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Engine breaking down in 4th & 5th gear

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by BOB R STEED, May 16, 2016.

  1. Gday riders. Recently purchased a VLX 400 STEED modified into a bobber. in the few rides shes done, theres a clear and definite breaking down in 4th n 5th gear mainly when yr screwin it on a bit. She'll go to approx. 100kph in 5th and the start to breakdown, however, she'll go thru to 120kph in 4th and then start to breakdown and then in 5th the same and will go like a bucket of crap losing power and speed. in the lower gears she seems ok and starts without issue. overall the bike is in excellent condition, certainly looks better than it sounds when it starts breaking down!!!!!!! The engine is stamped NC25E in the initial prefix if the series number helps diagnosis of what possible problems would be, :poop::poop::poop:

  2. where did you purchase from mate?
  3. what does it do when it starts to break down?
  4. I going to assume you are getting a misfire for the time being. If it's misfiring as described then that is load related. So I'd be looking at plugs, leads, coils and plug caps.

    The other guess from your description, would be clutch slippage. If the revs are rising, but you can't get any more speed, then it's this.

    A better description of what is actually happening is need here. "Breaking down" suggests you are stopped on the side of the road.
    • Agree Agree x 2
  5. #5 BOB R STEED, May 19, 2016
    Last edited by a moderator: May 19, 2016
    Gday Uncle greg, couldn't find how to continue thread and reply to each of the comments in one go so i'll reply to each of you.
    im grateful for your assistance.
    I swapped my kxf450 for the bobber with a bloke on gumtree.
    If the number prefix is your concern,ive checked it out and the numbers are legit, engine and vin, however the bike hasn't come to australi by usual Honda oceania importation.

    Gday Ibast, thanks for your reply n advice, by breaking down, I mean the engine stops produceing power, sounds like shit and doesn't run anybetter than the proverbial either.
    I would assume with a strong sense of accuracy, if the problem in 4th and 5th occurred in 1st or 2nd, momentum wouldn't be maintained and sheer inertia alone or lack of would bring the engine to zero rpm.
    Once 3rd gear is selected and or you back off on the juice in 4th the problem ceases and she rides beautifuly without any form of mechanical dramas.
    Misfire suggests timing issues,however, the problem is engine failure in high gears whilst screwing the throttle on.
    The clutch holds as well as it should, all fluids are at their levels and new, plugs new and at gap of .7mm, leads n cdi system are in new condition although I did suspect ignition to be the problem (DUH!!),
    fuel is clean , air filter brand new.
    I'll try a new cdi and see how things go then.
    Was hoping there mayve been an inherent issue and an easy 5min was the longterm solution.

    Gday Lliljan, thanks for yr question,
    basic loss of power,coughn n spluttering, failure to accelerate tho not complete stop due to clutch holding and forward momentum, coughs n splutters worse if you screw the throttle on to try to power through it
    but ceases to be an issue if yr happy to wind her back and cruise at approx. 80 in 4th!(n)
    Spewin a bit, I swapped my 2012 kxf 450 in near immaculate condition and not yet 100hrs for the Honda AND I found yesterday a bolt located low on inside of the V that just turns n turns firmly but doesn't bite down and tighten.
    The bolt runs horizontal and is on the front cylinder housing facing fro
  6. No, Pinging suggests a timing issue. What you are experieincing is a load based issue. The engine is loaded up more in 4th and 5th than it is in 3rd.

    Find out what the resistance limits are for your leads, caps and coils and test with a multimeter.

    The other thing that looks a bit like this is an alternator failure and/or a regulator failure. Have you riden it far? Is it charging all right? Hows the headlight strength? Does is vary with rev?

    Alternatively it could be the tank vent being partially blocked.

    Still leaning towards ignition.
  7. Yeah mate, the headlight could be brighter hey.
    Initially I jz took the light to be a bit of a 'blingy' type and decided to put a better one on.
    Theres no real reputable sparkys/mechanics within a couple hours drive of here so as pissed as the scenario is im resolved to fixing the problem
    here at home.
    Will give the fuel system another goin over and purchase a quality multimeter.
    You wouldn't be able to point me in the right direction to find/buy/borrow/download/copy a manual by any chance?
    Whats the abbreviation for grateful for your help again n hope I can return the favour someday??
  8. Could be fuel starvation also
    • Agree Agree x 5
  9. Cheap multimeter is fine. You are not doing small measurements on a circuit board or testing HV equipment. $20 for repcocheapbarn.

    I think your model is a grey import, so a workshop manual may be difficult. maybe only in Japanese.
  10. I'd be checking;
    - tank vent
    - fuel filter (inline if it has one)
    - fuel tap (filter in tank and vacuum operation if fitted)
    - fuel lines
    - needle and seat (in carbs)
    - float level (in carbs)
    - cleanliness of carbs

    Also spark plugs, leads and caps as suggested earlier.
    • Agree Agree x 2
  11. yeah sounds like a sumoto special
    what ever you do
    do not take it back to them for service
    find a good moto mechanic and take it there
    • Like Like x 1
  12. Hi BOB R STEEDBOB R STEED what years the bike ? some of the carby models had vacuum operated slides in the carbies and the diaphragm splits with age stopping full opening of the slides. This stuffs the air/fuel mixture. You can buy these parts on Ebay and fit them yourself - carbs are prob. Mikuni 32mm . Other thing to check is some of these bikes run a 12 volt fuel pump to boost flow at higher demands. Yours maybe cactus and running on gravity flow to a point then....... follow fuel lines from tank to carby and fuel pump will be in this line - inline cylinder type usually. With ignition ON (dont start bike ) you should hear the pump whirring under the tank or seat. Aftermarket ones are avail. on Fleabay too.
  13. Since the bike seems to be a "grey import", are we sure you aren't just hitting some kind of Japanese speed limiter?
  14. Gday Riders, again, thankyou kindly for yr suggestions.
    'GREY IMPORT' means a singular/group import outside of regular factory import channels yes?
    The bike is 1988 from a vin search, also I checked the vin and engine numbers on a site called 'THE SOURCE'.....
    Many of you guys probably are aware of the site and the models n pcm numbers etc.
    According to V-SOURCE she checks out as 1988-1989. (frame and engine)
    Although, theres aspects to the bike which suggest shes far newer or practically unused also making the 12thou on the odometer
    seem believable.

    im not sure what SUMOTO SPECIAL means, I gather theyre a bike refurbisher, turning old model moto's into newer custom look
    EAST COAST CRUISER might be onto something, the fuel pump doesn't 'wir' on ignition power-up, as elec pumps usually do.
    Anyone suggesting fuel starvation might've been right onto it although IBAST's thoughts on ingnition issue still seem right due to the
    sharpness of the "breaking down' symptoms....very instant and electric seeming rather than kind of soft n gradual.

    A speed limiter may well act in a way affecting both ignition and fuel systems CRAZY CAM?

    So today is remove battery and charge after checking output at idle and various mid range rpm's. And investigation of the diaphrams may have to wait until ive some kind of manual or instruction for them.
    So to re-hash, ive changed fuel, removed n re-gapped plugs, inspected fuel and air filters, checked all fluids, inspected lines, checked wiring for shorts or arcs.

    Theres no visble tank breather, so the breather must be a function of the filler cap?
    How would the breathability?!?? of the cap be checked?

    Save a seat for us BASE JUMPER, I may need one!!
  15. Just took her for a quick spurt ....
    After the problems started rode for a km or so and stopped on roadside , shut her down and removed fuel cap to release any vacuum.
    There wasn't any wooshing of air sound.
    Put fuel cap back on, fired her up and the issues started again as usual.
    However I did notice the same problems occurred in third gear if the throttle is screwed on hard.....same coughing and spluttering, no real production of power
    but not complete engine shutdown.
    She'll stay in cough n splutter mode without complete breakdown for aslong as you hold throttle on hard.
    Seems almost instant return to smooth running and power production once the throttle is eased off to a cruise.
    Re-checked for fuel pump 'wir' at ignition power up....no sound at all from fuel pump.
    Going to go over electricals with multimeter and put batt on charge just in case.
  16. OK........
    12.6volts direct from batt terminals.
    All fuses and components running from fuses working.
    EXCEPT FUEL PUMP...no power at fuel pump plug,
    HOWEVER, under direct power from battery the fuel pump 'wirs'.!!

    Will begin backtracking from fuel pump along wires to fuse cage.

    Fingers crossed!!!!
  17. If you could ride it with the throttle on hard and it coughing and spluttering, then pull in the clutch and hit the kill switch, then remove one or more spark plugs and have a look at them it might help narrow things down.
    If they're wet/black/damp it may reinforce the ignition/electrical issue theory, but if they are dry and white/grey it probably points to fuel starvation.
    Left is normal, middle is rich, right is lean.

    EDIT - Just seen your message above, must have added while I was writing mine.
    Good work, looks like you're onto something with the fuel pump.
  18. Thanks PWBIKE, no further luck with it tho im afraid.
    Fading light has seen an end to productivity.
    The two wires to the pump plug soon disappear into the main loom beneath neat and tidy taping and loom casing.
    Will try to find where they go/come out at again tmoz.

    Whats the foreseeable issues if I was to wire direct to the battery via a toggle switch and fuse?
    There'd be no computer bcoz not fuel injected, so the pump would then only do what it does by itself? IE- a constant supply whether by constant running
    or supply by a self regulated internal system and pump until pressure required is reached and then cease pumping once pressure is attained and so on and so on?
  19. the pump should probably only run when engine is running, not when ignition is switched on but not running.

    check with engine running

  20. ? Thanks OLDCOROLLAS, are you sure mate?
    Any electric fuel pump vehicle ive known , theres a distinct 'wir' sound as the pump supplies fuel pressure when the ignition is switched on.
    I'm quoting experience from cars ofcourse, not motorbikes.

    EAST COAST CRUISER gave some ideas on this earlier in this thread.