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Hot and bothered Hornet

Discussion in 'Technical and Troubleshooting Torque' started by gongrider, Dec 8, 2012.

  1. Well the Hornet from hornet has progressed but it still has an irritating issue.

    After some slower riding the temp will rise to about two notches from the top and the thermofan comes on. This isn't so much of an issue and is probably to be expected on a 30C day.

    However, when the bike gets this warm it starts running like poo. But only at low revs - taking off from a stop is particularly a problem. In many cases the bike will start moving then all power will disappear and it will stall. It also may stall at idle.

    At colder temperatures there is no apparent issue or at least nothing unusual for an ageing carby bike.

    I am now looking at the regulator/rectifier because I have had a few headlight globes and the thermofan fuse blow on a few occasions. My theory is that heat soak causes break down and the voltages at low revs are such that the ignition is too weak at low revs to run smoothly.

    Am I barking up the right tree?

  2. Maybe but the battery should compensate at low revs. I would say it is more than likely a fuel/carb issue. Measure the voltage across the battery at low revs and see what you get.
  3. Yeah the carb is what I was looking at originally. But I have thoroughly cleaned, checked and even swapped the carbs for another set and the behaviour is almost exactly the same, so I started looking at other areas.

    The problems don't seem to arise until I have been riding for a while and the temps get high.

    I have also changed the coils to the stick-coil type on the newer CBRs (no leads). Changed the ignition module (although it wasn't the problem, a diode was blown in the ignition barrel).

    Thought it was a vacuum leak from the carb-engine rubber insulators, but I have sealed those properly.

    The bike has come so far from barely being able to start so this last hurdle is all I need to rectify before enjoying the bike properly!

    Will get a multimeter on there soon. Going to have to get the bike warm first though.
  4. Given what you've said, electrical could well be the issue.

    But the problem also sounds a lot like rich fuelling, the idle mixture screws being the first and esiest thing to check/try.

    Even if you've swapped and cleaned the carbs, do you know if the jets and settings are standard and original? Also, any airbox, airfilter or exhaust sytem mods on your bike? Or the donor bike, for that matter. Wear in the slides/needles could be letting more fuel through, and so on.

    Either way, I'd at least check what the factory setting is for the idle mixture screws (maybe 2 to 2 1/2 turns out from closed for a Honda of that vintage). You might not want to play with fuelling much more than that if it doesn't improve matters until you can rule out the possible electrical issues you're looking into at the moment.

    Another possible simple remedy that won't add to any other potential issues is a new set of specified plugs, even if the current set are recent or otherwise seem OK. If there's no change you'll just have a spare set to go in at the next change.

    Worth considering too, is that the stick-coil mod isn't necessarily going to work properly on your bike's ignition setup just because the CBR has it.
  5. Rich fuelling is a possibility. The pilot screws I have fiddled with to no end and found they seem to be best at factory settings (1.75 turns out).

    I believe the jets are standard on both carbs. No mods to any area of the engine except the stick coil mod I mentioned before. This I don't believe is related as the bike behaves identically to when it had the factory coils.

    Have put a new set of plugs in (iridiums because I couldn't get standard ones locally).

    Wear in the needles is possible. I guess if they are letting a little bit of fuel through at closed/just cracked throttle it will run overly rich at low rpm and be especially bad when warm.

    Weird that it will do much the same thing with two different sets of carbs (one set are only supposed to be <40,000km old).

    I will probably find another regulator/rectifier anyway since the bike has blown more than its fair share of headlight globes and fan fuses.

    Cheers for the suggestions. Might have to pull the carbs out one more time and have a close look (they must be the cleanest carbs around on a 14 year old bike with all the times I've had them off).
  6. My partner has same bike and exact same issues. Fuses blowing here and there and thermo fan not kicking in till way too late. We ended up forking out bit over $800 recently to auto elec who specialises just in bikes. Basically he just lowered every possible load possible and Im still not convinced that this solved the issues at all, because it seems to have drained another battery. Trouble is she rarely rides it now days and the only run it gets is from me maybe 3-4 times a year, so naturally the battery is going to be a bit average. We replaced the rec/reg ages ago when we bought it coz as we know, its Hondas achilles heel, and we were told that its charging fine. Unfortunately from here its a process of illimination. My hunch is on the thermostat switch. I think its just cutting in way too late. Some KTM's had issues apparently and you could get two different cut in temperature. Like 90 something and 60 something degree. So if you find a fix, love to here it!:)
  7. I have about 3 threads going on the Hornet...

    Looks like I have finally fixed the hot running issue!

    I found a burnt connector between the stator and regulator rectifier a couple of weeks ago, and I believe it was only getting two phases from the stator! Cut the connector out and soldered the wires directly and it looked like the electrics had improved.

    However... hot running issue still there.

    Then by chance, a mate dropped in yesterday with a spare MOSFET regulator rectifier. I did some wiring modifications, got it in and idle voltage had come up from 12.5V to a niiiice 14-14.2V.

    Took it for a test ride today, got it hot.

    No change in running, the bike was very ridable and seemingly dealt with slow traffic with ease :)

    So in the end... When the thermofan was kicking in it was just enough extra load to drop the voltage and ruin supply of power to the ignition, resulting in stumbling and bucking. Repaired stator wires and new reg/rectifier and all is well in the world again :)
  8. Nope, seems I spoke too soon.

    After some heat soak the idle becomes choppy and it will cut out. Sounds like it's starving for fuel. But any sort of throttle % and it responds perfectly. I don't understand it.
  9. tried changing the coolant?
  10. Not yet, but the coolant in there looks quite good and is pumping through quite well. I have some radiator flush and I was going to use Water Wetter to replace it.

    It's not so much that it's getting hot - as far as I'm aware the thermofan comes on at two notches from the top by design. It's just that this seems to be the temperature where it also runs badly (after some heat soak).

    I was thinking of trying a cooler fan switch so the thermofan comes on a bit lower, in theory stopping the bike getting warm enough to run shitty.
  11. Coolant was changed at the service just before you bought the bike (a year ago, by the way), I wouldn't think it needs replacement. That said I'm wondering if there's an air-lock somewhere that stops the cooler water circulating back correctly.
  12. Had a bit more of a think about these issues and wondered if the problem was a bit of fuel starvation at idle when hot.

    Theres only two ways I could see this happen:

    1. The fuel line is getting hot and vaporising fuel in the line before it reaches the carbs, vapor lock.

    2. The petcock vacuum hose is soft and when it gets hot, collapses and cuts off vacuum supply and starves fuel.

    The vacuum hose that was on there was pretty thin and soft so I think it could have been an issue. I swapped it for a much more rigid line.

    Would it be possible for it to only cause issues at idle though? I know vacuum is highest at idle and this is when it's most likely to collapse, but would the bike be likely to respond instantly to a bit of throttle?

    Did a bit of work today, shortened the fuel line quite a bit, swapped the vacuum line as mentioned, rereouted some wiring that may have insulated the regulator/rectifier and sealed up some gaps in the airbox.

    Haven't taken it for a test ride yet but I'm expecting to have made a difference somewhere!
  13. The fuel tap was replaced too not long before you bought the bike.
  14. Yeah i have had it open before and it looks perfect. The vacuum hose might have been one I put on when I first did the carbies.
  15. I had a very similar problem with an older Kawasaki Vulcan that I had and it turned out that it didn't like the iridium plugs, ran like a pig and was hard to start. As soon as I put in the original type plugs it ran fine.

    You would think that iridium plugs would be better for it.
  16. The Hornet ran perfectly on iridium plugs when I had them in. They'd still be there if an idiot mechanic at a service had not pulled them out (at $16 a pop), THROWN THEM AWAY, and replaced them with crappy standard NGKs......
  17. [quote="gongrider, post: 2562521]
    2. The petcock vacuum hose is soft and when it gets hot, collapses and cuts off vacuum supply and starves fuel.


    This is close to the mark. seen this a few times when vacuum lines to the fuel tap get old. What happens is the line leaks when it gets hot. This causes the bike to lean out. When the bike leans out, it gets hotter and causes the vacuum line to leak, which cause it to lean out . . . . .

    Replace line and clamps.
  18. I do have some iridium plugs in there at the moment. Spark seems to be ok and it's not particularly hard to start (except the choke on carby 3 seems to be blocked and it runs on 3 cylinders until warmed up).

    Anyway. Took it for a ride through the RNP on Sunday and to work yesterday.

    It is definitely better, the low range response is much nicer and the idle is much more consistent (although I had it set maybe a tad low).

    It didn't seem like it was going to cut out when hot so that's a good start.

    I think the air box air leaks were responsible for the fluttering idle.

    All in all it ran like a normal bike over the last couple of days, quite enjoyed it!.

    I'll reserve saying "it's fixed" until I get it properly warm for a while though.

    I think you would be impressed with the way it's running now Paul :)
  19. I'm glad this torturous process seems to be near an end. It's obvious to me that I must have been 'riding around' some shortcomings for a while before you bought it.

    Anyway, I DO want to see it in its new livery, it looks fabulous in the photos...