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Running rough

Discussion in 'Fuel System & Electrics' started by Georgie Girl, May 5, 2018.

  1. Georgie Girl

    Georgie Girl New Member

    Messages:
    4
    Location:
    Gold Coast
    Hi to the problem solvers out there,
    Our 1975 2.0 L bay camper started suddenly ‘running rough’ a month ago. Blamed it on bad petrol and thought carbies (twin) were blocked. Van seemed to shudder and hesitate when more fuel was needed, like when acelerating out of a roundabout, moving from second into third gear.... up hills. All ran perfect when in top gear at good speed. Took it for a service. Tappets are now tight, compression is good, new fuel filter, points, diff, plugs, leads and carbies all clean..... but the van is still running rough and hesitating at 60 km/ hour. A very inconvenient speed to run rough as most local driving is at 60 km/hr. Any ideas on what else can make a kombi act like this? It is consistently jerky at 60 km/hr now. The mechanic put in ‘bigger’ carburettor jets but I don’t know if this has helped or hindered, as the kombi seems to be running slightly worse since the service. Your advice would be appreciated - I can’t afford too much more guess work!
    Georgi Girl
     
  2. Mordred

    Mordred Super Moderator Staff Member

    Messages:
    2,669
    Location:
    Penna, Hobart
    Looks like you have run through most things so here is a few more thoughts. You can have a blocked filter inside the fuel tank, a little piece of metal gauze,that was fitted to some, or the little filter in the fuel pump if you have a mechanical one. I would think those may show up at higher speed or on a long hill. Potentially a vacuum leak, possibly from the rubber elbows on the manifold, but they normally show up more when you are idling and the vacuum in the intake system is high.

    Half throttle looks to be about where you are describing so could be a carb linkage that is not set up evenly or the carbs might be not a matched set (lots are and still work ok), although that would have been more apparent for a longer time.

    Distributor might be worn, vacuum can may not work or wrong type of dizzy for the engine, 009 dizzys are known for flat spots. Accelerator pump might have failed on one side carb.

    Bigger jets are ok when you have been having issues with the old ones running lean, not normally changed unless there is a reason. Have the carbs been rebuilt or just cleaned. Big difference between cleaning and rebuilt, and after 40 years they should be nearing a rebuild.

    A few things to consider.

    Adrian
     
  3. Barry

    Barry Well-Known Member

    Messages:
    2,548
    Location:
    Abbotsford NSW
    what sort of carbs? Stock?

    I wouldnt be putting bigger jets into stock carbs on a stock motor
    Different story if you have Webers or Dells

    As said above - check your distributor
    Again - is it stock?
    It there in no advance happening it will cause problems
     
  4. Georgie Girl

    Georgie Girl New Member

    Messages:
    4
    Location:
    Gold Coast
    Thanks for the advice - sounds like our mechanic has worked through this problem pretty methodically. He checked the distributor and I think both carburettors and distributor are stock. He definitely replaced the distributor for a good one and the same problem occured so he put ours back. I am not sure if fuel pump filter was checked. I’ll make sure to ask.

    Seems like we have a couple of options left - check the automatic choke and/or clean the fuel tank filter. Thank you for such good advice guys. You are legends.
    Cheers
    Georgi Girl
     
    Mordred and David H like this.
  5. David H

    David H Well-Known Member

    Messages:
    3,154
    Location:
    newcastle
    So at this speed you're not using much fuel...just a trickle will do. Hesitating or 'hunting' at that throttle setting seems like vacuum side 'random performance' affecting spark position.
    Now that can be a filter problem;).
    Maybe 2 problems & that's hardest to diagnose:confused:.
    Was vacuum advance changed at the same time as distributor?
    Took me many years to work out the 'hill problem' in my previous Kombi as my mechanic (& 2 other shops) failed to notice another filter above the starter motor. Both between tank & engine. Must have been an Irish person somewhere in it's history....to be sure...to be sure! How that fits with that 'ethos' being above starter motor loses me unless its about being sure of a fire:(.
    Cheers
     
    Last edited: May 5, 2018
  6. cbus

    cbus Well-Known Member

    Messages:
    10,798
    Location:
    sunshine coast
    Seriously qn why has mechanic changed jets unless there were definate indicator of lean running.
    Guessing is counter productive.

    Water in fuel is an option but should have been evident in filter and carb bowls.
    As insurance you could drain ALL fuel and refresh with new premium.
    At same time check if you have the removable fuel outlet. It has a nut retaining the pipe. The other is brazed into tank.
    IF you have removable one, remove it and check the fine mesh filter , if its still installed.
    Check dumped fuel for sand or water.

    If that clear then likely not a fuel contamination issue , for now.

    Reason to change fuel is a long shot of bad blend. Old fuel can give observed symptoms . likely hood in this case very remote.

    If you had lean mix it would show up as a serious lack of power in 3rd and 4th in hills.
    Only able to give half ( ish) throttle before it breaks down .
    Engine would be NOTICEABLY hot at hwy speeds.
    A check if spark plugs would confirm overheating and lean running. Light grey to white and possibly blistering.

    Lower speeds would appear fine.
    Flat spot off idle if running a 009 dissy.

    Mechanical or electric fuel pump?
    Do a flow and pressure check.
    Basically at cranking it should give a steady stream ( a certain volume can be measured) and will give a pressure on finger which is felt but doesn't force finger off.

    My first thoughts given probably not water in fuel is a carbon track in dissy, closed points, leads or plugs breaking down under load, crossed leads, condenser, coil.

    Is the engine making internal noises or any indication of cam failure?

    You said tappets tight?
    They must have correct clearances unless hydraulic lifters.
    You can check this yourself by removing covers and running a tune up procedure on tappets but without altering any settings.
    Don't need feeler guages. Just wobble each and ensure a similar sound. Engine MUST be cold.

    Check vac line boots to brake booster.
    Do general vac leak tests. Base of carbs firmly screwed down?
    Test for air leak at inlet manifold/ head interface.

    Back to electrical..
    Was spare dissy confirmed serviceable from a running engine.?
    You could also try yours on another kombi of similar type engine.

    This will prove........cap, points, points gap, condensor, leads.
    All a good starting point.

    Is there a power imbalance between cylinders when removing one lead at a time at idle?

    Check timing and dwell if you have the gear.

    Pull plugs and fit new NGK B6ES or BP6EY.
     
  7. cbus

    cbus Well-Known Member

    Messages:
    10,798
    Location:
    sunshine coast
    Ratwell will have procedures for most tests.

    Ensure no sparks nearby when testing fuel flow.

    75 did not come with 2l engine so possible that carbs do not match engine.

    Sudden onset suggests fuel ( pretty much eliminated) , vac elbows
    ( usaly after a carb backfire) or another hose off , major imbalance between carbs (check they open evenly as a basic check) , electrical issue ( commonly points closure but that shows as ok at revs while doughy at low revs and off idle ).
    Ensure new points had grease applied to dissy shaft contact spot.
     
  8. David H

    David H Well-Known Member

    Messages:
    3,154
    Location:
    newcastle
    Chase vacuum as Cbus suggests;).
    Shitty fuel is consistent in it's behaviours as are 'gunged' fuel filters.
    Random perf indicates vacuum;) side of intake. Check all elbow connections from engine to intake manifold/carbs.
    Cheers
     
    Last edited: May 5, 2018
  9. Mellow Yellow 74

    Mellow Yellow 74 Active Member

    Messages:
    795
    Location:
    Sydney
    If you haven't driven it much for a while, stale fuel can cause all sorts of running problems - top up with fresh fuel or better yet drain the fuel and refill and see if that helps.
     
  10. Georgie Girl

    Georgie Girl New Member

    Messages:
    4
    Location:
    Gold Coast
    Wow - you folk are phenomenal mechanics. It may have been a fuel plus vacuum issue, as a cracked elbow was replaced. The mysterious running of our bus contnued for another few days. Perfect one day, hesitating and carrying on the next. Seemed very inconsistent. Mechanic put the regular carburettor jets back in place and replaced fouled spark plugs and she appears to be running sweet again. Took her to Brunswick Heads today for a Mothers Day picnic and she ran beautifully up and back. We were doing 100 km/hr uphill with no loss of power or hesitation. Fingers crossed she stays this sweet. Really appreciate the advice.
    Carmel
     
    Wayne murray, oldman and cbus like this.
  11. Alpal

    Alpal Moderator Staff Member

    Messages:
    8,289
    Location:
    Melbourne Bend of Islands
    Spark plugs seem to be a bit fragile these days? Had a few fail.
     
  12. cbus

    cbus Well-Known Member

    Messages:
    10,798
    Location:
    sunshine coast
    Indian made Bosch ?
     
    Wayne murray likes this.
  13. Mordred

    Mordred Super Moderator Staff Member

    Messages:
    2,669
    Location:
    Penna, Hobart
    NGK are the only spark plugs I use anymore. The Bosch ones are terrible.

    Adrian
     

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