High Fuel consumption(choke cable stuck?)

Discussion in '3rd & 4th Generation 1990-1997' started by Eward, Oct 17, 2018.

  1. Eward

    Eward New Member

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    I got myself a pretty nice VFR 750 91 for 600 $. Wasnt running right, found out it was running on 3 cilinders so i replaced all the spark plugs and now its running pretty good. Although i feel like fuel consumption is rather high and on the highway with steady mph it felt kind of nudgy..

    So im trying to figure out what to do next, feel like maybe there's something with the choke. If i open the choke when the bike is warm it stalls. I did have the carbs open and cleaned out the jets so i dont assume thats the problem. Another problem is the steering is kind of weird, but i already ordered some tapered bearings to replace them, hoping it fixes the weird steering.

    Any other things i should look into are welcome!
     
  2. squirrelman

    squirrelman Member

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    WELCOME ! :Yo:

    what kind of color dija see on the plugs you removed? with no real experience with the new bike, why think fuel consumption is too high ? any actual numbers ?

    if you had carbs off it would be easy to confirm chokes are closing properly without sticking. does the lever return to off position ?

    other things ? check the plug between the r/r and stator for signs of melting or burning.
     
    Last edited: Oct 17, 2018
  3. MechTech

    MechTech New Member

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    Apply the choke while your riding. If it causes the engine to get real blubbery then your choke probably isnt stuck. How does the bike run at low, medium, and high throttle? Main jets on that engine should be 130 I believe and the needle clips should be in the second slot from the top. Check the factory manual to be sure. Do you smell fresh gas around it? My 92 was leaking at the fuel pump as well as at the fuel level sender where it mounts in the bottom of the tank.
     
  4. squirrelman

    squirrelman Member

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    Leaking fuel pumps are extremely rare. :Scared: :Nono::Smokin:

    Honda gave you a fuel pump installed next to a common source of high-temperature, possibly sparky, electricks, not the best setup for safety. :Tsk:
     
  5. MechTech

    MechTech New Member

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    Gotta work with watcha got.
     
  6. Eward

    Eward New Member

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    I made a video for you guys to illustrate it, im also somewhat worried because someone said "That doesn't sound to good

     
  7. MechTech

    MechTech New Member

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    Doesn't sound particularly bad to me. The whine is the sound of the gear driven valve train which is classic for these engines. Also, it looks like the PAIR system may have been removed. The plates that cover the exhaust ports where the PAIR was installed can highlight a bit of a pinging sound in sync with the exhaust note. Not to be mistaken with engine knock.
    Check your carb sync and read your plugs to ensure your mixture is ok. I run non ethanol fuel 91 octane.
     
  8. Eward

    Eward New Member

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    Thanks mechtech! I honestly found it weird because the bike revs up nicely. I think it's time to build a carb sync tool with some clear tubing and fluid. Thing has been sitting with the last owner for some time. Next week i'll be swapping the head bearings for tapered ones because this bikes steering is rather weird..
     
  9. MechTech

    MechTech New Member

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    Check the height of the fork tubes in the triple clamp as well. Raising the fork tubes in the triple clamp changes the rake angle and will make the bike quicker in a turn. Too much and it will tend to dive into a turn. This is ok if you are racing on a tight course but not particularly comfortable for cruising on the street. Put the bike up on the center stand and weight the rear so that the front wheel is off the ground. Manipulate the front wheel and forks to see if you have excessive play in the bearings before you invest it new bearings. It could be that the stock bearings just need to be repacked with grease and tightened up a bit. Forks are easy to rebuild as well. Just be careful when removing the nut at the top. It is spring loaded and will fly off if you're not careful. Use an electric or pneumatic impact wrench to remove the 6mm bolt at the bottom. Lay all of the parts out carefully in the same order as they were removed and assemble in the reverse. Order new seals and dust scrubbers. You can typically use the old seal as an install tool for the new one if you don't want to invest in a new tool. Or you can take the forks to a shop and have them do the job for you. Not terribly expensive. The carb sync tool can be found at places like ProMotion for about $25. You can buy guages as well. Do a little research on them first or find someone who can calibrate them. I built a tool years ago before mercury was illegal to own.
    You can find pdf versions of the factory manual on line. Download one if you haven't already.
     
  10. Eward

    Eward New Member

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    Alright so i tried to sync the carbs with this contraption that i just made today, but it didn't really work. All the carbs tried to do is suck up the ATF that i put in the tubes which i gladly prevented from happening. About the bearing, i bet its toast because the bike also likes to wobble a little bit at slow speeds and considering the height of the forks, id have to look at that but sounds pretty interesting. It was a bit of a bummer that the carbs sync didn't work, i kept each hose at least 6.5 feet long so i didn't thought it would try to suck it in as much, although it was mainly one cilinder that was doing that. And then if it would have worked. how the hell am i supposed to reach those f*cking screws, haha.

    So i have done some research i'm going to make to bottled variant of this which is a lot safer, and the likelyhood of shit coming in my carbs is small, but im suspecting there so far off that its kind of hard to do this :p



    [​IMG]
     
    Last edited: Nov 4, 2018
  11. MechTech

    MechTech New Member

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    Check out this guide:
    750 91 - 97 Carb Balance Guide
    Its on the vfrworld site. ;
     
  12. RhINO

    RhINO New Member

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    I have a later model bike, but mine had the thermostat stuck open so the engine ran a bit cold. After I changed that the fuel consumption dropped a bit. How much is your bike drinking?
     
  13. Blackslide

    Blackslide New Member

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    I'll have to rack up more miles next summer and start keeping a log of the fillups. Didn't bother to do so yet, since a carb rebuild might be coming up. But my 3rd gen seems to swallow a bunch of fuel when starting cold.

    Interesting note about the thermostat. My bike only goes up to the 1/2 mark when idling for quite long or riding really slow, on the highway it is barely on the low mark. Is this normal?

    Riding on the storm
     
  14. MechTech

    MechTech New Member

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    Going to the half mark is pretty good. I replaced my thermostat with a factory new one and it still runs a bit on the cold side. As long as your fan cycles on and off I wouldn't worry about temp. Keep a log of your mileage and let us know what you are getting. Its typical to get crummy mileage when the engine is cold.
     
  15. Terry Smith

    Terry Smith Member

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    Very approximately, 1/4 on a temp gauge corresponds to the thermostat opening temp (usually around 80C), 1/2 to around 100C (fan operating temp) and 3/4 is around 122C, which is around the max safe temp.

    If you've got decent airflow speed, the temp should sit around 1/4 but not lower, in traffic/stationary it should get to 1/2 or a little more.

    If the thermostat is stuck open, you might see a lower temperature than 1/4 when riding. A better test is to monitor the radiator temperature with your hand from a cold start. If the radiator stays cold for a few minutes then quite suddenly gets too hot to touch, your thermostat is healthy. If the temperature creeps up slowly from the time the engine starts, it is stuck open.
     
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  16. Eward

    Eward New Member

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    Alright guys, i figured out why it was rattling like in the video. So i checked out the front headers and there we go, the left front header bolts where never there.... Well one barely in. So i put a new one in and fastened them nice and thight. No more rattling! I think that was part of the problem why it was running bad because it was backfiring right there, that one header was just loose

    Winter has arrived here and its getting bloody cold so i put her inside for now. When i got time i'll check the carbs sync again and i have to get started on that head bearing job.

    Sent from my ONEPLUS A3003 using Tapatalk
     
  17. Eward

    Eward New Member

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    So i decide to restart this topic. Still have try terry's method and did some testing myself.
    Let her idle for some time and she doesnt get higher then the picture, fan does jump on tho...

    Latest drive was a lot of highway driving with the misses on the back. Got 31.75 mpg (1/13,5) i still consider this bad on fuelly the avarage is about 0,4 liters less per km

    Im trying to find a thermostat online but its rather hard. Finding a lot of used ones tho..[​IMG]

    Sent from my ONEPLUS A3003 using Tapatalk
     
  18. Eward

    Eward New Member

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    So i did some new testing and such. Over on the dutch forum they told me to check the ail filter, but it looks fine. Also filled her up again and the usage was on 1/8,5 kms this time where is all this fuel going jeez.

    So i checked if the radiator suddenly gets hot after a while, but it just never gets hot. I could touch it bare handed easy al the time. Also the hose on the pic running from the thermos to the rad doesn't really get hot either. Bike runs pretty damn good so dont think its its in the carbs and the fuel pump doesnt seem to be leaking eather.

    Basicly did what terry told me to do.

    Some reported their vfr 750 usage and its around 1/19kms per litre so mine is half that's not right[​IMG][​IMG][​IMG]

    Sent from my ONEPLUS A3003 using Tapatalk
     
  19. squirrelman

    squirrelman Member

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    u need to replace the thermostat.
     
  20. Eward

    Eward New Member

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    Soo some progress. Had a look today and fuel was dripping from both these nipples, i smelled them ofcourse to check if it was fuel, and it was. Also the small one leaked a bunch of fuel. I fixed temporary like this rn. [​IMG]

    Sent from my ONEPLUS A3003 using Tapatalk
     
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