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  #1  
Old 18-04-2017, 10:35 PM
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Default LPG mixer tuning with AFR

Hey Guys,

Vehicle is RB30, dual fuel, carby with Impco 300A mixer & Impco model L converter/vaporizer.

I'm trying to tune the LPG system using Innovate MTX-L wideband AFR gauge.

The readings I've got for the existing LPG mixer tuning settings(Impco 300A mixer) is as below.

Idling AFR is 11.
Cruising AFR is around 15.5-16
Revving for power causes AFR to go as high as 17(thought it should get richer momentarily, but getting leaner instead).

I started adjusting the "POWER" screw to see if the AFR can be changed from 11 to 14 or so on idling, and obviously that screw is meant for AFR setting for power/cruising, not idling.

I started adjusting the "IDLING" screw(after removing the covering bolt as in the picture) to see if I can get the idling AFR to closer to 14.7 using that. Turning the idling screw clockwise did get the idling AFR to 14.

Am I going about this the right way?!
Should the idling AFR on LPG be around 11??!!


Engine is fully warmed up as I was doing the above tuning adjustments.

My target is to improve the LPG economy without pushing towards detonation.

Do I need to adjust the ignition timing along with the above mixer tuning?!

Thanks in advance for any tips, advice, etc.

Cheers
Dom
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Last edited by dom14; 19-04-2017 at 12:48 AM.
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  #2  
Old 19-04-2017, 12:03 AM
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Same setup.



The idle screw on the 300A will affect idle and cruise mixtures. Your power is for harder accelerating etc.



Garages that did not have a wide band commonly set up petrol idle, mixture etc first. LPG was adjusted by turning the idle screw in until the engine idle starts to slow, without placing pressure on the screw, then turn out until it idles smoothly. The power adjustment was adjusted to just into the rich zone.

Now, you have a wideband AFR so you really just need to plumb it up and drive. Check your mixtures under hard acceleration to confirm they are accurate and also your cruising mixture as this will be affected by the idle adjustment; then fine tune.

I forget the ideal AFR's but google should help. I've been told going too lean at idle means too lean ay cruise and you'll get worse economy.

The above is what I was told by a gas tuner; I can't qualify, however google seems to suggest similar
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  #3  
Old 19-04-2017, 12:10 AM
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Timing is different for LPG and petrol. If your going duel fuel you'll need to find a happy medium or you'll induce knock in one fuel or the other. Downside is neither fuel will run at its optimum but still good enough. If you don't travel remote you could go lpg only however im not sure how much better it works.

My TB gets 22-23l/100km on LPG, which seems on par from a forum search. I don't run petrol enough to know my useage.
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  #4  
Old 19-04-2017, 12:41 AM
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Quote:
Originally Posted by Jonesy_sa View Post
Timing is different for LPG and petrol. If your going duel fuel you'll need to find a happy medium or you'll induce knock in one fuel or the other. Downside is neither fuel will run at its optimum but still good enough. If you don't travel remote you could go lpg only however im not sure how much better it works.

My TB gets 22-23l/100km on LPG, which seems on par from a forum search. I don't run petrol enough to know my useage.
Thanx mate.
I would ideally wanna set the ignition timing for LPG, as I tend to run the vehicle on LPG all the time. Petrol is for outback trips when necessary. ATM, petrol runs pretty bad(too rich) 'cos the carby is bit stuffed. I was onto installing a dual curve unit to auto adjust the ignition curve for both fuels, but the project didn't get off the ground, may be it's about time I do it.
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Old 19-04-2017, 12:47 AM
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Quote:
Originally Posted by Jonesy_sa View Post
Same setup.



The idle screw on the 300A will affect idle and cruise mixtures. Your power is for harder accelerating etc.



Garages that did not have a wide band commonly set up petrol idle, mixture etc first. LPG was adjusted by turning the idle screw in until the engine idle starts to slow, without placing pressure on the screw, then turn out until it idles smoothly. The power adjustment was adjusted to just into the rich zone.
As you can see in the picture, the "factory" LPG power screw setting is towards LEAN direction.
Should I move that towards RICH?


Quote:
Now, you have a wideband AFR so you really just need to plumb it up and drive. Check your mixtures under hard acceleration to confirm they are accurate and also your cruising mixture as this will be affected by the idle adjustment; then fine tune.
At hard acceleration, the AFR hits near 17.5. Not sure if that's ok.

Quote:
I forget the ideal AFR's but google should help. I've been told going too lean at idle means too lean ay cruise and you'll get worse economy.
Well, the previous idle AFR was 11, and I adjusted it to around 14. It still cruises around 15.5-16, as before(when idle AFR was 11)

Quote:
The above is what I was told by a gas tuner; I can't qualify, however google seems to suggest similar
Thanx
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Old 19-04-2017, 04:58 AM
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Stoich for lpg is 15.5 best power/economy is 16.5 richen yr mixture up a bit.you will have trouble with an impco getting it perfectm

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Old 19-04-2017, 11:05 AM
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Originally Posted by Gasburner View Post
Stoich for lpg is 15.5 best power/economy is 16.5
Is that for idling or cruising(or both)?


Quote:
richen yr mixture up a bit.you will have trouble with an impco getting it perfectm
Thanx mate. Did you mean for me to enrich the mixture by using POWER screw(for cruising & WOT)? ATM, it's as lean as 17+ on WOT. That can't be good?

Did I do the right thing by leaning the idling mixture from 11 to 14 by turning the idling screw on Impco 300A?

Thanx
Dom
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Old 19-04-2017, 06:27 PM
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Power screw mate OR buy a blos etc haha

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  #9  
Old 19-04-2017, 06:27 PM
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Lean idle out to 15.5

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  #10  
Old 19-04-2017, 06:36 PM
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Power screw mate OR buy a blos etc haha

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I richened up WOT to 15.5 ish. Now it stays around that for WOT & cruising.

I just realized you advised to get it to 16.5 for WOT, I'll fix that tomorrow.
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Old 19-04-2017, 06:40 PM
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Lean idle out to 15.5

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I leaned idle to stoic 14.7 today, I'll lean it to 15.5 tomorrow.
Damn troll is running lot happier now mate.
She's purring now. (It was a HE up until today )

Cheers
Dom

P.S. I got a better muffler for the troll as well(from a GU).
Just need bit of mucking around with the welder to get it to fit.
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Old 19-04-2017, 06:59 PM
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Gas is finicky. Sounds like your getting it spot on. Pretty much an AFR is the only way to go.
The 300A and L actually do a good job of keeping mixtures where they should be. The down side is throat restriction etc for the carby.
I noticed you posted over at NissanPatrols; I cant remember my password ATM for the site but if you look in the general manuals section (below the Patrol workshop manuals) you'll notice there is some LPG material. Might be of interest to you.
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Old 19-04-2017, 07:02 PM
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Quote:
Originally Posted by dom14 View Post
As you can see in the picture, the "factory" LPG power screw setting is towards LEAN direction.
Should I move that towards RICH?
Thanx
In your case you have an AFR so you can follow that. The eye-balling method is useful to get up and running - for anyone else who stumbled across the thread.
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Old 19-04-2017, 07:11 PM
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Depending on where you live and what fuel you start up on i like to have my LPG idle at 14-14.5 for slightly easier cold starting.

I try to cruise around 15.5-16 and full throttle low to mid 14's. Although there is no cooling effect by running lpg rich it still does make more power i have found.

If you have patience you can play with the midrange by shimming the valve on the diaphragm. My midrange was very rich and have been able to lean out to 15 and guess what, it made no difference to fuel use hahaha
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Old 20-04-2017, 12:14 AM
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Depending on where you live and what fuel you start up on i like to have my LPG idle at 14-14.5 for slightly easier cold starting.

I try to cruise around 15.5-16 and full throttle low to mid 14's. Although there is no cooling effect by running lpg rich it still does make more power i have found.

If you have patience you can play with the midrange by shimming the valve on the diaphragm. My midrange was very rich and have been able to lean out to 15 and guess what, it made no difference to fuel use hahaha
Thanx mate, but I didn't understand what you meant by "shimming the valve".
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Old 20-04-2017, 12:22 AM
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I was running LPG to the empty tank today.
When the LPG ran out, I had to switch to petrol as I was on the road.
Then I pulled over to a servo and put few litres of LPG and started driving on LPG again.
AFR was closer to stoic 14 or so, and few minutes after engine started having few hiccups or backfiring.
I wonder what caused the backfiring while the AFR guage was showing near perfect AFR!!!
That wasn't the only time it happened. I wonder if it 'cos LPG pressure was still low 'cos I only filled the tanks with few litres(two tanks connected via a hydro T valve).
If it's the low pressure, then why didn't it backfire when the LPG was near empty and the AFR was starting to clearly lean as the gauge was showing?!!!?!
I'm bit lost about this.
I'm kinda sure that if I fill the tank(s) with enough LPG, backfiring is not likely to occur.
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Old 20-04-2017, 12:30 AM
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BTW, ignition timing is 15 BTDC.
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Old 20-04-2017, 05:29 AM
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Quote:
Originally Posted by dom14 View Post
I was running LPG to the empty tank today.
When the LPG ran out, I had to switch to petrol as I was on the road.
Then I pulled over to a servo and put few litres of LPG and started driving on LPG again.
AFR was closer to stoic 14 or so, and few minutes after engine started having few hiccups or backfiring.
I wonder what caused the backfiring while the AFR guage was showing near perfect AFR!!!
That wasn't the only time it happened. I wonder if it 'cos LPG pressure was still low 'cos I only filled the tanks with few litres(two tanks connected via a hydro T valve).
If it's the low pressure, then why didn't it backfire when the LPG was near empty and the AFR was starting to clearly lean as the gauge was showing?!!!?!
I'm bit lost about this.
I'm kinda sure that if I fill the tank(s) with enough LPG, backfiring is not likely to occur.
Impco's love to fart. shims can be placed between diaphragm and 'cone valve thingy'.paid $3.50 a few yrs ago from impco in Melbourne.allows tunning of mixture.

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  #19  
Old 20-04-2017, 07:58 AM
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Quote:
Originally Posted by Gasburner View Post
Impco's love to fart. shims can be placed between diaphragm and 'cone valve thingy'.paid $3.50 a few yrs ago from impco in Melbourne.allows tunning of mixture.

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I have a different Impco mixer but i'm sure the internals are similar.

I cut out shims from different cardboard and paper as small adjustments made quite a difference. Have lasted years so far.

Inside mixer there is a rubber/plastic diaphragm that moves a cone shaped valve. If you unscrew the valve and install shims behind it, it leans out the midrange but will also have some effect everywhere else! I did it because mine always ran a lot richer at light throttle and cruise compared with full throttle which is arse about. You can buy different diaphragms but shims seemed to have the same effect.
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  #20  
Old 20-04-2017, 11:23 AM
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Thanx guys.

Can you please have a look at below diagram of Impco 300A and point to me where the shims go.

http://rdhaglund.com/cts/Impco/Maste...93Carb300A.pdf

I'm guessing, by "shims" you mean pieces of cardboard or a circular gasket to fit above number 27(cone valve?) in the diagram?!!!
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