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1975 DT175 timing questions

10 May 2020 11:13
GJVGC
Sportsman
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1975 DT175 timing questions #1
Hello all,

Recently picked up a 1975 dt175.
Before setting the ignition timing I got new points, condenser and ignition coil.
Following the manual I kept the flywheel advanced in fully advanced position while setting the time to 1.88mm BTDC.
So the points should just begin to open at the 1.8mm.

I did my best by eye (pain) and the bike actually starts first kick and idles well. But has a hesitation at around 4K rpms. I’m thinking the ignition timing may be off a bit.

My question is how are you guys getting a reading from the black magneto wire at the plug to know exactly when the points are opening? I tried the ohms readings but they are all over the place.

I saw people using a buzzer or light. If so can anyone explain how they put one together?

Thanks for any help.

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10 May 2020 12:56
JimA
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1975 DT175 timing questions #2
Hi,
I also have a 75 DT175. I set mine with a test light. I have a test light that uses a standard 12v tail light bulb ( I think a 6v bulb would also fit). It’s been a while but I believe I ran one lead of the test light to the positive side of the battery and the other (negative) to the black wire going to the points and condenser. As the points open the light will become dull but will not go out completely. It worked fine. I also tried to use an ohm meter with no success.

I believe there is a video in the Tech library and I know there are some videos on Utube.

Jim

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10 May 2020 13:47 10 May 2020 13:48 by GJVGC.
GJVGC
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1975 DT175 timing questions #3
Thanks for the reply.
I saw the how to in the tech library but no video.

I did see how they used a buzzer on YouTube.
So basically have two wires from a light bulb, one to the + on the battery and other to black wire from magneto?

Thanks again.

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10 May 2020 15:44
Yammiedodger
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1975 DT175 timing questions #4
Hi there, you can find an old article in the tech library in the other tuning manuals section (how to build a buzz box), Its from 1975, but still holds good. I got myself a modern morse code practice kit of ebay along with a plastic box and a 9V battery (see attached).
There's some assembly and soldering needed. Total cost was around £12 and so far it looks good, although I've yet to use it on the bike.

While your'e at it double check the advance and retard arm on the inside of the flywheel as these are prone to wear on the pivot post.

I have a '75 DT175B also,

Hope this helps.

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10 May 2020 16:44 10 May 2020 16:46 by GJVGC.
GJVGC
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1975 DT175 timing questions #5
Thanks much. Looks like a solid way to make a buzzer.

Here is my advance mechanism in the flywheel. Does it look in good condition?



Also, is this mark on the flywheel to be aligned with anything on the stator or engine block?

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10 May 2020 19:02
RT325
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1975 DT175 timing questions #6
I don't think what you're describing is a timing issue if it's at 4 grand only & reads like you have the timing pretty good, & it's not make or brake having it a whisker out one way or other. Wonder if it's a richness on the slide needle but without audio its a bit of a guess. Have had cases of owner screwing the idle mixture hard in which mucks up more than just the idle. Not saying your doing 'that' but just talking to myself [which is the first sign of--Ahh, i'm loosing it lol].

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10 May 2020 19:14
JimA
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1975 DT175 timing questions #7

GJVGC wrote: Thanks for the reply.
I saw the how to in the tech library but no video.

I did see how they used a buzzer on YouTube.
So basically have two wires from a light bulb, one to the + on the battery and other to black wire from magneto?

Thanks again.



Yeah, from what I recall , one lead to the Positive on the battery and one lead on the black wire from the magneto. If you play around with it a little it was not hard to figure out. I don't remember a mark on my flywheel like the one on your flywheel, but my flywheel had more corrosion on the outside of it so it may have been there and I missed it. I don't remember reading any thing about that mark in the service manual. But someone else may know.

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10 May 2020 19:29
GJVGC
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1975 DT175 timing questions #8
Thanks for the reply.
So I soldered 2 wires to a bulb and connected one to the + of the battery and the other to the black wire from magneto and it worked. So thanks for the help!

In other news.
This escalated quickly.
I started the bike 3 days ago for the first time with no other issue than the hesitation at 4k rpm.
Today I start the bike and hear knocking sound from the head area. I had previously bled my autolube pump and seemed to be working just fine. And the bike was smoking making me believe it was getting oil just fine.

The knocking sound continued as I made this thread so I took the head off to investigate.
Here is what it looks like


Can I clean the piston up, make sure the timing is correct with the bulb method and run it?
Or is it toast?
Thanks for any help!

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10 May 2020 21:12
JimA
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1975 DT175 timing questions #9
I don’t have enough experience to say if anything looks abnormal or not. I don’t see any scoring in the cylinder so that’s good. I would pull the cylinder and check it and the piston for any scoring, and the bearing and wrist pin for wear. Mine had not been started for about 30 years and I wanted to get it started before I took the bike apart. I started it with pre-mix not knowing if the injection pump was working or not. I never rode it but did start it 4 or 5 times. It started easy but the last time I started it, it did not sound quite right to me.
When I pulled the top end apart, I did find some scoring on the lower piston on the intake side. Anyway I cleaned up the piston, honed the cylinder, put in new rings, top end bearing and wrist pin. So hopefully all will be good when I start it up in a month or two.
I’m sure someone will weigh in with more help and experience than I have.
Jim

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10 May 2020 21:35
MarkT
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1975 DT175 timing questions #10
What does the underside of the head look like?

Almost looks like you have some debris bouncing around in there.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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