Electrical geniuses please speak now!

Discussion in 'Mechanics Garage' started by Terry Smith, Apr 23, 2016.

  1. Terry Smith

    Terry Smith Member

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    A have another V4 Honda, an ST1100. Given that it has gear driven cams (plus a belt drive), I'm choosing to call it my VFR1100ST, but I digress...

    The bike was parked up for 8 years and was predictably clogged up in the tank, fuel pump and carbs, and I have spent many happy hours snorting carb cleaner, and fitting a new fuel pump. The ST1100 tank has a big flanged opening that you can get your arm into so I was able to scrub the inside clean.

    I've set the float levels carefully, verified the jets are OEM, checked the diaphragms are clean and the slides work well, then balanced the carbs. I now have a bike that starts from cold nicely with choke, and idles like a fine Honda should. It runs great at low revs (up to 4k) and small throttle openings, but when I open it up it gets the staggers, feeling flat and misfiring. It will rev right up to 8k with an effort but doesn't feel happy doing it.

    I have started looking at the electrical side of things, and the one anomaly is the power supply to the ignition control module. The manual states I should get normal battery voltage between this and the ground, but I only see 11.15V. The bike has got a brand new battery that gives 12.7V on its own.

    Is that lowish voltage at the ICM a cause for concern, and if so where would I go looking for the loss?
     
  2. NormK

    NormK New Member

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    I'm guessing voltage drop through wiring and connectors, I assume 12.7 is with the ignition off and 11.15 ignition on. I don't think that is abnormal and you are not having starting or low rev problems. What voltage are you getting with the revs up?
     
  3. Allyance

    Allyance Insider

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    A voltage drop indicates resistance. Given the length of time bike sat, I would first check all ground connections, then connectors. Here is a picture of my handy-dandy way of burnishing connectors (note slight discoloration on center connector).
    [​IMG]
    Get a package of emory boards for finger nails. Peel coarse sand paper off one side, and trim width to about 1/4". Do both male and female connectors. Brighten up any spade lugs under bolts for grounds. Corrosion will cause resistance and resistance will cause heat. The photo is of the stator connector which carries the most current of any of the connectors. Voltages should be consistent to all lights and devices excluding the charging circuit. It is the current (the amount of electrons going past a given point) that counts. You can have 12 volts at a lamp that draws 1/2 amp or 12 volts at the starter which will draw 30 amps or more. Size (gauge) of the wire will determine max current it can handle. Don't forget that those plug in fuses have same type of connectors too.
     
  4. Cogswell

    Cogswell New Member

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    Oxgard can be very helpful at getting current flowing through connectors and grounds. I treat most of mine with it. Many hardware stores and home centers carry it.
     
  5. Terry Smith

    Terry Smith Member

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    Yes you're right about the conditions of test. Across the battery with ignition on I get 11.98V, 12.7V ignition off. Head and tail lights are hardwired on and so I would guess there is 150W of lights, which would presumably sap the voltage a fair bit.

    At this point I have no concerns about the running voltage as the battery is staying nicely charged.
     
  6. Jeff_Barrett

    Jeff_Barrett Member

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    I'm not so sure this is an electrical issue.

    Out of curiosity, have you pulled the plugs to see what they look / smell like? It would be a good indicator of rich / lean conditions.

    At any rate, it almost sounds like vacuum leak to me more than anything right now ... but not a lot of a data to go on at this point.
     
  7. Terry Smith

    Terry Smith Member

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    Jeff I'm floundering around a bit here. My other bikes run great and I'm not really familiar with rich/lean symptoms. Maybe the bike is smellier than I'm used to, so that would suggest rich. As I said, it runs really nicely at low revs, starts to go flat from 4k up, and misfires and coughs if I rev it much higher with a big throttle.

    Almost seems like a chronically over-sized main jet, or maybe the slide is not lifting far enough so the intake vacuum over the main jet is too high.
     
  8. OZ VFR

    OZ VFR Member

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    Sounds like a fuel/air problem to me.
    Are you sure the diaphragms are good?
    It's been a long time since I've mucked around inside carbs.
    Sometimes they can look good, but are not.
    Not sure if you have E10 fuel in the land of the long white cloud (place that rains a lot), but it's a known killer of such items.
    It slowly dissolves them and maskes them porous. Old age and left dry can do the same, and it will cause similar problems.
    As was stated above, also check your vacuum lines.
     
  9. Jeff_Barrett

    Jeff_Barrett Member

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    The reason I think it could be vacuum related is that everything runs fine at lower RPM - but when you give it big throttle (should be accompanied by big vacuum) you end up with stumbling.

    OZ VFR makes a good point to check the diaphragms for the sliders in the carb. Be very careful inspecting them. They are expensive .. if they are damaged, this would create a vacuum leak and now allow for proper slide operation in the carb.

    Check the intake boots as well ... you may want to pull the spark plugs and snap some photos for us. Make sure you note which cylinder they are from in the event that they give an indication of what's going on.

    Did you sync the carbs? What are you getting for vacuum readings on each cylinder? How did you clean the jets?
     
  10. Terry Smith

    Terry Smith Member

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    Thanks for the non VFR related diagnosis chaps. I think you're right that this is an air/fuel matter.

    The diaphragms are good, I can blow down their vents and they lift nicely, so no leaks I'm sure. They are clean and clear.

    I extracted the jets and cleaned them with fine wire and carb cleaner, they are definitely clear, as is the bowl, but they were originally blocked.

    I have balanced the carbs and they hold a normal looking vacuum (my gauge is balancer not a measurer) similar to what I see on the VFR.

    The manifold rubbers are in great condition. Very few vacuum hoses, just 4 for balancing purposes, and they are good.

    I was not able to pull the plenum/trumpets off the carb tops (quite different to a VFR) due to stripped screw heads and so was not able to get into the air intake side as well as I would like. Might have to bike the bullet and drill the screw heads off, and get hold of a compressor to do the job properly.

    Makes dealing with FI seem simpler somehow...
     
  11. Grumpy old man

    Grumpy old man New Member

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    I am surprised that the float heights were adjustable the floats fitted to my 92 and 96 fireblades and 98 vtr were fixed and the tang was molded plastic as part of the float and not adjustable

    when you set the floats I Take it you did the measurements with the carbs on their sides so as not to allow the float valve springs to compress

    As I am sure you know if the float valve springs compress the float height measurement will be incorrect

    Carb floats set with carbs fully upside down and float valve springs fully compressed would create a lean setup when the carbs are the right way up and the bowls full of fuel as the float would be sitting too low which could cut the fuel off prematurely causing a lean condition

    Too low a float height is like being several jet sizes too small that then will effect the mixture range of the carb operation which the diaphragm slide needle relies on

    Float height is ALWAYS the first part that needs to be correct before any other part of jet selection then needle height setting then mixture screw can be set successfully

    Many years of dyno jet and "factory" jet kits hammered this into my thick skull
     
  12. Terry Smith

    Terry Smith Member

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    Thanks Grumpy. Yes floats have bendable aluminium tangs, and I was careful to orient the carbs so the floats were touching but not compressing the float valve springs.

    The more I think about this, the more I'm convinced the carbs aren't properly clean.

    The ST has curved trumpets inside an aluminium plenum which forms the bottom of the airbox. I need to get this off so I can get to the air intakes around the inlet, and also remove the air cut valve diaphragms, one is impossible to access otherwise. There looks to be two or three inlets here, and also two in the air side of the vacuum diaphragm. What do all these things do?
     
  13. Grumpy old man

    Grumpy old man New Member

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    Terry
    I have a PDF of an ST1100 service manual if you would like it PM me your email address I can't figure out how to attach it to a PM

    Cheers
    James
     
  14. Terry Smith

    Terry Smith Member

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    Thanks for the offer James, got that already.

    I was hoping that you could explain the various air inlets to me.

    [​IMG][​IMG]
     

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  15. Grumpy old man

    Grumpy old man New Member

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    Check this out it explains the basics of the carbs you have there and offers a couple of cheap enhancements

    http://www.steinborn.org/st1100.html

    I personally have never pulled apart an ST1100 carbs but the principal is the same for all cv type carbs

    the brass inserts are purely to restrict/control airflow through different circuits as needs require
     
  16. squirrelman

    squirrelman Member

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    *DISCLAIMER: by responding to this, no claim to expertise or genius is implied or expressed. Only concerning squirrels (Scirius Carolinensis) or black-tail prairie dogs (Cynomys Ludovicianus) am i any kind of expert.


    Could be a weak/failing fuel pump. Bypass the pump relay for testing. You're sure the float bowl vent lines are open ?
     
    Last edited: Apr 27, 2016
  17. Terry Smith

    Terry Smith Member

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    Well I did work my way through the various air circuits again yesterday and believe I have them all opened up clean now. I have reassembled the carbs, carefully reset the floats and set the airbleed screws in the stock position, but my running problem persists. Starts easily from cold, idles great when warm, runs well up to 3500, much over 4000 and a more open throttle and it starts misfiring/surging.

    Just as background, I bought the bike cheap on an as-is basis knowing it hadn't run for at least 8 years, and was not able to be started.

    As expected the fuel pump was choked with varnishy crud, the inside of the tank was a little rusty (but not too bad), the battery was completely dead, and there were blockages in the carbs. I have replaced the pump and battery, and checked fuel flow through the existing filter (quite a bit more than the spec minimum) so I'm sure I have no fuel supply issues; I also checked the tank air vent. The tank cleaned up quite well with a little scouring. I have replaced the plugs (although the old ones looked like new), and the air filter looks new as well.

    The one thing that I have done which may have been a bit stupid was I re-used the fuel that was in the bike when it arrived, something like 18L, and have added another 10L of fresh fuel (these bikes have BIG tanks) . Having never dealt with old fuel I'm not sure sure whether this is a potential issue? The fuel is clean and the right colour.

    I will drain this all out and start from fresh I think. In spite of a lack of perfect running, I still think I got a bargain, and have had a lot of fun working on the bike.

    [​IMG]
     

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  18. Jeff_Barrett

    Jeff_Barrett Member

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    Haha, yeah, drain that shit fuel out of there and report back.

    Dumb question - but did you check / replace the fuel filter? If there's a bit of rust in the tank, it could have been / is plugged. The bike looks to be in amazing shape on the exterior.

    Squirrelman pointed out the next thing I'd check if all these are above board - test the fuel pump / regulator.

    Can you also snap a photo of each spark plug?
     
  19. Terry Smith

    Terry Smith Member

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    Thanks Jeff, the exterior is in great shape for a 1992 bike, gets better every time I wax it. There was the expected surface corrosion on some alloy, but no road rash, and a bit of a jacket buckle scrape on the tank, but otherwise the bike is in great, straight shape, and really nice to ride. Came with new (in 2006) tyres, I have replaced all the fluids, battery, plugs, steering head bearings and back brake pads. I paid the equivalent of US$880 for it.

    I'm hoping for a Homer "D'oh!" moment with some new fuel. However it's my wife's birthday today so I will be in the dog box if I spend much time with my bike this evening...

    I checked fuel flow after the filter (so at the infeed side of the carbs) and there's about 5 times what the Honda manual calls for. I am using an in-tank pump intended for a 1990's Honda carbureted car as the OEM ST part is $390 or something. This has been done by many other ST/Goldwing owners with good results, the pressure is pretty similar to stock.

    I'll sneak into the garage and get the plugs out for some photos this evening. The ST layout makes most maintenance matters very easy, I'm almost looking forward to doing a valve clearance check one day!
     
  20. RobVG

    RobVG Member

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    "A primary factor in manifold vacuum is throttle plate position. When the throttle is closed, manifold vacuum should be higher than when the throttle is open. With an open throttle it is easy for the outside air to get into the engine and there will be less difference in pressure between the outside air and the air found in the intake manifold. As the throttle plate closes, a restriction in airflow is created and manifold vacuum increases. "

    http://www.linnbenton.edu/auto/perform/vacuum.html
     
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