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1974 DT360 problem

28 May 2020 08:06
dirttrackstar
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1974 DT360 problem #1
Hi all, first post on this website.
I have a farm shed/barn find 1974 DT360 that has developed a problem and Im stumped as to how to correct it.
The bike has 800 miles on the clocks, ist oversize piston and new rings, its otherwise perfect and almost spotless. It has electronic ignition.
A few days ago I was heading out to get the bike registered and it started on the choke and idled but when fed some fuel it blubbers and while it doesn't stop, it continued to idle going pong, pong, pong and on and on, but wouldnt rev and eventually I turned it off...…….I dismantled the top end again and checked everything and Ive had the carb off a 5 times and blown all orifices etc and it seems to be getting lots of fuel, maybe too much even.
Yesterday I reset the timing at .114" [2.9mm] BTDC as per the manual and the bike started and ran backwards....grrr……
so I added 1/4" to the setting as a test and it started instantly and ran for a while then stopped, now it wont start at all on that ignition setting.
Ive suspected for some time that the CDI or the pulser coil are shot , most likely the CDI and its playing with the advance or maybe working intermittently.
My son is an engineer and he tested the CDI and says its fine in accordance with the workshop manual specs, so what gives??????
Air filter is clean, there is an in-line filter in the fuel line, two new B8EC plugs. Pipe was decoked last month. Plugs are oily/dark and wet.
Comments or help appreciated.
Al

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28 May 2020 08:22
Gr8uncleal
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1974 DT360 problem #2
I suspect that it could be the pulser or maybe the CDI box - might test ok on the bench, but intermittent when on the bike. Others can confirm or otherwise.

If I'm right, options are conversion to the 1974 DT250A points system (don't know if 1975 and 1976 will fit - maybe) or an aftermarket CDI kit, some of which come with a 12v conversion.

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28 May 2020 09:18
Schu
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1974 DT360 problem #3

Gr8uncleal wrote: I suspect that it could be the pulser or maybe the CDI box - might test ok on the bench, but intermittent when on the bike. Others can confirm or otherwise.

If I'm right, options are conversion to the 1974 DT250A points system (don't know if 1975 and 1976 will fit - maybe) or an aftermarket CDI kit, some of which come with a 12v conversion.


The 75 DT250 components work on the DT360.
For what it's worth, I had nearly identical running issues with my CDI setup on a DT360. Simply could not resolve the problem. Switched to the DT250 components and have been running fine ever since. I had to swap the stator assembly and the flywheel.

Schu

70 Yamaha CT175
71 Yamaha CT175
71 Yamaha JT60
72 Yamaha JT60 (2)
74 Yamaha DT360
75 Yamaha GT80
75 Yamaha DT100
75 Yamaha DT125
75 Yamaha DT175
76 Yamaha DT175
75 Yamaha DT250 (2)
75 Yamaha DT400
76 Honda Z50
17 Yamaha SCR950

"Someday, you'll own some Yamahas"
The following user(s) Liked this Post Gr8uncleal

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28 May 2020 09:47
Gr8uncleal
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1974 DT360 problem #4

Schu wrote:

Gr8uncleal wrote: I suspect that it could be the pulser or maybe the CDI box - might test ok on the bench, but intermittent when on the bike. Others can confirm or otherwise.

If I'm right, options are conversion to the 1974 DT250A points system (don't know if 1975 and 1976 will fit - maybe) or an aftermarket CDI kit, some of which come with a 12v conversion.


The 75 DT250 components work on the DT360.
For what it's worth, I had nearly identical running issues with my CDI setup on a DT360. Simply could not resolve the problem. Switched to the DT250 components and have been running fine ever since. I had to swap the stator assembly and the flywheel.


Thanks Schu.

I guessed that they might, as you'd have to change the flywheel anyway, but it's nice to have this confirmed.

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28 May 2020 12:33
run103
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1974 DT360 problem #5
I would check the pulser. It needs to be 90 ohms hot or cold. I've had them measure 65 to 80 ohms and they act like your bike. Out of about 20 bikes I've done with this system I have had no CDI box failures. Just my opinion of course
Doug

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28 May 2020 12:36
run103
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1974 DT360 problem #6
One other thing is the ignition coil I have had 2 of them were flaky and wasn't expecting it so it gave me some headaches
Doug

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28 May 2020 16:44
dirttrackstar
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1974 DT360 problem #7
well Im replacing the coil tomorrow, and my son will check the pulser and CDI but ultimately that DT250 points fix looks pretty attractive. A complete replacement pulser coil/CDI from Rex Speed Shop in the UK is 175 pounds plus shipping so that makes it almost $400 CAD. I can buy a lot of 75 DT250 parts for that number of Canuckbucks......
Thanks everyone for the comments and input, its appreciated....
Al

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29 May 2020 07:33
run103
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1974 DT360 problem #8
Hi Al Where in canuck land are you I am in Swift Current Sask
Doug

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02 Jun 2020 17:51
dirttrackstar
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1974 DT360 problem #9
Hi Doug, yes I know exactly where you are, Im in Edmonchuck.....
Al

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02 Jun 2020 17:56
dirttrackstar
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1974 DT360 problem #10
So my next and most obvious question is: What parts are required to retro-fit the points system to my bike if the tests being done tonight on my cdi and pulser coil come up negative? Points plate and assembly of course, rotor??? What else- wiring harness, coil - hope not......
I also have access to an earlier model DT360 at the local wreckers and these are points for sure. Will that assembly fit?
Al

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