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I'm having trouble getting a decent AFR. Currently it'll idle at a reported 18/19:1 AFR and will cruise around 16/17:1 with the power adjustment all the way anticlockwise (I'm told that's open / more fuel) if I floor it I get a misfire and the AFR never reports lower than 15. I did a similar test on petrol and the AFR hit around 9 (I'm on open loop) and it felt WAY more powerful.
I wondered if I was having a vacuum leak issue, but I figured my petrol test would have similar results with a vacuum leak. Am I missing something here, can someone point me in direction I should be looking?
Thanks
You could have an air leak between the mixer and the throttle body. Check the gaskets and sealing surfaces of the mixer and adaptors. A leak before the throttle body will not affect the gasoline operation. Next, check the idle diaphragm on the side of the 425. Make sure you back the idle screw all the way out when removing and installing the plate. It sounds like you could have a diaphragm leak or the idle screw is on the wrong side of the lever under the plate. You can check this by just removing the idle screw and then reinstalling it. Also check the lever height in the model L. It may be set wrong.
Thanks for your reply. I managed to tighten the screws between the adapter and the mixer slightly, this seemed to aid a slightly more stable AFR. Although still not what I'd be expecting. I've got to do some more testing, but I don't "live with" my van, it's stored at my folks place, so only get to go there once a week or so.
With regard to the mixer screws, my mixer screws appear somewhat different to others online. I appear to have covers over the screws? Worried if I unscrew it all the way I'll lose the screw behind the cover. Please ignore the huge gaps etc, this is just an old picture from when I was initially setting it up...
As for the lever height in the model L, how do I know what's correct? I've seen a tear down, so know what to expect mostly inside.
Thanks for your help dude, really appreciate you taking the time as it's tough finding LPG advice online these days. You are awesome!
At this time let's presume your lever height is correct since the engine runs. The picture helped as I can answer some of your questions.
1. I noted a large gap between the original carb spacer and the adaptor. I have to assume you are aware of this and it is only there because you are working on the system. If not, you must get the mounting correctly placed so the adaptors are properly sealed.
2. The carburetor you have is what is called tamper resistant. After the kit was installed and the mixer fuel air ratios set the dealer placed an aluminum plug inside the adjuster screw bore and seated it in place by gently tamping it down with a hammer. This prevented inexperienced people from playing with the mixtures. At some time, mixer adjustments became necessary, the plug was drilled through to allow adjustments. Just drilling the plug still restrict the adjustment stroke. At this point you can pry the plug out allowing you to richen the idle and full power an additional amount. The screws are adjusted using an Allen key. The power adjuster, the bigger one, cannot be adjusted out beyond a certain point. It will stop at the maximum unless adjusted forcefully. The idle screw can be completely removed for inspection and to ensure proper alignment in regard to the idle control lever. Removing it completely or most of the way will ensure its placement is correct as the lever naturally assumes the correct position and then you can adjust it in. Note: On tamper resistant mixers adjusting the power and idle screws takes more effort since the screws have a nylon locking system making them harder to turn then older models.
3. One important point missed by many dealers. In your picture you show the factory spacer with a hose coming off it. That hose is for the fresh air intake of the PCV (positive crankcase valve). On gasoline it draws clean air from in front of the throttle body. The air travels through the crankcase allowing the PCV to draw oil fumes into the carburetor base and burn them off. When converted to LPG this hose should be removed from the spacer and relocated ahead of the mixer if possible or if not possible place a small filter in the hose. Older carbureted engines have the filter required as a separate item. It was located inside the carbureted engine air filter canister and held in place with a C clip. The spacer should be plugged off. You can use a piece of hose and a plug. Failing to do this draws an uncontrolled fuel air mixture through the crankcase disrupting the ratio. In addition, it is possible for the fumes to be drawn up the shaft that drives the distributor and for them to ignite in the distributor cap, blowing it apart.
Thank you so much, given me plenty to look at! I'll pull the tamper covers off and double check the idle screw etc.
Point no3.... Holy shit I can't believe I missed that. I will plug it immediately and get a filter on the crank case. That could well be the solution to the issues I've been having, or at least help. Can't believe this hasn't caused me any other issues at all!!
I will report back as soon as I'm able to get up there and get it sorted.
After plugging both the PCV breathers from the TB and just free revving the engine to check everything was good, there was a loud POP and this is what I ended up with :
The gasket between the TB and the factory spacer decided to exit the building... or engine. I have no idea why this would have happened? Could anyone shed any light on it? I've never had any issues with backfiring before.
