38 dgas/dgms carburetor issue

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Mr B
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38 dgas/dgms carburetor issue

Postby Mr B » Sat Nov 11, 2017 8:55 pm

Hi all,

I have a 1980 3 litre ghia and have a Weber 38 dgms (manual choke) feeding the fire, only problem is to get a smooth idle the mixture screws need to be almost 7 turns out, bought the carb brand new from Burton power around 3 year's ago, and it's always been the same, according to literature the most they should be is 1 and a half to 2 turns out, checked the idle jet's against an original carb and they match (45''s) also checked for vacuum leaks and none can be found

Any ideas guy's?

Wayne

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Re: 38 dgas/dgms carburetor issue

Postby Peter-S » Sat Nov 11, 2017 10:47 pm

Define a full turn. If the screw slot is level and you turn it anti clockwise until it is level again that will be half a turn so it will be round once more for a full turn. Apologies if you already realise that but it might mean you are only turning the screw around three turns out, which is about what I've always done with the 38 on my 2.0.
If it's running well and mixture is OK for the MOT tester than may be no need to worry.
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Re: 38 dgas/dgms carburetor issue

Postby Mr B » Sat Nov 11, 2017 11:12 pm

Hi Peter, thanks for replying mate, yep nearly 7 whole turns, I use a screw driver with writing on one side of the handle, half a turn writing on bottom full turn writing back up on top if that makes sense, other Weber carbs I've had have never got anywhere near 7 turns out for a smooth idle, totally standard engine only mod is a K & N air cleaner, when I took her for MOT they didn't put her on an emissions test apparently she is too old and doesn't require it

Wayne

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Re: 38 dgas/dgms carburetor issue

Postby Peter-S » Wed Nov 15, 2017 6:57 pm

Just a thought, you haven't got more than one spacer plate between the carb and manifold have you?
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Re: 38 dgas/dgms carburetor issue

Postby Mr B » Wed Nov 15, 2017 8:46 pm

Hi mate,

just the standard spacer with the pipe connection that goes to the pcv valve on the rocker cover

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Re: 38 dgas/dgms carburetor issue

Postby Peter-S » Sun Nov 19, 2017 5:47 pm

As you may see elsewhere I've just put a new 38 on my 2.0 as the old one was no longer running well. With your settings in mind I would out the mixture screws 3 full turns and left it to warm up. Seemed to be running reasonably well but I put my Gunson tester on it and it was way too rich. Had to back off by about 1 1/2 turns. I know yours is on a 3.0 but I'm a bit perplexed. Be interesting to know what your emissions are.
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Re: 38 dgas/dgms carburetor issue

Postby nickm » Mon Nov 20, 2017 8:47 pm

Might be worth trying some 50 or 55 idle jets.
One of the DGMS idle jets is different to the DGAS.
Nick

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Re: 38 dgas/dgms carburetor issue

Postby Mr B » Mon Nov 20, 2017 10:31 pm

Hi Nick,

Funny you should say about the jet's being different, comparing this carb to an original dgas and it seems that the screws to remove the idle jet's are different, the near side screw matches the original dgas but the screw on the off side is much larger and the jet itself is physically bigger than it's counterpart on the opposite side although both jet's are 45's, I just thought it was a design revision made by Weber, do you think this could be part of the puzzle?

Wayne

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Re: 38 dgas/dgms carburetor issue

Postby Peter-S » Mon Nov 20, 2017 11:30 pm

Mr B wrote:Hi Nick,

Funny you should say about the jet's being different, comparing this carb to an original dgas and it seems that the screws to remove the idle jet's are different, the near side screw matches the original dgas but the screw on the off side is much larger and the jet itself is physically bigger than it's counterpart on the opposite side although both jet's are 45's, I just thought it was a design revision made by Weber, do you think this could be part of the puzzle?

Wayne


The screws and jets are different on my new dgas as well but both marked as 45s
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Re: 38 dgas/dgms carburetor issue

Postby Mr B » Thu Nov 23, 2017 4:57 pm

Just checked Ebay and there is a listing for the bigger jet, the listing does say some dgas/dgms carbs had a bigger jet fitted well physically bigger but still a size 45 but doesn't explain why.....

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Re: 38 dgas/dgms carburetor issue

Postby nickm » Fri Nov 24, 2017 1:28 pm

I don't understand it either.
I only realised when I rejetted my DGMS.
Are the jets definitely size 45 because when I took the jets out of my new
carb the idles were 50s and mains were 135s?
The carb was supposed to have 142 mains and 45 idles.

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Re: 38 dgas/dgms carburetor issue

Postby Clockwork Orange » Mon Nov 27, 2017 9:41 am

nickm wrote:I don't understand it either.
I only realised when I rejetted my DGMS.
Are the jets definitely size 45 because when I took the jets out of my new
carb the idles were 50s and mains were 135s?
The carb was supposed to have 142 mains and 45 idles.

would be better checking all the jets, the emulsion tubes and the air correctors ..
idle jets 45, main jets 142 (145 up to 1976) air correctors 185, tubes F50.

your original DGAS will (should) have been set-up properly, so investigate that, then if the parts are different then order correct sizes for your new carb .. I suggest a known weber dealer, not just any eBay gamble ..
http://www.fastroadcars.co.uk/store/index.php
http://www.webcon.co.uk/

hope that is of help to you

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Re: 38 dgas/dgms carburetor issue

Postby Not_Anumber » Thu Nov 30, 2017 2:33 pm

I had a 38/38 with different physically sized jets on a kit car i had a couple of years ago. I asked around and apparently some of them were like that whilst others had the jets the same physical size.
I never quite got to the bottom of why that was but the jets all seem to be available in the bigger size so it doesn't restrict choice when rejetting.

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Re: 38 dgas/dgms carburetor issue

Postby Mr B » Thu Nov 30, 2017 11:11 pm

Does seem strange that considering the jet's on both carbs old and new are the same size and yet the mixture screws on the new type of dgas need to almost be fully wound out to get a decent idle yet 1 - 2 turns out was/is adequate on the original dgas


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