UPDATE 2 Adjusting timing propane engine and impco 425 mixers

Propane, Butane, LPG, GPL, C3H8, C4H10
Caddy123
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UPDATE 2 Adjusting timing propane engine and impco 425 mixers

Post by Caddy123 » Sun Dec 02, 2018 1:45 pm

Hello im Danny from europe and looking for some answers, about tunning my propane set up.
I have a twin impco 425 on a homemade adapterplate, and twin impco E vaporizer.

Engine specs:
Cadillac,
514 cui
Cr 10.2
Mild comp cam (270H)

1 setting my timing i have read raso site and i read most common propane engine timing 14 initial 30- tot mech and 42 tot timing. 14-14-14
2 But how do i know if this the good timing is for my engine.
Every engine is different!!
3 i have 2 425 impco on a adapter plate, if i closed 1 425 set the other with a co meter and do the other also is that a good id now i have set the idle allen head equal but the engine idle rough and low cold and 300 rpm more if its warm.
4 how do i set the power valve can that afterwards or must i check co again after that.
Ps adjusting with or without air cleaners

Gr Danny thanks for help
Last edited by Caddy123 on Sat Feb 09, 2019 3:01 pm, edited 2 times in total.

storm
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Re: Adjusting timing propane engine and impco 425 mixers

Post by storm » Mon Dec 03, 2018 3:13 am

Caddy123 wrote:
Sun Dec 02, 2018 1:45 pm
1 setting my timing i have read raso site and i read most common propane engine timing 14 initial 30- tot mech and 42 tot timing. 14-14-14
This is a starting point to get you going. Once the engine is running you can get it tuned to optimise it for your particular combination.
Caddy123 wrote:
Sun Dec 02, 2018 1:45 pm
2 But how do i know if this the good timing is for my engine.
Every engine is different!!
As above it is a starting point to get the engine going.
Caddy123 wrote:
Sun Dec 02, 2018 1:45 pm
3 i have 2 425 impco on a adapter plate, if i closed 1 425 set the other with a co meter and do the other also is that a good id now i have set the idle allen head equal but the engine idle rough and low cold and 300 rpm more if its warm.
Are the 2 425s mounted to a common plenum? Pictures would be helpful.
Caddy123 wrote:
Sun Dec 02, 2018 1:45 pm
4 how do i set the power valve can that afterwards or must i check co again after that.
Ps adjusting with or without air cleaners
Full throttle run set the "power valve(s)" so that the engine is making maximum power or the fastest trap speed at the end of a 400 metre run (drag race 1/4 mile). Always tune with the equipment you intend to run during normal use. if you intend to not use air cleaners (I would advise against this) then tune without them. if you intend to use them then tune with them.

I suggest you take a look at this thread https://fuelsforum.rasoenterprises.com/ ... ?f=5&t=387 and buy the book mentioned in it. Franz is a member here and an expert on LPG.
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Caddy123
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Location: Netherlands

Re: Adjusting timing propane engine and impco 425 mixers

Post by Caddy123 » Mon Dec 03, 2018 5:53 am

Thanks for help storm.
Pics comes soon

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Steptoe
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Re: Adjusting timing propane engine and impco 425 mixers

Post by Steptoe » Mon Dec 03, 2018 2:42 pm

At any given rpm and load combo there is approx +/- 1.5 deg tolerance for best performance.. racing even less.
To do that you will need data logger and at least knock sensor 02 sensor, preferably IMAP sensor.
I have spent many decades dialing engines, old school thru to modern data logger/ sensor technology.
The latter is hands down every time superior.

Running loads and te4sting timing.. do not go from low to high.. start high and reduce timing.
Going low to high you get a rise in performance and a steady increase for a few degree after that... from thereon you get a sort of 'optical illusion' as the engine sounds nicer , impression of more pressure in the seat but reality performance drops off.
Going from high to low there is a point at a given load and rpm the power drops off quick.. within a couple degrees.. then add 2 1.2 deg note/map that degree at that load and that rpms.

For a street vehicle the cent needs to be mapped and adjusted by weights and springs right thru the curve... then the vacuum also done for light loads, right thru the curve.
'adjustable ' VA s only adjust the spring inside.. ie if change start point the tension is say higher and number degrees in the VA reduces.
To adjust degrees requires adjustable stops each end on the leg of the VA.. rate by adjusting tension...

As you adjust timing , you will also need to adjust mixtures...Generally for an efficient street weekend racer car, with mixture close in ball park thru rpms and loads (02 sensors) them ap and set up timing curves to that, readjust timing , then newmap , readjust mixtures and should be spot of ot at most smidgen off not enough to worry about unless going for a split second would record.

If one has 2 identical engines in identical cars, and if each is dialed in independently you will still get surprisingly large differences between the 2 vehicles..
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Caddy123
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Re: Adjusting timing propane engine and impco 425 mixers

Post by Caddy123 » Tue Dec 04, 2018 3:57 pm

Steptoe thanks for the tech tips👌

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Re: Adjusting timing propane engine and impco 425 mixers

Post by Steptoe » Tue Dec 04, 2018 4:26 pm

Make good use of the forum search function.. detailed how toos on changing weights.. fixing weight to establish a curve on paper, filling off/ reshaping weight tails to limit advance.. making stops for weights and VA s etc
and lot of other stuff.
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storm
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Re: Adjusting timing propane engine and impco 425 mixers

Post by storm » Wed Dec 05, 2018 2:44 am

These Ignition Timing Computers are a great improvement and help to make tuning much easier.
http://www.cbperformance.com/CB-s-Black ... p/2013.htm
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Caddy123
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Re: Adjusting timing propane engine and impco 425 mixers

Post by Caddy123 » Thu Dec 06, 2018 5:15 pm

Storm my inglish is not so good.
The black box interessting, but what do it exactly.
Tels me what the best initial mech and vacuum advance?
Thanks Danny

storm
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Re: Adjusting timing propane engine and impco 425 mixers

Post by storm » Fri Dec 07, 2018 1:46 am

Your English is alot better than many native speakers.
The Black Box is a programmable ignition module. To use it you must lock the advance mechanisms so they cannot move and you then connect the Black Box using the instructions supplied. You then install the tuning program and adjust the timing map to suit each load point at each RPM the engine will see.
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Caddy123
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Re: Adjusting timing propane engine and impco 425 mixers

Post by Caddy123 » Fri Dec 07, 2018 2:12 am

Storm i understand now read it a few times.
If i take a black box.
And a AFR wideband i can do it my own.
I have put the softesd mech springs in already is that a good id.
Started best with 10 initial.
So i order now the stuff.
But can i drive carefully?
Gr Danny

Caddy123
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Location: Netherlands

Re: Adjusting timing propane engine and impco 425 mixers

Post by Caddy123 » Fri Dec 07, 2018 2:14 am

I send a few pics to you Email.
My photobucket doesnt work! ( i must pay😈

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Re: Adjusting timing propane engine and impco 425 mixers

Post by Frank » Fri Dec 07, 2018 2:24 pm

You should be able to attach photos to your post. In the edit screen, look below for the Attachments tab and "add files"

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Steptoe
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Re: Adjusting timing propane engine and impco 425 mixers

Post by Steptoe » Fri Dec 07, 2018 2:41 pm

I have put the softesd mech springs in already is that a good id.

Be careful doing that, you may find that at lidle the spring is not strong enough to hold the advance weight in
This results in it moving out, advancing the timing/ that increases rpms,
Since you are running on the idle circuit only, in the carb/ mixer, the engine leans, ineffect runs out of mixture.
The rpms drop.
And repeats.
Very confusing if don't know about this.
Weights should not move off till around 950/ 1200 rps
You will also notice that LPG fuel enables you to run a very stable in drive, idle at very low rpms..down to 450/550 rpms.
Even with a very low stall convertor.. 1200 rpms.
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Caddy123
Posts: 30
Joined: Sat Dec 01, 2018 2:41 pm
Location: Netherlands

Re: Adjusting timing propane engine and impco 425 mixers

Post by Caddy123 » Fri Dec 07, 2018 3:43 pm

Ok last question.
1 mixer doos not respond on the idle screw (2000 miles on it) only if i screw it in far.
Ps mixer 2 is new! Respond perfect.
Or do i have a vaccuum leak?

storm
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Re: Adjusting timing propane engine and impco 425 mixers

Post by storm » Fri Dec 07, 2018 4:05 pm

As Frank said you can attach pictures to your post, take a look at the screenshot below. See the Attachments tab and then click Add files, select your file and attach it.

As Steptoe said, btw good to see you posting Steptoe, to soft a spring will let the advance move to early and to quickly which can possibly cause other issues. If you, anyone, retains the standard mechanical advance mechanisms it is best to start with stock springs and weights and go from there. This will give you a base line which you can modify with aftermarket parts as the need arises. Just be careful though that the top end RPM advance isn't to much. LPG likes advance all in up to 2500-3000 RPM, Petrol will take it at higher RPM and this is because of the differences in the fuels and their burn rates. I have found that the first thing I change is going to a lighter weight which limits total advance more than the standard weight does because if you start with a base timing higher than the original setting on Petrol you will end up with to much timing advance on LPG (e.g. if your engine started with a base timing of 6 degrees and you change that to 10 or 14 you have just added 4-8 degrees more total timing which wont be beneficial to the engine).

The weights in the distributor determine how much advance (from base timing) the engine will get this is Centrifugal Advance or CA, the springs determine how quickly the timing will advance (loose springs advance earlier and quicker, tight springs advance later and slower), and the Vacuum Advance or VA determines how much advance is provided at particular vacuum pressures.

The beauty of a timing computer is that all of these thing are removed, or disabled, from the distributor and a timing map is created that does it all.
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