Timing a 350 on Propane

Propane, Butane, LPG, GPL, C3H8, C4H10
Steptoe
Posts: 1504
Joined: Fri Feb 02, 2007 8:32 pm
Location: JAFA , New Zealand

Re: Timing a 350 on Propane

Post by Steptoe »

The 425 power valve when set to the stock out of the box setting , will be damn near spot on...
There are 2 posts in old threads that have the number turns out, or height from body, ant rem which... and these are a bitch to find
Also from memory it was C3H8 that posted it up

be careful with the 425 mixture screw... if u take the side cover off... again very careful not to break the gasket or diapham... u will see it is very easy to have the mixture adjusting screw sit on the wrong side of the plate..
If the adjusting screw doesnt seem to change idle mixtures then either the screw is on the wrong side or could have a leak in the diapham , or the port under the diapham is blocked with crap.
My Spelling is Not Incorrect...It's 'Creative'

AdrianL
Posts: 6
Joined: Mon Aug 11, 2014 2:53 pm

Re: Timing a 350 on Propane

Post by AdrianL »

Power screw: was is 29/32" from washer to base of bolt? Seem to remember reading that but didn't write it down
1985 GMC Vandura; 5.7L V8 on LPG with IMPCO 425 Mixer and "E" Vaporizer

C3H8
Posts: 1129
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Timing a 350 on Propane

Post by C3H8 »

Good memory step. Also good reminder on the idle diaphragm gasket and screw position. AdrianL, the 29/32 is from the washer face at the base to the top of the hex head of the bolt. This applies to old style mixers only of course, not the tamper resistant model.

Steptoe
Posts: 1504
Joined: Fri Feb 02, 2007 8:32 pm
Location: JAFA , New Zealand

Re: Timing a 350 on Propane

Post by Steptoe »

iut is nice when ppl make comments lkike that... ppl who do their homework and not simply pile ahead excepting everyone to do everything for them
U have made my day m8

I tend to rem where info is rather than the actual info... even a manual or a magazine I last read 40yrs ago.. I will know say its 3/4 of the way thru right hand side 1/4 of the way down the page... but forum stuff thats harder , but easy to rem what web site or how to get back to it and search.
not the tamper resistant model.
no such thing :wink: .. give a Kiwi a screw driver a hammer and a bit of number 8 wire and we will build or fix anything :shock: ...
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bumpstart
Posts: 133
Joined: Wed Jan 20, 2010 9:09 pm

Re: Timing a 350 on Propane

Post by bumpstart »

geraldm wrote:I' going to go for one of these when I get to it .. they now have a gen 4 that does even more things /.. don't know as I have not had one but is suppose to be a good bang for the buck .. I want to be able to monitor my boost pressures and temp with the same unit ,just needs different pickups . after returning to the pits You can go back and monitor everything that was happening during the run .. ?? Not really up on them but seems like a good unit ..http://www.ebay.ca/itm/PLX-Wideband-O2- ... b3&vxp=mtr
while it is going a little off topic for the OP .. i will set the record straight regarding these units.. apologies to OP

first.. i have no association with PLX..

the problem with home LPG tuning is that guys with older vehicles often lack the OBD2 system and or an aftermarket ECU to help log the data from the wideband

and so these vapour mixer guys are often forced to watch the gauge on the wideband whilst trying to tune on the road

.. a dangerous exercise

the PLX AFR / DM6 system ( now gen 4 and offering LSU 4.9 probe )
whilst being a unique touch gauge and a reliable aftermarket wideband being able to display LPG AFR or lambda
( and there is many very unreliable brands that also cant display in LPG AFR )

offers the simple user a few seconds of onscreen trend .. which allows you to drive .. and glance back at the short log if you have a glitch

it is only a few seconds long .. i hope it is a short ride back to the pits !!

the system will record low and high thresholds , and can be setup to flash warning with multiple trigger flags when several logging devices are daisy chained together


however .. the system will log ( realtime ) to a PC ( software free once you buy the cable ).. but not much good to a guy on a bike !!!

so better still. combines with another product .. called PLX kiwi.. which will send the data wirelessly to most modern mobile phones equipped with the app
( where it can be logged , or viewed live during run by the pit crew )

the PLX kiwi is designed to work with IMFD ( DM6 system ) and the PLX DM100 / OBD2 plug in later cars
( where it extracts much more data )

for those without OBD2.. they only require the female OBD2 plug,, and hook up earth ( OBD2 pin 4) and power ( OBD2 pin 16 ) to power up the kiwi and make it broadcast the DM6 data

the only issue here for those oldschool guys .. is PLX neglected to include an RPM module for the DM6/ IMFD system
.. ( the DM100 system steals it from the OBD2 )

and so .. if logging.. then they are best to get the vacuum/ boost module and so it can tie up the data from the wideband a little better for tuning

not everyone needs one .. but those tuning for power or for economy will find a wideband that can log ,, a very handy inclusion that has payback if you use it right

and for those who get very serious.. i can recommend the PLX SM-EGT as also a reliable enough K couple for just past 1000 C exhaust temps and is especially handy for LPG tuning in conjunction with the wideband

there is other brands of loggers out there..some very good .. but few offer these functions down at this price
when the going is hard, don't retard, remember your lubrication

AdrianL
Posts: 6
Joined: Mon Aug 11, 2014 2:53 pm

Re: Timing a 350 on Propane

Post by AdrianL »

So I finally took my van into our local propane specialist. I followed all the advice in this thread (which was greatly appreciated). Mechanic hooks up the van and basically I was running so rich he says he's surprised I made it two blocks on a tank of propane.

I learned a valuable lesson---you can't tune a propane system "by feel" or whatever. You need an analyzer unless you want to be way off specs and fail emissions testing every time (my van passed with flying colours after the professional service).
1985 GMC Vandura; 5.7L V8 on LPG with IMPCO 425 Mixer and "E" Vaporizer

Steptoe
Posts: 1504
Joined: Fri Feb 02, 2007 8:32 pm
Location: JAFA , New Zealand

Re: Timing a 350 on Propane

Post by Steptoe »

you can't tune a propane system "by feel"
Bottom line.. u cant "tune" or dial in any fuel by feel....and any of the 'old guys' who recon they can on the old vintage cars...
Well have gone thru that exercise in the vintage car club workshop....they tune it by feel...
then we hit it with basic data logger 02/ knock sensors etc
The the NOx are usually high if not real high... inaudible detonation.. usually part way up in the curve and at cruise
Then compare the 2 tunes with economy and power with a atop watch..again significant difference.
The amazing part is the denial of the numbers
Tuning is setting up the timing / mixture specs within the manufactures specs....but with significant changes in the fuel compositions, compressions octanes and most engines are not original bore/ stroke.....it means re dialing in.. re-establish the new 'factory' tuning specs.
My Spelling is Not Incorrect...It's 'Creative'

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Timing a 350 on Propane

Post by storm »

AdrianL wrote:I learned a valuable lesson---you can't tune a propane system "by feel" or whatever.
Actually you can, I have seen it done with extremely good results, but you need to know exactly what you are doing and you need a very accurate butt! People that can do this have years of experience, very detailed tuning methods, and have plenty of time.
AdrianL wrote:You need an analyzer unless you want to be way off specs and fail emissions testing every time (my van passed with flying colours after the professional service).
It is always best to get setup properly and then write all the baseline specs down. Then, if required, the engine can be checked after 12 months to see if it is holding the settings and retaining emissions compliance.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

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