Additional mixture base leaning

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jono
Posts: 362
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Additional mixture base leaning

Post by jono » Sat Feb 23, 2019 7:44 pm

Having found I cannot lean my 200 mixer out enough using the idle mixture screw - and hand flowed leaner diaphragm selection has become difficult, I am considering trying a permanent hole drilled into the inner housing to lean mixtures further.

This is only to get a lean base in prep for dialling in an O2 controlled Lean Bias Logic system by Peel Instruments in Victoria, Australia

Looking down the intake air horn I can see what I think should be perfect location to start my drilling. Now I have a reason to beg,steal or borrow an old friends number drills!

An option could also be some sort of adjustable air bleed valve using the brass screw in vacuum hose fitting used in FB or is it dual fuel applications

Has anyone done similar in the past to gain leaner mixtures?
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C3H8
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Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Additional mixture base leaning

Post by C3H8 » Sun Feb 24, 2019 2:51 am

You can use leaning rings to lower the valve. They go between the gas valve and the diaphragm lowering the gas valve into the bore. They are approximately .003" thick and several can be used if required. The IMPCO part # is R1-30. They come in brass or plastic.

jono
Posts: 362
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: Additional mixture base leaning

Post by jono » Tue Feb 26, 2019 5:23 pm

Sorry, I should have said I have already got the maximum of three leaning rings in. I need to get a crude lean base rather than the finer tune the rings give. Another method suggested is balance tube but with small bleed holes drilled in the converter end brass fitting to act as a damper to the leaning effect - I would prefer no chance of dust ingress

evranch
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Joined: Thu Dec 13, 2018 11:11 am
Location: Saskatchewan, Canada

Re: Additional mixture base leaning

Post by evranch » Tue Mar 05, 2019 11:55 pm

My mixer on the tractor was idling rich and I couldn't lean it out any more either. So I'm effectively doing this with the oiler system I posted about, it's drawing air right into the manifold. I put a small valve on it to adjust the mixture but the ideal setting turned out to be wide open.

So it will lean out your mixture, but unless it's just a tiny hole for idle air, it's going to throw off your AFR curve like any vacuum leak would, as the uncontrolled flow will vary with vacuum and RPM. That might be fine though, since you are going to control the mixture with an O2 sensor.

jono
Posts: 362
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: Additional mixture base leaning

Post by jono » Fri Mar 15, 2019 7:42 pm

Thanks for comment

Mind you the hole I propose is essentially between the same two chambers that the idle air mixture screw is between so I am hoping there will not be those issues you mentioned as it will all before the throttle body

jono
Posts: 362
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: Additional mixture base leaning

Post by jono » Wed Mar 20, 2019 8:57 pm

and thinking this through a little more before I go swapping my spare old body in to muck about drilling holes ...considering the idle air mixture adjust screw is about 8mm dia and buts up to close a slightly smaller hole inside I could likely make a hole as large as 6mm and use the screw in circuit for a finer adjustment regardless of the electronic control unit. The 200 may be theoretically a bit big on my 1.8 litre boxer so likely richer to suit bigger capacity engine - needs a bit of leaning out :)

C3H8
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Location: Winnipeg, Canada

Re: Additional mixture base leaning

Post by C3H8 » Thu Mar 21, 2019 2:43 am

There is still something that does not make sense here. From the day they were first produced 200 and 225 series mixers have been notorious for being lean at idle. Also as you state the mixer is on the large size for your engine. I that case it should even be leaner since the air flow would be reduced and even less gas would get into the airstream as the gas valve would not lift as high. I didn't reread your posts but has the regulator been checked for lever height, high primary pressure, leaking, secondary, etc. I don't believe in 37 years I have ever had one contact that claimed a 200 mixer was too rich at idle except if they tried modifying the mixer. some worked correctly and could be richened up if the air adjuster was turned all the way in but the usual complaint is they could not be richened up. Has the gas valve been modified at some time? Are the markings wrong? It's just not adding up.

jono
Posts: 362
Joined: Wed May 16, 2007 11:46 pm
Location: New South Wales, Oz

Re: Additional mixture base leaning

Post by jono » Sun Apr 07, 2019 8:59 am

well C3, that may be the case on the 2 hundred series having a lean idle with their usual applications, but I am finding most knowledge and interest especially in the US is with larger capacity fours, sixes and eights. I recall when I did my first turbo 1800 cc every Impco specialist and Impco themselves (local headquarters techies and the old book with Don Bass in it) said to do blow throw except one guru who said draw through due to the odd pattern of intake pulses of a four pot, or maybe that was the boxer character. Draw thru was my second set up due to blow through being undriveable.

So, tinkering in this territory seems to be different from the norm in the propane world.


Talking to the designer / manufacturer of the lean bias logic system I get the impression the controller needs to be continuously adjusting and wont be happy to sit back and watch the ancient system perfect the mixtures.


The system can't be tricked as it needs a constantly varying O2 signal or it will go into an over ride enrichment on the rich side

Currently run a mixture LED bar graph in dash off the O2 sensor and the clean air Impco does an amazing job at keeping things stoich _ so much so I feel I am wasting my time
in order to please what I expect an engineer is going to want to sign things off on it as I have fitted an originally O2 sensor controlled engine into a non O2 controlled vehicle, but come to think of it ...the engines came out in both so may be able to get its emissions side signed off without O2 control

Been going a bot slow on this and just this week ordered a new Impco silicone air valve to reduce dismantle and swaps between housings with my tinkering

until then

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