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Daddiojoe
PostPosted: Sat Oct 31, 2009 10:00 am 
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Location: Chelsea, MI
Car Model: 71 Dodge D100 64 Plymouth Valiant Wagon
So, I'm continuing to have problems with my propane burning 225. It will idle roughly, but then really miss when I put it in gear. I don't know whether the problem is:

1. Electrical. I've got Autolite long-reach platinum 985s, Magnecor wires, MSD high-po coil and stock Mopar electronic ignition. Timing is set at a conservative 6 degrees BTDC. As per the advice of a propane-guru, the plugs are gapped at .030. WHAT DO YOU THINK ABOUT THIS PLUG GAP?

2. Fuel System. Just installed a new vaporizer. Everything is in working order and using a propane diagnostic tool I can get optimal air/fuel mixture.


3. VACCUUM? I get 20" Hg at idle (approx 1000 RPM) and when I put it in gear get 15" and missing. Should the needle be dead-steady at idle? It ticks back and forth a little bit. When blipping the throttle plates the vaccuum goes way down, (of course) but jumps back up fairly quickly.

This has been driving me nuts for close to a year now--I keep thinking I've got it figured out, but then.....

So, any help would be greatly appreciated.

Thanks,
Joe

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71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

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Aggressive Ted
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PostPosted: Sat Oct 31, 2009 10:26 am 
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Supercharged
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It should be a steady 16" of vacuum at 600 rpm in gear. You may want to re-check the valve lash to firm up the reading. If you want a real soild reading go .012 and .022 on the lash. The vacuum will come up a bit and be steady as a rock as long as there are no intake manifold/carb base gasket leaks.

Hopefully your not plugged into the port on runner 6. That will give you a bad inaccurate reading. Be sure your using one off the base of the carb. I "T" into the choke pull off for my gauge.

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Aggressive Ted

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madmax/6
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PostPosted: Sat Oct 31, 2009 1:19 pm 
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try plain plugs,have had platnums cause me troubles.mark
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SlantSixDan
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PostPosted: Sat Oct 31, 2009 1:39 pm 
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madmax, he's not running platinum plugs. He is, however, running Autolite plugs, which are now rather poorly made in China.

A switch to NGK ZFR5N plugs, without the metal ring washers, might be a wise idea to eliminate poorly-made plugs as a cause.

I don't have much knowledge of propane engine operation but I have a hard time imagining why an extra-narrow plug gap like 0.030" would be anything but a hindrance.

What kind of Mopar electronic ignition are we talking about? Orange box...?

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madmax/6
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PostPosted: Sat Oct 31, 2009 2:19 pm 
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I just assumed he was running platinum plugs because in his post he said he was running autolite long reach platinum 985s.Mark
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SlantSixDan
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PostPosted: Sat Oct 31, 2009 2:56 pm 
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Durrr...it helps if I read every word in the post. D'oh! (whacking self) You're right.

I'd still swap the Autolites for some NGKs.

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madmax/6
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PostPosted: Sat Oct 31, 2009 3:07 pm 
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Yea,for a second there I thought I was the dummy,you win and I agree with the NGKs,Mark
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emsvitil
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PostPosted: Sat Oct 31, 2009 4:33 pm 
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With the mopar ignition, I'd run .040-.045 gap on the plugs.

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Charrlie_S
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PostPosted: Sat Oct 31, 2009 5:22 pm 
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With the mopar ignition, I'd run .040-.045 gap on the plugs.
Not with propane.

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SlantSixDan
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PostPosted: Sat Oct 31, 2009 5:31 pm 
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Well, now I'm even more curious: Why does propane warrant narrow plug gaps?

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emsvitil
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PostPosted: Sat Oct 31, 2009 8:31 pm 
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Well, now I'm even more curious: Why does propane warrant narrow plug gaps?
X2

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Daddiojoe
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PostPosted: Sat Oct 31, 2009 9:54 pm 
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Location: Chelsea, MI
Car Model: 71 Dodge D100 64 Plymouth Valiant Wagon
Ted-- I was using the vacuum bung for the power brakes, so I need to check that. It is normal to lose some vacuum when in gear, then?

Dan--Do you have the number for long reach NGKs handy?

Also, according to Franz Hoffman in his Diagnostic Guide to Alternative Fuels "All spark plugs should be gapped at least .010" closer on a gaseous fuel than with gasoline."

I'm really not sure why. I should ask him. Good question!

Thanks for the tips.

Joe

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71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"
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Aggressive Ted
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PostPosted: Sat Oct 31, 2009 10:11 pm 
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Ted-- I was using the vacuum bung for the power brakes, so I need to check that. It is normal to lose some vacuum when in gear, then?
Yes! I set my idle for about 750 rpm out of gear. Once you put it in gear with the lights, wiper and heater on, it drops down to about 600 rpm.

Out of gear is 18 to 19" of vacuum, in gear 16".

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74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG
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SlantSixDan
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PostPosted: Sat Oct 31, 2009 10:32 pm 
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Dan--Do you have the number for long reach NGKs handy?
As above: ZFR5N. Application is 2000 Jeep Cherokee 4.0-litre Six.
Quote:
Also, according to Franz Hoffman in his Diagnostic Guide to Alternative Fuels "All spark plugs should be gapped at least .010" closer on a gaseous fuel than with gasoline." I'm really not sure why. I should ask him. Good question!
Please do. I'm still coming up utterly blank as to why this would be a good or necessary thing.

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SV162
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PostPosted: Sun Nov 01, 2009 4:10 am 
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I lifted this from the Australian NGK website.
Quote:
There are two critical factors that need to be understood when converting a vehicle from petrol to LPG:

LPG burns hotter
LPG increases the voltage requirement at the electrode gap
In an attempt to correct these two factors, as a general rule we suggest to:

Use a spark plug that is one heat range colder than standard to compensate for the increased heat from LPG:

The temperature profile of an engine may vary between vehicles. As such, the effect of LPG on the operating temperature of one vehicle may not be the same for another vehicle.
For example, lets say that LPG increases the average operating temperature by 200°C. If the average operating temperature of a Holden Commodore (which uses a 6 heat range) was 700°C the addition of LPG would exceed the operating range of 870°C. As such a colder plug may be required. However, a Ford Falcon for example (which also uses a 6 heat range) may have an average operating temperature of 500°C, the addition of LPG is still within the 450 – 870°C operating range and a colder plug may not be required. Please note that these values have only been used for illustration purposes.

Reduce the electrode gap by 0.1mm to compensate for the increased voltage:

It is difficult to gauge exactly how much the voltage requirement has changed as other factors such as engine wear, loss in compression and ignition system weakness for example may provide an influence. As such the electrode gap may need to be adjusted several times until the correct gap setting is achieved for that unique vehicle.

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