Fuel starvation...or what the he#k?

Discussion in 'Mechanics Garage' started by bigoledave, Jan 13, 2018.

  1. bigoledave

    bigoledave New Member

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    Greetings fellow unemployed mechanics..

    Bike: 1997 VFR 750 23 k miles...been indoors always..USED to run great. Been sitting almost
    all the time for a few years.
    Symptom: Starts "OK' and idles. I THINK all four cylinders are firing. Now..when giving it
    a sharp twist, big RPM drop..then slowly climbs. Rider test: Starts OK, put in first gear and
    runs ok at VERY low throttle twist. Shift to second..runs kinda ok at VER low twist throttle.
    If throttle is twisted just a little, noticeable LOSS of power. If ckoke applied and same throttle
    twist is used..same problem. Bike is just about un-runnable ...if a slight hill is encountered and throttle
    is just twisted slightly, power goes DOWN. Only way to climb the hill is to downshift to first or maaaaybe
    second.

    Recent work done:
    All new plugs put in.
    Carb assembly removed, carbs "rebuilt" ( cleaned internally adter dissasembly) by me months ago.

    Current "big idea why it runs like crap"
    I read some internet garbage about fuel pumps...so..I bought a new one on EbAy for $17....hasn'tn arrived yet.

    Fun facts: I rode a Honda CB35o nd in high school drunk ar 102 MPG
    I bought an SL350 in 1969 and rode it r/t from LA to Zihaetenaho Mexico
    I bought the very first Honda VFR 750 in Poulsbo, wa in 1983.
    I had one of the VFR's with major oil-cam wear 1983 problems.

    I think of abandoning biking.....but no!!

    So........whatcha think mhy VERY poorly running 1997 VFR 750 probkem is?

    1) Weird poor connection electrical resistance problem.
    2) All carbs are clooged with ??? and afe the root cause.
    3) Weird clog in plumbing between tank and carbs.
    4) The electrical fuel pump..or it;s rela are "bad".

    Cheers...

    Dave
     
  2. RllwJoe

    RllwJoe Member

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    Welcome to VFRW Dave!

    Have you looked into the gas tank for rust?
    You may have a plugged up filter or fuel pick-up.
    That would be my second guess, you already covered my first when you cleaned the carbs.
    If you have rust in the tank, you will need to reclean the carbs in case you sucked some into them.

    From your discription, it sounds like a lack of fuel.
    I would stay focused on fuel, and eliminate all possibiities there first.
     
  3. squirrelman

    squirrelman Member

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    remove airbox top and filter so you can see whether the vacuum slides move in response to throttle with engine running. all should be the same.
     
  4. fink

    fink Insider

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    Are all 4 pipes hot. To me it sounds like a blocked pilot jet or a bit of fuel starvation.
     
  5. bigoledave

    bigoledave New Member

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    Yep..thanks very much....I am more and more coming to the conclusion that it is
    fuel starvation as the bike acts like any vehicle ( car or mc) acts when it
    is at those last few seconds when you run out of gas, So...
    I will check the whole fuel supply system, tank crud, clogged filters, bad fuel
    pump relay or pump itself.
     
  6. bigoledave

    bigoledave New Member

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    ok..good simple test..thanks very much
     
  7. bigoledave

    bigoledave New Member

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    ok...got it..i will check.....thanks very much
     
  8. Terry Smith

    Terry Smith Member

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    Does this model have a vacuum petcock for the fuel? If so you might check there and make sure it is functioning properly as if not you can get starvation problems. Find the vacuum line, suck on it and check that fuel flows freely into container.

    I had a dodgy running problem on my ST1100 that felt similar, ran fine at low revs but over 4000 it coughed and farted and did not want to rev out. This one turned out to be low voltage reaching the ECU due to corrosion in some of the intervening connectors, in my case the big red plug that connected to the right switch pod (kill switch/starter etc). I was able to diagnose this with a voltmeter into the ECU plug. However I cleaned my carbs out six times before I found that...
     
  9. bigoledave

    bigoledave New Member

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    well...you have me thinking about the entire problem maybe being electrical now. Coincidentally to the running problems, the charging circuit also does not work!! I have measured the voltage at the battery and read 12.45 volts. I started it using jumper cables and read the same voltage when it is running at any RPM. I have been thinking it was a weird coincidence that I have a charging failure ...at the same time that it runs so badly. And..the battery is not great. So.... had been pretty convinced I had a problem relating to getting enough fuel to the carbs. Now I am not sure at all.
     
  10. Terry Smith

    Terry Smith Member

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    I was going down the carb/fuel path on my ST but even though I was sure the carbs and fuel lines were all clean, the problem persisted.

    You "should" be able to run with no fuel pump provided the tank is close to full; the pump is only needed when the level is low/below the carbs. My VTR1000 has no fuel pump at all. That would enable you to eliminate the fuel pump and relay as a possible problem.
     
  11. bigoledave

    bigoledave New Member

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    Ok....so....the bike a few days ago had two BIG problems:
    1) Started kind of OK but ran like crap.
    2) Charging system not working as voltage was always about 12.5

    I learned a lot reading this site and decided to fix the charge issue first...and bought a cheapo
    rectifier. Works GREAT....charge issue fixed....and maybe the engine sounds a little better??

    Then, I began debugging the poor engine running. First I listed for any sound from the fuel
    pump ( after learning a lot on this site ). NO sound heard when ignition switched on. I then
    used my Clymer manual and fussed around with my voltmeter and some jumpers and looked
    at the pump relay and pump. I proved to myself the relay WAS getting 12v when the ignition
    was turned on. I then was thinking of just putting some 12v to the pump and see what happens.
    I did that and only hear a "click" when the jump is touched..but no other sounds. So0000..
    I jumped on Ebay, bought myself a fuel pump for under $16 !! and bought a used relay for
    $18. Bottom line. I think I am on the right track...all the performance issue seem right in line
    with fuel STARVATION. I will follow up when I get the parts.... -Dave
     
  12. squirrelman

    squirrelman Member

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    good luck but that cheap chinese fuel pump won't last long. you missed the section in the service manual that shows how to bypass the relay for testing ?
     
    Last edited: Jan 19, 2018
  13. bigoledave

    bigoledave New Member

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    I think I invented my own minor variation on the test....and, in the end just decided to buy both pump and relay as I keep telling myself how many dollars I am saving in not having some "mechanic" spend 3 hours "diagnosing" at about 90 per hour. I only ride very locally and occassionally ( being 70 now).....so if my Chinese pump craps out is not a big deal. ( And why would it crap out??)............Thx for your comments,...-Dave
     
  14. Diving Pete

    Diving Pete Insider

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    Because it is built out of crap components, there is no quality control, & its been reverse made without any understanding of why it's been made that way, no comprehension of mellurgy, & also not tested to the same standards.


    BUT good luck....
     
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  15. bigoledave

    bigoledave New Member

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    Thanks for the input.....A new Honda pump is about $145. My pump had this is the Ebay ad:

    "......★★★★★10 YEARS EXPERIENCE
    ★★★★★ISO/TS16949 & QS900 STANDARD
    ★★★★★ 1 YEAR WARRANTY


    ..."Since 2001, we have started to manufacture the fuel pump for after market. These fuel pumps are all made up of first-class material in order to strengthen the durability and extend the usage life. Some competitors' pumps use cheap material inside leading unstability and short life. The all procedures are executed strictly according ISO/TS1649 and QS900 standard which is highest quality class for OEM in auto industry.Every pump is 100% tested before shipment. Customers can purchase these pumps without concern. .."

    Of course, that may be all BS in the ad....who knows? But...again..I am just riding very close to home and very occasionally. So....I will take the "chance" of premature failure and use my $136 savings on some good wine.
     
  16. Diving Pete

    Diving Pete Insider

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    Lets examine that a little as I’m really bored – its raining here:

    10 YEARS EXPERIENCE
    So the engineer has been building these for 10 years but they have been making them since 2001...!!

    ISO/TS16949 & QS900 STANDARD
    All ISO/TS 16949 certificates should be issued by certification bodies accredited by IATF and these organizations are listed on their website - http://www.iatfglobaloversight.org/certification-bodies/under-contract/ - Is the company here?

    1 YEAR WARRANTY
    Doesn’t include the postage or other taxes back to China & then back to the US – in other words not worth the paper its not written on…

    These fuel pumps are all made up of first-class material in order to strengthen the durability and extend the usage life.
    What material, OEM spec - somehow I really doubt it. Does each pump they have pump the same amount continuously - lol

    All the rest is just blah..

    This sort of thing I'd have got a 2nd hand OEM pump from a wrecked bike.
     
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  17. skimad4x4

    skimad4x4 "Official" VFRWorld Greeter

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    A bit harsh for the newbie Pete - especially as nowadays some OEM parts for some Harleys and loads of other motorbikes are indeed sourced from a few really good factories in China but always under very strict quality control.

    The problem with CrapBay purchases is the frequency of very dubious stuff where you have no idea who the real supplier(manufacturer) is. I personally would prefer fitting a used but genuine Honda part for anything mission critical - and a fuel pump failing whilst on an interstate HOV would certainly not be a good thing.

    However as you have already laid out cash for Chinese parts then fit them and see if they will do the trick.

    If the problems persist or return later on, then you might wish to investigate sourcing an OEM replacement from a breakers yard as plan B. For now go Chinese and see if the old gal comes to life. PS where are the photos of your VFR and why no post yet in the introductions part of the forum?

    Take care


    SkiMad
     
  18. squirrelman

    squirrelman Member

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    the exact same (or easily converted) fuel pump was used on many pre-FI bikes from several manufacturers on many models over many years, so finding a good one at a salvage yard is EZ. :cool:
     
  19. bigoledave

    bigoledave New Member

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    Wow..sorry about the poor introduction on my part.. I will fix that soon..sorry! Update on my poor running VFR. I put on my $12.95 rectifier and charging-voltage issues are resolved. Secondly, I installed a "used"Honda fuel pump relay and my new cheap fuel pump. ( BTW..it looks of high quality ).
    Results: Starts way better..idles fine. Road test: Runs poorly, small throttle moves kinda work but
    anything more ...it does not respond.....but!!.. one time I had a one second long "good engine" and it
    about threw me off the bike backwards...then it resorted to being able to be ridden at posted speeds
    but again..but ANY excessive twist of the throttle is met with zero increase in power. Then..I applied the
    choke to FULLY on while driving it at 40 mpg....and there was very little difference in how it ran. Maybe it even ran better!. So.....the bike is kinda "runnable" for putting around town but has some major issue still.
    It seems to me I still am dealing with a fuel starvation issue. When I replaced the fuel pump today, there
    was extremely good flow from the rubber tube entering the pump. Huge stream of good looking gas. So..
    my next moves seem to be to bite the bullet, pull the carb assembly off the bike, look closely at fuel
    blockage issues entering the carb assembly, then if nothing obvious is seen, go through the disassembly-clean up procedure as described in my Clymer manual. I did that procedure two years ago but the bike
    has been just sitting for a looong time with the fuel valve on and 10 percent alcohol gas in it. Being lazy and retired....I have thought of just driving the bike to Burton Motorsports near where I live and saying.."fixit" but my ego can't handle that.....yet.
     
  20. Diving Pete

    Diving Pete Insider

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    Dave,

    sounds like your carbs are out of whack...

    As you have now just about realised bikes hate sitting still.. lol

    Buy a gasket kit for the carbs (doesn't need to be original)
    You may also need to get 4 x intake rubbers - these get brittle over time - does not need to be original..

    Get the carbs off
    fix 1 at a time - be careful with the screws !
    check jets & pilots - its very easy for your carbs to be gummed up - had to do mine 3 times - lol
    take pictures
    set your float heights
    DO Balance your carbs after...

    Its not that hard to do but be methodical - DO NOT strip the carbs into the 4 separate units. The plastic joints are brittle & not easily replaced..

    Use a remote bottle for bench testing - to see if they leak.
    Then once carbs are back on bike then use the remote fuel bottle to start the bike - leave the tank out of the way.
     
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