Carb not drawing in air

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Tomc1958
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Carb not drawing in air

Post by Tomc1958 »

Briefly, engine rebuilt, new Solex/Brosol twin carbs, mechanic says offside one isn’t drawing air in from the top. Is it a carb fault or something else please? I’m a complete novice. Carb supplier is mystified how it can be but I’ve yet to send them back. Now looking into a different setup.

Many thanks in advance.
Tom 👍👍

davidoft1
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Re: Carb not drawing in air

Post by davidoft1 »

Check the valve settings first, the carb isn’t whats draws the air , the pistons draw the air the carb is just a valve to meter that air , what’s carbs , what engine? What was done to the engine , what’s the fault exactly?

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Re: Carb not drawing in air

Post by ajsimmo »

No follow up to this thread from OP, but 2 days later the carbs are in the bin and a cruddy Weber has been put on instead? Is that right?
I too am mystified how your mechanic claims no air is being drawn through one carb, and blames the carb!?

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Stesaw
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Re: Carb not drawing in air

Post by Stesaw »

How would a carb not draw in air if its been put on the engine correctly? 
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Rosie n' Jim
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Re: Carb not drawing in air

Post by Rosie n' Jim »

As already stated, the carb doesn't draw air, the pistons and valves act as a pump suckling air. The carb is basically a tube with a flap in it. Either the engine isn't pulling air through the carb, or the flap (throttle butterfly) is not open. Either way, it'll at best run on two cylinders, except maybe on idle when the idle circuit supplies the air.
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Re: Carb not drawing in air

Post by Stesaw »

Rosie n' Jim wrote: 06 Dec 2020, 19:10 As already stated, the carb doesn't draw air, the pistons and valves act as a pump suckling air. The carb is basically a tube with a flap in it. Either the engine isn't pulling air through the carb, or the flap (throttle butterfly) is not open. Either way, it'll at best run on two cylinders, except maybe on idle when the idle circuit supplies the air.

I wonder if there are pistons in that side of the engine!  :rofl
 
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Re: Carb not drawing in air

Post by Rosie n' Jim »

Rather a drastic weight saving measure! 
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sarran1955
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Re: Carb not drawing in air

Post by sarran1955 »

Hello,

So let's guess that it is a CU engine.. just rebuilt...
Have we done a compression test.. :?:

and how many times did your 'mechanic' set the tappets.. :roll:

Probably no compression on 1 side...slack off to contact + 1/2 turn, start, live with the clatter for 20 mins. Reset tappets 1 1/" turns..

I suspect that the carb will miraculously 'come to life'..with compression on all 4 cylinders this time.. :wink:

Cordialement,

:ok
 
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Tomc1958
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Re: Carb not drawing in air

Post by Tomc1958 »

Hi, sorry for not getting back to anyone regarding this.  As said I'm a complete novice and asking advice.  I couldn't find the replies.  I was told the carb wasn't pulling air in and shown...put my hand over the near side and there was suction and none over the offside.  So is it looking like an engine fault?  The engine was completely stripped down and rebuilt with new pistons, bores,  camshaft and I was told the compression is good.  It's a 2.00 CU engine.  Two separate mechs....one did the rebuild and now it's with another setting up the LPG.  It's the LPG guy who said there was no suction and it wasn't drawing the LPG in.   It was running fine after the rebuild on petrol, surely if no compression on one side of the engine it would be rough as anything??   Thanks everyone for your comments and thanks for not chucking names at me for not responding, having a bad enough time at the moment with Covid going around, isolating and a very close friend dying from cancer.  Not angling for sympathy just having a crap time and seriously peed off with the van.

Also....since posting the original post the mechanic tried the old offside carb back on and told me that was drawing the lpg and air in.
Last edited by Tomc1958 on 10 Dec 2020, 16:59, edited 6 times in total.

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tobydog
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Re: Carb not drawing in air

Post by tobydog »

Have you checked whether the carb (butterfly) is opening when accelerator is pressed?
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Tomc1958
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Re: Carb not drawing in air

Post by Tomc1958 »

tobydog wrote: 10 Dec 2020, 14:40 Have you checked whether the carb (butterfly) is opening when accelerator is pressed?

Thank you.    Not knowing much about these things that's a conclusion Im reaching, I'm wondering if it was snagging on something?.  Just added to my latest comment that the mechanic put the old original carb back on and tried it with that and told me that air was being drawn down...that would indicate it is the carb and butterfly and not the engine??

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Re: Carb not drawing in air

Post by Stesaw »

If the original carb is a single carb it will draw air though because the one side of the engine still was pulling air in, whereas the other side with the "duff" carb wasnt. I'd do as Saran says and slacken off the tappet screws on the side that has no air being drawn in. To my understanding he knows air cooled engines more than most on here.

Or as toby said make sure the butterfly on the carb moves freely. If that's stuck closed then that could be a problem. 

If you can get a video of it running on the old carb, people will be able to tell you right away if it's running on all 4.

This sounds daft but there isn't any kind of plastic film or cover over the head ports, manifolds or carb that has been left on by accident?

 
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Tomc1958
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Re: Carb not drawing in air

Post by Tomc1958 »

Stesaw wrote: 10 Dec 2020, 15:17 If the original carb is a single carb it will draw air though because the one side of the engine still was pulling air in, whereas the other side with the "duff" carb wasnt. I'd do as Saran says and slacken off the tappet screws on the side that has no air being drawn in. To my understanding he knows air cooled engines more than most on here.

Or as toby said make sure the butterfly on the carb moves freely. If that's stuck closed then that could be a problem. 

If you can get a video of it running on the old carb, people will be able to tell you right away if it's running on all 4.

This sounds daft but there isn't any kind of plastic film or cover over the head ports, manifolds or carb that has been left on by accident?



Hi and thanks.   The original set up was twin Solex and I had them replaced with twin Solex   All seemed to be running fine but when lpg was being setup turned out no air was going down the offside carb so not pulling in the LPG. Mech put the original offside carb back on and said that drew air down. So it suggests the butterfly was shut on new one?  I was driving the van for months on petrol on the new Solexes with no problems.  Would this be possible if no compression on one side of the engine?   I've got the new Solexes here with me and checked for any plastic but no blockages and everything moves freely.  Mech has the van looking at a different carb setup so it's not possible to do a video. I've a video of it running on the new Solexes on petrol but no idea how to add it here.  Thanks

Stesaw
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Re: Carb not drawing in air

Post by Stesaw »

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.
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Re: Carb not drawing in air

Post by lefty67 »

I would recommend you watch these videos made by sarran 1955 (posted earlier on). Will help you learn about your van, I was in the same boat as you when I got my first t3 and found his vids invaluable when I had my air cooled van.
It's all a big learning curve but you'll get there in the end :ok
https://youtu.be/najLc9GlLJ0
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