be intersting to compare and contrast the values, I'm not going to be a race winner this year, so I may as well look to be a crowd pleaser

Regards
Iain

[Blitzracing]

That controls effects the fueling up to 2500 rpm. The ECU can only adjust its fuel map plus or minus 10% with lamda sensors so you could tweek it out too far. You really now need to measure the output from the lamda sensors to ensure you not running too lean or rich. Sunpro do a gauge for about £40 that connects to the lamda sensor(s) and will show you if the mixture is correct. Otherwise get it to an MOT test station and do the emission tests bit and get it tweeked back in spec.

[Griffter]

Presumably it affects the mixture and hence CO?

If I were to book a rolling road session to play with this, would it be worthwhile - does it affect mixture through the rev range, or just at idle? I have a precat car so no lambdas.

What CO value should I be aiming for? At idle and/or under load through the rev range?

[andy-w]

Going to have to have a play with this later today...!!!

I assume that winding it in or out will make the mixture weaker or richer depending wich way it is turned?

Think i shall wind it right in and find out how many turns it takes before i start.

Chassis33 - which way did you turn yours to get it popping and banging?

[pupp]

Think I'd go easily as little movements make a significant difference both in terms of running and in terms of measured output.... although tempting to think of it as akin to a 'slow-running' adjuster on a carb, it's worth remembering the thing is electric/electronic in effect and not a mechanical valve. Even by counting the turns to fully in/out, there's no guarantee it will behave as before just by returning it to the 'same' position, it's a measured output you're setting to with particular outputs equating to particular CO production (and this relationship obviously will vary engine to engine depending on health and spec etc, and will only be properly discerned by gas analysis). Job for a digital multimeter at least and I'd want to keep within the range of readings described on the RPI site etc unless I was completely sure what was occurring. Having said all that, with some experimentation, I found a definite 'sweet spot' where the motor 'felt' and sounded happiest but, then again, I'm pretty used to listening to engines and used to playing with fuelling. Not a substitute for proper measurement however.

[chassis 33]

The details for "correctly" setting the AFM are here www.rpiv8.com/carbs-2.htm#setting-up

Mine has been tweeked by so many people, that I really should go and measure what I'm running at. During a recent RR session the car was running around 0.84lambda throughout the who power run (getting over 240hp from a 4l, I was happy at that). The trick to getting it to pop and flame is run it on Optimax, get the engine up to temperature, then rev to about 4.5k then back off, and catch it again just under 4k. Sadly the noise tester has me reving to 4.1kish, which is going to be fun if I'm popping and banging!

I've only recently had it start doing this, and only statically (except when the fueling was to cock at the start of the season). I'll let you know how I get on at Mallory this weekend

BTW the car has had the "full decat" but is running a standard silencer box.

Regards
Iain

[andy-w]

Just got the info from RPI and am going to have a play with the AFM and the throttle pot.

Must confess i did by a new airflow meter ages ago and just bolted it on without checking any settings.

Curious to see how far out the settings are and if it will make any difference to the running...?

Will post results at 1pm after lunch break and see what settings i need for optimum pops and bangs!!!

[chassis 33]

Make sure the engine is up to temp though, I'd hate for you to damage anything playing on a cold engine.

Regards
Iain

[andy-w]

I noticed that bit on the site...!

I shall go for a spin for a few miles and then let it tick over for a while before doing anything.

Not too fussed about the pops and bangs...more interested at the moment in what the settings are at the moment...can experiment a bit later!

[Griffter]

Mine was at 0v for years. It's now at 1.0v. Idle CO is 2%, but the car feels absolutely no different. Any further info very gratefully received please/thanks.

[andy-w]

Well the settings for the throttle pot were at .35 and the AFM was 1.0...changed to 1.8 and have not really noticed much difference apart from when it got to 5k revs it would do a double back fire...now it goes to 5.5 and does multiple back fires (rev limiter???) but i assume this is down to straight thru pipe so no back pressure?

Funny thing was i took it for a blast, did about 4 miles and it cut out, blown fuse for the ecu, changed that and started off again...did about another 2 miles and went over a railway crossing which sent the horn off and it woouldnt stop so i had to remove the radiator grill and disconnect the horns...!!!

Note - do not leave chim for two weeks while i go on holiday, it feels neglected!!!