Vff30 with ohg vacuum hookup

Propane, Butane, LPG, GPL, C3H8, C4H10
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dayzedandkonfuzed
Posts: 15
Joined: Wed May 28, 2014 1:12 am

Vff30 with ohg vacuum hookup

Post by dayzedandkonfuzed » Mon Aug 20, 2018 3:58 pm

I thought this would be an easy one to find, but I'm having no luck. Turns out I've had the vacuum lines connected wrong for some time on my car. Now that I've rebuilt my model E, and installed the proper orange spring, I'm having runability problems on my 454.

My OHG x450 has 3 provisions for vacuum. 1 on either side of the mixture screw on the back, and 1 below and left of it. The port to the right of the screw I've always used for the vff30 with no troubles. Turns out that port is supposed to be plumbed to manifold vacuum. Doing this solved my heavy throttle issue, but now the car wont idle. The port to the left of the screw appears to exit right under the air breather, I cant imagine there's much vacuum there. I have the lockoff plumbed to the lower port, which exits between the throttle plates and air valve, which seems right, but the car wont idle and I can hear propane feeding the mixer for 3 or 4 seconds after I turn the engine off or stop cranking.

So what gives?


dayzedandkonfuzed
Posts: 15
Joined: Wed May 28, 2014 1:12 am

Re: Vff30 with ohg vacuum hookup

Post by dayzedandkonfuzed » Mon Aug 20, 2018 7:23 pm

I've been searching for 2 days.... and soon after I posted this I found some answers lol.
franz wrote:
Tue Oct 05, 2010 9:41 pm

Above and to the right of the idle screw is a 1/4" port which connects to the enrichment valve. This typically connects to a manifold vacuum source (a PCV valve is a common location).
Below and to the left of the idle screw may connect to the idle mixture solenoid if used, or to a vacuum lock off, again if used, or just plugged if not.
The black hex plug above and to the left of the idle screw connects to the vaporizer vent with a 3/8" vacuum hose.

This is all there is on the X-450.

Franz
So why is it that my vaporizer keeps feeding propane after key off when the lockoff is hooked up correctly, but does not when hooked up incorrectly? I'm going to have to verify this tonight, right after pulling all my hair out.

dayzedandkonfuzed
Posts: 15
Joined: Wed May 28, 2014 1:12 am

Re: Vff30 with ohg vacuum hookup

Post by dayzedandkonfuzed » Mon Aug 20, 2018 11:47 pm

So I can only make it run and drive if I have the lockoff connected to the port to the right of the mixture screw, and it doesn't keep feeding propane to the mixer after i turn the key off, but I dont like that its hooked up wrong. I'm shooting for the best mileage I can get, and would like to be confident it's all done correctly.

burbfixer
Posts: 17
Joined: Mon Nov 06, 2017 10:07 am

Re: Vff30 with ohg vacuum hookup

Post by burbfixer » Fri Aug 24, 2018 1:28 am

It should not keep feeding fuel after the engine stops, no matter where the lockoff's vacuum source is.
The mixer sends a varying vacuum signal thru the large dry gas hose, acts on the the secondary diaphragm, opens the valve, and fuel begins to flow. Once the engine stops there's no vauum signal, and the secondary valve should close and stop fuel flow.
The secondary lever is possibly adjusted too high and installing the cover pushes on the lever and opens the valve. Just adjust the lever by bending it to fix it.
It's also possible the primary side of the vaporizer isn't regulating pressure properly (supposed to be 5psi if I recall - at the test port).In this case, the pressure is too much for the secondary side to hold,and it's blowing right through, and on in to the engine.
Hope this helps.

dayzedandkonfuzed
Posts: 15
Joined: Wed May 28, 2014 1:12 am

Re: Vff30 with ohg vacuum hookup

Post by dayzedandkonfuzed » Fri Aug 24, 2018 9:46 pm

burbfixer wrote:
Fri Aug 24, 2018 1:28 am
It should not keep feeding fuel after the engine stops, no matter where the lockoff's vacuum source is.
Strange... because it does, but only when connected to the lower port on the mixer. Even if the engine doesn't start, it will continue feeding after I stop cranking, but will not when its hooked up to the upper-right side port.

Maybe it's something to do with this mixer? This is a new-to-me mixer, but its obviously been recently rebuilt, as its clean as a whistle and has someones initials written on it. I might try throwing my old mixer back on (another X450,) and failing that, try my X1 vaporizer that I just found while moving.

Also, what is the harm in connecting the lockoff to full manifold vacuum? And what would be the harm in having the secondary lever adjusted too low? I'm sure it was bang on 1/32 from the cover, but I'm willing to try bending it down a bit more if it won't drastically affect anything.

storm
Posts: 565
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Location: NSW, Australia

Re: Vff30 with ohg vacuum hookup

Post by storm » Sat Aug 25, 2018 4:12 am

Do you have a copy of Franz's book? If not I suggest you get it.

Do you have an electric lock off on your tank(s)? If not please fit one so that the fuel that is released by the VFF is limited to what is in the fuel lines.

Please also follow Franz's suggestions (to the letter) with regards to hooking up the lockoff to the OHG mixer.

From the IMPCO Training manual:
" IMPCO vacuum fuel locks are normally closed.
They use air valve vacuum from the air fuel mixer to open the fuel lock.
If the engine stops or is turned off, engine vacuum dissipates and the fuel lockoff closes automatically, this is a desirable safety feature.
When the engine is cranking or running air valve vacuum is transmitted from the mixer to the lockoff through a 3/16-inch vacuum hose.
The vacuum acts upon a diaphragm assembly, atmospheric pressure forces it inward against the valve operating lever.
As the valve operating lever is depressed it moves the valve operating pin.
As the valve operating pin moves it lifts the valve off of its seat.
This allows propane to flow through the lockoffs 10 micron filter and on to the pressure regulator."

and

" Lockoffs with filter elements should be positioned so that the filter can be changed as easily as possible.
Vacuum lockoffs should be positioned so that the atmospheric vent is not restricted.
Vacuum lockoffs should be positioned so that debris will not enter the atmospheric vent.
Vacuum lockoffs should be connected to air valve vacuum, not manifold vacuum."

So if the lockoff is not closing when the engine is shut down you have a problem somewhere.
With the engine running pinch (so you are causing a vacuum restriction) the vacuum line to the lockoff and listen for or better yet watch on a digital tacho to see if the engine rpm changes. If there is an rpm change you'll need to replace the O ring seal in the VFF.
Another test, also with the engine running, disconnect the vacuum line from the VFF and see what happens. It should stall, if it doesn't the lockoff isn't sealing and needs servicing with a rebuild kit.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

burbfixer
Posts: 17
Joined: Mon Nov 06, 2017 10:07 am

Re: Vff30 with ohg vacuum hookup

Post by burbfixer » Tue Aug 28, 2018 10:32 am

dayzedandkonfuzed wrote:
Fri Aug 24, 2018 9:46 pm
what is the harm in connecting the lockoff to full manifold vacuum?
The VFF30 needs very little vacuum to operate, so manifold vaccum over-stresses the components inside the lockoff. Over the years working in the industry, however, we did see many vehicles hooked up that way, and operating just fine.
dayzedandkonfuzed wrote:
Fri Aug 24, 2018 9:46 pm
what would be the harm in having the secondary lever adjusted too low?
Only that the manual prime button may no longer contact the diaphragm, plus the lever cannot travel as far when wide open, and that could potentially lean out the power mixture.

One other thing comes to mind. If memory serves me correctly, there were times when the new secondary lever that came in the rebuild kit was not holding the secondary valve 'squarely' on the seat, and therefore not allowing the valve to seal properly - might be worth checking.

As long as the vaporizer/regulator is functioning properly, an engine could function quite normally with no lockoff. *NOTE* I'm not recommending this. But for diagnostic purposes, just making the point that the vaporizer should shut off and hold fuel flow all by itself once there is no draw from the mixer.

dayzedandkonfuzed
Posts: 15
Joined: Wed May 28, 2014 1:12 am

Re: Vff30 with ohg vacuum hookup

Post by dayzedandkonfuzed » Tue Aug 28, 2018 1:28 pm

storm wrote:
Sat Aug 25, 2018 4:12 am
Do you have a copy of Franz's book? If not I suggest you get it.

So if the lockoff is not closing when the engine is shut down you have a problem somewhere.
With the engine running pinch (so you are causing a vacuum restriction) the vacuum line to the lockoff and listen for or better yet watch on a digital tacho to see if the engine rpm changes. If there is an rpm change you'll need to replace the O ring seal in the VFF.
Another test, also with the engine running, disconnect the vacuum line from the VFF and see what happens. It should stall, if it doesn't the lockoff isn't sealing and needs servicing with a rebuild kit.
I have Franz's book, it has been very helpful.

So I pinched the line, and there was no rpm change until I kinked the hose and the engine stalled. So that seems to check out. I'm starting to think my issue has nothing to do with the lockoff, and its just residual vapor from the vaporizer that is entering the engine after I shut it off. I'm going to play with this a bit this week, swap vacuum lines around and try my old mixer. At the moment I've got around 15.5 afr at idle, and 13.6-13.8 from cruise all the way to WOT. Obviously this isn't ideal, but it shows that it the WOT enrichment is not there which makes sense as my vacuum lines aren't hooked up correctly. I also don't have my timing quite dialled in, I was having come consistency issues last time I had my light on it, so I'm going to start there before making any other changes.

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