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Propane Issues

Austin

Austin

Blame Canada
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Joined
May 1, 2020
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3,112
Loc
St.Louis, MO
I hooked up a propane kit on my Unimog and it ran like a top out of the box with no adjustments. I removed the standard points from the stock distributor and put in an electronic points system, changed out the plugs, wires and changed the oil. It still ran decent, I needed to get a timing light on it but still pretty decent. I only ran it for a minute or two because I spilled a bit of oil and when the engine got warm it would burn off. We had a nice day the other day so I opened the shop, and let it run for 20 min or so to burn it all off. Hasn't ran worth a damn since. If it starts, it turns over very slow till it dies in a few seconds. Once in a blue moon it will start and run, but if I try and bring the rpm back down to around 800, with either the distributor or the mixture, it dies. I can't say I 00% feel like the idle screw does a damn thing anyway.

The mixer gives a bit of a hiss after it dies,
I've had it spit (if you will) up out of the mixer,
it's actually backfired up out of it
and just a bit ago the engine backfired out of the exhaust

If I try and run it lean or rich I get all the same symptoms....

I seen Mr Stubs post about his propane issues related to his air filter. I havent got an air filter on it yet because havent figure where I want to duct it to yet. Could the burning off of the engine oil have screwed with the mixer?

... not sure where to look next
 
Were you able to check for vacuum leaks? I never worked on anything propane but that's where I would start.
 
Who's propane kit are you running. My advice would be to pm or call Cary Gleason from got propane.
 
When it backfired did it tear the diaphragm? That will make it run like shit. Check it out to be sure.

Also, you mentioned it cranking for a short time and dying. Are those batteries buried under the floor any good? Is the alternator charging when its running? It might be something as simple as weak batteries and/or a bad alternator.
 
HELL BOUND said:
Who's propane kit are you running. My advice would be to pm or call Cary Gleason from got propane.
Click to expand...

https://carbturbo.com - There was an online mog shop that specked out this system for this motor years ago and when it went under they turned over the parts list to these guys. THey sell them, but aren't that familiar with tuning this motor.

SLOWPOKE693 said:
When it backfired did it tear the diaphragm? That will make it run like shit. Check it out to be sure.

Also, you mentioned it cranking for a short time and dying. Are those batteries buried under the floor any good? Is the alternator charging when its running? It might be something as simple as weak batteries and/or a bad alternator.
Click to expand...

Being a newb, I didn't know that the diaphragm could be damaged, or that there was even one in there to be honest. I'll have to pull it this afternoon.

The batteries crank over well, they are surprisingly strong for the age. It will start, run at a very low rpm until it just dies.
 
Id agree with slowpoke if it backfired out of the mixer the diaphragm is probably screwed. But I'm not much help with the tuning part of it.
 
Just pulled the car apart and everything looks fine to me, it goes up and down smoothly and I get a nice little gas smell every time I do LOL

E1EA6A52-8BC2-49EB-9AC8-035AA8889495.jpeg
455D50BD-79C2-4FF7-A333-CB36DFBC074E.jpeg
 
Just had a pretty lengthy call with the propane guys and they are leaning towards a new ignition issue.

My main concern was burning off the oil that had spilled and that causing some issues with the carb possibly sucking it in but they weren't worried about it at all

.... off to call the ignition people
 
Have you adjusted the valves in that thing yet?

I would seriously pull the valve cover and have a peek if not.

Not likely the main issue but it won't help anything if it's the case.
 
Lil said:
Have you adjusted the valves in that thing yet?

I would seriously pull the valve cover and have a peek if not.

Not likely the main issue but it won't help anything if it's the case.
Click to expand...

It's not a diesel ! :flipoff2:

No, and when it was running on propane with all the new wires, plugs and coil it sounded good.


Just talked to the guy who I got the ignition from, he said it sound like classic loss of power after the ignition button it released ... so ... maybe not a propane thing. Time to break out the meter this evening
 
I sat out in the shop with multimeter and tested points all along the ignition. Everything looked good. I pulled a plug and cranked it over to check spark and it’s a good spark.

It was then I noticed, I didn’t smell gas from the cylinder without the plug.

I went and disconnected the tank I just had filled and no psst.

Hooked up another tank that I stopped using because of all this, cranked it over a few times and it started right up.

It ran good for a few before it got smokey in the shop so it turned it off, opened all the doors and was getting ready to play with timing ...... aaaand now I’m back in the same boat. It won’t start again, with either tank.



as to vacuum leak, I made new gaskets & checked the one line there is, zip tied them back up and it did nothing. This was all before it started and ran as mentioned above.

so .... leaning back to a propane and not ignition
 
What are you running for:

lock-off

vaporizer


Mixer

any “iceing” occurring on the lines or fittings near the tank? Have you set timing with a light? Propane is happier with more timing. I run high 20’s, all-in.
 
slightly bent diaphragm plate hard to see it, replace it, been there many times while chasing down a backfire issue, i kept spares

every time it would backfire it wouldnt start, replace the plate(find the part# so you dont have to replace the entire diaphragm i could get plates for $2.55 each) in the diaphragm it would start right up
 
Last edited:
Wilson said:
What are you running for:

lock-off

vaporizer


Mixer

any “iceing” occurring on the lines or fittings near the tank? Have you set timing with a light? Propane is happier with more timing. I run high 20’s, all-in.
Click to expand...

Impco CA125M Mixer

IMPCO VFF30-2 Vacuum Fuel Lock-Off

Impco Cobra Vaporizer

No frosting, and timing is set at a max (for now) 13*

It runs like a top when is starts, very fast throttle response. I just can't get it to restart after it runs for more than 5-10 min
 
The duration is what had me leaning towards a freeze up. Just to be sure, put your hand on the lockout and vaporizer next time. It shouldn’t be cold to the touch.

I’ve had the plates bend as Rockyota suggested, but that should be a permanent issue, not an intermittent one.
 
Wilson said:
The duration is what had me leaning towards a freeze up. Just to be sure, put your hand on the lockout and vaporizer next time. It shouldn’t be cold to the touch.

I’ve had the plates bend as Rockyota suggested, but that should be a permanent issue, not an intermittent one.
Click to expand...

when it runs it will get warm, i've never seen frost on it
 
What shuts the propane off when you turn the key off? Is there some kind of electric solenoid in there somewhere that is failing or bad maybe?
 
Wilson said:
I’ve had the plates bend as Rockyota suggested, but that should be a permanent issue, not an intermittent one.
Click to expand...


when they are barely bent it wont start when its hot

let it sit over night and get cold it will start, warm it up shut it off and it wont start
 
if it backfired i can pretty much guarantee the bent plate on the diaphragm is your issue

ive literally replaced a dozen of them :laughing:
 
Mr Stubs said:
Their should be a electric on/off solenoid in the system. They are usually wired in turn key on.
Click to expand...

the vff30 is a vacuum operated one. I have used them on 50% of my builds. No isuues
 
rockyota83 said:
if it backfired i can pretty much guarantee the bent plate on the diaphragm is your issue

ive literally replaced a dozen of them :laughing:
Click to expand...

Took your advice and ordered a couple silicone ones and put one in tonight ..... no luck.

The guy that sold me the propane kit said to gap the plugs between .03 and .032 which is down from the .04 mog guys say.

I pulled the new plugs and they all looked like some degree of of this:

IMG_0467.JPG


Please tell me that white milkiness is a propane issue. :shaking:

Either way, after adjusting the gaps and cleaning them off it fired right back up. It bellowed white smoke for about 10-15 seconds but it was running like it never missed a beat.

I can turn it off and it fires back up again.
 
rockyota83 said:
put the old diaphragm back in
Click to expand...

I bought a few new ones so I just pitched it, also it’s a PIA given the location of the carb on a Unimog

I go out today and I’m back to it not starting.

First time it started and ran for about 10sec before the idol slowed and died. Now it just turned over and doesn’t even try to start.

Tank is full.....
 
Austin said:
I bought a few new ones so I just pitched it, also it’s a PIA given the location of the carb on a Unimog

I go out today and I’m back to it not starting.

First time it started and ran for about 10sec before the idol slowed and died. Now it just turned over and doesn’t even try to start.

Tank is full.....
Click to expand...

propane fuel filter?
put the old ignition back on?
when it doesnt even try to start can you smell propane?

i went through hell trying to chase down a backfire issue, i tried absolutely everything, multiple distributors, advanced and retarded timing and everything in between, locking out the mechanical advance in the distributor to even putting pro dual valve springs. it ended up being a stupid shitty ass boost gauge was wrong and i was getting more boost than i thought :homer: needed to adjust the waste gate (which i had prior but not enough)
 
rockyota83 said:
propane fuel filter?
put the old ignition back on?
when it doesnt even try to start can you smell propane
Click to expand...

There is no specific filter.
its gone
i do not smell propane

here is a video of it trying to start, then starts and runs rough, after tweaking the idle screw on the cam (not the idol mixture screw) it takes off and eventually I idol it down and it runs fine

 
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