Carb not drawing in air

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Tomc1958
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Re: Carb not drawing in air

Post by Tomc1958 »

Stesaw wrote: 10 Dec 2020, 18:55 If you had no compression on that side you'd hear the difference when starting the engine. The Starter motor would alternate between spining faster and slower as the engine turns over.

Sorry remind me, did these new carbs run fine on petrol? Because to me if the van was running fine on petrol on those carbs then they shouldn't be the issue. Sorta points to something up with the LPG system.. but I know nothing about those things.



Hi, yep ran fine on petrol, I was driving it since May until a couple of weeks ago going up and down hills without even dropping down a gear or two. The LPG goes in just under the air filter and gets sucked in with the air, no suction therefore it wouldn't run properly.  I wish my knowledge was greater because I don't like not understanding things like this. It's a mystery 

Tomc1958
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Re: Carb not drawing in air

Post by Tomc1958 »

I was easily hitting 50 mph as well so I reckon the compression must be ok
 

Stesaw
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Re: Carb not drawing in air

Post by Stesaw »

Maybe check for vaccum leaks on that side of the engine? But I would say there is something not right with the LPG setup as they ran on petrol, but again I'd be out of ideas at that point as I know nothing about LPG systems.
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Tomc1958
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Re: Carb not drawing in air

Post by Tomc1958 »

Really appreciating everyone's help on this folks.  Made a contribution to the fund raising for the forum, wish I could afford more but my pension isn't great 

Tomc1958
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Re: Carb not drawing in air

Post by Tomc1958 »

Stesaw wrote: 10 Dec 2020, 19:16 Maybe check for vaccum leaks on that side of the engine? But I would say there is something not right with the LPG setup as they ran on petrol, but again I'd be out of ideas at that point as I know nothing about LPG systems.

Thanks for your help, it's definitely not the LPG though because there really was no suction down through the carb, put my palms over both carbs with the filters off and the LPG wasn't connected. Plenty of suction on the near side and nothing on the offside.  Hopefully I'll find out more tomorrow. I'm trying to find out as much as possible before I send the carbs back...I don't want to be told they're fine and end up paying courier charges for nothing.  Certainly on petrol it ran well, good speeds, acceleration up hills in 4th which I used to have to drop down to 2nd before the engine was rebuilt. The mechanic told me the compression was good on all cylinders. I can only guess the bottom butterfly was either stuck shut (but I've got the carb here and it moves freely) or air is being drawn in from somewhere other than the top.

Rosie n' Jim
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Re: Carb not drawing in air

Post by Rosie n' Jim »

At what revs are you seeing/feeling no air draw? At idle very little air passes through the car body, rather it is supplied direct to the manifold from the idle circuit. If the carbs are not accurately set up, one might be slightly open whilst the other is closed. But it'll still run, and off idle, run very well.
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ajsimmo
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Re: Carb not drawing in air

Post by ajsimmo »

Rosie n' Jim wrote:At what revs are you seeing/feeling no air draw? At idle very little air passes through the car body, rather it is supplied direct to the manifold from the idle circuit. If the carbs are not accurately set up, one might be slightly open whilst the other is closed. But it'll still run, and off idle, run very well.
Yes, another way of explaining what I have said above. Many people mistakenly have too much draw on the main carbs at idle, and not enough through the idle circuit, and these are often left unbalanced, as I suspect in this case. The throttle stop screws should not quite touch at idle, as this would hold the butterfly open and increase airflow too much. The base setting is preset to allow a tiny airflow, and the fuel at idle is adjusted via the mixture screw on the lower outside body. The idle is then adjusted via the air and fuel screws on the third carb.
However, with the (Gasure) LPG set up as it is it's difficult to get the right mixture at idle as there's no individual adjustment per side on gas. It can be modified to take gas/air mixture from below the LHS mixer and feed it into the idle circuit via the idle air intake (currently connected to the airbox by the small bore L shaped hose).
Is there any way you could get the vehicle to someone else with the required knowledge for a second opinion? It might save you a lot of time, money and grief in the long run.

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Tomc1958
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Re: Carb not drawing in air

Post by Tomc1958 »

Hi Guys, thanks all for your knowledge, helpful suggestions and feedback.....I'm learning.  I'm going to be getting the van back next week.  It runs on petrol so is useable and I've got it booked for bodywork repairs early in the new year and want to see how it is driving around for a while and will look at the LPG later if it doesn't work.  I may end up with more than one set of working carbs which whilst has cost me money I can recoup some of it.  I'll post again when I know more.  Thanks all very much for the help, hugely appreciated  
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Rosie n' Jim
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Re: Carb not drawing in air

Post by Rosie n' Jim »

As an aside, who are you using for your LPG conversion? My Danbury has what looks like a diy install that I'd like recommissioned. Sadly Campershack has moved too far away. What area of East Anglia are you from?
1982 Holdsworth poptop. 2L CU Aircooled.
1982 Danbury tintop Caravelle. 2L CU Aircooled.

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