Single dcoe 45 intial jetting please.

Discussion in 'Carburettor' started by Pete17, Mar 30, 2019.

  1. Pete17 New Member

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    Hello,

    Looking for help please,
    I have a mk2 rocco ( originally 1.8 8v ), now 2.0 3a bottom end with lightweight flywheel and big valve tsr head and 203 cam.
    I have put a single 45 carb and mani on. I have exhaust all wrapped and heatshield,d up for carb.

    The carb was running on a modified 1.9 8v engine of similar spec so figured jetting should be close.

    I have got it started and idling nice n smooth. But when i drive it i can only give it light throttle, basically just staying on the idle circuit. Engine just bogs down or pops n spits if i try and give it more.
    Fuel pressure is set at 3 psi

    I got some of the jet sizes for your opinions,
    Chokes 34
    Aux vent 3.5
    Air corrector jets 180
    Main jets 165
    Emulsion tubes f16
    Idle jets 55 f8
    Pump jets 55

    Hopefully someone can shed some light on my problem
    The carbs were all stripped n cleaned prior to fitting.
    Thanks in advance guys...
     
  2. Jon Olds Forum Junkie

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    Popping spitting is usually weak idle setting, Not having any real experience of single carb setups cant help further.
    Dash mounted AFR gauge essential though..
    Jon
     
  3. Pete17 New Member

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    Hi Jon,
    I have been to doing some reading on weber carbs so also figured i must be running lean.
    I have an assortment of weber parts so i put in some 60 f9 idle jets which made it only slightly better.

    Can you reccomend any afr gauge setups?

    I'm coming from bike carbs which were very simple to setup just a pita to adjust with the bowls underneath.
    Thanks

    Pete
     
  4. Jon Olds Forum Junkie

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    What I use (and love) is probably the cheapest non Chinese one on the market. AFR4 or AFR3 (Lumenition) Work fine
    Have one on each of my race / rally cars.
    Narrowband, but seems to work fine
    The Weber tuning book (from Weber themselves) is ACE
    Jon
    One of my racers (twin 45's) runs 55F9 idles but they are on full race cams, so inefficient at idle
     
  5. Jon Olds Forum Junkie

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    I would go up on choke size, as an aside
    Jon
     
  6. Pete17 New Member

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    Hmm this has got me thinking. I like the idea of afr gauge, so know im not getti g close to melting pistons haha. Suppose i would need to weld a boss on my downpipe somewhere...
    I was kind of hoping that the single weber would run ok on what jetting it had, but as its not i went and dug out my twin 40 webers out. They were going on my mk1 golf but screw it...
    Surely i will get better gains with the twin 40s?
    And if I'm going to have to adjust the jetting i may as well do these and ppl have more experience with twins over the single i suppose.

    Here is the jetting they have.
    50 f9 idles
    140 mains
    F16 emulsions
    185 air corrector jets
    45 pumps
    4.5 aux
    34mm chokes

    Hopefully get them on by the end of week and see how they go and report back.
     
  7. Pete17 New Member

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    Just a quick update,
    Fitted the twin 40s. Gave them a good going over and adjusted float levels.
    I had a problem initially where the fuel was pissing out of the overflow/ hole above trumpets... this was due to me accidentally bending the float and making it squint in the chamber so it got stuck. Sorted it now and its running very good and smooth transition from idle through to mains at WOT.
    Very pleaed at this stage.
    Had a quick look at the plugs and they are a nice colour so now off on the dyno next month hopefully.
    Cheers.
     
    Sirguydo likes this.
  8. Mk2 driver 1800 New Member

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    Hi Pete you dont by any chance want to sell the single 45 do you.
     
  9. Pete17 New Member

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    Hello,
    Afraid I'm not selling.
    The lynx mani is a bit of a rare thing these days and its a bit different so its just staying on my rocco as its only the summer toy kinda thing... they do pop up on the bay now n again.

    Pete
     
  10. Mk2 driver 1800 New Member

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    Ok m8 dont blame you for keeping it been looking for one for a while as I thought it would be an easy upgrade but you cant find them anyway
     
    Pete17 likes this.

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