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chinkamon

1500 precrossflow Gt carb flat spot

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Hi all

So when I 'give it some beans' the car hesitates to go yet if I drive gently it's fine and if I have the choke out a bit ( manual) it doesnt do it, thought may be some poop in the jets but wen I pulled it apart to blow thro it, wot I assume is the secondary accelerater jet is actually solid, not blocked, solid?? Is that right??? 

So one pic shows primary and can just about see the little hole in the top 

Other pic shows secondary with the little brass coloured pipe and next to it a solid filled jet?? 

IMG_20181108_161402.jpg

IMG_20181108_161348.jpg

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I'm not 100% sure but don't think they have accelerator pump on second Venturi. You've fitted a carb from a GT which has a higher lift cam bigger valved head and poss different advance curve. You will need to get the carb re- jetted slightly to run properly on your current set up.

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You can buy pump jet nozzles that spray into either the primary or secondary separately, or you can buy one that does both at a time. 

Is that carb a DGV carb? Doesn't look like a proper 1500gt carb (ie DCD 28/36), I'm almost certain it's not a DCD as yours has choke flaps. Where did you get your jetting figures / settings from? 

One thing that does spring to mind - did you put the aux venturi's in correctly and not blocking off the main delivery channel? They can go in the carb in two ways but only work properly one way. You'll see how they're meant to be if you remove them. 

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On 09/11/2018 at 18:18, colr6 said:

I'm not 100% sure but don't think they have accelerator pump on second Venturi. You've fitted a carb from a GT which has a higher lift cam bigger valved head and poss different advance curve. You will need to get the carb re- jetted slightly to run properly on your current set up.

When I open the throttle no fuel seems to go into the second venturi at all that's why I'm slightly puzzled? 

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On 10/11/2018 at 15:57, BeigeAl said:

 

Is that carb a DGV carb? Doesn't look like a proper 1500gt carb (ie DCD 28/36), I'm almost certain it's not a DCD as yours has choke flaps. Where did you get your jetting figures / settings from? 

One thing that does spring to mind - did you put the aux venturi's in correctly and not blocking off the main delivery channel? They can go in the carb in two ways but only work properly one way. You'll see how they're meant to be if you remove them. 

Ummmmm well bought off eBay..... Looks identical to what's in my Haynes book? 

Cars not here so I'll have to take a look tomorrow, the guy sold it as bought bike carbs I think? Looks pretty much new so haven't looked at jet sizes ?

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3 hours ago, chinkamon said:

32 36 dgv if my eyes are working correctly?! 

IMG_20181112_155332.jpg

Mk2 Escort and Capri etc 1600gt carb. 

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Ooh my knowledge of carbs is limited, as you might if guessed ? 

So apart from leaving the choke out a touch or driving gently 

What can I do to stop the flat spot 

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Check the jet and choke sizes for a proper 28/36 dcd and compare with what you have and you may be able to do some jet adjustments yourself

You will find the jet sizes for the original GT carb in a manual.

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I remembered now. I couldnt find a gt carb for sensible money an Burtons tuning guides said the gt carb from a crossflow works too

Thats why I bought it

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Thanks col, both my books are down the workshop so I can look from the warmth and comfort of my house instead Of going back out tonight now thank you! ?

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Looking at that, it says, 

Delivery pressure gt and lotus 

Other engines, 

Do I need a different mechanical fuel pump? 

It's only the carb and exhaust manifold changed, the cams still stock 1500 and heads not been touched? 

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That's good then! As I say it goes really well, very different old girl to what she was before, I'm guessing then if I jet it similar to the proper gt carb all should be well? As I suppose the prev owner could've had any jets in it couldn't they? 

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Check the choke sizes, if I remember correctly they have the size printed on them. If they are the same size as dcd carb then changing the jets to the correct sizes should help it. If the choke sizes are different then I'm afraid you'll need to take it to someone to set up correctly.

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