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Old 06-17-2014, 07:18 PM   #1
ThatDude114 OP
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1980 DT175 Problems

Hey guys,
So I've been having some problems with a DT175. First off, my top end is making a rattling noise(If I get the chance I'll post a video of it). I suspect that the needle bearing is shot and needs to be replaced, I say this because: there is no crank play, both top ends that I've tried(Bored out with a Wiseco piston, and a completely stock top end) are almost brand new and the clearances are well within spec, so the only other thing I can think off that could be causing that kind of noise would be the needle bearing, which admittedly I didn't replace with either of the top ends. How do you check a needle bearing/wrist pin beaing? My next problem is, I cannot for the live of my get my carb set right. It's perfectly clean, with all ports and holes are clear. I need to soak my float overnight to make sure it isn't leaking. The running problem that I'm having is that it won't idle and the thing leaks fuel crazy. The bike revs very smooth and returns to idle like it should but it will not stay running. I've set the 21mm several times and it always leaks fuel, but I read somewhere that the float should be set with the float needle spring uncompressed where I have always set it while compressed, which is the proper way to set float height? My final problem is that my throttle won't snap back by itself, no matter how I adjust the cable (However adjusting throttle cables is not my strong suit), any suggestions on how to fix it? I appreciate all the help guys.
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Old 06-18-2014, 04:20 AM   #2
YZEtc
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You need to take the engine apart and try feeling for free play between the piston pin and piston pin bearing.

Even with everything 100% correct, there will be some noise coming from the cylinder with all of those cooling fins amplifying any natural rattling sounds.
That's why the bike came with pieces of rubber shoved between the cooling fins:
To dampen the noise.

Measure float height WITHOUT the needle valve spring-loaded pin being compressed.
The parts need to touch, but not compress the spring.
Service Manual?

There has to be a little bit of free play at the throttle grip.
A lubricated set of cables is good, too, especially if they are showing their age.
Does the throttle cable snap back if you remove the end of the cable from the throttle grip?
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Old 06-18-2014, 04:29 AM   #3
stainlesscycle
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Originally Posted by ThatDude114 View Post
The running problem that I'm having is that it won't idle and the thing leaks fuel crazy. The bike revs very smooth and returns to idle like it should but it will not stay running......but I read somewhere that the float should be set with the float needle spring uncompressed where I have always set it while compressed, which is the proper way to set float height?........My final problem is that my throttle won't snap back by itself, no matter how I adjust the cable
sounds to me like the float needle is worn - if it won't shut the fuel off, the bike will never idle, it will burble bad off idle, foul plugs, and leak all the time. if you set the float height wrong (you did) that could also be your issue.

float height is set with the tab just touching the float needle. not compressed.

3 things on the throttle not returning:
1:throttle tube is hanging up - either the grip is rubbing on the handle (common issue...) or the tube is shot. something binding in throttle assembly. tube is hanging on bar - gunked up with dirt or something..
2:throttle cable is shot - if cable does not move easily, it will not shut.
3:something binding with slide/spring (rare)...

first unhook cable from throttle tube. pull on cable end and see if slide snaps shut. if it does, throttle/tube has an issue.
if not throttle itself, unhook other end of cable, check cable for smooth motion. if ok. remove carb and reach in to airbox side of carb - push slide up with finger, does it return on it's own? if not, you have a slide/carb issue.

there should be almost no play in the throttle cable - but there needs to be slack or else the slide will not be hitting the idle screw - DO NOT adjust idle with cable - use the carb idle screw to set idle. .. - i like 1mm of gap or less, anymore than that and you get a throttle lag feel...i like instant throttle response... loosen throttle cable adjuster so there is a bunch of slack.. set idle with idle screw on carb. then remove slack in cable with adjuster - play with it till you get it where you like it.
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stainlesscycle screwed with this post 06-18-2014 at 04:35 AM
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Old 06-18-2014, 12:50 PM   #4
ThatDude114 OP
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Quote:
Originally Posted by YZEtc View Post
You need to take the engine apart and try feeling for free play between the piston pin and piston pin bearing.

Even with everything 100% correct, there will be some noise coming from the cylinder with all of those cooling fins amplifying any natural rattling sounds.
That's why the bike came with pieces of rubber shoved between the cooling fins:
To dampen the noise.

Measure float height WITHOUT the needle valve spring-loaded pin being compressed.
The parts need to touch, but not compress the spring.
Service Manual?

There has to be a little bit of free play at the throttle grip.
A lubricated set of cables is good, too, especially if they are showing their age.
Does the throttle cable snap back if you remove the end of the cable from the throttle grip?
The rubber pieces could actually be part of it! I put a new coat of engine enamel on the cylinder last time I took it apart so I took off those rubber pieces and completely forgot to put them back!

Okay so lesson learned, float height is set with the float tang and the float pin just touching. That could explain why I always have problems tuning carburetors... Well now I feel like an idiot!
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Old 06-18-2014, 01:00 PM   #5
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Originally Posted by stainlesscycle View Post
sounds to me like the float needle is worn - if it won't shut the fuel off, the bike will never idle, it will burble bad off idle, foul plugs, and leak all the time. if you set the float height wrong (you did) that could also be your issue.

float height is set with the tab just touching the float needle. not compressed.

3 things on the throttle not returning:
1:throttle tube is hanging up - either the grip is rubbing on the handle (common issue...) or the tube is shot. something binding in throttle assembly. tube is hanging on bar - gunked up with dirt or something..
2:throttle cable is shot - if cable does not move easily, it will not shut.
3:something binding with slide/spring (rare)...

first unhook cable from throttle tube. pull on cable end and see if slide snaps shut. if it does, throttle/tube has an issue.
if not throttle itself, unhook other end of cable, check cable for smooth motion. if ok. remove carb and reach in to airbox side of carb - push slide up with finger, does it return on it's own? if not, you have a slide/carb issue.

there should be almost no play in the throttle cable - but there needs to be slack or else the slide will not be hitting the idle screw - DO NOT adjust idle with cable - use the carb idle screw to set idle. .. - i like 1mm of gap or less, anymore than that and you get a throttle lag feel...i like instant throttle response... loosen throttle cable adjuster so there is a bunch of slack.. set idle with idle screw on carb. then remove slack in cable with adjuster - play with it till you get it where you like it.
I definitely should've joined earlier, this is great advice that I hadn't heard from any motorcycle mechanics in my town. I'll check and see if the cable snaps back, but last time I checked it did. So that means something is up with the throttle tube correct? Does the throttle tube need to be greased/lubed?

I have 2 Mikuni's that I've been trying to get tuned right (I actually have 3 of these 175's, definitely one of the best bikes I've ever ridden) and the current one that I've been working on looks almost brand new on the inside, so I'm guessing that it wouldn't be a worn float needle, but I'll make sure to take a look at it. And thanks for the simplified way to adjust throttle cables, that'll definitely help me.

I'll get back to you guys probably later today on what I find. Thanks for the help guys!
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Old 06-18-2014, 02:40 PM   #6
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Originally Posted by ThatDude114 View Post
I'll check and see if the cable snaps back, but last time I checked it did. So that means something is up with the throttle tube correct? Does the throttle tube need to be greased/lubed?
probably. could be worn tube, or many other things. proibably just dirt on the bars/on the inner of the tube. you'll figure it out when you take it off. i rarely lube throttle tubes. as long as the handle bar and tube is really clean it should be very smooth. any lube you add will collect dirt. i may use a little grease in the throttle housing where the throttle cam is - depends on the design/how well it's sealed.
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Old 06-25-2014, 04:57 PM   #7
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Alright guys, so sorry for taking awhile to respond, I've been pretty busy. I took the engine out of the bike and when I took the top end off this is what I saw:
1. Cylinder head, it was wet from fuel.


2.Top of the piston was wet. And the cylinder sides were wet.


3. Bottom end had some gas in it, and what looked like a little bit of oil.


The gas is from when my carb was overflowing, should I be worried about it? Or just drain it out and be done with it? I adjusted the carb and it stopped leaking and it seems to run pretty well, but it still won't idle just yet. Any suggestions? And I still need to check out the throttle cable. My new needle bearing just came in so whenever we get the gas in the engine thing sorted out I can put it back together, and the last thing I'm waiting on is my new rear tube to come in. Then hopefully I'll be able to get the Idaho OHV tag before we go camping for the 4th!
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Old 06-27-2014, 06:47 PM   #8
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So I decided on this bottom end that I wanna run my Wiseco top end on it. It's bored 1mm over so I was wondering what kind of adjustment if any I need to make to the jetting in the carb, also I'm running premix not the autolube system.
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Old 06-28-2014, 03:26 AM   #9
stainlesscycle
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Originally Posted by ThatDude114 View Post
So I decided on this bottom end that I wanna run my Wiseco top end on it. It's bored 1mm over so I was wondering what kind of adjustment if any I need to make to the jetting in the carb, also I'm running premix not the autolube system.
should be no jetting changes for a new bore. unless you changed jetting to try to compensate for the original worn top end....
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