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Thread: Carb choice for xflow

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    Racer mexicotait's Avatar

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    Carb choice for xflow

    Hello folks
    i have a 1640 xflow in my mk2

    has as a standard gt head 234 cam 1300 pistons

    currently runs on a single 40 dellorto

    it runs well but wondering would I gain anything by going up to 45?

    At at the moment it feels a bit restricted in the midrange it didn't before I rebored and rebuilt it
    Im guessing it needs to be retuned on the rolling road so before I do I was wondering if it's worth trying a 45

    Also is it worth having the head ported

    I can run twin 40s for some events but on road rally's I need to use a single carb

    so any gains to be had?
    Last edited by mexicotait; 01-10-2017 at 19:57.
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    Re: Carb choice for xflow

    Anyone
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    Re: Carb choice for xflow

    what choke sizes in your 40?

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    Re: Carb choice for xflow

    They measure 39mm across the front

    Can't get them out to check
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    Carb choice for xflow

    Quote Originally Posted by mexicotait View Post
    They measure 39mm across the front

    Can't get them out to check




    Got them out eventually



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    Carb choice for xflow

    Look inside on the curved lead in. Should give a size.


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    Re: Carb choice for xflow

    Quote Originally Posted by mexicotait View Post




    Got them out eventually



    Sent from my iPhone using Tapatalk
    Are they not aux venturis, they don't look like chokes?

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    Re: Carb choice for xflow

    They are indeed, chokes fit in the ends of the aux venturis, the size will be stamped on the inside of the choke, or measure the parallel ID.

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    Re: Carb choice for xflow

    I took the trumpets off then undid the grub screw and pulled that out
    Thought they were the chokes
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    Re: Carb choice for xflow

    Should be two grub screws the inner one holds the choke.

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    Re: Carb choice for xflow

    Quote Originally Posted by Graham View Post
    what choke sizes in your 40?

    33 chokes graham
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    Re: Carb choice for xflow

    ok thats as big as its worth going regarding choke in the current carb, so IF it wants more in the way of carb then yes 45 is next, BUT i would of thought the head is the most restrictive part of the package

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    Re: Carb choice for xflow

    I have a ported gt head to swap on soon
    Will the 40 match to this or should I go up to a 45

    Really looking for as much low down torque as possible is there anything to lose from going to a 45
    Rallying is dirty and you love it !!!!!!

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    Re: Carb choice for xflow

    Really looking for as much low down torque as possible is there anything to lose from going to a 45
    yeah low down torque and flexablity

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    Re: Carb choice for xflow

    Really looking for as much low down torque as possible is there anything to lose from going to a 45
    yeah low down torque and flexablity

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    Re: Carb choice for xflow

    So stick with the 40 and change the head
    Cheers
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    Re: Carb choice for xflow

    get it properly jetted, a good place should bring it back to singing again.

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    Re: Carb choice for xflow

    As you say I think a setup will sort it out but I want to do any mods before taking it to rr
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    Re: Carb choice for xflow

    the head on any engine but especially on an xlfow, is always the biggest retriction on power potential. The fuel is not a problem, you can dump as much of that in as you want.. the ultimate limit comes from the flow capability of the head, if the cylinder head can't flow that air then the cylinders can't fill. Total inlet valve area and the heads ability to flow around it is the limit of any engines potential. on an xlfow this is more aparent using a big enough carb on a puny head. Ive been there!
    a proper head will trasform an engine often surprisingly so to many owners as its often overlooked. invest in a really good head and i think you'll be much better off.
    I've never ran an xlfow on a single 40, but arent these setups notorious for dead mid-range thats very hard to tune out?

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    Re: Carb choice for xflow

    yes but I had it setup before the rebuild and it was spot on
    I seem to have lost that now

    Still gives good power but mostly at the top end although quick is harder to drive
    Rallying is dirty and you love it !!!!!!

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    Racer mexicotait's Avatar

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    Re: Carb choice for xflow

    yes but I had it setup before the rebuild and it was spot on
    I seem to have lost that now

    Still gives good power but mostly at the top end although quick is harder to drive
    Rallying is dirty and you love it !!!!!!

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    Re: Carb choice for xflow

    Just got to find a head now
    Any for sale or anyone recommend someone to do the head

    Graham?
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    Re: Carb choice for xflow

    Like any second hand head be very careful, Big valve X flow heads are notorious for cracking valve seats as there's very little material between the inlet and exhaust. Then there's a chance it could be porous.

    They do pop up occasionally on the bay of flees for sale. I see quite a few Pinto heads on there, damaged repaired and over priced.

    Vulcan did a good X flow head back in the day. You can expect to pay strong money for someone to modify your own head as there's a lot of labour involved to get it to a high standard.

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    Racer mexicotait's Avatar

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    Re: Carb choice for xflow

    I have a ported gt head that has been repaired in the past
    Needs new valve guides putting in and new valves

    Been quoted by throbnozzle racing for 250 quid to port my standard head

    Not sure which way to go
    Rallying is dirty and you love it !!!!!!

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    Re: Carb choice for xflow

    Quote Originally Posted by mexicotait View Post
    Just got to find a head now
    Any for sale or anyone recommend someone to do the head

    Graham?
    sadly i just sold a bloody good x/flow head, it flowed 99Cfm, which is about 50% up on std, although being big valve it wasnt unleaded and the risk of cracking is high because theres so little material between the ports unless you start buggering around with off set guides.

    TBH, im not interesting in doing a mad full race head, simply because it takes forever so i either loose a fortune or it becomes so dear no one wants to pay the price. but i could do something less extreme

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    Racer mexicotait's Avatar

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    Re: Carb choice for xflow

    Sent you a pm graham
    Rallying is dirty and you love it !!!!!!

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