Replacement Engine Running Rough

Discussion in 'Mech Tech' started by Bay Dreamer, Sep 18, 2022.

  1. So I managed to source another engine for my 72 bay after the unfixable hole in the case and massive end float of my last one.

    I bought a long block and I transferred all the ancillaries from my old one. I replaced the oiler cooler seals, reshimmed the end float, new flywheel seal, new spark plugs, E5 fuel.

    The old engine was running relatively okay until the oil leak in the case. The new engine seems to struggle to start up and then bogs down at low rpm. It also seems a little underpowered and sometimes stalls when stopping at junctions/roundabouts.

    I took the carb off, stripped it, cleaned it and replaced some of the gaskets. I set the two adjuster screws to 2 and 1/2 turns out. The engine still seems to be running rough at low rpm.

    I set the timing statically and then a neighbour with a late bay used a basic timing light and advanced it a little. It is a 009 distributor.

    Something still isn’t right and I’m not sure. I have ordered a good timing light but it won’t be here for another 10 days. Any suggestions? Here are some videos of it running.

    https://youtube.com/shorts/XbRGuD8zFn8?feature=share

    https://youtube.com/shorts/2dnXuxztSo4?feature=share

    https://youtube.com/shorts/q0lt0dr7TSA?feature=share
     
    Bob Alatt likes this.
  2. Sounds a bit like mine did when a few degrees short on advance, I've had to go right up to 32 max where its happy but ive got a bit more lift/valve size/compression than it should.
    I'd be guessing an electric side of things issue, .. timing, leads not sat fully etc

    Sent from my SM-T580 using Tapatalk
     
  3. Zed

    Zed Gradually getting grumpier

    Tell us about this. What was it when you got the engine?
     
    snotty likes this.
  4. Yes, given I have new fuel lines and cleaned carb and pretty much the same, I am thinking electrical.
     
  5. The engine is an old Vege recon engine. It has been sat in storage for about 4 years.

    The end float was within spec, but at the upper end so I replaced one shin from my dead engine that was fractionally thicker. This just brought it to the lower end.

    I think there were three 0.24 and I swapped one for 0.30. The end result was something like 0.8mm end float.
     
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  6. Zed

    Zed Gradually getting grumpier

    Well, those are the "hopefully it'll start" settings, not the real ones which vary from engine to engine, so...
    Unscrew the small one half a turn at a time, any popping in the exhaust should stop and it should run smoother until the next 1/2 turn doesn't make any difference. The revs should also increase as you do that because it should be running better. then set the speed with the big one.
    Then screw the small one in until it starts running rough again and repeat unscrewing it, but listening for the sweet spot more carefully. when you find it, unscrew it another half turn.


    You may find it helpful to do both screws at once initially if it's idling too slow or too fast, get in the ball park and it's easier to adjust the small mixture screw.

    Once it's drivable after doing the above, drive it for 1/2 hour so it's completely warmed up and repeat because the engine must be fully warmed up to set the screws correctly. If you do it on a cold engine you'll find it idles faster when it's warmed up because a cold engine likes a richer mixture.

    Note these carb settings are ONLY for idle, they do not really effect the running at all... unless they are miles out.
     
    Last edited: Sep 18, 2022
    Soggz, Chrisd, redgaz and 1 other person like this.
  7. Zed

    Zed Gradually getting grumpier

    Then... if it's still rough, you could check out your engine further with a compression tester. Quite a cheap tool that will show if you have uneven compression on your cylinders. Generally that would show up more at lower revs, but hopefully you just have a setting up problem you can tweak with the carb screws..
     
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  8. mikedjames

    mikedjames Supporter

    Also make sure that the shutoff solenoid is operating correctly on the carburettor, and clean it out, you may have disturbed some crud swapping things over.

    But apart from timing and electrical wiring , if you swapped everything over off a running engine then the difference with the "new" engine is inside the long block.

    I did find with my first VEGE engine that it was set up with quite low compression, it had cylinder head spacers it didnt need (deck height with spacers about 2mm) probably to protect them from returns through overheating issues..

    I would do a compression test..
     
  9. 0.08 mm ?
    Bin the 009
     
  10. Interested to see how you get on with this as my engine - also a vege recon - flips between running fine and having the exact symptoms you describe.
    I’m running an SVDA and have replaced one vac canister after about 1000 miles. Still get the low rev bogging after moving from an 009.
    I’ve read around this as much as poss (on here and the samba) and ‘air leaks’ are often suspected / suggested as the cause. Whether that’s right or not, I have zero clue…
     
  11. mikedjames

    mikedjames Supporter

    You also need hot air feed and heat risers that work to warm up the carburettor.. previously having a 009 says a PO succumbed to marketing.. and the stock air cleaner isnt as "pretty"..
     
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  12. Thanks Mike, without wanting to hijack the thread, I know for a fact my heat risers are clear as I unblocked them ~ 1000 miles ago - unless they’d re block that quickly? My air filter is stock too. ‘
     
  13. Zed

    Zed Gradually getting grumpier

    The fact it flips between the two makes me think of bad electrical connection or sticky cut-off valve or the choke only working sometimes. It won't be anything inside the engine.
     
    Bob Alatt likes this.
  14. Soggz

    Soggz An inquisitive supporter

    Coil? Mines doing something similar,at the moment.
    Going to swop it out for another I have,later,just to see…
     
  15. mikedjames

    mikedjames Supporter

    Another thing that can happen is that its idling fast when warm so you set the timing at over 1000rpm. The distributor feeds in a bit of centrifugal advance. So you set 8 degrees but the dustributor gives one or two degrees of that figure.

    Then when its colder the idle is slower, drops to more like 5-600 rpm, centrifugal advance is zero, engine sounds rough, and now the timing is now say 4 degrees, it bogs and hesitates and dies at idle.

    A sticking centrifugal weight mechanism can do this as well.
     
    Bob Alatt likes this.
  16. Thanks for the feedback, I got quite bad flu over the weekend so I’m not able to have a look further at the moment.

    I have a compression tester that sat here for a month and I have just put it back in storage so will get it out again.

    I have ordered a digital contact tachometer so that I can properly tune the idle while at the engine bay. I will try and get that right.

    I still think there could be something electrical or the timing still isn’t right as it just seems gutless at 2000rpm driving and almost sounds like it’s misfiring just above idle.

    At the moment it does seem to be running a fast idle when warm.
     
  17. mikedjames

    mikedjames Supporter

    It should idle progressively faster as it warms up.

    The choke element rotates an endstop for the stepped cam so that when the choke is warmed up, the stepped cam under the throttle end stop screw will drop down to reduce the idle when you blip the throttle.


    The stepped cam is held in place by the spring pressure on the throttle end stop screw.

    If you leave it idling without touching the throttle, it will idle pretty fast as it warms up, maybe up to 2000 rpm but the idle will drop if you blip the throttle.

    If you adjust the timing while the throttle screw is still resting on one of the cam steps, then you may have set the timing a bit less advanced than you need (as mentioned before)

    Having an 009 , it wont accelerate quite as well as it could, as the engine has to spin up to gain timing advance, as opposed to gaining vacuum advance to produce a little more torque to spin up.

    If you have points (you havent mentioned), if you set the dwell angle (via points gap) incorrectly, you can end up with having points that barely close, resulting in a weak spark, or opening very late resulting in the spark having to jump a bigger gap from the rotor arm to the peg in the distributor.

    Condensers can do strange things like suppress the spark for a while as they break down, then heal themselves for a while - all to do with quality control and damp in the factory..

    I tested a dodgy condenser the other day with a high voltage power supply - it kept on breaking down at 150 volts (too low) until the arc burnt away the rubbish bit of the condenser , then it held back over 1000 volts.

    Also a cantankerous electronic ignition unit (apart from Pertronix Ignitor 1 ) can easily mimic several different classic ignition faults without there being anything else wrong.

    Try borrowing a different distributor in case there is something wrong there.
     
    Last edited: Sep 20, 2022
  18. Zed

    Zed Gradually getting grumpier

    All this kit was running perfectly well on his old engine, the one that sprung a hole in the case, so... one would think it's still fine, just needs setting up properly?
     
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  19. The things that have changed from the last engine are 1. New spark plugs, 2. Timing from swapping distributor over. 3. Points gap, which was adjusted by a friend (competent with mechanics) while I was busy on something else as he said it was less than 0.4mm and needed adjustment. I haven’t had a chance to check the points gap myself yet.

    Interestingly the engine ran rough like now on initial startup, then I stripped and cleaned the carb and put the settings to 2 and 1/2 turns out on both screws. The settings before were 1 and 1/2 small screw and 1 and 1/4 big screw and it ran pretty much the same.

    The only other thing I am not sure about is after I swapped the distributor I noticed in the manual that it says there is a spring which goes up through the centre. I couldn’t see this on either engine.
     
  20. Zed

    Zed Gradually getting grumpier

    First, totally forget about counting turns on the screws, it's meaningless, they must be adjusted by listening to the engine, particularly the small screw. It's called Lean Best Idle which means the leanest you can set it to idle smoothly... but then VW aircooled engines actually like a tad richer idle hence the 1/2 turn out extra. So, what you are doing is screwing the mixture screw in to make it so lean it runs rough and pops in the exhaust, then slowly out until it runs as fast and smoothly as it wil - at this point unscrewing it further to let even more fuel through won't increase the revs or make it smoother. Do it 10x for practice then when you have a feel for the least unscrewed where it's running best, 1/2 a turn more out. Could be 2 turns out from seated, could be 5 turns, turns do not matter, forget turns. Don't even seat it and count them!

    Did you gap the plugs? They should be 0.6mm but are always IME 0.8 or bigger out of the packet.


    That spring is ESSENTIAL. Please get one. :)
     
    Last edited: Sep 20, 2022

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