Drawthrough Turbo Help
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  1. #1
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    fall-apart-dave is offline

    Drawthrough Turbo Help

    Hello all!

    I have a VW Beetle Volksrod running a drawthrough turbo setup on a flat 4 air cooled.

    Now, I don't want to debate the actual set up, it is what it is and it's staying put. But, I am having issues with it running. I'm aware of the issues normally associated with this method (a bit hesitant, a bit of a handful etc). However, I can't get it to rev cleanly at all.

    It will idle (after a bit of nagging to start), but when I open the throttle it bogs down badly. Lots of backfiring, lots of firing through the carb (I do have a video somewhere but no idea how to upload it?), and the revs just wont build. I can get them to build a bit by bipping the throttle loads though.

    I have seen videos of this very engine running and being used in a car before, so I know that it does run and work, but I have obviously done something silly somewhere.

    I have a delorto side draft (40) feeding into a garret turbo, the outlet of which is pointing downwards to a T which then branches off either way to the 4 intakes on the heads.
    Ignition is a 009 with the advance limited to 28* with a little lock off screw (I modified it myself). I've checked checked and rechecked for vac leaks (and about to check again!), but short of that can anyone suggest anywhere else to look?

    I have found that when I turn the dizzy anti clockwise, the idle increases and the backfiring etc is not as bad.
    I am going to check the pump jets and diaphragm tomorrow, perhaps the backfiring through the carb has ruptured it?
    Strip and clean the carb is another thing on the list (thinking that perhaps it's just not fuelling properly).
    I would try and set the timing but I can't do anything other than static timing as obviously I can't get the revs to build, and my timing light is broken Hahaha!
    The only thing I can really think of is that something is causing it to lean out when I open the throttle. I used to think that perhaps the carb is chucking too much fuel in it, and that it was pooling in the turbo. I moved the turbo closer to the engine and clocked the outlet 45* (it used to sit horizontal which meant that the air and fuel had to get through two right angles before getting to the T-branch on the intake), but it runs worse since doing this which makes me think that I've not resolved the original issue of poppin through carb and not running great, and intruduced more issues lol!

    Anyone got any personal experience with these systems? I will add pics later on when I work out how to do it.

    Thanks in advance!

    Dave

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  3. #2
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    stevieturbo is offline
    If you do not know for sure what the ignition timing is.....you're starting from a bad place to diagnose other running faults.

    The Symptoms you describe, generally sound like a lack of fuel, rather than too much ( assuming of course the rest of the install is sound and there arent other mechanical problems, valve clearances, cam timing, ignition etc etc )

    Is it only fast throttle openings or just any throttle openings ?

    And are you saying the carb was fitted and working perfectly before, on the exact same engine ? But now this is a new fault ?

    And for mixture related tuning, widebands are so cheap these days, you're ****ing in the wind trying to do it without one.

  4. #3
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    fall-apart-dave is offline
    Hello dude.

    Right, I know the static timing is 7* BTDC - as it should be with a 'dub. Obviously, I can't time it at full advance without the revs!

    Lack of fuel is my thinking too. I did chuck a good sniff of petrol directly into the manifold via the vac takeoff for the boooooooost gauge, which made it wake up a bit but obviously I can't do that while the engine is running!

    Clearances are good, cam timing good... It's any throttle openings, but holding open just bogs it down completely. Bipping the throttle lots of times in quick succession makes the revs build which makes me think even more it's lack of fuel.

    This very set up with carb ect was working once, I bought it, had some issues after a huuuuuuge backfire which resulted in the flywheel rattling loose damaging the dowels and doing all sorts of other interesting things.

    Widebands... Keh..? Are we talking about fancy pants electronics? Do tell me more!

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  6. #4
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    stevieturbo is offline
    I didnt say you need to measure advance at full revs, just confirm 100% that it is what you think it is when running around idle speeds etc.

    So this carb has never ran on an engine anything like this ? And this is the first time this engine has ran ? So all jettings, choke sizes etc could be miles off ?

    Working once, isnt the same as working on an engine/build the same as yours.

    And widebands are electronic devices, not overly fancy by any means..

    In no particular order, so of the cheaper ones, but there are literally dozens of brands out there.. Basically install the sensor into the exhaust pipe and you'll get a pretty accurate indication of the mixture ( again though, engine must be running half correctly and firing on all cylinders, as misfires etc can skew the reading.

    Innovate Motorsports MTX-L Wideband Lambda AFR Gauge with Sensor - 3844 | eBay

    PLX DEVICES SM-AFR, DM-6 WIDEBAND AFR GAUGE COMBO 897346002719 WIDEBAND GAUGE | eBay

    New AEM Digital Wideband AFR UEGO Controller w/ 4.9 LSU Sensor # 30-4110 | eBay

    https://www.ecotrons.com/products/ac..._lambda_meter/

    Wideband AFR : R-Spec Performance Products Ltd, Performance Products For Performance Cars


    http://www.enginebasics.com/EFI%20Tu...%20Basics.html
    Last edited by stevieturbo; 18-04-2016 at 19:30.

  7. #5
    Official RnS Addict mygasser's Avatar
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    if that particular carb was on that engine and it ran fine other than the backfire it ought to be ok. you say you altered the dizzy, was this not the dizzy that ran fine before? if so why alter it? if not can you fit/ borrow the original one to eliminate the 'new' one from the list of suspects. can you list all and any changes you've made to the engine since it ran fine, however insignificant it may seem?
    need a job done on your project? i may be able to help.

  8. #6
    Stroker Kustom Jim's Avatar
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    I have the innovate afr and its bloomin awesome.
    Instant mix reading any rpm/load. Cool as.
    "I'm not going to take this defeatist attitude and listen to all this crap any more from all these people who have nothing except doomsday to predict."
    Carroll Shelby

  9. #7
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    stuvy is offline
    Check for an air leak in the system I know a lad that had a similar issue on his and there was a tiny crack in the intake letting air in and giving dud symptoms

  10. #8
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    fall-apart-dave is offline
    Thanks for the responses lads!

    To clarify:

    This setup, this actual engine, carb, turbo, the whole shebang, was once a working unit.

    I received it without a dizzy.

    I took a standard 009 and modified it to stop it advancing too much and pinking, but still maintaining the advance curve through to 28* so that I can static time it at 7* BTDC (the USA way of doing it with these engines is to just lock out at 28* but since this car will be used on the street and drag strip, some progression would be nice).

    Now, I have just been out, got her started. Checked the timing, and it is at 7* BTDC or near as damn it static. Idle will be the same unless something crazy is going on! Points gap has been checked and is 0.4mm so that's fine.

    Checked over everything, she ticked over lovely once warm. Open the throttle, the moment its opened she bogs down, starts to backfire through the carb etc.

    So, I got a washing up liquid bottle full of petrol, gave a sniff through the carb as I opened the throttle and she sang all the way through the rev renge. Opened the throttle a few more times, and slowly slowly the popping started, backfiring, general misbehaviour until she wouldn't rev at all.

    So I am absolutely convinced that this is a vac or fuelling issue (or both). If anyone has whatsapp I can send you a video of the symptoms along with photos of the actual set up.

    I will invest in a wideband methinks. The rule for this car was absolutely no fancy electronics, hence using a draw through system etc. I want it to be absolutely old skool, I appreciate there are cheap fancy tech solutions to these issues, but I want to avoid them as far as possible. I *may* use alcohol injection for the strip when I dial the boost up, but for now keeping it low until she actually runs properly.

    I shall check very carefully for cracks etc when she's cooled down, for the resst of the morning though (and early afternoon) I shall be tinkering with the wiring. Once cooled, I will also whip the carb off, make sure the pump jets are working properly (the popping may have damaged something), maybe whip the jets out and chuck them in the sonic bath... I did find a couple of exhaust leaks while I was messing about so I shall sort those out. Lots of moisture inside the exhaust when I started her up this morning which I thought was odd... Must be getting in through the vertically mounted supertrap smokestack.

    Thanks again fellas! As soon as I learn how to internet properly I'll post pics and videos up but as I said, drop me a PM if you want me to privately send videos and pics (no dickpics though guys, sorry!).

  11. #9
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    stevieturbo is offline
    A wideband is simply a gauge, for you it would not be performing any control functions. So the engine package is still basic, no frills. Information is never a bad thing ! I would maybe suggest to opt for the AEM failsafe wideband, for the only reason it can datalog other information too. ie give it a boost signal and rpm signal and you can monitor/record fueling as you race.
    There are others that offer this too, but it's probably the cheapest and other than perhaps a tach adaptor, it should do everything without needing to buy additional parts.
    This will be a huge help for tuning.

    Also check and ensure you have adequate fuel pressure at the carb at all times. Ensure float level in the bowl is as it should be.

    As for the dizzy...do you have another unit you can test as is, without altering or modifying it ?

    Advance curve wont matter for revving the engine stationary. Just in case something got messed up with your existing one.

  12. #10
    Official RnS Addict fozwanger's Avatar
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    I had a suck thru set up on my V8 moggy, I would either look at an air leak or general delivery from your pump (defo sounds like lack of fuel), what pump are you using? What size fuel line as I was running a 6mm line with a red top and it was starving and causing it to cough and splutter.

    I would also look at your dizzy. I also had similar symptoms and it turns out the dizzy was dying (early electronic type) and the easiest was to describe it was the spark was "blowing out" on anything other than idle.

    It doesn't sound like a massive issue, just time consuming. Timing should be roughly the same tick over but I cant remeber was the advance was on boost, 8 deg springs to mind but it was a few years ago.

    Let us know how you get on

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