out for a sunday thrash and BANG.

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JonW
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Re: out for a sunday thrash and BANG.

#16 Post by JonW » Tue Dec 22, 2015 9:32 pm

Mark, do you have a fuel filter in there? Im wondering if your carbs were starved of fuel on the freeway, you just noticed the seize when you decelerated - lots of seizures happen at that point it seems. The other thing is the oil, running on a constant throttle is not the 2 strokes finest hour. two more things to think about?
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
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silverstrom
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Re: out for a sunday thrash and BANG.

#17 Post by silverstrom » Tue Dec 22, 2015 10:02 pm

It melted the pistons, so it wouldn't be an oiling issue. The melted metal suggests fuel metering.

Mark, did you try pressure/vacuum testing with the plug loose like you found it, just to see what happens?

And having said that, did you vacuum test, or just pressure test? Both would be useful diagnostic tools. It's possible to leak under vacuum and not under pressure.

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two-stroke-brit
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Re: out for a sunday thrash and BANG.

#18 Post by two-stroke-brit » Tue Dec 22, 2015 10:10 pm

silver ,i didn't do the vacuum test but will do before i tear it down .
all useful info


hi Jon, yes i had filters on the lines and its quite possible it the carbs dry ,
but as to the oil i had the pump refurbed by arrow and set to give a tad more semi synth oil.
but i was hammering it up the on ramp redlineing until it we bang.
my money is on the loose plug/air leak but maybe it ran dry or a terminal combo of both.

thanks for the input.
i am going to re read your hybrid build.

nothing says a 2 stroke like a xmas rebuild
cheers mark
350LC,Athena 392 big bore,stock porting,swiss cheese air box,stock reeds,spec11 pipes.(now TSA big bore pipes)
She might not be pretty but she will always be a fun ride


1982 YAMA RD350LC
98KDX 220R
1967 TRIUMPH TIGER
2001 TRIUMPH TT600

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JonW
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Re: out for a sunday thrash and BANG.

#19 Post by JonW » Tue Dec 22, 2015 10:20 pm

good point John, Id forgotten about that and with a refurbished pump then thats not the problem anyway.

Im a bit wary of small filters after I found that on one of my bikes (XL500R actually) with a nice clean tank that when i switched the fuel on the filter dripped rather than ran once it had been in use for a few weeks. The modern fuel had either swelled the gauze or there was micro dust in the tank that i didnt see, the filter was a protection i added as was actually a small one for a car so a large unit for a bike. With the filter off the fuel ran out like a water hose, with the filter on it was a very slow drip. So, yeah worthwhile to have a quick look at the fuel flow out of those filters as that could well have been a factor as you were revving it hard up a hill.

Have fun mate, better than watching telly I guess... and I bet the US doesnt show The Great Escape on xmas day like they do in the UK LOL
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

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silverstrom
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Re: out for a sunday thrash and BANG.

#20 Post by silverstrom » Tue Dec 22, 2015 11:04 pm

I've always been an opponent of inline filters. Always will be. I don't think there is any need for them. The petcock has a filter that is more than capable of flowing enough fuel and filtering as required. Anything in the fuel line downstream of the petcock is an obstruction. Just my view, but I don't see inline filters being worth the risk they impose.

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L.B
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Re: out for a sunday thrash and BANG.

#21 Post by L.B » Tue Dec 22, 2015 11:28 pm

Oh no Mark.......so sorry to hear this.

gordo555
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Re: out for a sunday thrash and BANG.

#22 Post by gordo555 » Wed Dec 23, 2015 1:11 pm

So sorry to hear about your blow-up Mark…. I figured guys like you were so dialed in that things like this never happened to them. I guess we're all at risk and eternal vigilance is the cost of running a two-stroke.

Thanks for the head bolts, I really needed them…. just finished my LC bottom end, and waiting for my top end back from the machinist to finish the bolt up and pressure test.

Merry Christmas, and a Happy Re-build!

Gordo

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two-stroke-brit
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Re: out for a sunday thrash and BANG.

#23 Post by two-stroke-brit » Wed Dec 23, 2015 3:37 pm

thanks everyone the frustrating part is i did the hard part of building and testing ,just got sloppy on the simple stuff ,like tightening the spark plug enough.
i not am going to run gas filters anymore either.
happy Christmas .
cheers mark
350LC,Athena 392 big bore,stock porting,swiss cheese air box,stock reeds,spec11 pipes.(now TSA big bore pipes)
She might not be pretty but she will always be a fun ride


1982 YAMA RD350LC
98KDX 220R
1967 TRIUMPH TIGER
2001 TRIUMPH TT600

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2smoke
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Re: out for a sunday thrash and BANG.

#24 Post by 2smoke » Wed Dec 23, 2015 11:32 pm

I am currently going thru a timing issue with my 4L0 and its got me wondering about yours.
Wondering if the O-ring squish head requires less advance, and if you changed or rebuilt your crankshaft, your old marks could be off.
So in short, did you check your timing with a dial indicator and timing light after the rebuild?
Colin
79 RD400F Daytona Special
81 RD350LC
89 TDR250
75 Kawasaki H1 500
77 Can-am Tnt250

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jimrd
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Re: out for a sunday thrash and BANG.

#25 Post by jimrd » Thu Dec 24, 2015 3:42 pm

hi Mark

I also have a LC

just curious were the pistons fairly new

less than 500 miles ????


Jim
1964 Austin Cooper S 1071cc
1967 Austin Cooper S vintage race car
1999 Ducati ST 4
1981 RD350LC , R1 Front,toomey pipes, Barnet Clutch, ported , PJ carbs, R1 Speedo 01
1983 RZ 350 - stroker bike,R6 rear shock,tapered stem bearings,progressive springs,

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two-stroke-brit
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Re: out for a sunday thrash and BANG.

#26 Post by two-stroke-brit » Thu Dec 24, 2015 4:51 pm

to 2 smoke i re set the base plate to the new head using the indicator and checked with a strobe light (two stroke friendly light).
it wasn't much from the original settings .
and used 1.8mm as the dimension.

to jinrd,
and it was a on a complete strip and rebuild.
new seals on the old crank new pistons about 1000 miles ago.
ran in on the stock set up then udgraded.

i am as confident as i can be it was the loose plug air leak .

thanks mark
350LC,Athena 392 big bore,stock porting,swiss cheese air box,stock reeds,spec11 pipes.(now TSA big bore pipes)
She might not be pretty but she will always be a fun ride


1982 YAMA RD350LC
98KDX 220R
1967 TRIUMPH TIGER
2001 TRIUMPH TT600

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jimrd
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Re: out for a sunday thrash and BANG.

#27 Post by jimrd » Fri Dec 25, 2015 4:38 am

Were they Rz or banshee Pistons ?

Did you remove the bridge port tab ?

Mine blew up at 1000 too
1964 Austin Cooper S 1071cc
1967 Austin Cooper S vintage race car
1999 Ducati ST 4
1981 RD350LC , R1 Front,toomey pipes, Barnet Clutch, ported , PJ carbs, R1 Speedo 01
1983 RZ 350 - stroker bike,R6 rear shock,tapered stem bearings,progressive springs,

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two-stroke-brit
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Re: out for a sunday thrash and BANG.

#28 Post by two-stroke-brit » Fri Dec 25, 2015 2:23 pm

jimrd wrote:Were they Rz or banshee Pistons ?

Did you remove the bridge port tab ?

Mine blew up at 1000 too
this is what i got,
YAMAHA RD350 & RD400 VITO'S STOCK STYLE CAST PISTON SET
thats weird yours blew at 1000 miles too or would that have been kilometers
cheers mark
350LC,Athena 392 big bore,stock porting,swiss cheese air box,stock reeds,spec11 pipes.(now TSA big bore pipes)
She might not be pretty but she will always be a fun ride


1982 YAMA RD350LC
98KDX 220R
1967 TRIUMPH TIGER
2001 TRIUMPH TT600

Hooligan
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Re: out for a sunday thrash and BANG.

#29 Post by Hooligan » Sat Jan 02, 2016 7:11 pm

jimrd wrote:Were they Rz or banshee Pistons ?

Did you remove the bridge port tab ?
I need to do this on my LC build. Any suggestions as to the best method?
'82 RD350LC in '81 colours, OEM pipes, UNI filters
'85 FZ750

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L.B
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Re: out for a sunday thrash and BANG.

#30 Post by L.B » Sat Jan 02, 2016 8:40 pm

I too need to do this soon.
I've read of ppl cutting with a dremel & file finish but to me that seems very dodgy brothers.....
Personally id take to machine shop to get done. Maybe get them done same time as getting bores done? If decent workshop they should be able to handle it.

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