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Digger65

DT175 air leak?

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Hi forum

DT175 76 twinshock

been having some troublesome issues with my DT of late, any advice would be greatly appreciated?

had the bike suddenly lose power on me and limped home a few months back

since then have:

..rebuilt carb

lined tank, some rust issues

new fuel filter

set points

new air filter - came without one but still doesn't have air filter cage

primed oil pump

checked piston and barrel-all good

got back to running well, loads pull idles well

ran well for a couple of days until today when it started losing power on run to work, smoking (not Blue) also from air box

took it to mean air filter was fouled again so removed it and was running better but lacked pull on run home

since then have checked air screw on carb and can screw it all of way in and it has very little effect

so am thinking air leak and running lean?

crank seals next on the list then..

any other advice inbetween would be bloody marv

thanks

D

 

 

 

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has it got wet recently? We've had lots of wet weather for a few months!

It's always worth taking the carb drain screw out just in case there's water in the float bowl

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Hi

I have a 1976 1g1 twinshock DT too,

I am not saying this is your problem,

My bike had running issues that I couldn’t pin down, eventually I found that I a

bigger main jet than standard cured the fault, I think I ended out with a 150 or 155 jet,

I cannot recall as I was playing jet swap with the jets a local bike shop had in its mikuni carb spares box

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Hi there":welcome:.  Al souund advice,,,  if you can screw that air screw in, and it dosnt Stall.   the pilots too small,  or needin cleaned,   your shud look like this,,  i had one New in 1976 B)

FN9irdk.jpg

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Yes thats the kiddie

Mine may have a little more "patina" I guess..

Good call about jet will grab a few sizes and try them out, also check for water in carb, tried again today and screwing air screw in did actually stall the bike without air filter, seems ro want to run better with screw out 3.5 turns so it seems to wanting more air, or getting too much fuel, pulling out choke stalls it instantly in any condition, will start without choke easily...once.it stalled.on air screw was hard to start and idle was down.for a while if that helps shed any light on it

Thanks

D

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Ok, the pilot circuit & choke circuit are working,.  did you says it starts without choke ?.[ cold ] ..and its looking for more,AIR,  ?, SOUNDS LIKE YOUR CHOKE washer,  is passing,,  un screw it,,  its the pullout type,,  take alook at rubber  on bottom,, 

 

Hey digger,,,,,, join here,,  http://yamahadtclub.proboards.com/

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Hi forum

Just wanted to update this thread. Well not really an update as I still haven't got to the bottom of this issue..

Basically runs great for 15 to 20 minutes then runs like crap, will rev but no power and idle goes down to where it won't idle without some revs

time factor always seems fairly consistent, so perhaps a heat issue of sorts?

plug dry-carbon fouled

about to de-coke the exhaust next..perhaps its getting gunked up and the heat is making it gasp for air?

then piston rings..

then perhaps crank seals?

have just replaced carb with a new one as it was leaking from float bowl

would greatly appreciate any thoughts on this

D

 

 

 

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Gigger, my money"s on the pipe,[ carbon] ,  crank seals cause the revs to rise ,[ runnaway, esp at idle]  heres a vid,, 

 

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yeah i think so too, thanks

looks like torch to get it hot the heat gun?

this looks probably a little quicker?

 

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Aye digger " if this dont work  it has to be stator,-  soarse coil - or condencer, ,  breaking up wen hot,

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weird thing come to think of it was briefly disconnecting the oil feed to carb seemed to bring it all back to life?

haven't tried this with new carb so it may have been just a coincidence

will de-coke and update and if it persists try removing oil feed again to see if it makes a diff

D

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20 hours ago, Digger65 said:

weird thing come to think of it was briefly disconnecting the oil feed to carb seemed to bring it all back to life?

 

D

So more air is curing the problem ?,  does this carb have an  0  ring on the emulsion tube ,?

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On 3/20/2018 at 8:08 PM, blackhat250 said:

So more air is curing the problem ?,  does this carb have an  0  ring on the emulsion tube ,?

unsure as haven't had it apart yet as its new, decided to change the old one out as i was convinced it was carb issue

here is a vid of it doing its power drop thing, as you can see it drops on idle quite suddenly after 10 or so minutes of riding and is accompanied by subsequent drop in power

this is recorded after 10 minutes of riding, idle set to 2k from cold, then aftrer 10 minutes and presumably when hot loss of power and idle down, you can see this clearly at 24 seconds or so in

 

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You know digger,", my dt 175  sounded a lot better, esp at tickover,   yours sounds limp,   am saying its rebuild time, maybe am wrong,, 

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With how slow the revs drop and how wimpy and flat the engine sounds the seals have to be high on the list.

How does it start in poor power mode.

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7 minutes ago, blackhat250 said:

You know digger,", my dt 175  sounded a lot better, esp at tickover,   yours sounds limp,   am saying its rebuild time, maybe am wrong,, 

haven't got much to compare it to really to be able to decide if this is correct diagnosis but i will say off the bat from cold it goes like stink and doesn't miss a beat, only after the 10 minute period does it start to act up

1 minute ago, Cynic said:

With how slow the revs drop and how wimpy and flat the engine sounds the seals have to be high on the list.

How does it start in poor power mode.

hard to start tbh without presuming to know too much i would have thought seals would be a more gradual decline in power with perhaps the idle not returning to base quite so quickly but its probably my next port of call

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Ok , is it good for compression when cold, .does it feel tight to kick -over, ? 

 

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1 hour ago, blackhat250 said:

Ok , is it good for compression when cold, .does it feel tight to kick -over, ? 

 

feels about right i guess, again not too much to compare it to really as this bike has always had this issue in one form or another since picking it up end of last year.. thought it was rust in tank, then carb, blockage in exhaust, all of the work done (new carb, decoked exhaust, tank lined) improved the issue and overall performance but it is still present, will look at getting compression tested and check seals, anyway to do this without cracking the cases? perhaps wd40 around the seal while running?

thanks again

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