DT175 Yamaha Enduro issues [Archive]

Yakman12

16th February 2013, 17:37

Hey everyone

Recently purchased a 1980 road legal enduro yamaha DT 175.

Problem: runs like a bag of crap in the lower revs (less than say 5500) kinda makes a 2-stroky uneven sound, its a real pain in the butt when you are trying to drive around town at 50kmph, its sort of jerky and not smooth.

Although... once you hit the power band she goes like a cut cat! It also starts really easily, spark plug is looking good etc. Its just ugly in the lower revs, seems to use a fair bit of gas too.

I pulled the carb and checked the jetting, main is 135 and pilot is 25, everything was clean and clear. Air filter is clean and in good condition (looks like someone has drilled some holes in the airbox thats all).

After looking in the manual a main of 135 seems quite small, but then again it runs great in power band... or with the throttle wide open.

Any ideas?

Woodman

16th February 2013, 18:11

My first bike was exactly that model and year. Good reliable bike but i still managed to wreck it.

Your problem could possibly be that the reed valves are munted.

Padmei

17th February 2013, 20:00

My first bike was a 79 dark blue one. Unbelievably slow compared to an IT175.
I recall mine used to "miss" sometimes when not on the pipe. Took it back to the shop a few times & had the mechanic ride it - he swore there was nothing wrong with it- there was but I was a young kid with not enough confidence to call his BS.
Anyway the pipes on those get really really clogged up. The only way back then was to burn the shit out of it with a gas torch.

How many kick starts have you been thru? I went thru 3 before I left the last one off & just crash started it.

Oh & did you know when they first came out they cost $1500 & when they brought them out again 10 years later with better this & that the price was exactly the same. Crazy huh.

Yakman12

18th February 2013, 07:36

Hi thanks for the replies!

Woodman I have pulled out the reed valves and look OK, they seem to be sealing fine and opening OK, is there anything specific I should be looking for in stuffed reed valves?

Padmei, I'll have a look at the state of the exhaust and see if that is an issue. I haven't had any broken starters yet haha! Although the bike only has 9,000kms on it (imported from South Africa) so not overly surprising!

ktm84mxc

18th February 2013, 13:14

With reeds check for frayed edges and chips, exhausts do clog up with oil/carbon residue on 2 smokes if the muffler packing is clogged this will effect the bottom end power .
Get it replaced and de carbon the muffler core .

RDjase

18th February 2013, 16:17

Here a link to a old DT thread, and a quote i put on it,

Do you know if your timing side crank seal is still good and not dried out and hard from doing bugger all kms in 30 years?

http://www.kiwibiker.co.nz/forums/showthread.php/20034-Yamaha-DT175-help

Took the carb off my DT today, 1979 model

160 main jet

20 Pilot jet

1.5 Slide cutaway

4J6 Needle

267 0-8 Needle jet/holder/Emulision tube?

VM28 round slide, 3U5 00 code on it

The needle clip was on the top position, leanest, will put back to the centre position as its a mongrol cold, never had the carb off the old girl, was chocka full off crap in the Needle jet

Yakman12

19th February 2013, 12:58

Thanks Jase that is very helpful!

But how do I check the crank seal exactly?

F5 Dave

22nd February 2013, 16:04

well 'exactly' you do a leakdown test but you need a tester + a bung for the inlet manifold & the exhaust. In a pinch you can see if it smokes heaps even when warm which would indicate GBox oil entering crank, or if it is oily under flywheel cover (excepting chain oil that has gotten in).

It does sound lean at low throttle (rich is burbly, but feels similar if less bitchy), try taping up the airbox holes and/or adjusting the idle mix screw (in is richer, out leaner).

Yakman12

22nd February 2013, 16:17

Thanks Dave

I have played with the mix screw.

Basically (following what someone on the interwebs said) I adjusted the air/fuel-mix screw till the idle rpm was at it's highest.

Ended up with the mix screw out by about 3 turns (lean) before it ran at its best.

My guess is my pilot jet is a bit too rich.

Thoughts?

F5 Dave

22nd February 2013, 16:29

Could well be esp if Jase's is a 20, it is hard to figure rich or lean some times. I probably have a 20 in the toolbox if yer coming out to the racing in the weekend (you'll have to clue me into who you are).

Woodman

22nd February 2013, 18:25

F5 Dave

25th February 2013, 18:24

will be steel reeds & they last forever.

Yakman12

18th March 2013, 17:00

Just going to drag this thread back to life...

Over the last couple of weeks I have tried multiple different pilot jets in the hope it will fix the problem (from .20 - .30, was .25 standard) but to little avail.

No matter what, I still have a rough running bike when I'm driving around town, with the throttle only slightly open.

Any other ideas?

ktm84mxc

19th March 2013, 08:12

It could be the way your riding it a 2smoke hates being idled around at partial throttle as the plug gets oil fouled, ride it like you stole it and it will love it.Take it for a 10k up the motorway once a fortnight to burn the excess oil outta the barrel.

F5 Dave

19th March 2013, 08:20

Nah thats largely a myth perpetuated by conservative rich jetting on MX bikes meaning they sputter to heck. Want proof? Ride a decent trials bike.

I'm suspecting you have an airleak if you've got to a point where changes are not doing anything. Or a faulty choke, blocked passage in carb.

Yakman12

19th March 2013, 08:27

Yeah I do actually beat the cr*p out of it quite regularly...

Dave I completely agree, I have a KDX200 Enduro bike and it is smooth at low speed / revs, much much better than my DT.

One other thing I have noticed...

Just as it is about to run out of gas (ie: I have to switch to reserve) it suddenly starts running a whole heap smoother... after it dies, I flick to reserve and its back running rough again.... very odd???

I'm only getting around 70-80km a tank as well.

merv

19th March 2013, 08:45

So that makes it sound like the float level in the carburettor is too high.

F5 Dave

19th March 2013, 11:07

or float jet dribbling gas. might be onto something there.

Yakman12

19th March 2013, 11:12

Brilliant!

I'll pull out the float jet and see if I can get a replacement.

I'll check the float height also.

Silly question, but how the heck do you measure the float height? I've looked online and people seem to be using vernier calipers or specialist tools.

Is there a cheat way to do it?

ktm84mxc

19th March 2013, 11:27

If it's getting 70-80 k's per tank the carb is flooding, do you turn the petcock off when you've finished the journey?

merv

19th March 2013, 11:45

Silly question, but how the heck do you measure the float height? I've looked online and people seem to be using vernier calipers or specialist tools.

Is there a cheat way to do it?

Usually you can do it with a small ruler as long as you can find the right setting measurement i.e. at what point the needle valve is meant to close in mm to say the bottom of the float from the body of the carb when the bottom of the carb is off if that makes sense to you.

Yakman12

19th March 2013, 11:48

Cool thanks Merv.

ktm84mxc yes I do turn off the petcock (occasionally forget, but not often).

If I'm chewing through gas I'm guessing my float level could be too high.

merv

19th March 2013, 12:52

You can tell if it's float valve problem by leaving the fuel tap on when you stop the bike provided its not a vacuum tap if it is put it on prime. If it starts leaking fuel out the breather pipe after a while then it's buggered otherwise adjusting float height might be all it needs.

F5 Dave

19th March 2013, 13:09

And it might be some fluff behind the valve seat preventing the valve closing, it might be during running it leaks with vibration but almost seals at a stop. It might be that o-ring around the valve seat so pull it out & look. To reseat the valve, drop a small ball bearing in it & give it a tap with a centre punch (don't go silly).

Oscar

19th March 2013, 14:23

Sounds like the power band bearing to me.

Yakman12

20th March 2013, 11:47

F5dave are you talking about the float valve? Didn't realise it needed to be re-seated?

It is an odd float valve, just a washer on the seat, no o-ring.

Oscar... 'power band bearing'... are you taking the piss?

F5 Dave

20th March 2013, 13:02

Yeah he's hilarimouse.

"It is an odd float valve, just a washer on the seat, no o-ring"

oh yeah like this
http://www.smebike.com/image/cache/data/NV0126-250x250.jpg
rather than
http://www.smebike.com/image/cache/data/NV0072-74 KYV24016-25-250x250.jpg

er, hold on just try here

http://www.smebike.com/carburetor, parts, jets/float-valves-needle-valves/yamaha-4?page=2

Yakman12

20th March 2013, 13:14

Looks a lot like this actually:

http://www.smebike.com/image/cache/data/NV0044-47%20%20KYV03015-25-500x500.jpg

F5 Dave

21st March 2013, 08:20

cool, I don't see those types often, just make sure it is clean underneath. The reseating isn't often required but can be handy if you think it looks a bit messy & has been leaking.

Yakman12

22nd March 2013, 08:44

Update time.

Checked the float height, I have it set dam near perfect (21mm according to the interwebs).

Still having the same issue though, I have ordered a new float-valve and seat... will see if that helps.

Also I discovered this morning (a rather cold morning as well) the bike will start with one kick, dead cold with no choke! Strange?

I now have two symptoms that make little sense to me:

1. I don't need any choke to start the bike from dead cold.
2. Just as its about to run of of fuel, it runs perfectly smooth (like it should).

More thoughts anyone?

F5 Dave

22nd March 2013, 13:23

Indeed that is unusual. if one had the carb in your hand & pushed a bit of plastic hose against the carb intake (small but open hole at carb bellmouth) & blew, assuming a decent seal it shouldn't pass wind (Oo-er). then when you open the choke it should. If you shine a light up there you may see the choke bottoming. Take choke out & check it hasn't got any grit down there. its just a sliding shaft with a lever & spring mechanism.

Yakman12

24th March 2013, 12:45

Choke is good, replaced the float jet and seat.

.... still running like a bag of crap at 50km round town, like seriously crap.

I really don't know what else to check on this thing.

F5 Dave

25th March 2013, 08:42

humour us & change the plug again, actually while you're about it check the plug cap with a meter & see that it is about 5-7k resistance.

Yakman12

25th March 2013, 09:03

Yeah I'm ahead of you, already changed the plug after I did the float valve.

Will check the resistance, it is a brand-new spark lead mind you.

Wonder if it is an ignition timing thing?

F5 Dave

25th March 2013, 15:55

Timing will be fixed where the plate bolts on & CDI ignition in 1980 for sure. Whether all is in good order. . .

SCREECH. . .Wait up, :blink: sorry the spark lead is new?

Explain please. Please tell me you haven't replaced the plug lead with car type carbon lead?

Yakman12

26th March 2013, 08:21

No I haven't replaced the spark lead myself... but it does have a new shiny one from the previous owner, he had it replaced by a mechanic so I presumed it would be correct?

How do I tell if it is a car-type carbon lead? Why would this be an issue?

F5 Dave

26th March 2013, 09:03

take off (twist) the spark plug cap, should be strands of copper wire, then all good, its bike stuff.

Strange though as most coils have bonded leads, not that many are replaceable. Some 4 stroke coils have replacable & people buy car type silicon (carbon inner) leads which look pretty but are unsuitable for tiny bike coils & cause misfires.

I'd be interesting in the coil if its std.

trapster66

20th April 2013, 20:19

if it runs fine flat out, the main is o.k. starts good?, pilot is o.k. mid range riding is the needle jet responsibility, have you tried altering needle hieght ?

trapster66

21st April 2013, 14:17

nevermind my lasty post mate looks like you would have addressed that issue(needle hieght) a while back,
F5 Dave sounz like he'z on the money. cheers

Yakman12

21st April 2013, 23:22

Actually you are nearly on the money!

I finally lost the plot and took the dam bike to the guys at Boyle Kawasaki.

They figured out that the needle has worn the casing the of the needle jet bit (the seat the needle sits inside).

The quick fix was to lean it right out (20 Pilot) and lean out the needle by another notch.

I was on the right track with it running rich in the bottom end, I just didn't go far enough.

The ultimate fix will be a new needle and casing.

Should also be mentioned the choke may have been not closing properly, which the chaps at Boyles also sorted (but said they didn't seem to think that was the problem).

All in all she is now running perfectly, thank god!

gammaguy

22nd April 2013, 03:47

F5 Dave

22nd April 2013, 09:50

Hah, funny, I've given that advice many times but didn't even think of it this time.

Look down the tube with a bright torch & check for ovality, just a little will create a path for big wet droplets which are hard to burn. Seen a KDX which was dreadful & my old RF did it pretty bad.

I ended up making some brass inserts & drill & supergluing them into the tube after carefully drilling them to the right size (actually I paid an engineer who could work that accurately on small stuff, it was well out of the scope of my lathe).