OzVMX Forum
Clubroom => Tech Talk => Topic started by: twinrock on August 07, 2008, 04:43:17 pm
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ok i put together a dt175 1980 top end is near new.. bottom end is suspect..the crank and trans are in great shape bike went together well and started ..i went for a ride on it spent about 5 hrs on it..it all went well except for a dragging clutch..then i rode it home from my day in the bush about a 40 road ride..with about 10kms to go it started to miss fire at higher revs/speeds(over 80kms) then died..i got it home and since have gone over every thing..top end still in great shape, it has good spark but i swapped coil new plug and fresh cut lead cleaned our carb..still nothing...fuel seems to be getting thru as the plug is wet when i pull it out..! seems to be enough spark..ive tried with pipe on and off incase of blockage..not a damn thing.!
which leaves only compression..now i have a hard time telling if it has good compression or not as im used to kick starting bigger road 2 stroke 2wins ..im thinkin could a crank seal be the prob..altho it had no signs of white smoke..it was a lil hard to start usually took half a dozen kicks when cold..any help would be great ..if it is a crank seal ..do i have to split the cases to change it..
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does that model have an external magneto flywheel with a woodruff key? If that isn't tight enough, it can shear, still great spark, just at the wrong time. Could fit the symptoms.
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Still reckon its the woodruff key.
They'll run happily with virtually no compression - Anna's one had a leaky head gasket and virtually no rings left, and it still went pretty well.
When they do finally get too low on compression to run properly, they become really hard to start by the lever, but will clutch start easily.
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i did look at the woodrift key when i pulled the flywheel off..it seemed to still slide in and off as it should with the flywheel lockin into place..ill replace it and see what happens thanks again..
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try another new plug i've been caught by brand new ngk plugs --duds! i avoid ngk if i possibly can. cheers wally.
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yeah i tried different ones i even took one straight outa my rz350 which i knew worked...it seems funny such a simple engine..and im sure its a simple problem..lol
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check the ignition timeing as my dt360a ran with the seal blown out of the crankase.it didnt run well but it did go.the plug will be wet and black.some times a lot of smoke but not white.
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do you have reed valves?
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twinrock,
a while back i sheared the woodruff key on my little MX125 and same symtoms, had great spark, couldn't kick start it but when clutch started it would miss and backfire. it is a simple fix though.
good luck with it.
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hey guys ..just an up date the woodrift key is all as it should be, so back to the drawing board..stator maybe?? i have a spare but its off a different modle and looks quite different..anyone(ie nathan..lol) got a stator for 81 dt175??
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its been said before, so I'll say it again,
:-[ :-\ Did you check to see if the fueltank cap breather over flow tube is blocked :-\ :-[
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why check the stator you have spark.
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if it is a crank seal ..do i have to split the cases to change it..
The first thing I do before starting these old bikes is fit new crank seals.
Then you know you don't have to worry about them.
You don't have to split the cases.
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Check the timing if you've got spark but no go. Dont make assumptions about whats happening, changing stators etc. Check when it is firing.
Use a el cheapo timing light from Super Cheap that plugs in line with the spark lead. Kick the bike over and check when it fires. Mark the correct degrees before TDC on the flywheel and cases and see where the flywheel is when the timing light triggers. The light will be feeble so you need to do it in a low light place. I couldnt get inductive pick up timing lights to work but the el cheapo worked great. Good luck.
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thanks guys i will check the timing again, how ever i have noticed that the stator plate timing mark is still lined up with the the mark on the crank cases, now if that has not moved and the woodrift key is still in tact i find it strange that the timing would be out...im sure it is something silly i will change the crank seals too..i dont get much time to work on it tho ,,when i do have spare time there are other projects that get priority..hey mark i just got a tzr3ma engine. im workin on putting bike together for it..:)