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Makotosun

DT175mx Resto as it currently stands.

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Replied by Pete-RT1 on topic DT175mx Resto as it currently stands.

Looks amazing, well done!
Yamaha CT1-B
Yamaha CT1-C
Yamaha AT1-C
Yamaha CT3
1978 Yamaha DT175MX
2020 Honda CB500X
20 Mar 2022 02:58 #21

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Replied by Tinkicker on topic DT175mx Resto as it currently stands.

Just gave it a 15 mile shakedown ride without incident, so looking good so far. It's funny how the mind plays tricks. I remember it being quite zingy back in my youth with a pronounced powerband that kicked you in the back.

I guess it's faded memories and the fact that I had only ever owned trials bikes and small capacity road machines at that time.

These days, having owned over 160hp, fire breathing monsters of bikes, and still own a 150mph one, I have noticed a distinct lack of zing, but however a very tractable engine pulling strongly from 2000 rpm to 5000rpm with no noticeable step in the power delivery. Still running it in, so no full throttle to the redline activity.

Power seems very linear. It seems happiest around 4000rpm so far, but the odd time I took it to 5000 rpm, there is a distinct vibration developing through the pegs. Not revved it higher than 5000, so no idea if it is a specific zone or not. It is butter smooth below 5000.

The six speed box is very closely spaced, so accelerating to traffic speeds means changing up through the box as fast as you can and I lost count of the number of times I tried to hook up a seventh gear.

Maybe my experience with big sports bikes has affected my memories of how this little yam behaved. With a 65 mph top speed and 16bhp, it certainly cannot have been as fierce a power delivery as I remember it.
26 Mar 2022 06:31 #22

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Replied by Schu on topic DT175mx Resto as it currently stands.

"the odd time I took it to 5000 rpm, there is a distinct vibration developing through the pegs."

My DT175C has that exact same vibration thru the foot pegs. I have yet to figure it out, and I wonder why it's the only one that does it out of all my bikes.
Schu

CT1B, CT1C, JT1, JT2, DT360A, GT80B, DT100B, DT125B,
DT175B, DT175C, DT250B, DT400B, Z50, SCR950

Someday, you'll own some Yamahas
26 Mar 2022 08:25 #23

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Replied by adguy2112 on topic DT175mx Resto as it currently stands.

My CT2 also has that peg vibration. I wondered if the two sides of the crank are misaligned or out of balance somehow. The CT1 doesn’t do that. 
26 Mar 2022 11:20 #24

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Replied by jims175 on topic DT175mx Resto as it currently stands.

Check the engine mount bolts, my CT2 started vibrating suddenly one day and one or two were a little loose I tightened them and it went away! 
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27 Mar 2022 09:01 #25

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Replied by mdscott on topic DT175mx Resto as it currently stands.

Very sharp!
Thanks Mark
Roseville, Ca.

'03 ST1300
'75 Norton
'73 CB500K
'81 Honda CT110
'87 PW50
'64 McClane Edger
'02 Honda XR70R
27 Mar 2022 18:11 #26

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Replied by Tinkicker on topic DT175mx Resto as it currently stands.

Happy holidays.

Was planning to change the wheel rims over the winter, the chrome is not great up close.  In fact looking at the earlier pic, you can see a rusty blemish at the top of the wheel, even with the heavily compressed pics on here.  This blemish continues into the rim face.

No idea why the previous owner would have the wheels rebuilt with new spokes, but with the original blemished rims.

Came across a NOS front wheel rim at a bargain price and that changed my plans a little.  Rim arrived, but still waiting for a new rim tape and inner tube to appear.  If they appear later today or Saturday, I will change out the rim this weekend, but I have no intention of disabling the bike over the weekend otherwise.

New arrival.


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Last edit: 14 Apr 2022 07:49 by Tinkicker.
14 Apr 2022 07:47 #27

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Replied by Tinkicker on topic DT175mx Resto as it currently stands.

Made a modification to the gearing on Friday to make it a bit more road friendly. I went up two teeth on the front sprocket from the stock 15 teeth to 17 teeth, I figured it would be the most I would get away with without having to buy a longer chain. In fact there would not be enough room in the sprocket chamber to fit one any bigger it turns out.
There is a 3 mm gap between the chain and a strengthening lug, which is getting uncomfortably close when the chain reaches the end of its life.

The bike has 75 miles under its belt now and has had around ten heat/cooling cycles, so I felt it was time to try a bit of full throttle action with the new gearing.

Turns out the new gearing is "square" with the revcounter in top gear - 30mph equals 3000rpm, 50mph equals 5000rpm and so on.

So full throttle. Hmm 50mph reached quite quickly, then it would slowly creep up to 55mph and hold there. It would not rev any higher than 5500rpm and the red line is 8000rpm. Gear down into 5th and full throttle. 7000 rpm and 60mph just..

I figured that I have overgeared it. I am pretty sure remembering my brand new "old" DT175mx would hit mid to high 60s, so something not right. OK I probably weigh twice as much as I did then, and the DT came a few years before I took up bodybuilding, so I probably weigh twice as much and have shoulders twice as wide. I was a skinny little runt back in the day. Even though; it should rev out. Maybe I need to drop a tooth on the front sprocket to 16 teeth.

Got back home and pulled the plug to see what the mixture is like at full throttle. Very dark brown, so very rich at the top end. This could be where the missing power is going. I reckon its putting out maybe 10 to 11bhp judging by the top speed, when it should be producing 16bhp and also why it is bogging down and unable to reach red line.

It has a 140 main jet fitted and I have just ordered a 130 main jet and will see if it makes an improvement. Some models had a 140 and others had 130 jets fitted as standard, so maybe there are differences in the exhausts and airboxes. No idea what mine had originally because the previous owner had fitted a 120 jet which is from the DT125mx, not the 175.

Got back home and found the inner tube and other parts had arrived, so out with the front wheel, remove the tyre and rip out the spokes. I have not built a wheel in over 15 years and man, I forgot just how tedious it is lacing a wheel. The DT spoke pattern is not the simplest either with an odd configuration and three types of spoke.

I had a go yesterday afternoon, screamed in frustration, took to a darkened room and laid down with a cold flannel on my forehead, had a quick cry and thus fortified, commenced battle again. Job done.

Bits arrived.

 

New Vs Old.  Chrome was not great close up.

 

A tedious job completed.  

 
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17 Apr 2022 03:41 #28

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Replied by Ht1kid on topic DT175mx Resto as it currently stands.

I will repair ANYTHING on my Yamaha’s but will not lace another rim one was enough for me
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17 Apr 2022 07:11 #29

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Replied by Tinkicker on topic DT175mx Resto as it currently stands.

New 130 main jet arrived and was duly fitted.  I also dropped the needle a notch and double checked the float height, as my initial testing at mid throttle showed it to be on the rich side at a very dark chocolate brown with a new B8ES plug.

Same plug at full throttle was showing a very dark brown, heading for almost black with the original jet I fitted... Turned out to be a 135, not a 140 as I remembered.  With one model carb sporting a 130 and the other sporting a 140 on the same bike, I must have decided to split the difference.

With 130 fitted and the needle lowered, the difference was immediately noticeable with the engine being much snappier through the gears.  It was too windy for a definitive top speed run, but the bike maintained 50mph into a stiff headwind and at one point the Speedo needle was quivering around 65mph on a very slight uphill stretch with the wind quartering at my back. 

Got home and pulled the plug for a quick look, as much to check for melted alloy as much as anything else.  It was clean and chocolate brown in colour, although it did have a patch of tan colour in it.  If course riding it sensibly back home through the village, I blew any chance of a definitive plug reading, the tan likely being coloured by lower end rpm deposits on the way home, and the plug is too old now anyway with 100 miles under its belt.


I have ordered four more plugs and intend to ride to the end of a one mile straight close to the house, swap the plug for a new one and give it wide open throttle for the mile, kill the engine and coast to a stop to get a definitive WOT reading.

I have a new Chinese VM24 carb sat on the shelf which I "borrowed" the floats from as the original Mikuni ones were found to be poor swimmers.  I  intend to pull the choke plunger from it and measure it against the original.  It may be that the 44 year old seal on the plunger is also contributing to the rich mixture.

Edit:  the plunger is about 3mm longer with the genuine Mikuni.  When screwed in, the genuine one backs out about 3mm, giving some "freeplay" for the plunger to bottom out.  The Chinese plunger does not, so the seating would be a case of is it, or isn't it?
The original plunger seal has not gone hard and is not split or cracked.

Once I have the carburation somewhere close to where it should be, I can have another look at the gearing and decide what I want from it. 
The stock gearing seemed too low for road work, first being ridiculously low as to be almost unuseable, but with a big jump to second that meant much slipping of clutch if first was ignored.
The engine was being worked too hard in sixth year at close to traffic speeds around my area - living in a rural area means most of the roads are 60mph limits around these parts and I do not enjoy the sound of engines being abused.

I suspect that with the 17t front sprocket I am overgeared and the knock on to that is a reduced  top speed, yet the engine sounds happier when keeping up with the traffic.

As always, gearing is a compromise.  I need to decide what I want from it.  Do I want power wheelies off the throttle in the lower three gears, or sedate rpm at highway speeds?

Of course, I want it all.  Unfortunately the Lord of Parasitic Drag says no.
 
Last edit: 24 Apr 2022 07:12 by Tinkicker.
24 Apr 2022 01:53 #30

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