OzVMX Forum
Clubroom => Tech Talk => Topic started by: rohan on June 20, 2011, 05:04:18 pm
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I have a recently rebuilt PE400 engine that pings (quite badly) right at the top of the rev range. In an attempt to correct this I have checked the carb specs, the ignition timing and rode it without the muffler as I was concerned the head may have been getting to hot as the gasses couldn’t get out properly (exhaust flange was leaking oil slightly).
I am now thinking to up the main jet by a size or two to make sure the bike is getting enough fuel up top. Does anyone have any ideas on why I am getting this pinging or how to fix it? Or could I simply be over revving the engine?
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HAve the same problem on a few YZ, still not sorted it out. Tried jets and timing no real change just shifted the problem and scope.
I have had better luck with changing fuel supply, I suspect its not dence enough. Try some avgas and see if it still happens
thats my next step
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Rabbit, use a dial indicator to check timing and check this against factory settings. I tend to short shift mine and not rev it out as they tend to develop most of thier power about mid range.
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Yeah I agree with Stew on the shortshifting the 400 you don't need to rev it out like a 125 I find mine dies off up top too on stock jetting.
I found it performed better with a clean new muffler also the flange they always leak I have had good results though with some high temp red silastic no leak anymore. ;)
Also I run Premium I have heard there is no difference in some people's opinion but I think you get alot more bang also there is further octane additave you can buy and try. :)
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You could also check the thickness of the head and base gaskets you rebuilt with, If they are thinner, you may have raised the compression. This can sometimes bring on the death rattle, with dodgee feul.
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I had the same problem with my KX 420. they are a very peeky motor and make all there power at the top so need to be reved. I have had to retard the ignition and it will run fine on BPpremuim (98). I have secured a suply of avgas that i run my Tracker on and the KX likes a 50:50 mix of this with premium.
None of the fuel today is as good as super was with lead!
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It's a universaly shit ignition.
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Try a colder grade plug and experiment with different oils. I favour plain Mobil 2 stroke and Nippendenso plugs - certainly fixed the problem with my 465.
If that fails try adding an inch or 2 to your header pipe length, that will add some more exhaust radicals to the mix at top end cooling and slowing the combustion burn a little.
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Guy on the PE forum (elsewhere) simply machined his head to drop the compression ratio.
Ugly fuel .
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If that fails try adding an inch or 2 to your header pipe length, that will add some more exhaust radicals to the mix at top end cooling and slowing the combustion burn a little.
How would hot exhaust gas cool anything?
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Do a plug chop at wound out,for Main jet. If ok then Av gas
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Ahhh a big bore 2 stroke pinging. Bring back memories.YZ 490's did it all the time.Take the advise from above.Pinging usually means lean ( and power). Does it have the std air box etc still on it? If not that could also be not helping the problem.
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What are you running I run 8's or 9's
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8 is hotter though try an iridium 9 or 10 I know they cost like $20 but then the bike starts easier and I have had a good run lately with iridiums. ;)
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Look on ebay for iridiums. They are pretty cheap in boxes of 4, well under $20 each ;)
Otherwise the head mod on the PE forum seems to have worked.
What fuel you running by the way?
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Premium fuel with a 25:1 mix - I know it should be 20:1 but this wouldnt be causing the problem would it?
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Premium fuel with a 25:1 mix - I know it should be 20:1 but this wouldnt be causing the problem would it?
Na
You have a large motor with a high compression ratio , older ignition and shit fuel .
It,s gotta ping , can,t do anything else.
You could prove a point by putting some AVGAS in it.
Betcha it stops pinging. :)
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Avgas it is, next question - where can I get some on the Gold Coast?
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Premium as in 95? That is the minimum required for PE's back in the day as per the handbook but i honestly think you should use higher. Get some BP98 or race fuel. Pump fuel is pretty crap these days, but really you should be able to tune it to suit the fuel.
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In the "OLD DAYS " the fuel had that ugly poison LEAD in it , guess what it was there for. ;D
Avgas and BP racing fuel ( which is very close to avgas if not the same ) both still have lead in them.
Or as LW says start to detune it until it stops pinging.
Drop compression , retard the ignition , up the jetting until it blows black smoke.
I,me over stating it a bit but you get the general idea.
Avgas you get from the airport . :)
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For those that remember, you used to be able to get AVGAS from the Tiger Moth hanger at the old Surfers Paradise Raceway on the Gold Coast about 15 years ago. The same location they used to have operation drag - where the cop’s would race the locals in a 400 chev powered VN cop car – great fun.
I was in my early 20's and used to put it in my VL commodore, fuel was around 55 cents a liter at the time and we used to pay 90 cents a liter for AVGAS (what a rip off :)). Thought my VL was the fastest around with the AVGAS in her...
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Rabbit , can you remember a green 2 door Hatch back Torana that used to kick arse.
That was me .
You can buy AV gas at Auto Barn stores or try old mate at Oxenford opposite the pub
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Unfortunately I don’t remember that Torry, now she would be worth 3 – 4 times what she was worth then.
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How would hot exhaust gas cool anything?
http://en.wikipedia.org/wiki/Exhaust_gas_recirculation
PR, try an equivalent but 1 grade colder ND brand plug (Toyota dealer) and glass bead blast your spark plug threads and plug seat as well as the head gasket surfaces on the head and barrel, the buildup of muck over the years can hurt heat transfer from the plug to the head to the barrel.
It's not thick with paint is it (head and barrel)?
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How would hot exhaust gas cool anything?
http://en.wikipedia.org/wiki/Exhaust_gas_recirculation
Not anything there that remotely refers to a 2T engine. ???
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Not anything there that remotely refers to a 2T engine. ???
2 strokes have a combustion cycle the same as a 4 stroke.
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Premium fuel with a 25:1 mix - I know it should be 20:1 but this wouldnt be causing the problem would it?
If you went to 20/1 Peter you would increase your chances of pinging because you would be running your bike leaner. (just a little )
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20 to 1 will bring it closer to standard specs and what the stock jetting was set up for. I would be starting at factory specs first. What is your compression like? did you use mineral oil for bedding in the rings? The thick paint is a good point. The guy on the PE forum with the same probs as you found a big part of his prob was caused by powdercoating on the engine which he ended up removing and just painting it. Apparantly some Canams came out with powdercoated engines had this problem too as it keeps the heat in.
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Compression is good but havent checked it with a gauge,
Barrel and head were painted but not with an excessive coat,
Mineral oil was used to bed the rings.
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Sounds good well done now you can enjoy riding it, thanks Michael.
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a chap on the PE forum filled his PE400 tank with new fuel and... WOOSH! Life Is Better.
You just never know what it might be.
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Yeah after a few weeks or a month (depending on how much fuel is in the tank) it starts to stink and then you know its usless. Pretty common issue that we have to live with these days.