My Vf1000 frustrations

Discussion in 'Mechanics Garage' started by techno, Jan 27, 2007.

  1. techno

    techno New Member

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    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 ( not called interceptors out here in Oz)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).

    Other
    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.I really want to ride it again as its in pretty good condition for the age and there aren't many left.

    Cheers

    Techno
     
  2. Ferris

    Ferris New Member

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    When it starts to cough, is it loading up rich (see / smell fuel), or dying out? Is it gradual, or abrupt (stuttering)? Any backfiring through the intake or exhaust?

    One thing I didn't see in the fuel issue list was a check of the CV slides in carbs. Do they all pull up when revving engine? If not, it would only be running on primary jets.
     
  3. GenLightening

    GenLightening New Member

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    If all the fuel issues check out fine, it could be a bad ignition module. I would really go through the carbs again, as that seems more likely. Also make sure the fuel line is not pinched when the tank is set into position. Does it run the same whether the tank is in place or running off an auxillary tank? When you cleaned the fuel tap, did you remove it and check the screens?
     
  4. Rev

    Rev New Member

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    I don't see where you swapped in a different CDI module; could be you have a bad one.
     
  5. RVFR

    RVFR Member

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    Pretty much what I'd say if I got here before Ferris ;) sounds like carb issues, are these the same carbs that were on your previous engine? or the ones that came with the other engine, if they are the ones that came with the other engine take then off and put on yours. I'm with ferris here sounds like the slides are not working. and I'm pretty sure there's a vacuum thingy going on there.
     
  6. techno

    techno New Member

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    Thanks Guys. So many options.

    I haven't swapped the CDI unit because I only have one. Getting another might be difficult.

    The fuel line isn't kinked. It was once and it wouldn't even idle, so thats not it.

    I tried running fuel from a container to rule out tank contamination - no difference.

    When I pulled the fuel tap I didn't get to any screens. I pulled off the handle and save three holes, one for on, off and reserve. I didn't think I could get to anymore. The rest appears to be inside the tank.

    When it stutters it does it abruptly when it gets to certain revs. It doesn't matter whether you gradually increase revs to sneak up on it or get there quickly.

    Without the airbox, looking down the carbs, the black plastic cylinders are still largely blocking the throat but are fluttering. Should they be retracting to open the throat?

    There is some backfiring but not much. I think it is loading up rather than dying out.

    I am going to try to pull the plugs again and take some photos. That may help analysis.

    Thanks for all the replies.:smile:
     
  7. GenLightening

    GenLightening New Member

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    The screens are inside the tank, they are pre-filters. It does sound more like a jetting problem, but the plugs should tell us more.

    Doug
     
  8. RVFR

    RVFR Member

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    still sounds like the slides are not opening, are these the old carbs off your engine? or the ones that came with the so call new engine?
     
  9. techno

    techno New Member

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    These carbs are the ones of my old motor because I knew they were working OK before. When I put the new motor in I just fitted them and it had this problem before I even did anything else.

    The carbs dont seem to have any connection other than a fuel line. Is there supposed to be a vaccuum line somewhere. How does it get vacuum?
     
  10. Ferris

    Ferris New Member

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    The vacuum port for the slide is the kinda oval shaped hole at the top of the carb throat. It is integral to the carb body - no hoses.

    Use your finger to lift each slide. They should move freely all the way up, with no binding or stickiness. As you lift them, you should hear air being expelled through the vacuum port.

    Look at the needle while the slide is raised - it should be centered in the little insert at the bottom of the carb bore, not dragging up sideways. Be aware, too, that the inserts can be installed upside down - the needle should be passing through the flared end of the insert. The slides should then lower themselves immediately as soon as you let go.

    To test them, use a compressed air blower held at an angle across the vacuum port. The slide should raise in proportion to the velocity of air you put across the port.
     
  11. Rev

    Rev New Member

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    hmm, a partially blocked pre-filter WOULD allow only a certain amount of fuel through, say up to 2500 rpm. Then after that, since a larger amount of fuel couldn't get through the blockage, the engine would starve, stutter and perhaps die. Another thought i have is does the choke function correctly?
     
  12. techno

    techno New Member

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    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 soem 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?
     
  13. Rev

    Rev New Member

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    plug wires go bad, did you check it? Look for wear/cracks or other damage. you could also check the resistance of the wire looking for an 'open' condition. In other words, if you have a functional plug wire, you will get some resistance through the wire, if it's damaged, you won't. Use an Ohmmeter and test the #3 wire.
     
  14. reg71

    reg71 Poser Staff Member

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    I've got to say this is a great troubleshooting thread. I have been lurking here nearly every day in hopes that I'll find you have solved your problem. Good luck, I'm sure there are others like me rooting for you!
     
  15. Rev

    Rev New Member

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    Another thing i thought of is just because the coil is hooked up doesn't mean it works. You need to check for 12volts to the coil and voltage coming out. Easiest way to do that is to pull the plug, put it back in the plug wire, ground it to the chassis and turn the engine over looking to see if the plug fires while you do.
     
  16. Minax

    Minax New Member

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    first.... do a compression test on the #3 cyl. in comparision to the rest of them.
    If you get a major difference, and if your sure the cam and valves are times right try putting a teaspoon of oil down the spark plug hole and cranking the engine for a few seconds ( with the spark plug out) to oil up the cyl walls. then check the compression again. Personally I would have done this b4 ever starting the motor and do it to all the cyl.

    If the compression is good.. this means mechanical timing and valve seats are good, go to the next thing up.. coil wires... ohmmeter against the rest of them. Large difference.. Replace wires all of them (yea it;'s expensive, so judge at your discretion, how long do you plan on keeping this bike... and how much money are you willing to spend to get it running.)

    if the compression is to high recheck you exaust valve for that cyl. it might be bent or just plain jammed closed. and since you in there check the other valve for movement just to be sure... The way you explained it you might have an intake valve getting stick open (causing a slight backfire) and low vacuum so the cyl won't run.

    Next thing up coil packs... you said you had tried both sets... now change packs from side to side and run the bike again... if one of your front cyl stops running you have found your problem, if the #3 still doesn't run the problem is mechanical or carb, if the 2 or 4 goes out its the coil (make sure when you install the coils, make sure to change their locations on the rail so that each coil runs a different cly than b4. Each coil runs 2 cyl and it fires both cly at the same time, if half the pack is out you will know at this point.

    Its hard to try to diagnose for online But I have one of these bikes and have done my fair share of work on them. These are just a few ideas... Don't kill the messenger if they don't work.:rolleyes:

    But if you have check and varifieds every thing to the best of you ability, the CDI box would be the next step... I know their expensive, but I also know they very rarely go out... so the pick up magnets would be a more likely suspect, their cheaper and their verry tempormental and go out at the drop of a hat.

    Let me know if this helps any... I have plenty of experience with the older V4's 750 and 1000... I have one of each and do my best to keep them out of the dealership cause the bike shops in the area I live are just too expensive and they don't do very good work for the money. Good for parts, but not on service if you know what I mean.

    Hope your bike gets better... It's nice to know I am not the only person who likes the 1000 vf.
     
  17. techno

    techno New Member

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    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?

    BTW, thanks for all the support. I now feel like I'm at least eliminating some of the potential causes of the problem.
     
  18. Ferris

    Ferris New Member

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    Since you have eliminated spark, that leaves fuel and compression....

    If you can't lay your hands on a compression tester (or better yet, a leakdown tester) you are left a little hamstrung. These are sold in auto parts stores here in the U.S. for as little as $20. I'd want to know, especially with a used engine.

    If the slide in that carb moves, the next thing I'd check is what is below it. Try cracking the bowl drain screw open a bit and making sure fuel runs out. Capture it - the amount should roughly equal bowl capacity. If the bowl is full, on to the main jet.

    Checking this would require removal of the bowl. Remove the main jet, of course checking to make sure it is clear. Then, remove the emulsion tube, again checking for it to be clear. Last is to check the fitting the needle passes through, insuring mainly that it isn't installed upside down.

    Reg is right - people are pulling for you. Send me a plane ticket. I'll work on it for beer and chicken wings. OK, maybe just beer.
     
  19. chesthing

    chesthing New Member

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    Techno, it sounds to me like the carbs are gummed up from sitting around with the same gas for too long, and the carb sending fuel to #3 cylinder is the worst - this is the only thing I can think of that would explain the clean spark plug, the fact it has good spark, and the fact the #3 header pipe doesnt get hot. Bad compression would still result in burned gas which would show in the temp of the header and the color of the plug. How long between the last time you put fresh gas into those carbs and now? I'd take them all apart and let the parts soak in a gallon of carb cleaner.
     
  20. Nailer45

    Nailer45 New Member

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    I had a 84 VF750F that did the same thing ..I found that the fuel pump was going bad and would lose pressure when trying to rev past 3,000 rpm.. I replaced the fuel pump and it ran fine...
    I hope this helps.
     
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