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Clutchup.co.za
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Discussion Starter · #1 ·
We went on a trip this weekend we had a blast! about 10 or so bikes and just the dust of the namakwaland here in the Karroo of the Western Cape.

Average speed must have been 80-120kph on the GPS and the bike really handled it like a champ. It was pretty hot (33-35c) so we wanted to push on and the last 30km stint to the camp site we opened her up a little and started cruising 150-165kph on the gps. After about 5 or so km, the bike developed a misfire and felt like it does when you run out of fuel. I then tapped off a little, flipped the tap and she came to life again. I get back up to speed and the same thing happens. I tap off again and by now we are riding at 90kph and it seems like its only going on one cylinder. I slow down even more and the second cylinder comes back to life.


We got to the camp site and the bike was perfectly, idles smoothly, revs smoothly and still pulls pretty good. I decided to leave her for the night and and nurse her home in the morning.

The morning comes, we are packed and ready to roll, checked the oil, start her up and shes idling (or purring like a kitten) we are off. I set the cruising speed at 110kph and things are going well. We do have 300km day ahead and its going to be about 35-38c, so naturally I want to move on to get home. After about 120km, I push a little harder because I want to move on, hello misfire!

I tapped off again and all is fine.



Now my conclusion to this is that when when I got the bike I had to do a plug change. Instead of the regular DPR8EA-9, I fitted the DPR9EA-9 instead and im assuming with the extra load(wife and luggage) the bikes plugs are running too hot at certain speeds and is starting to break down.

Possibility of being fuel related is slim - I have a Mikuni Vacuum pump and I also have a Mosfet Regulator.

I have not checked the fuel filter yet. :color:


Could the 9's cause this under more extreme conditions (heat, speed, load) ?

Come eye candy

 

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Registered
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I doubt it's the plugs. I ran a Mikuni vacum fuel pump on my AT for quite some time and it worked well
until it developed the fuel starvation symptoms like you describe. Somehow fuel is introduced into the vacum line and disables the pump. It's
been well documented and African Queens even came out with the T fitting to trap this fuel...but it never seemed to work
for me. I went with the Facet after that. You can try bypassing the pump with the hoses straight to the carbs for further troubleshooting...but I'm
betting on the pump being the culprit here. You can let it sit for awhile after it happens and it will fire right up...only to die again later.
 

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Space Emperor
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657 Posts
Hey Stev0

I had something similar happen at one time, although it happened way below the speeds you're talking about. It proved to be an electrical issue, caused by the poor contacts in the starter relay, and a bad connection on a wire under the front of the tank, a duff battery.

I had the one cylinder thing happen quite a few times before I found out that the choke was stuck and the carbs were way out of balance.

If you're sure it's not the fuel, only air starvation comes to mind ... did you check the airfilter?

Sorry, that was probably not much help ...
 

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Clutchup.co.za
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131 Posts
Discussion Starter · #4 ·
I've also read up on the plugs and it seems its not the plugs. I've not checked the fuel filter, but I got one to replace it with either way. Airfilter is a foam pipercross (not checked it yet)

Doubt its the choke too as I also have metal choke nuts.

Ill have to start trouble shooting things, little by little ;)


Thanks for the ideas! Keep em coming!
 

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I've also read up on the plugs and it seems its not the plugs. I've not checked the fuel filter, but I got one to replace it with either way. Airfilter is a foam pipercross (not checked it yet)

Doubt its the choke too as I also have metal choke nuts.

Ill have to start trouble shooting things, little by little ;)


Thanks for the ideas! Keep em coming!
Furthermore on the Mikuni and fuel blocking the vacum source. It was more prone to happen during high ambient temps
as you experienced when outside temp was in the mid 30's Celsius. Following pic was when my Mikuni was installed showing the
(vacum line) and the modification to trap the fuel so it would not block the vacum source. It never worked and I still had fuel starvation symptoms.

 

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Clutchup.co.za
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131 Posts
Discussion Starter · #6 ·
I've changed the fuel filter to a bigger one and took the bike for a ride. It seems to run pretty well up to 160kph, but I would need more testing to confirm that it solved the issue. For the time being, im satisfied that its gone.

Keep you guys up to date.
 
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