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Post subject: Nipp up
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johnlc  Powerband Master Joined: 14 Oct 2006 Total posts: 793 Location: John O'Groats |
Finally got brakes etc sorted ,went out for a spin .and engine had a slight nip up .Right hand plug was a nice tan colour but left one had a grey look like shotblasted steel ,running vcdi and pwk's on Farhon tuned motor .What could be the cause .oil pump is slightly higher than normal setting,Pwk's on 140 mains ,needle 2nd notch from top ,vcdi has 26.5 degrees from 3000rpm to 7000rpm
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Posted: Tue Jun 17, 2008 9:16 pm
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| Rich |
John, I had the same thing on my Yamagamma last week running the 420 main jets, even though they gave a rich tea brown on a plug chop and everyone was saying they were too big. I was giving it beans along the bypass on the way to the Kent meet (chasing a Scooby) and it lost power so I instantly pulled the clutch in and coasted to a stop. It fired up again so I carried on as normal and it was OK but I wasn't happy when I tried the PWKs on it at the weekend (idle wouldn't settle) so my curiosity got the better and I pulled the head. My left hand plug sounds just like yours and the left piston had just started to go on the middle of the crown. Something Gareth said about a possible crank seal has been bugging me so I've pulled the engine out and am going to fit new seals and a left piston for peace of mind. It's evident the rings have just been touching the power valves (it's on +2mm) so I'm going to trim them back while it's apart. God knows how long it's been like that for - no wonder it rattles! I'll get some pics up tomorrow
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Posted: Tue Jun 17, 2008 9:45 pm
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hybrid  Rear-wheel Steering! Joined: 07 Aug 2003 Total posts: 2591 |
You've got an air leak somewhere I'd say.
Possibly the left crank seal, but could also be base gasket, manifolds etc.
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Posted: Tue Jun 17, 2008 10:16 pm
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VindaloobeastRear-wheel Steering! Joined: 25 Aug 2005 Total posts: 2623 Location: Gloucester |
Well screw my old boots did Beast not tell you an air leak was there somewhere...duh...!
Mr Beast.
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Posted: Tue Jun 17, 2008 10:35 pm
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Post subject: Re: Nipp up
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bryanbengal All-gear Wheelie! Joined: 03 Oct 2006 Total posts: 1988 Location: Eastwood, Essex |
| johnlc wrote: |
| Finally got brakes etc sorted ,went out for a spin .and engine had a slight nip up .Right hand plug was a nice tan colour but left one had a grey look like shotblasted steel ,running vcdi and pwk's on Farhon tuned motor .What could be the cause .oil pump is slightly higher than normal setting,Pwk's on 140 mains ,needle 2nd notch from top ,vcdi has 26.5 degrees from 3000rpm to 7000rpm |
think its worse than that beast, you have answered you own question with the shotblasted steel look, you have way way too much advance in your powerband and have deternation.
what are your points above 7000rpm?
With a tunned engine you should be down to about 17deg once in the powerband and come right down to about 0deg at max revs. I had 18.5deg with just skimmed head and nearly holed the piston, took it down to 17deg and new pistons are fine.
My max advance is 27deg at 3000rpm, then 20deg at 6000rpm, 17deg at 7000rpm, 12deg at 9500rpm, 5deg at 10000rpm and 0deg at 10500rpm. Not saying you should use these points but sure this is your problem.
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Posted: Tue Jun 17, 2008 11:12 pm
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| Rich |
| Vindaloobeast wrote: |
Well screw my old boots did Beast not tell you an air leak was there somewhere...duh...!
Mr Beast. |
Not confirmed yet, just a suspicion at the moment. Right side head dome and plug are still perfect brown 
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Posted: Tue Jun 17, 2008 11:34 pm
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Post subject: Nip up
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johnlcPowerband Master Joined: 14 Oct 2006 Total posts: 793 Location: John O'Groats |
Why would it detonate on just one cylinder.Not questioning any replies just wondering why thats all 
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Posted: Wed Jun 18, 2008 10:30 pm
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bryanbengalAll-gear Wheelie! Joined: 03 Oct 2006 Total posts: 1988 Location: Eastwood, Essex |
my right one after blow up, disregard the dammage from the piston skirt, but notice no deternation.
http://i87.photobucket.com/albums/k148/bryanbengal/DSCF1116.jpg
left hand piston on its way to extra breathing hole. 
http://i87.photobucket.com/albums/k148/bryanbengal/DSCF1113.jpg
can a slight air leak on the rotor seal, or twisted crank contribute to it on that side.
This was a second terminal problem that day, had a total lock/seize at 85mph b4, may have twisted crank.
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Posted: Wed Jun 18, 2008 11:08 pm
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Billy One-handed Stoppie! Joined: 12 Oct 2007 Total posts: 2198 Location: Sweden arise! |
Nasty.  Did the barrels make it?
Btw i think the reason for this might be the carbon build-up on the piston crowns. It's one explanation anyway, can be something else. Carbon build up are very very bad when it gets that thick!
I (Tha pro!   ) suggest a polished piston crown (It doesn't attrack the heat from the ignition/explosion as much. Try it yourself and heat up polished alloy with hot air, it's almost impossible, but once the surface are raw it makes the heat travel through the metal, so this must be a good thing on a piston crown!) and running fully synthetic. 
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Last edited by Billy on Thu Jun 19, 2008 12:12 am; edited 1 time in total
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Posted: Thu Jun 19, 2008 12:05 am
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bryanbengalAll-gear Wheelie! Joined: 03 Oct 2006 Total posts: 1988 Location: Eastwood, Essex |
yep and only 1 size up on rebore, but it was on 1.75 so now 370cc.
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Posted: Thu Jun 19, 2008 12:08 am
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jante350 RD/RZ Jedi Master Joined: 05 Aug 2003 Total posts: 5220 Location: Bergen, Norway |
Bryan, did you check your crank for twisting? Big difference between the two sides for no good reason is usually down to a slightly twisted crank..
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Posted: Thu Jun 19, 2008 8:35 am
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bryanbengalAll-gear Wheelie! Joined: 03 Oct 2006 Total posts: 1988 Location: Eastwood, Essex |
I compleetly rebuilt the engine in October, but didnt check the crank for twisting when I took it out, just got it totaly rebuilt as big end was f***ed.
http://i87.photobucket.com/albums/k148/bryanbengal/DSCF1128.jpg
and this was the cause.
http://i87.photobucket.com/albums/k148/bryanbengal/DSCF1125.jpg
Had been running fine for over a year till it locked up on earlyer that day, was going for a test ride on a Super Duke, so had to get to North Essex, got there but on the way home it let go big time.
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Posted: Thu Jun 19, 2008 10:35 am
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