Author Topic: Flooding Weber 30DGF3 but float and level OK  (Read 3762 times)

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elanman99

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Flooding Weber 30DGF3 but float and level OK
« on: April 21, 2018, 07:23:34 PM »
I bought an unfinished 126 Bis and having problems getting the engine to start and then when it does getting it to run consistently.

Once the engine has fired and run for a few seconds I can see petrol pouring into the choke tube and sitting on the butterfly. (the number two choke tube). There is no leak in the float so I thought the float height/fuel level might be too high but it appears to be close to the recommended 6mm. In an attempt to locate the cause I adjusted the float to about 10mm so lowering the fuel level significantly but fuel still floods into the choke tube.

I could not get the engine to run last year but I have since completely stripped and rebuilt the carburettor. I did not find anything that looked to be faulty or worn out so I am baffled as to what the problem is.

This topic has come up quite a bit on the forum but I could not find an answer to this.

Ian
Located in Sunny Sandiway

Bar Vitelli

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Re: Flooding Weber 30DGF3 but float and level OK
« Reply #1 on: April 21, 2018, 10:13:33 PM »
There is one for sale on eBay at the moment should you need to replace the part or use it to prove that the carburettor is not the problem and that the root cause is elsewhere.

https://www.ebay.co.uk/itm/Fiat-126-Bis-WEBER-30-DGF-Carburettor/323219411473?hash=item4b4160d211:g:~8UAAOSw9sZa23Ec
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Amateb8

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Re: Flooding Weber 30DGF3 but float and level OK
« Reply #2 on: April 22, 2018, 12:03:58 AM »
Ciaoflyer is actually a member here!!! He used to have a 126 Bis for some years. He sold it, and bought a 2CV.

Rusty's Uncle

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Re: Flooding Weber 30DGF3 but float and level OK
« Reply #3 on: April 22, 2018, 06:11:44 AM »
I might be inclined to reexamine the float. As I discovered the hairline cracks they can suffer from can be almost invisible.

elanman99

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Re: Flooding Weber 30DGF3 but float and level OK
« Reply #4 on: April 22, 2018, 04:43:48 PM »
Thanks for the replies but so far have not had any success.

The float is intact, definitely no leaks and I tested it by actually floating it. The needle valve too seems to shut off when the float is lifted. I can start the engine but it only runs for 20 to 30 seconds and never really gets running sweetly. I still see petrol pouring into the second choke after the engine has run, presumably its (excess) fuel coming from the float chamber.

I cannot find a replacement needle valve for the DGF (unless I buy a service kit) but this one for a DGV Weber is marked '150' and looks identical to the one in my carb.

http://www.burtonpower.com/needle-valve-weber-dgv-dgas-150-webjetn2-150.htm

Does anyone know if this one will work?

Ian
Located in Sunny Sandiway

elanman99

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Re: Flooding Weber 30DGF3 but float and level OK
« Reply #5 on: April 28, 2018, 07:17:55 PM »
Lack of time has prevented me doing any more investigating of the carb flooding but an idea has come to me that might be relevant to the problem.

The seller of the car had fitted a new fuel tank, fuel pump and all the fuel piping, before I bought it and it occurred to me that maybe the pump is too high a pressure. If the pressure was too high it would definitely overcome the needle valve

Are there different versions of pumps that fit the Bis?

Ian
Located in Sunny Sandiway

Amateb8

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Re: Flooding Weber 30DGF3 but float and level OK
« Reply #6 on: June 05, 2018, 09:08:27 PM »
Did you manage to fix it?

elanman99

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Re: Flooding Weber 30DGF3 but float and level OK
« Reply #7 on: June 05, 2018, 10:15:35 PM »
Not fixed as such but I can get it to run.

I reduced the fuel pressure by packing up the pump and it no longer seems to drip petrol into the manifold. If I pump the accelerator a few times and then start the engine it dies after a few seconds. It will do that consistently but I found that I could get the engine to run continuously by using my hand as a choke over the carb inlets.

I cant get it to run just by using the choke as I think it still lets in too much air (compared to my hand).

I suppose I now know for certain that the problem is carb/fuel related but I am reluctant to by a new carb as I have very carefully checked every bit of this one and can see no reason why it is faulty....

Ian
Located in Sunny Sandiway

michaelodonnell500

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Re: Flooding Weber 30DGF3 but float and level OK
« Reply #8 on: June 06, 2018, 10:32:52 AM »

The seller of the car had fitted a new fuel tank, fuel pump and all the fuel piping, before I bought it and it occurred to me that maybe the pump is too high a pressure.

Trying to second guess the thought process of a previous seller might lead you down the wrong path. The previous seller may have replaced the tank and pump to try and cure the poor running issue.

I'm not aware of the pumps having different fuel pressures. I have changed a number of fuel pumps on my aircooled and there has been no difference in specification.

If you're initial problems are caused by over-fuelling, altering the pump position will reduce the amount of fuel, but it won't alter the ratio which is why it's failing in a different manner now.

I am inclined to agree with Rusty about the float from what you've said. I've recently discovered 2 carbs that have had a float failure, I had stripped both of them several times and didn't discover the issue at the start:

http://club126uk.co.uk/forum/index.php?topic=11245.0

I had poor running at mid -high revs.
excess fuel leaking onto the manifold, especially as soon as the engine was switched off

have you tried submerging the float in a closed jar of petrol? Pack something on top so it's entirely submerged and leave it over night.
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elanman99

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Re: Flooding Weber 30DGF3 but float and level OK
« Reply #9 on: June 06, 2018, 11:18:11 AM »
I wasnt trying to second guess really. The seller bought the car as part restored and got a local mechanic to finish it off but sold it to me before he put it on the road. The old tank was apparently rusted through and the fuel lines perished so he just replaced everything (unfortunately not the carb!).

The float seems airtight, I have tested it in water, also if I take it out of the float chamber immediately after the engine has been running there is no petrol inside that I can hear by shaking it. Following your suggestions I will test it again in petrol though.

On the watercooled 126 Bis the manual details the procedure to set the fuel pressure by putting shims under the pump to alter the effective throw of the eccentric/push rod.

Ian
 
Located in Sunny Sandiway

michaelodonnell500

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Re: Flooding Weber 30DGF3 but float and level OK
« Reply #10 on: June 06, 2018, 03:03:53 PM »
Hi Ian,
I wasn't aware of the fuel pump shim on the bis.

I'm not sure how you could measure the output pressure on the pump to ensure it is correct, but you could apply pressurised fuel to the carb with an eeziblead kit. That way you could tweak the fuel pressure to find out what works. I'm surprised the 30DGF3 is that dependant on correct fuel pressure, but I've never worked with one, maybe another bis owner knows better.
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elanman99

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Re: Flooding Weber 30DGF3 but float and level OK
« Reply #11 on: June 06, 2018, 03:28:30 PM »
I put a (low) pressure gauge in the fuel line. Hard bit was checking pressure at 4000rpm.

Ian
Located in Sunny Sandiway