check my start assist

Propane, Butane, LPG, GPL, C3H8, C4H10
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kikkegek
Posts: 416
Joined: Thu Nov 17, 2011 2:12 pm
Location: Netherlands, The Hague

check my start assist

Post by kikkegek »

he guys,

In have a SV start assist on my generator.

Image

sinds a while the engine takes pretty long to start in cold starts. like 15 seconds.

I took a 12V from the battery and tapped the 12V connection of the start assist directly, but didnt hear a click nor a release of pressure when I energized it.

so how do I check the start assist, without setting my engine bay on fire :-)
storage/project: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.10 gears - IMPCO425 mixer
driver/project: 1977 GMC C15 Suburban - 454 big block - 4L80E- LPG VSI - 3.08 gears
sold: 1986 Chevrolet Suburban K20 Silverado

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

Re: check my start assist

Post by C3H8 »

First add a few more details on what you have. Considering it is an IMPCO SV I assume you have an IMPCO regulator.
- What kind of engine?
- Where is the valve installed?
- Where is the vacuum hose attached?
- Is the valve wired to the starter solenoid wire or to a spring loaded switch? Typically the SV is only used on 4 cylinder or larger engines?

This valve has a very small piston made for very light vacuum. Therefore it is very quiet when it opens. Feeling it open can be hard even by placing a finger on it. It can be tested by removing it from the regulator. Shut off the valve at the tank and disconnect the LPG lock off before removing it. Power up the solenoid and blow through the threaded end or suck on the hose barb end. If it is open it is working. Also check the vacuum hose. It must be attached to air valve vacuum source only (above the throttle plates). If the hose is attached to intake vacuum three things can occur. The first is the vacuum during cranking may be strong enough to hold the SV valve closed against the power of the coil. The priming could be way too rich for the engine. The fuel mixtures may be richer then necessary when running as the high vacuum may pull fuel past the valve even though it is closed.

kikkegek
Posts: 416
Joined: Thu Nov 17, 2011 2:12 pm
Location: Netherlands, The Hague

Re: check my start assist

Post by kikkegek »

thanks man. I'll look into it this weekend and shoot some pics when I am at my car again.

It has been running unexplainably rich during idle and cruise....this might clear it.

It is connected above the thottle blades and to the primairy side on the bottom of the converter (I believe).

Ill post some pics this weekend.
storage/project: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.10 gears - IMPCO425 mixer
driver/project: 1977 GMC C15 Suburban - 454 big block - 4L80E- LPG VSI - 3.08 gears
sold: 1986 Chevrolet Suburban K20 Silverado

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

Re: check my start assist

Post by C3H8 »

The SV is not designed to fit there. The primary port puts out a positive pressure of 2 PSI during running and as high as 7 PSI on initial key on. I doubt very much that the solenoid is capable of opening the valve against that pressure. Also during normal running fuel is likely being forced past the closed piston accounting for some of the reason your idle and cruise. The SV is designed to be installed into the port that is connected to the secondary chamber. This port is approximately 2 to 3 inches from the vapour outlet and about 1/2 inch below the regulator lid on a model E regulator. Picture the regulator with the vapour outlet straight down at the 6 o'clock position and the top lid facing you. The port is at about the 8 o'clock position.

kikkegek
Posts: 416
Joined: Thu Nov 17, 2011 2:12 pm
Location: Netherlands, The Hague

Re: check my start assist

Post by kikkegek »

ok, found a picture on my computer

is this OK?

(yes it looks bad, but cleaned it up and this is old picture. SV is still like this though.)

Image
storage/project: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.10 gears - IMPCO425 mixer
driver/project: 1977 GMC C15 Suburban - 454 big block - 4L80E- LPG VSI - 3.08 gears
sold: 1986 Chevrolet Suburban K20 Silverado

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

Re: check my start assist

Post by C3H8 »

Your location is correct. The only issue is the orientation of the regulator. It may not be critical depending on how much oil (heavy ends) you have where you live. Too much separation could block your SV opening eventually. Also the oil could hamper the diaphragm movement in cold weather. Typically model E regs are installed with the vapour outlet facing down. As I remember Holland does not have high amounts of oil separate from the LPG. Just keep an eye out for it. The next thing to check is the size of orifice you are using. The valve came with a 6 and 8 cylinder jet. If starting is taking too long use the largest jet or in some cases no jet to speed up starting.

Another trick to hasten starting is too turn the engine over for about 2 seconds when cold. Release the key. Wait 3 or 4 seconds and then start it. In many cases the engine will start almost immediately this way reducing the cranking wear on the starter.

kikkegek
Posts: 416
Joined: Thu Nov 17, 2011 2:12 pm
Location: Netherlands, The Hague

Re: check my start assist

Post by kikkegek »

well...got some time to check out the SV start assist.

took it off and with and without power applied, you can suck air through it. so that is why my engine has been running rich as a pig. took it of and closed the port off. also closed the port on the IMPCO425 of.

idle AFR went from 12-13 to a very lean 18-19...and it doesnt seem to respond to the idle mixture screw for some reason.

but then again cruising AFR are very nice...they are about 15 when I an under 3000rpm and low throttle..

medium throttle they drop to about 14 and WOT is 13ish...

just need to fix that very lean idle...and see if I can fix the start assis valve.
storage/project: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.10 gears - IMPCO425 mixer
driver/project: 1977 GMC C15 Suburban - 454 big block - 4L80E- LPG VSI - 3.08 gears
sold: 1986 Chevrolet Suburban K20 Silverado

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

Re: check my start assist

Post by C3H8 »

The number 1 reason for no response from the idle screw is it is frequently on the wrong side of the lever. This happens when the diaphragm is changed and the plate is reinstalled with the idle screw already in place. To check this simply remove the idle screw all the way with the engine off and then reinstall it. When you remove it the spring loaded diaphragm will be pushed to its correct position. At this point the screw automatically ends up in the correct location.

If that is not the problem start looking for small vacuum leaks that could affect the idle but not the cruise or power..

kikkegek
Posts: 416
Joined: Thu Nov 17, 2011 2:12 pm
Location: Netherlands, The Hague

Re: check my start assist

Post by kikkegek »

C3H8 wrote:The number 1 reason for no response from the idle screw is it is frequently on the wrong side of the lever. This happens when the diaphragm is changed and the plate is reinstalled with the idle screw already in place. To check this simply remove the idle screw all the way with the engine off and then reinstall it. When you remove it the spring loaded diaphragm will be pushed to its correct position. At this point the screw automatically ends up in the correct location.
I'll check, but I am always very keen on this when opening this lid. I have the new type of mixer, so I dont think I can take the allen-screw out all the way? can I?
C3H8 wrote: If that is not the problem start looking for small vacuum leaks that could affect the idle but not the cruise or power..
[/quote]

alrighty. thanks. Any ideas what connections would influence idle and not cruise?

and as far as the start assist valve, I have taken it off. cleaned it thouroughly with brakecleaner...then tried loosening it with WD40. But its open powered and unpowered. Any tips? or is it just broken and should I trash it?
storage/project: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.10 gears - IMPCO425 mixer
driver/project: 1977 GMC C15 Suburban - 454 big block - 4L80E- LPG VSI - 3.08 gears
sold: 1986 Chevrolet Suburban K20 Silverado

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

Re: check my start assist

Post by C3H8 »

Trash the SV. Never seen one that was repaired and there not very expensive anyways.

Your correct about the idle screw. I don't think I have seen one removed. My bad for thinking you had an old model on the engine. I just assumed you did based on the picture of the older looking equipment. In this case just be sure the lever is properly in place in the idle casing before installing.

Vacuum leaks: Several considerations. Mixer or throttle body base plate leaks. EGR valve or the plate used to block it off. Incorrect PVC valve (too large). Brake booster diaphragm leak (clamp off the brake booster line to see if mixtures change, not driving anywhere of course). Depending on transmission, a leak in the hose or valve that controls downshifting. Vacuum pot leak on the distributor advance if equipped with that style. Worn out throttle body seals or shafts.

kikkegek
Posts: 416
Joined: Thu Nov 17, 2011 2:12 pm
Location: Netherlands, The Hague

Re: check my start assist

Post by kikkegek »

well, gotta order some 1/8 NPT plugs then. Now I put a bolt in a piece of hobber hose to shut it off. Isnt helping either I guess.

thanks man. I guess the start assist is lost.
storage/project: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.10 gears - IMPCO425 mixer
driver/project: 1977 GMC C15 Suburban - 454 big block - 4L80E- LPG VSI - 3.08 gears
sold: 1986 Chevrolet Suburban K20 Silverado

kikkegek
Posts: 416
Joined: Thu Nov 17, 2011 2:12 pm
Location: Netherlands, The Hague

Re: check my start assist

Post by kikkegek »

and found my vacuum leak:

leaking idle mambrane

Image
storage/project: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.10 gears - IMPCO425 mixer
driver/project: 1977 GMC C15 Suburban - 454 big block - 4L80E- LPG VSI - 3.08 gears
sold: 1986 Chevrolet Suburban K20 Silverado

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

Re: check my start assist

Post by C3H8 »

Nice tear. Nice lime green ignition wires too :D . Replacing the diaphragm and lever should solve a lot of the problems. Congrats on finding it.

kikkegek
Posts: 416
Joined: Thu Nov 17, 2011 2:12 pm
Location: Netherlands, The Hague

Re: check my start assist

Post by kikkegek »

C3H8 wrote:Nice tear. Nice lime green ignition wires too :D . Replacing the diaphragm and lever should solve a lot of the problems. Congrats on finding it.
hehehe, thanks. Yeah, they are "Monster" green, because of the name of out car and green of the engine (VHT kermit Green). And they are only 350ohm/ft for better spark with LPG.

I replaced the membrane last week and AFRs are perfect again and very goed tunable idle now. I am happy to find the start assist problem and torn membrane.

idle AFR is now ..little over 14
cruise AFR around 15 (higher for lower rpm and lower for higher rpm)
and WOT 12-13

very happy with the result.
storage/project: 1974 GMC 25HUNDRED Suburban - fresh rebuild 350 small block - TH350-NP203 - 4.10 gears - IMPCO425 mixer
driver/project: 1977 GMC C15 Suburban - 454 big block - 4L80E- LPG VSI - 3.08 gears
sold: 1986 Chevrolet Suburban K20 Silverado

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