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Fluctuating timing

Discussion in 'Fuel System & Electrics' started by emby, Aug 25, 2012.

  1. emby

    emby Active Member

    Messages:
    2,006
    Location:
    Wights Mountain, QLD
    Bugger, bugger, bugger.....

    How come when you go to gear up the bus after a winter spent sitting doing relatively little you always seem to finid problems?:mad:

    Serviced the bus a couple of weeks ago and went to check the timing / idle and all was still good. Went for a drive and 4km down the road I come to a junction and the bus dies as the idle speed drops to less than 600rpm. Drive home to check, pull into the driveway and the idle speed is still sitting around 900rpm:wtf:

    To put a long story short it seems that when I rev the engine and then let it drop down to idle it either sits at about 1200 rpm (timing shows at around 12 to 15 BTDC) and then slowly drops to 900rpm (timing at 7.5 BTDC), or it drops to 600 RPM and timing drops to just above 0BTDC.

    I've checked for vacuum leaks. Have replaced the elbows at the manifold / brake booster line. Have replaced the grommits in the brake booster line at the fire wall and at the brake booster non-return valve and have replaced the blocked off tube in the middle of the idle circuit pipework. Checked them all with a squirt of Start ya bastard and there's no change in revs so am assuming that there is no leak there.

    Thought it might be the distributor. Swapped out the rebuilt 205 SVDA dizzy for the old 205 SVDA dizzy (both fitted with pertronix ignition). Results were the same. Fluctuating idle and timing.

    I'm also noticing a blip in the timing. Every now and then I get a bounce where the ignition seems to be even more advanced and there's a corresponding blip in the idle from 900 rpm to about 1050rpm. It's not a regular pattern. This hapens with both dizzys.

    Tried checking the idle cut offs. Removed wire from central idle cut-off (the big one) - engine stumbles and dies. Removed wired from left side idle cut off - engine stumbles and dies. removed wire from right side idle cut off - no difference in engine revs:wtf:

    Started pulling plug leads. All leads producing a spark. Pull leads off 3 and 4 (one at a time, not both togther) - engine speed drops and returns once plug is reconnected. Pull leads of 1 and 2 and only notcie a slight drop in revs. This is confusing as both leads and plugs are sparking.

    What could be the problem? Any one offer a possible soultion?

    Cheers

    Matt
     
  2. Rossco WA

    Rossco WA Member

    Messages:
    360
    Location:
    Bateman, Perth WA
    Have you checked your idle jet on the carb. might have a bit of crud in it, give it clean and blow out, fuel filter as well.
     
  3. emby

    emby Active Member

    Messages:
    2,006
    Location:
    Wights Mountain, QLD
    Chhers. I'll give the jet a blow out in the morning and see how she goes
     
  4. emby

    emby Active Member

    Messages:
    2,006
    Location:
    Wights Mountain, QLD
    Well cleaned the jets out (also noticed that I had a 50 in one side and a 52.5 in the other:umm: Cleaned up 2 x 55's and put them in.

    Problem is still there though (although the bus is definitely running smoother.). It just doesn't seem to want to return to it's idle speed. Set it to 875rpm at 7.5BTDC, went for a spin and now it's sitting at 1150rpm at 10BTDC:wtf:
     
  5. matberry

    matberry Member

    Messages:
    62
    Location:
    Cooroy near Noosa
    Has the choke linkage come loose or the lock nuts moved. It's the little verticle rod close to the carb body. Once the chokes are off, these should hhave play and not hold the throttle arm on in any way. You know when the throttle arm isnt all the home if the throttle stop screw isn't touching it's stop.

    Or you could take it to a mechanic. Where's Whites Mountain, out near Samford? If so go see Andre at Scorpio Motors at Mitchelton (or close by)
     
  6. emby

    emby Active Member

    Messages:
    2,006
    Location:
    Wights Mountain, QLD
    Cheers for the heads up. I checked the nuts and they're all fine.

    I took this short video to show anyone what's happening to see if they might know a simple solution. Note I only touched the throttle twice. Once at the begining and once at about 1.15. The rest of the work is being done by the engine all on it's own :wtf:

    [YOUTUBE]GxvegdYdBRc[/YOUTUBE]

    And this is what's happening in the engine bay.... agin, only two blips on the throttle. It takes an eternity to return to the baseline setting.

    [YOUTUBE]IHpg9b2Axog[/YOUTUBE]
     
    Last edited: Aug 27, 2012
  7. matberry

    matberry Member

    Messages:
    62
    Location:
    Cooroy near Noosa
    There's your problem, you found it and people above had suggested it, the distributer advance is siezing up and so takes an 'eternity' to get back to zero advance. Each service, every 5000 km the felt pad under the rotor should get a drop of oil to lubricate this mechanism. This should respond to some fresh lubrication and with the dist cap off, turn the rotor back and forth a few times, maybe some spray grease into the advance mechanism under the points plate will also help. The lubed felt is the one that makes the difference, but the lube has to work it's way down. Drive it, if lubed, it'll free up.
     
    Last edited: Aug 27, 2012
  8. leithbro

    leithbro Member

    Messages:
    575
    Location:
    Cairns
    Surely that has to be a vacuum issue??? Is it a SVDA dissy?

    Where did you get your tacho BTW? I want one! :)
     
  9. matberry

    matberry Member

    Messages:
    62
    Location:
    Cooroy near Noosa
    That's easy to proove, do the same with vac hose off and plugged
     
  10. emby

    emby Active Member

    Messages:
    2,006
    Location:
    Wights Mountain, QLD
    Cheers Matt. I'll get on to that tonight. Would this explain the rising and falling over the idle without touching the too? I'll grease up both and also think I'll try points in one of them rather that the Petronix.

    Mark, the tacho is just a standard vdo tacho order from a car parts shop. I had to cut a hole in the blank plate to mount it though.
     
  11. emby

    emby Active Member

    Messages:
    2,006
    Location:
    Wights Mountain, QLD
    Well, tried greasing up the mechanical advance plates. I even swapped the dizzy out and put the old one back in after a bit of a service and reinstalling the Pertronix (i'll try points and condenser at the weekend). No joy. Exactly the same symptoms.

    I've set the timing correctly and at the right revs, can and carb plugged. Go for a drive and the revs and timing drop down to just above a stall. Pull in the driveway and it's back to normal. Could it be that both dizzy's are stuffed in exactly the same way? You know what they say, "Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth."
     
  12. Kai

    Kai Well-Known Member

    Messages:
    4,775
    Location:
    Sydney, NSW
    Seems like a blocked jet or needle and float issue.
     
  13. roqsta

    roqsta Member

    Messages:
    571
    Location:
    Bayside Brighton Brisbane
    Ive had multiple dizzy issues in a past life where the bushes in the arms of two separate ducillieur distributors where worn. They both ran fine at idle and through the rev range but would die randomly. When everything cooled down they would start again. You couldnt tell until you pulled them apart. Could be an issue but I think it more likely a fuel issue. Did you say its been sitting for a while? Might be worth cleaning out the bowls.
    roq
     
  14. matberry

    matberry Member

    Messages:
    62
    Location:
    Cooroy near Noosa
    "I've set the timing correctly and at the right revs, can and carb plugged. Go for a drive and the revs and timing drop down to just above a stall. Pull in the driveway and it's back to normal." Sounds to me that 'setting timing correctly' isn't happening, when the revs are lowest and the timing least advanced is when the timing should be at 7.5* BTDC, if you set it at 7.5 then it strangely goes lower, you have actually set it without the distributer being at it's base setting. I say this because the timing can't move by itself, the only mechanism that effects it is the distributer advance. As a further check, when the revs are low nearly stalling, check the timing with your light, what is it?
    I agree carb settings don't sound perfect, but other than via engine rpm and vacuum advance, carbs will not/can not effect ignition timing.

    My 2c
     
  15. emby

    emby Active Member

    Messages:
    2,006
    Location:
    Wights Mountain, QLD
    I agree that's exactly what's happening. However, getting it to rev at it's lowest point is the problem. It's set at it's lowest point at the time of setting it. There's just no way of knowing if it's going to go lower.

    I pulled one of the dizzy's apart last night. There definitely looks to be a problem with the weights in the mech advance not returning to it's base setting. They're moving apart fine but need a bit of a prod to get them to fall back to the centre. They're stopping about 1-2mm short of a full return. I've greased them up and will put it back in the bus at the weekend to see if a bit of running at temperature wil free it up.

    What makes you think the carb settings aren't perfect?
     
  16. matberry

    matberry Member

    Messages:
    62
    Location:
    Cooroy near Noosa
    What makes you think the carb settings aren't perfect?

    Just the sound of the engine and the way it revs/returns to idle (taking into account the distributer)
     
  17. emby

    emby Active Member

    Messages:
    2,006
    Location:
    Wights Mountain, QLD
    Right. I thought it was more to do with an occasional misfire which is causing the jump / drop in revs. I've also noticed that with the timing light at 3,000 rpm the jump is a lot more pron
     
  18. T1 Terry

    T1 Terry Well-Known Member

    Messages:
    1,546
    Location:
    Mannum South Australia
    Try disconnecting and plugging the vac advance off and see if the timing and idle speed settles down. It sounds more likely the two throttle linkages are not synronised so one carby is running the engine at idle. If this is the case then I expect it's the carby the vac advance hose is connected too. Try droping both link arms off and see how the engine idles then and if the spark plugs being removed from either side now makes a difference? My line of thought is that the adjustable linkage rod has self adjusted and one throttle butterfly is partly open, the side that has the vac advance hose, the vac advance port is expossed to manifold vacuum just slightly further open than idle so this butterfly being partly open is expossing the vac advance to some vacuum depending on engine speed.

    T1 Terry
     
  19. emby

    emby Active Member

    Messages:
    2,006
    Location:
    Wights Mountain, QLD
    Gotta love Father's Day for some kombi maintenance without complaints:lol:

    OK. Got back into it today and may have stumbled across something (maybe not though).

    Before I started it up this morning I removed and checked the plugs. All in a nice condition and gaps seem to be around perfect and currently sitting at about .025. (I read that it was best to run them with a tighter gap running towards optimum .027 rather than set them at optimum and have them moving away)

    Removed air horns and reconnected horn and pipe to idle air.

    Started up bus and watched chokes. Both working perfectly.

    Looked at step in throttles. Both working perfectly. Starts and idles at about 1500RPM until I blip the throttel and goes back down to around the 900 mark with the occasional blip lower and higher.

    Removed tube to vac can. Put on a blocked tube. Also blocked tube feeding left hand carby. (No noticeable change in revs). Removed throttle bar linkages from carbs.

    Checked timing (a little low... maybe 6 to 6.5 BTDC). Readjusted and checked idle speed. Slight adjustment. Rechecked timing. Slight adjustment. Checked idle which is more often than not at 875RPM but bounces somewhere between 840 and 970 wihtout being in a regular pattern.

    Waited a bit to make sure all was good and (reasonably) steady.

    Blipped both throttles manually. Revs climbed and then dropped to settle at about about 1175RPM. Timing mark had moved around to about 15.

    Checked plates in carbs with a bit of tubing. Both seated and not moving back to reduce revs.

    After leaving a few moments it settled down to about 10BTDC and revs dropped to about 1050.

    Reconnected throttle arm linkages. No noticeable change in revs.

    And this is where I think I may have hit on something.....

    Removed idle cut off wire on right hand carby. Revs dropped to about 600 and stumbled. Reconnected and revs returned to 875RPM. Blipped throttle again. Revs rose to 1150RPM. Removed wire. Revs dropped. Recoonected wire. Revs returned to 875RPM.

    Did the same thing with the left hand carby. Got exactly the same results. High revs on throttle. Revs and timing return to normal after removing and then plugging idle cut off wire back.

    Then tried the main idle cut-off on the left hand carby. Blipped throttle. 1150RPM. Removed cable. Revs drop to 600rpm. engine stumbles along but doesn't cut out. Reconnect cable.... NO CHANGE!. Stays at 600 RPM. Give the throttle a blip. Back to 1150 RPM.

    Now to me this sounds like a sticking needle / valve on the main idle cut off. Does this sound right??? (I bloody well hope so). It seems to mirror the symptoms I'm getting on the road. Moving along nicely. Come to a junction. Revs drop down to 600 rpm. Need to put foot on gas to being it back to revs.

    Any thoughts?
     
  20. emby

    emby Active Member

    Messages:
    2,006
    Location:
    Wights Mountain, QLD
    Bugger. Just swapped over for a different cut off and symptoms are the same.....

    Even worse... the starter motor has now decided to pack up and the bus will only start with it in gear, clutch depressed and slightly rolling forward. I just get a grinding noise when trying to start standing still. Battery???

    Could be time for an overhaul
     
    Last edited: Sep 2, 2012

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