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Problem when held flat out for a while?

F

Freaky

Joined Apr 2008
204 Posts | 0+
Worcestershire England
Hi all, haven't posted a problem for a while, everything has been quite good so far this year apart from this little niggle.
Bear in mind my 650 is a road going supermoto, when held flat out in top on a long road after about 15 20 seconds at 100+mph it cuts out and miss fires, pull the clutch, give it a few revs then try again and it's ok for about 10 secs then does it again.
My thinking is fuel? Maybe at such high revs for such a long duration it's daining the bowl of fuel? Float height? Although it's been ok up until now.
Tried new plug before you ask!
The only thing i have done is altered the crankcase breather by putting a k&n style cone filter on a length of hose out of the rocker cover, works well and not blowing any oil from it, blocked the frame where the breather originally went, can't see that altering anything for the worse?
Your input would be appreciated as usual.
 
My first thought as I was reading the thread was that the oil coming from the crank case breather was blowing oil up into the air boot, but, it looks as though you have that sorted.

However, here's what comes to mind:

Float height has you mentioned, and if you're running the dellorto there's a filter screen on the inlet to the carb where the fuel lines hook up to, is it clean?

How's the tank vent?

How's the carb vents?

What does the plug look like? Look deep inside, what' the color, see any metal bits? How's the jetting?

There's no rev limiter on these ignitions if memory serves, are the valves floating?

What level are you running the oil level at?
 
i would say wrong heat plug. what is the MJ and needle code? exhaust? state of tune.

regards

Taffy
 
Thanks for the input guys.
DaleEO
Tank vent is good.
Carb vents are clear.
Plug looks good, nice tan colour.
Jetting is as good as I can get it, will not run with any smaller main jet.
Oil is at the bottom of the glass.
Haven't got round to float level yet, hopefully check that tomorrow.

Taffy
Plug is one of your Denso's and new.
Main jet is 205, new atomiser and needle from yourself, can't remember the codes but will look tomorrow.
Exhaust is full Doma system.
Tune is standard.
 
Codes are DR272 and K51 if that helps chaps.

Why do you say wrong plu heat Taffy?

Cheers all.
 
it's breaking down with the temps so high possibly...

regards

Taffy
 
Come to think of it I do seem to encounter problems with anything but the standard NGK DCPR8E plug, tried the NGK iridium and had problems with the park being snuffed out from idle and now with the Denso version I have this, well maybe, can't blame that until I've slotted the old standard plug in and ridden it, that'll have to wait until the weekend now as the usual british summertime wet season has begun, I can't get wet or I melt.
 
Just a quick note to confirm it was the new Denso plug at fault, not saying the plug itself is faulty but my bike just doesn't like anything but the standard NGK, ran perfect today even when it was flat out for nearly two miles.
 
Better yet, Take just the vent off, streatch out like superman and blow in the tube. Naked with a swim cap on.

Be careful though, you could get dizzy.
 
Freaky said:
Just a quick note to confirm it was the new Denso plug at fault, not saying the plug itself is faulty but my bike just doesn't like anything but the standard NGK, ran perfect today even when it was flat out for nearly two miles.
Click to expand...

well i can't prove otherwise from here but I don't believe that there's anything wrong with the plug. that's just daft!

it'll be something else in the end I'm sure....

regards

Taffy
 
Taffy said:
well i can't prove otherwise from here but I don't believe that there's anything wrong with the plug. that's just daft!

it'll be something else in the end I'm sure....

regards

Taffy
Click to expand...

It is odd I agree but you were right in saying it could be the plug, all vents are clear for sure. I'm not going to delve any deeper at the moment as it's running great, it ain't broke so I ain't gonna fix it!
 
Hello!
I experienced a similar thing last weekend. At the end of the straight (spending some time above 8k) the engine misfired or died. After the braking it was OK again. i thought it was typically a problem with the fuel supply. I checked hoses, vents, jets, vibrations and float bowl level. No problems found and no adjustments helped. When I got the pace up, the problem occurred more than just at the end of the tall straight. To this event I had mounted a brand new Iridium 27. As being the only thing changed from last time, I switched back to my old and used NGK DCPR9EV - Problem gone! Went from 6th place in the qualify, lost appr. 1,5 sec and ended second at the race!
 
no plug likes filthy rich to stinkin lean. they can't cope. somewhere along the line the two plugs are struggling with the mixtures? 205MJ is over the recommended main. I see they used to fit 175s to FCs Freaky?

I don't know your jetting Mats. might start a new thread for you?

regards

Taffy
 
Taffy said:
I don't know your jetting Mats. might start a new thread for you?

regards

Taffy
Click to expand...
I do not know the jetting myself! It is a Lectron carb and the jetting was carefully adjusted at the Dyno, but I can not read the id of the needle! :D As the NGK DCPR9EV has not let me down so far, I'll just stick to it - No problem! Although I'm pretty sure I could fill a thread of my own with all problems, failures, questions I'm facing! :D
 
mine did the same thing with the iridium plug, the pilot was rich. after that I did some mucking about if its lean it backfires trying to start it.... 693cc ..... turned the kicktarter into a sideshow ride ouch! need real boots to kick the beast or a higher ceiling in the shed :lol:

I havent tried it back in with the new engine and bigger valves but it seems the old fat electrode plug might be less sensitive to jetting at least on the pilot than the irridium plug is...
 
I have a Denso Iridium plug where the "porslinpart" with the electrode has seperated from the body so when i gave my bike full throttle it blew the cap of!
Took me a some time to figure out that strange problem ;-)
Perhaps i am the one hat destroyed the Denso with my cleaning metod with CRC Bräkleen.
Regards
Jampe
 
i know that the heat range won't tolerate the wrong fuelling, whether it's a 7 saying no to lean or a 9 saying no to rich but an iridium 9 has to be the way forwards and all the jetting needs have to be modified to go with it. as for yours bushie well where the phuq do you start?

you moved the goalposts to the halfway line and then tell us to play the same game! :p

regards

Taffy
 
wot a load of Tosh :p

Start rich at the top and come down ironing out the bumps along the way, its in the doc don't you know :D

I simply noted as others have that the irridium plug appears to be a fussy lil beatch in some situations

of course Im going to have to wait for you to work it out for me as well though, its getting too complixiaciated for a bushmechanic I think ill just get my gearing sorted and buy one of those blue switches :oops: :oops: 8O :lol:
 

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