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Thread: Fuel Starvation? Vapour Lock?

  1. #1
    Join Date
    Sep 2013
    Location
    East Sussex
    Posts
    31

    Default Fuel Starvation? Vapour Lock?

    Hoping for some advice on an issue I had today. Sorry it's a long post but best to give as much info as I can I think.

    My '92 851 Strada was running perfectly, did about 20-30 miles on open roads without issue. Then coming into Hastings (May Day Run!) I got stuck in traffic. Properly stuck so about 20-30 minutes barely moving with an occasional car length movement. The bike got hot, the fan kicked in and the temperature stabilized around 100 on the gauge. All was then OK but still not moving. Then it spat a little coolant out (from under the seat so guess from the header tank somehow) but as the temp had stabilized and I'd recently just changed the coolant I assumed it was just "finding its level". Still not moving, it stayed hot but didn't get hotter or cooler. After about another 10 minutes we started to move but the bike wasn't running well at all, miss-firing and felt like I had fuel starvation. If I kept the revs up it wasn't as bad, but cruising at around 4,000rpm there was a noticable surging. If I let the revs drop it cut out but always restarted fine. When missing it was popping/banging and my friend following me said it smelt of fuel. Luckily we were near my parent's house so we stopped there for a cup of tea (how British!!).

    After being parked for 30 minutes the temp had dropped but the poor running was still there. It isn't the vent pipe as whilst at my parent's house we opened the filler a few times and it made no difference. As there was no obvious issue and it looked like a fuel issue I decided to try to ride the bike home and keep the revs up. It was missing and surging quite badly but after some miles improved a little. After the next fast bit where I could hit 60-70 for a mile or two it was much better. After about 10 miles and a few faster stretches the fault had completely disappeared and the bike is now running perfectly again.

    If it was my car I would swear it was fuel vapourisation, but the bike shouldn't suffer from that being injected.

    Do they just hate getting that hot (even after sitting for over 30 minutes the underside of the fuel tank still felt warm)?
    Is it possible to get some kind of airlock in the fuel system?
    I guess it could be "dirt" in the system somehow that has washed through but would that happen or would anything out of place block an injector?
    I did think that maybe the heat had softened a fuel hose and maybe it had collapsed causing fuel starvation, but again that's guessing.

    What would you check (and if it's technical how would I check it)? Any advice is appreciated.

    I hope to get the bike out in the next week or two and give it another run to see if it recurrs but I doubt I'll be able to get it that hot again.

  2. #2
    Join Date
    Oct 2011
    Location
    Vancouver B.C.
    Posts
    166

    Default

    Al that I can say is that these bike were never meant to sit on the starting line too long.
    It may have just started to gum up(foul) on the spark plugs, then after you took it out for an "Italian tune up" it cleared up...?

  3. #3
    Join Date
    Apr 2007
    Location
    bakersville, NC
    Posts
    2,759

    Default

    The first thing I would check is the fuel filter and hoses inside the tank.

  4. #4
    Join Date
    Nov 2007
    Location
    North Carolina, USA
    Posts
    692

    Default

    Quote Originally Posted by marvin View Post
    The first thing I would check is the fuel filter and hoses inside the tank.
    one vote in agreement with Marvin-- almost every time I found swelled and split hoses.

  5. #5
    Join Date
    Jun 2007
    Location
    Bris Vegas
    Posts
    3,404

    Default

    High probability on dodgy fuel hose hot fuel expanded hose which may have exposed faults in the hose.....but how about this.
    Air temp sensor is in standard location, it went to full hot air trim, which means lean out mixture. Hot air tells the air pressure sensor to lean out as well because it thinks it’s at altitude. Hot fuel makes it run even leaner. The effect would be similar to running out of fuel. Over flow bottle spewed green which means coolant seriously boiled, temp gauge possibly has an error of 10+%. Fan should come on at 92-95 and hold under 100C.

    I’ve moved the air temp sensor to the front sub frame like every model after the 888. Thermal blanket is fitted under the tank. And I flushed and used radiator cleaner on the cooling system. Let the bike run until the fan comes on and check engine temp with a lazer thermometer to see temp gauge accuracy. You may need to reduce your oil change interval, because if you scored 115-120c water temp, then oil temp was similar and you reduced the oils service life. Haven’t had a problem with mine since. Bastard thing use to get over 100c just going through town on a 35c day and ran like a pig with a digestive complaint. Find some clear road and blow air over it and it simmered down.
    Last edited by griff851; 05-08-2018 at 10:20 AM.
    Griff
    To infinity and.......

  6. #6
    Join Date
    Apr 2007
    Location
    Kuala Lumpur, Malaysia
    Posts
    453

    Default

    Yes, I had the same problem here. Always hard to pull away from traffic lights until I moved the air temp sensor out of the bottom of the air box.

  7. #7
    Join Date
    Aug 2008
    Location
    West Pennine Moors ,England
    Posts
    203

    Default

    I'm in agreement with Mark T and Marvin and what other's have said..they're not designed to be stood still at that sort of temperatures, need to keep moving ,or turn the engine off if you're stuck in trafiic. They just boil up and overheat ..hence the poor running symptoms....

    cheers,adie851

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