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Makotosun

1974 DT125A Build/Restore

  • torqueflight
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Replied by torqueflight on topic 1974 DT125A Build/Restore

The plug didnt test good through the meter though and I even sanded the pole down.
19 Nov 2023 01:24 #141

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Replied by RT325 on topic 1974 DT125A Build/Restore

It's the black baked on oil on the insulator that drags the spark to earth deep down past the porcelain.
I just found this sand blasting plug cleaner on Amazon but likely lots out there.
We had a good commercial size sand blasting plug cleaner at work that was in constant use [& wearing out nozzles from the sand]. Put my thumb over it once haha--never did that again, young & dumb lol.
Anything with sand the plug needs to be dry of wet oily fuel.
Squirt something in the plug & compressor dry it or sand & wet oil just makes a mess.
Then i used to get something long & sharp to get down to the base of the plug & scratch around so no sand left there. Then a final air blow.
New plug wet with fresh oily fuel won't short out.
Might not run due to flooding but just blow it dry & try again.
As i said, it's when it gets a black deposit baked on there that shorts it.
That's how i see it anyway.
I'm not recommending my methods but I'll run any plug i have to get a motor going & not worried about being correct until i'm going to ride it hard.
Mind you i've lost count of how many times i've used champion N12Y out of my car or a BP5ES then forgot in the excitement until after belting around the track. So just be careful.
www.amazon.com/ABN-Pneumatic-Spark-Plug-Cleaner/dp/B07RH9CBGG
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Last edit: 19 Nov 2023 02:02 by RT325.
19 Nov 2023 01:40 #142

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Replied by Ht1kid on topic 1974 DT125A Build/Restore

Be sure you gap your new plug I had a similar problem with a Ngk b8es would run for about 10 min then die waited 5min it would run again  it was a new plug I wasted a bunch of time trying to figure it out MarkT recommended Autolite works great that’s what I use from now on
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19 Nov 2023 08:03 #143

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Replied by torqueflight on topic 1974 DT125A Build/Restore

Been busy the last couple nights.

Got the autolite plugs. Run good now. Could prob use a little bit teaks though.

Took it out the past 2 nights on shake down runs. 6 miles each.

Clutch still slipping. New friction plates on the way. Will probably get new plates and springs too, just so I can be done with that.

On the shake down run tonight it died a couple miles out, which wasnt really fun pushing back. It would kick but wouldnt start. When I got back I checked the plug, no spark. I pulled the left side cover off and oddly enough the spring that puts pressure on the points broke. Looks like I need to buy a new points setup. Not sure what one is best.

Also wont idle when hot. It will idle for just a short bit but will die. It used to idle, not sure why it wont now. I messed with the idle screw and air screw and nothing. I do have race gas in it now (101) not sure if that would casue it, it really wouldnt think so.

Its not too bad riding, but most likely I need to get it swapped over to a 175, I need that extra little umph to cruise 50mph. Right it I kinda have to fight for it on grades and its pretty much redline at that speed too.

I noticed, its seems like it wants to pull pretty hard past redline but just feels plugged up. If I play with the throttle, as soon as I back off it picks up a little. I could be wrong but it feels clogged up. I already have the air cleaner cover flipper backwards for more air. How restrictive is the stock pipe? I still have the spark arrestor and screw on baffle on too.

Not sure if its running lean too. It runs best with the air screw in all the way and the revs still seem to hang a little. It has a 140 main in it. I assume since I flipped the air box cover and if I remove that stuff from the exhaust, Ill have to go richer.
Last edit: 21 Nov 2023 00:09 by torqueflight.
21 Nov 2023 00:04 #144

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Replied by torqueflight on topic 1974 DT125A Build/Restore

I have boysen reeds in and Im wondering if it makes a difference if I use the stock reed stop with them or not. I think it says to use without but I missed that when I installed them.
21 Nov 2023 00:44 #145

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Replied by RT325 on topic 1974 DT125A Build/Restore

In my opinion boyesen reeds are not worth the cost in a 125. We used to run them 40 years ago because we thought ya had to have them to go fast lol. Yep meant to run without the stops. Think they just had a bar across the base?. Nowadays I'd run the original stops though as my theories change. Ran them in my kids yz80 in 1980 & they bent way open halfway through a day's racing & had to push start it. Turned them over & saw the day out ok. Mind you was running methanol which softened them causing the problem so went back to originals.
Breaking a points spring would be a very unlikely thing to happen.
Also to have the idle mixture screwed home she must be very lean or drawing air from else ware. I'm a believer in a clean exhaust system for best performance, but you say it goes better rolling back from full song which has me thinking lean on the mainjet rather than an exhaust issue. I think, if it was exhaust related it'd limit out & 4 stroke rich if restricted enough. True it might go better rolled back if reaching 4 stroking limit, but umm, video would be great but I know it's a bit of a pain to organise.
Sorry lost where I'm going with this playing on my old iPad which keeps freezing up. Hope someone else wades in to help.
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21 Nov 2023 02:02 #146

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Replied by torqueflight on topic 1974 DT125A Build/Restore

Thanks Ill see if I can get a video together.

Point spring def broke. The top point is just flapping free. Part of the spring that broke was rusty dust sitting in the bottom of the left side cover.

llI see what other jets I have. I bump up from the 140 on the main and see what happens.
Last edit: 21 Nov 2023 03:57 by torqueflight.
21 Nov 2023 03:56 #147

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Replied by Ht1kid on topic 1974 DT125A Build/Restore

Hey Torqueflight I would use Yamaha points I know they are more expensive but you have a piece of mind also I would super clean your carb again ultrasonic cleaner would be best most motorcycle shops have one and burn out your exhaust just to have all your bases covered also are the jets genuine mikuni?
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21 Nov 2023 07:28 #148

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Replied by torqueflight on topic 1974 DT125A Build/Restore

Just checked and the jets I had were for a different carb so Ill need to find them. I was gonna buy legit ones just so I dont run into problems. I have an ultra sonic cleaner here.

Also need to find a set of real Yamaha points. I dont want to cheap out.

Edit, just looked up points,  183-81421-19-00  seems to cross over to the RD series bikes too? Does that sound right?

thanks
Last edit: 21 Nov 2023 15:04 by torqueflight.
21 Nov 2023 14:58 #149

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Replied by Ht1kid on topic 1974 DT125A Build/Restore

Yes that’s the correct number partzilla has them says RD125,200 and AT2-3 the same your dealer can order them and might give you a discount 
21 Nov 2023 15:45 #150

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