IMPCO start assist

Propane, Butane, LPG, GPL, C3H8, C4H10
C3H8
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Re: IMPCO start assist

Post by C3H8 » Wed Jan 15, 2014 7:21 pm

OK. I believe it is used to lock out the secondaries by activating the lockout lever until the engine is warmed up. Going strictly from memory. Not 100% sure. It was probably controlled by a temperature activated vacuum switch. Either way it should have been retained on LPG. There was no reason to disable it. Perhaps someone can jump in to confirm.


storm
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Re: IMPCO start assist

Post by storm » Wed Jan 15, 2014 8:33 pm

C3H8 wrote:OK. I believe it is used to lock out the secondaries by activating the lockout lever until the engine is warmed up. Going strictly from memory. Not 100% sure. It was probably controlled by a temperature activated vacuum switch. Either way it should have been retained on LPG. There was no reason to disable it. Perhaps someone can jump in to confirm.
The TVS was usually mounted in the air cleaner housing, 1 hose feeding vacuum to the TVS and 2 out (1 to the secondary lock out and the other to wherever the manufacturer wanted but often the hot air flap on the air cleaner housing).
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C3H8
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Re: IMPCO start assist

Post by C3H8 » Thu Jan 16, 2014 12:33 am

Took me a while but I finally found the proper description of the break valve.

The vacuum break on a Q Jet serves a couple of purposes.

One is to provide a "shock absorber" function to the opening of the secondary air valves so they don't just "slam open" as soon as the secondary throttle plates open down below (a nasty bog is the result if that is allowed to happen). The actual secondary throttle plates on a Q jet are opened mechanically. The upper vacuum controlled plates are held closed by vacuum and open when the vacuum decreases if the throttle plates are opened suddenly. The plates are balanced by either a spring in the valve and/or air flow that will force them open as the vacuum decreases.

The lock out lever actuated by the choke spring keeps the vacuum secondary from opening until the choke is completely open and the engine reaches a specific temperature.

I noted on some models the vacuum line is attached directly from the break to manifold vacuum. On others it is routed through a temperature operated vacuum valve as an extra precaution it is not functioning too soon. I would expect that changes in emission rules necessitated the use of a temperature controlled valve. These showed up in the 80's while pre 80's usually were attached directly to vacuum with only the lockout lever keeping the secondary's from functioning.

C3H8
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Re: IMPCO start assist

Post by C3H8 » Thu Jan 16, 2014 1:02 am

Now I'm feeling silly. The position of this vacuum break has been bothering me so I did some in depth research. I have mixed up the functions of the front and rear vacuum break. The front controls the secondary air plates. The rear controls the choke unloader and prevents opening of the secondary throttle plates until the choke coil heats up and unloads. A complete explanation of the rear break and front brake is in the document located here. front break Page 9, rear break page 11.

http://www.buick-riviera.com/serviceman ... -40-60.pdf

The rear break was considered basically an emission device as I first suspected to ensure the secondary system did not activate until the engine warmed up.

Sorry for the confusion.

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kikkegek
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Re: IMPCO start assist

Post by kikkegek » Thu Jan 16, 2014 2:28 am

he Guys,

I havent gotten around to checking the start assist yet. But I found out something else.

I noticed that the voltage at the BAT connection of my HEI was only 11.4 Volts. Also during cranking the voltage dropped to 7-V. and thus noticed that the spark plug had very weak small spark. Not very well for a good spark. its a common problem with old cars that go from points to HEI. And from sealed beams to H4 blulbs. The IGN gets a bigger load and old wiring causes voltage drop.

So I added a 30A relay and connected the HEI to the firewall junction of my alternator (where the field connection is made).

Image

Image

Image

result:
- strong spark
- easy cold starts in the morning
- and not one backfire since I made this upgrade

thought I should share this info
daily: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.1 end gears - IMPCO425 mixer - IMPCO model E vaporizer
project: 1977 GMC C15 Suburban - 454 big block - TH400 - gasoline
sold: 1986 Chevrolet Suburban K20 Silverado

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kikkegek
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Re: IMPCO start assist

Post by kikkegek » Mon Jul 10, 2017 3:00 pm

in the end I removed the start assist. I found that it was constantly open, causing a rich condition.

tonight I opened up the valve and found the rubber seal that should close the valve with a small piston was not sitting flush, thus always causing an NO condition.

Ill add the start assist again to my setup and see if it will improve cold morning starts and report back here.

I am also looking for a simple method to just prime the regulator i the morning without opening the hood, but those are about $100,- (the electronic primer buttons)

anybody ever make a home made solution? I am open to ideas
daily: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.1 end gears - IMPCO425 mixer - IMPCO model E vaporizer
project: 1977 GMC C15 Suburban - 454 big block - TH400 - gasoline
sold: 1986 Chevrolet Suburban K20 Silverado

kuchen
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Re: IMPCO start assist

Post by kuchen » Mon Jul 10, 2017 4:06 pm

I suggest using a Hana Injector for about 20€ instead of the Impco SV and connect it to the primary side. As this is a low-z injector, a 2Ohm resistor in series is advisable.

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kikkegek
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Re: IMPCO start assist

Post by kikkegek » Mon Jul 10, 2017 5:26 pm

kuchen wrote:I suggest using a Hana Injector for about 20€ instead of the Impco SV and connect it to the primary side. As this is a low-z injector, a 2Ohm resistor in series is advisable.
that is a good idea. So use a propane vapor injector connected to the primary side for start assist.

OK, but the primary side is the side where the liquid LPG comes into the regulator. So using that for a start assist? I would be shooting liquid propane into my intake? can you tell me a little more on your idea?
daily: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.1 end gears - IMPCO425 mixer - IMPCO model E vaporizer
project: 1977 GMC C15 Suburban - 454 big block - TH400 - gasoline
sold: 1986 Chevrolet Suburban K20 Silverado

kuchen
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Location: Stuttgart/Germany

Re: IMPCO start assist

Post by kuchen » Wed Jul 12, 2017 5:05 pm

kikkegek wrote:...the primary side is the side where the liquid LPG comes into the regulator...
No. Impco refers to the pressure after the first reduction stage as the primary pressure.

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kikkegek
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Re: IMPCO start assist

Post by kikkegek » Thu Jul 13, 2017 3:45 am

kuchen wrote:
kikkegek wrote:...the primary side is the side where the liquid LPG comes into the regulator...
No. Impco refers to the pressure after the first reduction stage as the primary pressure.
ok thanks, so you are referring to the same port as the IMPCO Start assist valve uses?

Image
daily: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.1 end gears - IMPCO425 mixer - IMPCO model E vaporizer
project: 1977 GMC C15 Suburban - 454 big block - TH400 - gasoline
sold: 1986 Chevrolet Suburban K20 Silverado

kuchen
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Joined: Tue Oct 25, 2011 12:38 pm
Location: Stuttgart/Germany

Re: IMPCO start assist

Post by kuchen » Thu Jul 13, 2017 1:27 pm

Again no. As you can read from your own post, the Impco SV is connected to the secondary pressure after the second reduction stage.

C3H8
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Re: IMPCO start assist

Post by C3H8 » Sun Jul 16, 2017 2:06 pm

You guys are sort of on the same wave length not quite. Kuchen is suggesting you install the injector in the primary test port. This port will provide 2 PSI of vapour pressure normally. You are thinking of it as a liquid port but it is not. When liquid enters the regulator at the primary valve it immediately flashes to vapour because of the pressure drop. The primary valve seals as soon as the primary pressure reaches 1.5 to 2 PSI. On a cold engine this pressure can be 5 to 7 PSI but it drops as soon as the engine is cranked over. In extreme cold -25C or colder it is possible for the LPG to stay partially liquefied in a primary chamber however this will become vapour almost immediately as soon as the engine is cranked over.

The vapour at the secondary port is a negative pressure. Using an SV here, which is only designed for very low pressure and vacuum, allows fuel to bypass the gas valve directly into the throttle plate area and speed up starting.

Should you choose to use Kuchen's injector idea I would add a momentary switch at the dash. This is a spring loaded button that would allow you to press it while cranking and shut off as soon as you released it. Primary primers offer very quick starts, however they can also lead to fairly easy flooding if used too aggressively in very cold weather. At the same time the switch allows leaving them off vs wiring them directly into the cranking circuit.

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kikkegek
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Re: IMPCO start assist

Post by kikkegek » Sun Jul 16, 2017 3:54 pm

My IMPCO 300A and Model E generator is very hard to cold start in the morning. it takes about 20-25 seconds with the throttle closed and about 10-15 seconds of cranking with the throttle at WOT. I dont like the throttle open at WOT, cause I am a bit scared of backfires and lean conditions.

that is why I am considering a start assist. The solution from kuchen sounds like it will improve cold starting a lot.

@ Kuchen: do you have a photo of your setup? or was it just an idea?
daily: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.1 end gears - IMPCO425 mixer - IMPCO model E vaporizer
project: 1977 GMC C15 Suburban - 454 big block - TH400 - gasoline
sold: 1986 Chevrolet Suburban K20 Silverado

storm
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Re: IMPCO start assist

Post by storm » Sun Jul 16, 2017 6:15 pm

The injector mounted in the regulator has been around for a very long time. Here's a pic of one mounted in a B2 for a GRA setup.
g002.jpg
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

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kikkegek
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Re: IMPCO start assist

Post by kikkegek » Mon Jul 17, 2017 2:24 am

storm wrote:The injector mounted in the regulator has been around for a very long time. Here's a pic of one mounted in a B2 for a GRA setup.
g002.jpg
Cool. What part in the photo is the injector?
daily: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.1 end gears - IMPCO425 mixer - IMPCO model E vaporizer
project: 1977 GMC C15 Suburban - 454 big block - TH400 - gasoline
sold: 1986 Chevrolet Suburban K20 Silverado

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