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  #1  
Old 20-11-2006, 06:07 PM
HeavyMetalGod HeavyMetalGod is offline
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Default Gilera DNA 125 Serious problem. Help!

Hi all,

Basically, my Gilera DNA 125cc (l/c four-stroke 125 for those who haven't come across it) usually starts and idles like normal pretty much, and runs fine for the first few miles. However, after this, when I release the throttle after going a steady speed for a while, the bike often looses power, sometimes for just a few seconds, other times until I come to a complete stop. Often this is accompanied by some backfire, however it usual runs a little better after some backfire. Once it starts doing this on ride, it keeps doing it regularly, usually when slowing down.
Once it stops, its always difficult getting it going again. It just turns over and nothing happens, and then eventually it idles very rough for a few seconds, and then it goes vaguelly back to normal. Feels find of like it runs out of fuel.

Few technical points -

Once at full speed, the bike runs just like normal (problem usually only occurs slowing down)
Spark plug seems in order (tested against the spark plug chart)
Only happens once bike is warm (after a few minutes)
I have a very slight coolant leak on the coolant tube going into the cylinder head (I've been told by garage that this doesn't matter), but it is only slight. I keep it topped up.

Any help would be very much appreciated,

Cheers - Peter
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  #2  
Old 21-11-2006, 04:07 PM
Simon B Simon B is offline
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Have you cleaned the fuel tap/filter?

Check the tank for muck, that would be me first port of call
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Old 21-11-2006, 05:27 PM
HeavyMetalGod HeavyMetalGod is offline
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Thanks for the reply, unfortunately I will be unable to check the fuel tap and tank before Friday, but the fuel filter is only 100 miles old. I was also to do a few small tests. Results below

I started the bike up, let it run for a minute or two (just idling), worked fine. So I stopped the engine. I then drained the float chamber to see what the state of the fuel was in, and it seemed fine (no water or crap in it). I then tried to start it again, and it wouldn't go. It was as if it had just cut out on my on one of my journeys. Eventually, after a little struggle, it goes again. (again, just like as if I'd cut out on a drive).

I further tested the bike by trying to start the engine with the fuel lead disconnected from the carb, and put into a jar (vacuum tube still in place). I noticed that it took a little while (5 - 10 seconds) before fuel would flow. Before I had this problem, my bike always starts staight away.

I'm suspecting fuel problem, but I'm not entirely sure where to look? Fuel pump, fuel leads?

Again, any help would be very much appreciated.
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Old 21-11-2006, 05:37 PM
Simon B Simon B is offline
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Check the petrol tap, prob got a filter attached to it which is inside the tank, if its full o ****e and only running well on a full tank souns like the bottom of the filter is clogged
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Old 21-11-2006, 06:28 PM
HeavyMetalGod HeavyMetalGod is offline
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That sounds about right, but I though about that too, but I though that if the fuel flow is constrained by muck in the fuel pump or tank, then wouldn't the top end be affected? This problem only really happens upon re-acceleration after slowing down a bit. At full throttle it doesn't miss a beat. I mean I don't know much about this really, so I might be getting the wrong end of the stick, but the problem happens only in certain situations (i.e. same place along a route that I take to work, give or take 200 meters), not randomly.

I'm grateful for any ideas you might have.
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  #6  
Old 21-11-2006, 10:15 PM
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have you checked the genny as it sounds like it cuold be that if its taking awhile to start
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  #7  
Old 22-11-2006, 12:22 PM
pyro pyro is offline
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Vaccum tube to tap is split or not on properly.
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  #8  
Old 22-11-2006, 12:51 PM
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just about to say from the first post the vacuum hose sounds like its split or not on properly, great minds think alike

from memory your will find that the vacuum is different on the overrun, ie slowing down, hence the problem only occuring then

so check along the hoses, either its not on properly or possibly gone hard and not sealing properly, or the diagphram in the fuel tap is dodgy

does the tap have a prime position??
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  #9  
Old 24-11-2006, 05:32 PM
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It sounds like a two stroke...46 Years ago I had this problem with mine and it was caused by congealed oil in the two stroke mix..but water and sh:t in the tank or carb could cause it on any bike...only cure I can think of is to empty the tank and flush it out, then the fuel hose, finally the carb..no good doing part of the job...John
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  #10  
Old 24-11-2006, 08:41 PM
HeavyMetalGod HeavyMetalGod is offline
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crap or water in the fuel has to be my guess, plus its practically free to fix. Lol - but it is defenitely a four-stroke, I'm no mechanic, but I know that much. It's strange because I didn't think they made four-stroke twist and go
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Old 26-11-2006, 09:40 AM
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Have you checked the vacuum hose yet? I'm willing to bet thats what it is, sometimes they perish and collapse or even a pinhole will cause problems.
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Old 26-11-2006, 04:20 PM
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My son' Tashain is a 4 stroke twist and go he had a similar problem only solved it by putting another carb on it even though we had done every thing else surgested here including taking the carb out 3 times and cleaning it and a mate who's a bike machanic did the same he couldn't find the problem so replaced the carb.
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Old 02-12-2006, 09:34 AM
HeavyMetalGod HeavyMetalGod is offline
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Ok, a little update. Yesterday I had the bike apart, to access all the parts of the fuel system. I drained the tank, and rinsed it out with unleaded, replaced the fuel tap and fuel pump with some spare ones that I got off eBay. I noticed that there were two fuel filters, so I cut one of them out (the older one). I also saw that the fuel hoses were in good condition. I wasn't able to inspect all of the vacuum hose, but from the parts I did see, it was in good condition. This took 4 hours, cos its such a fiddly procedure!
Anyway, I took it for a drive. And all the old problems are there sadly! They may be marginally better, but it still cuts out as if its running out of fuel (and all the problems listed in my previous posts)

I'm out of ideas really, please help me out!
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Old 02-12-2006, 04:41 PM
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Take it where the local arseholes dump there stolen stuff, set light to it, leave rapidly, phone police next morning when you find it's missing, claim insurance. Most important of all don't get caught. Alternately give local scumbag a few quid to take it away and loose it
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Old 03-12-2006, 03:15 PM
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You might want to try the solution that I found when I had a similar problem decades ago on an FS1E.

It would run for so long then loose power until it died. Would then be a bastard to start back up.

The solution was that the fuel breather hole to vent fumes to air in the petrol cap had got bunged up causing a partial vacuum as the fuel was used. Unblocking it allowed the pressure to equalise with outside air pressure and allow the full fuel flow.

It sounds vaguely like you might have something like that so perhaps try loosening the filler cap or seeing if you can find the breather to unblock it. I just jabbed a small drill through the hole and it worked. Alternatively, when it fades and dies, loosen, remove and then replace the cap and see if it starts. Give it a short delay before attempting the restart so it has chance to get the fuel lines filled again.

Hope that helps.

Last edited by Rhythm Addict; 03-12-2006 at 03:18 PM.
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  #16  
Old 03-12-2006, 03:53 PM
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Hi again, another update. I removed the vacuum hoses to inspect them, and one of them appeared a little damaged. Now I don't know what level of damage is serious enough to stop them working correctly. So I've got some photos. This hose goes into the fuel pump. Thanks again in advance
Attached Images
  
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  #17  
Old 03-12-2006, 05:08 PM
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Quote:
Originally Posted by HeavyMetalGod
Hi again, another update. I removed the vacuum hoses to inspect them, and one of them appeared a little damaged. Now I don't know what level of damage is serious enough to stop them working correctly. So I've got some photos. This hose goes into the fuel pump. Thanks again in advance
if that is a hole that goes all the way through, then replace them chap
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  #18  
Old 03-12-2006, 06:44 PM
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Quote:
Originally Posted by kitkatman
if that is a hole that goes all the way through, then replace them chap
Even if it doesn't,change the pipe.Cheap enough and easy enough.
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  #19  
Old 03-12-2006, 10:53 PM
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sounds like it could be the coil breaking down. check for a spark next time it cuts out!!! only stating the obvious
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Old 04-12-2006, 11:23 AM
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1.jpg shows your problem, replace the damned hose!
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  #21  
Old 04-12-2006, 05:58 PM
HeavyMetalGod HeavyMetalGod is offline
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Another update. I replaced the all the vacuum hoses for some in better condition. I replaced the spark plug cap, and changed the spark plug for a spare that I know works. I also ran the bike with the fuel cap undone (to allow breather).
Sadly, however, there is absolutely no improvement at all. In fact, it felt worse than normal.

Personally, I am out of ideas. I have heard mention of a bad head gasket, or carb-icing, but I am suffering very specific symptoms with my bike.

Any help would be very much appreaciated
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  #22  
Old 04-12-2006, 06:20 PM
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I refer the honorable gentleman to my previous post.
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  #23  
Old 04-12-2006, 08:50 PM
HeavyMetalGod HeavyMetalGod is offline
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it's starting to look that way!
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  #24  
Old 04-12-2006, 09:55 PM
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have you tried draining the carb
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  #25  
Old 04-12-2006, 10:53 PM
HeavyMetalGod HeavyMetalGod is offline
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yeah, a few times. It just acts as it does when it's just cut out. (Very difficult to star, followed by a very rough idle). Even when it hasn't actually been used. The fact it behaved exactly the same way tells me that the problem is fuel related
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  #26  
Old 04-12-2006, 10:59 PM
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how olds the fuel ?, try draining the tank, and putting fresh petrol in it ! and try using new spark plug
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  #27  
Old 05-12-2006, 06:59 AM
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ive done both of those
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Old 05-12-2006, 07:10 AM
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is there a prime setting and can you remove all the fuel filters and try it or leave the fuel cap loose
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  #29  
Old 05-12-2006, 04:05 PM
pyro pyro is offline
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I'd get a hose running directly from the carb and connect it to a container with fuel in and bypass all the vacuum tap crap, I still think its to do with fuel not getting to the carb under certain conditions.
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  #30  
Old 05-12-2006, 04:33 PM
HeavyMetalGod HeavyMetalGod is offline
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I've tried running with the fuel cap undone, and it made no difference.
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