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My Vf1000 frustration

Discussion in 'Technical and Troubleshooting Torque' started by techno, Jan 28, 2007.

  1. I need some technical help as I am now at a loss to know what to do next. Bear with me. This could be long but I don’t want to miss out anything that might be important.

    I have a 1984 Honda VF1000F which I rode for a few years until the motor became noisy. I was able to buy a used motor to do a transplant. It was from a 1985 VF1000F and there didn’t appear to be any physical differences. Apparently it was running fine before I bought it. I bought it from interstate so I couldn’t test it out. After fitting it and hooking it up it starts and runs OK but only up to about 2500 rpm. Then it starts to cough, splutter and misfire and won’t rev any higher. Let off the throttle and it goes back to idle OK and increases again until it gets to 2500 rpm.

    As I have my original motor I have tried changing various parts back to see if they are causing the problem. I have been fiddling with it for months but it always runs the same. I believe its either fuel or electricals. Here is a list of what I’ve done:

    Fuel issues
    Emptied tank and used fresh fuel.
    Cleaned fuel tap.
    Carbs removed and cleaned.
    Carb vacuum rubbers checked. One replaced due to split.
    Carb boots checked for cracks. Best ones refitted.
    Replaced all fuel lines and new filter.
    Carbs balanced (as best as possible – not easy on a v four).
    Run with fuel cap off to exclude blocked breather.
    Run with airbox removed to exclude obstruction.
    Run without exhaust cans to exclude obstruction.
    Checked for rag in exhaust collector box.

    Electrical Issues.
    New spark plugs correctly gapped. (Tried both resistor and non resistor types)
    New plug leads.
    Coils swapped over with old ones.
    Pickups on crank changed.
    Wiring connections checked for obvious breaks.
    New Battery
    Run with fuse for instruments removed to exclude faulty rev limiter (apparently its in the tacho).

    Checked valve clearances.
    Removed rocker covers and turn over engine to test if cams correspond with firing order.

    I’m open to any realistic ideas or useful suggestions. If I can’t get it going soon I’ll end up doing something drastic.


  2. Did you get carbs with both motors? Try your origional carbs if so. About all I can think of is the diaphrams which open the slides may be leaking/perished. They should not affect the idle but as you crack the throttle & airflow increases it may upset things.

    PS Are you totally sure the coil wires are connected correctly? Check the exhaust headers when you first fire it up to see if any are cold or colder than the others. The V4 runs a bit lumpy & it's sometimes really hard to notice a cylinder out
  3. Thanks Roarin.

    I do have 2 sets of carbs. I had Iffracem check them out and put together the best set. We checked all the diaphrams and replaced one as it was split. It also had this problem with the original carbs on it as they were.

    I will check the heat in the headers to make sure they are all firing.

    As for the coils, VF's spark on two of the four strokes. I have tried swapping 1 and 3 (the 2 rear cylinders) and there is no noticable effect. One set of coils has the cylinders numbered on it so I think they are in the right position.
  4. whip out the spark plugs, remember which cylinder they are from and post up pics of each. you will be surprised wot people can see from the condition of the pplugs sfter some running of the motor.

    to me, sounds like its not firing on 1 or 2 cylinders.
  5. It sounds more like an electrical fault to me, but yep could be fuel related.

    Are the earths in good condition, and all present on the engine? Does the fuel tap work via a vacuum, and is this line connected to the manifold (or other)?

    It sounds a lot like the carbs aren't seated properly, although you said you checked that. Check that they are by smearing some detergent or soap around them and watching for bubbles when the engine's running.

    If it were running on only 3 cylinders it would rev higher, albeit slowly.
  6. Thanks guys.

    I will try to get time to pull the plugs and take photos today.

    I think the earth is OK and the carbs seated. They attach to the block by short hard rubber boots. As I have eight and only need 4 I checked them all out for cracks and put the best ones on.

    I will keep working on it.
  7. Ok, here's an update after spending some more time in the garage.

    I started the motor and let it idle for a while to warm it up. It seems to idle ok with the occasional misfire but nothing much. I could feel heat building in the headers of the front bank but didn't appear to be much heat from the rear two. Not wanting to burn my fingers I put some water on a rag and put it on the end of a screw driver. Testing it on the front headers, they were hot enough to cause steam. Same with the back cylinder on the left (the side the chain is on) which is number one. Number three (the other rear side) was warm but no where near as hot as the others. No hiss of steam, just made the rag warm.

    I then took out the plugs. I tried to take some photos but couldn't get close enough focus to be of any use.

    No 1 was black.
    No 2 was grey to black (front right side)
    No 4 was black shading to grey (front left side)
    No 3 was almost as clean as when I put it in new. This is the cylinder thats not generating much heat.

    Obviously not running on number three.

    I changed the coil over that feeds the two rear cylinders but no change. I then checked the wires running to the coil but couldn't find any faults.

    I haven't got to look at the carbs yet. Hopefully will do that tomorrow.

    What causes a particular cylinder to fail to run?
  8. you checked for spark at #3 by removing [edit] sparkplug from motor, earthing the threaded portion to the block and cranking her overwhilst visually inspecting for spark??

    thats the first step in finding out why it isnt running.
    then on to fuel....
  9. *i think - from very rough memory*
    1 is on power when 3 is on inlet. the coils should spark on both cycles therefore switching the leads between 1 and 3 should produce the same spark timing. this will at least tell you if it is your lead or coil that is causing that cylinder to not fire.

    correct me if i am wrong doods :?
  10. Hey techno, Roarin here. Just one question -have you done a compression test to see if all cylinders are within spec? Just a thought.
    Also try swapping plug (high tension) leads to see if #3 lead is faulty. Or better still replace with a lead that is known to be fine.
    Oh -one more thing. Can you get at the carby bowl drain screws? Try draining & compare volume of others to see if enough fuel is there. Number 3 plug should be quite black if sufficient fuel is getting through but not enough spark.
  11. Another hour or so in the garage after work tonight.

    I used another coil lead to cylinder 3. No difference. I then put a plug in it and grounded it to the motor. It looked like it had good spark. Nice and fat and blue.

    When I increased the revs it appeared to be weaker but didn't disappear altogether. The same test on number 1 showed the same. It should still be enough to ignite the fuel shouldn't it.

    I then pushed up each of the slides in the carby throats. Each one felt smooth and went back down as soon as I let it go. I could also hear an explusion of air when I pushed each one up. I took the cover off the carb that feeds no. 3 and there were no cracks or splits in the rubber so I put it back together.

    I haven't been able to test piston compression as I don't have a gauge. I'll ask around to see if I can borrow one.

    Does this info give anyone more clues about what is happening?
  12. clean spark plug with spark present -> usually means no fuel exiting the carby to reach the combustion chamber.
    if there was fuel getting in there, and fouling, leaning out or only partially burning there would be some amount of discolouration to your plug.

    petc_ock on -> whip the fuel line off the carb, fuel spills everywhere?

    there is a drain screw at the bottom of the carb - is there fuel getting in to the bowl?i know you said you cleaned the carbs, is it possible the needle is jammed in the needle & seat?

    or are your jets simply just clogged?

    it will be something simple, i'm not saying compresion is within specs or good but even with fugged rings you would still get some form of ignition in the combustion chamber to colour the plug.
  13. poor mans compression test-

    1-bike on centrestand
    2-in 4th gear
    3-remove sparkplug of cylinder to be tested and also cylinder that is known to work.
    4-with one hand, roll the rear wheel slowly whilst putting your thumb over the sparkplug hole.
    5-notice it will blow your finger off and suck it back in as the piston goes up and down.
    6-repeat for working cylinder and ask yourself if there was a noticeable difference.
  14. Couple of thoughts.

    I recently had some problems and a large part of what it come down too was I didn't have resitor type plugs in so J9A instead of j9Rb. turns out it was sparking strongly on one cylinder (per coil) but not the other.

    also check your plug cap resistances. No. 3 cap amy be buggered.

    the other thought was the difference in VF1000 engines. the early vf engines had 180 deg. cranks. The high performance models had 360 deg cranks. So the rc30 and the 1000R.

    Perhaps they went to 360 deg. cranks on later vf1000's. Though I suspect it would run a lot worse again.
  15. Did you check the float levels when you had the carbs off?

    Is the advance set correctly?

    Is the fuel pipe kinked anywhere restricting fuel?

    Just thoughts.
  16. Spoke with a VF1000 owner yesterday, describing your dilema. He said one word. Carbies.
  17. Man sounds like a tough nut to crack. I have had a high tension lead that was ok under low load and idle, ran fine, then under high revs, it was breaking down. Drove me funkin nuts :tantrum: till I found it. Was intermittent though, just replaced the lead and whala. That does kinda explain the clean plug thats happening. Unfortunately its a trial and error, illiminating 1 by 1 all the factors. O-ring on intake manifoldsnot sealing?-leaks and crack on the intake manifold?

    Im just wondering too,are these like the old CDI ignition on Honda's. You can occasionaly have those sealed CDI units fire on low revs, but again fail under higher load.
    Sounds like a real barstard.
  18. Well, just to round out the topic.....

    I spoke to the mechanic today and he can't cure it either. After taking up room in my garage for two years I am calling it quits and moving on.

    I will pick it up on Thursday. I'll then see what the local wreckers will offer me and consider whether its worth selling it whole or parting it out.

    Another old bike bites the dust... :(
  19. Dibs on rear tyre and braided front brake lines :grin: I reckon the GS would like a new back tyre and braided lines :cool:

    Might do some research on the other front brake components (m-cyl, calipers) as well, may just be that the VF has better stock bits than the suzy

  20. Dibs on the forks. There is an SR500 cafe in Kingston that would like some better forks.